- Email: [email protected]
Demonstrating correction of low levels of astigmatism with realistic scenes
G Model CLAE 832 No. of Pages 12
Contact Lens and Anterior Eye xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Contact Lens and Anterior Eye journal homepage: www.elsevier.com/locate/clae
Demonstrating correction of low levels of astigmatism with realistic scenes Andy Miltona,* , Michael Murphyb , Ben Rosea , Giovanna Olivaresc , Borm Kim Littlec, Charis Lauc , Anna Sulleyd a
Innovia Technology Ltd., Cambridge UK Proxama, Norwich, UK Johnson & Johnson Vision Care, Inc., Jacksonville, FL, USA d Johnson & Johnson Vision Care, Wokingham, UK b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 18 March 2015 Received in revised form 26 June 2015 Accepted 16 July 2015
Purpose and Method: Modern standard visual acuity tests are primarily designed as diagnostic tools for use during subjective refraction and normally bear little relation to real-world situations. We have developed a methodology to create realistic rendered scenes that demonstrate potential vision improvement in a relevant and engaging way. Low-cylindrical refractive error can be made more noticeable by optimizing the contrast and spatial frequencies, and by testing four different visual perception skills: motion tracking, pattern recognition, visual clutter differentiation and contrast sensitivity. Using a 1.00 DC lens during iteration, we created a range of still and video scenes before optimizing to a selection 3-D rendered street scenes. These were assessed on everyday relevance, emotional and visual engagement and sensitivity to refractive correction for low-cylinder astigmats (0.75–1.00 DC, n = 74) wearing best spherical equivalent correction and then with astigmatism corrected. Results and Conclusions: The most promising visual elements involved or combined optimized textures, distracting patterns behind text, faces at a distance, and oblique text. 91.9% of subjects (95% CI: 83.2, 97.0) reported an overall visual improvement when viewing the images with astigmatic correction, and 96% found the images helpful to determine which type of contact lens to use. Our method, which combines visual science with design thinking, takes a new approach to creating vision tests. The resultant test scenes can be used to improve patient interaction and help low cylinder astigmats see relevant, every-day benefits in correcting low levels (0.75 & 1.00 DC) of astigmatism. ã 2015 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
Keywords: Subjective refraction Toric Low-cylinder Correction assessment Relevance
1. Introduction Routine patient visual acuity (VA) tests used during subjective refraction typically bear little relation to real life. Take, for example, the Snellen chart. While this tool is essential for eye care professionals (ECPs) in assessing VA, for the patient, the appearance of the chart is not something they will often come across in daily life. The outcome of such an assessment can also be difficult for patients to understand—the common benchmark and term heard by patients of “20/20 vision”, for example, might make some kind of sense when explained, but it can be difficult for the patient to visualise what these numbers mean. Sitting in an ECP practice, how should one visualise 6 m? Or understand what difference a
* Corresponding author. E-mail address: [email protected] (A. Milton).
refractive error of 1.00 D makes to daily tasks, like reading or driving? There is a significant gap between the artificial visual experience in the ECP’s consulting room and its static nature, and the real benefits of improved vision quality in the patient’s day-today life. The difficulty for the patient becomes more apparent at small refractive errors. In particular, patients with low levels of astigmatism (1.00 DC) may opt not to correct their astigmatism at all when using contact lenses, perhaps due to a true lack of comparison beyond artificial acuity tests, or by the ECP not demonstrating the vision performance benefit over spherical contact lenses. Despite the prevalence of clinically significant astigmatism (0.75 D) in at least one eye of 47% [1], industry figures in 2014 showed that only 21% of soft contact lenses sold in the UK were toric designs [2]. This suggests that there is still room for improvement, even for astigmats using spherical lenses as opposed to torics [3]. Several studies have also shown the impact that proper optical correction can have on everyday life [4,5]. Other
http://dx.doi.org/10.1016/j.clae.2015.07.004 1367-0484/ ã 2015 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
2
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
studies have shown that even moderate visual impairments degrade drivers’ ability to see pedestrians at night—even a relatively modest amount of refractive blur, equivalent to 20/ 40 vision, meant that drivers responded to pedestrians at a 3.6 shorter distance [6]. This highlights the need for patients to use full refractive error correction, whether using spectacles or contact lenses. The purpose of this work was to develop a methodology for creating a novel visual assessment test – or visual “target” – that highlighted improvements to visual performance with cylinder correction. Visual elements in a scene that are particularly sensitive to refractive error were designed to demonstrate the benefits of full vision correction in a way that is more engaging, noticeable and important for the patient. 2. Methods The steps of the development method are depicted in the flowchart (Fig. 1) and are described in this section. 3. Exploration of vision optics and perception The effect of refractive error on the patient’s ability to resolve different visual elements is well documented [8]. One example is contrast sensitivity: take a one-dimensional sinusoidal grating (Fig. 2) projected onto the retina. The visual system’s ability to discriminate troughs and peaks of the light level depends on both the frequency of the light pattern (typically measured in cycles per degree) and the amplitude (or modulation, i.e. the difference in light level between troughs and peaks). Typically, a healthy corrected visual system can discriminate up to around 40 cycles per degree (LogMAR 0.10), but this is reduced as optical defocus increases [9,10]. Another example is the patient’s ability to resolve optotypes, even at high contrasts. Typically, a corrected visual system can resolve optotypes up to around 30 cycles per degree (LogMAR = 0.00), but increasing optical defocus by 1.00 D reduces this typically to less than 20 cycles per degree (LogMAR > 0.18). More precisely, given sphere (S) and cylinder (C) defocus at an axis a, the blurring strength |u| is given by qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi C C C juj ¼ M2 þ J 20 þ J245 ; M ¼ S þ ; J ¼ cos2a; J45 ¼ sin2a 2 2 2 M represents the equivalent defocus, J0 the vertical/horizontal astigmatism, and J45 the oblique astigmatism.
Fig. 2. One-dimensional sinusoidal grating.
Remón et al. [10] found empirically [11] that for a standard Snellen letter chart, the relationship between the blur strength |u| and VA was best fit by the linear equation LogMAR = 0.28|u| 0.08. So, even relatively small amounts of defocus can lead to measurable differences in VA. Using these equations we can predict the change in logMAR expected by 0.75 diopters of astigmatism. For |u| = 0, logMAR = 0.08. For |u| = 0.375 (0.75 D uncorrected cylinder), logMAR = 0.025. So DlogMAR = 0.1, equivalent to about 1 line on a VA chart, is the predicted loss in monocular high contrast acuity for 0.75 D of uncorrected astigmatism. In both cases, optical defocus causes a “blurring” of visual elements as they pass through the eye and are projected against the retina. However, while the eye optically limits the resolution of visual elements, the visual system is sometimes able to compensate for missing information. One well documented example is hyperacuity [12], where the alignment of two lines can be resolved with up to ten times better accuracy than VA typically allows. Other learning effects are also known to influence VA results, particularly in the case of optotypes [13]. These effects highlight the role of perception in vision to make sense of the world around us. Visual illusions play on these effects to great success, fooling the visual system in ways that surprise and engage. In the development of the scene, a number of different visual illusions were explored, and two illusions were of particular interest. Fig. 3 shows an example of the “Dr Angry and Mr Smile” illusion [14], of which the “Einstein/Monroe” illusion is a variant. In this image, low spatial frequencies are used to create the image of a calm face, while a high-spatial-frequency image of an angry face is superimposed over the top. When the image is placed at a far enough distance (or the viewer’s optical defocus is high enough),
Fig. 1. Flowchart highlighting main activities carried out in the scene development.
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
3
Fig. 3. Dr Angry and Mr Smile illusion. A high frequency angry face is superimposed over a low frequency calm face. Reprinted with permission from Elsevier [14].
the high-frequency angry face cannot be resolved fully by the viewer’s visual system, leading them to only see the low-frequency calm face. After bringing the image closer (or after optical correction), the high-frequency image becomes resolvable. Importantly, the change is binary: compared to standard VA tests that normally present a sliding scale, most visual illusions present only two options, making the change more noticeable. This takes advantage of the contrast sensitivity function to reveal the highfrequency image only when the visual system is able to detect it. Fig. 4 is an example of the “John Lennon” illusion. Here, a dark grey outline of a face (in the original, John Lennon’s) is placed onto a slightly lighter grey background. Overlaid on top is a hard grating of black lines at a relatively high frequency. At distance (or with defocus), the grating becomes blurred, allowing the face underneath to become visible. As the viewer moves closer (or is corrected), the grating becomes visible. Since the grating has a much higher contrast than the underlying face image it becomes impossible to see the face. This effect is a result of both contrast sensitivity and contrast discrimination [15], where the eye is unable to detect two different signals (the high-frequency grating and the low-frequency face) because of their different modulation (or contrast). It is worth noting that this effect is inverted: ideally a visual element provides a benefit when the patient is properly corrected, but in this case the face becomes visible when uncorrected. In addition to existing knowledge on VA and the exploration of visual illusions, aspects of the patient’s life where vision is also impaired were also considered. For example, driving at night, one is often confronted with very high contrast from sources of light in darkness, which can serve to distract or dazzle the driver. This can be made worse when driving in poor weather, such as rain. Typical city and town scenes were also investigated, picking out elements that exhibit high contrasts, complex textures, or embed important information for the viewer. Moving media was also considered: many patients are exposed daily to TV images which show moving text (such as a news channel ticker tape). The effect of defocus on patients in these types of environment is relatively unknown, but it is precisely in these environments, particularly activities such as driving, where improved vision is most important for the patient. 4. Prototyping visual elements Given this understanding, the goal was to create a number of visual elements that create an engaging, noticeable, and important
difference to patients with small refractive error (particularly astigmats with cylindrical error 1.00 DC) when their vision is corrected. “Engaging” means that the element is able to hold the attention of the viewer and encourages them to interact with it and further explore it. “Noticeable” means that the viewer perceives a clear difference in the element before and after correction, ideally binary, in the sense that something that was completely invisible before is suddenly made visible. The meaning of “important” is more difficult to quantify: different things are important to different people. In general, this is classified as something relevant to the viewer (e.g. recognizable, familiar, or meaningful) but also where it makes a real difference in the viewer's life; for example, the ability to do something better or more safely (such as driving a car, or working with machinery). By combining all three, it could create a “wow” moment for the patient that is quick and intuitive; this is covered further in the discussion. The primary focus at this stage was noticeability, and four broad areas were explored whose effect could make a noticeable difference: motion tracking, visual overstimulation, pattern recognition, and contrast sensitivity. Note that with some of the elements discussed below these areas overlap, particularly with contrast sensitivity. In many of these elements, gratings are referred to with particular frequencies measured in cycles per degree, as well as computed contrast, which is a measure of the amplitude of the grating. The computed contrast is given by ratio of the difference in brightness between the lightest and darkest colours in the grating with the maximum possible brightness (white colour). In each case, low cylinder astigmats (1.00 DC) were particularly targeted. 4.1. Motion tracking Moving visual elements pose problems for the visual system. In general, moving elements are harder to recognize and provide less time for the visual system to process them before they move outside the eye’s foveal vision, requiring constant movement of the eye. Two particular elements were looked at: rotating gratings, and text in motion. Fig. 5 shows a snapshot of a rotating grating. The animation consists of two letters, placed next to one another, which are created from a masked grating (35 cycles per degree, simulated contrast ratio 0.2). The edges of the letter forms are blurred to prevent artefacts caused by the visual system’s ability to detect
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
4
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
Fig. 5. Snapshot of a rotating grating (contrast increased for publication).
screen at a typical reading speed of 1–200 wpm. This suggests the predominant effect is the astigmatic blur increasing the time required for the brain to recognise each letter and word, rather than difficulties in the eyes tracking the words due to their angular speed across the field of vision. The optimal speed for the test is when the brain can keep up reading the text without astigmatic blur, but not with astigmatic blur, creating a clear and binary distinction. Using names also has the advantage that learning effects can also be partly bypassed, particularly for unusual names that the patient might not be familiar with. This kind of animation will be recognizable to the patient from film credits, but scrolling the text in other directions could be reminiscent of ticker-tape text on news channels. 4.2. Visual clutter
Fig. 4. (a) John Lennon illusion. A man’s face with glasses with low contrast is set behind a high contrast grating. (b) The man’s face with increased contrast without the high contrast grating.
edges, and the black cross acts as a fiducial marker to allow the eye to properly accommodate and bring the plane of the animation into focus. The gratings for each word rotate around the centre of each letter. Each word “flashes” as the grating becomes alternately aligned and anti-aligned to the principle axis of the astigmatism. The speed of rotation was not especially critical for the effect; it should give a perceptible pulsing effect (so not too fast), but the patient should not have to wait too long for each cycle. A rotation rate of around 1 Hz worked well. Fig. 6 shows a snapshot of text in motion. This animation scrolls a list of names, much like film credits, within a rectangular area. At a threshold rate of scrolling, viewing the animation with a small amount of astigmatic blur (0.75 DC) of any axis produced a noticeable difference to the ease of reading. This threshold rate of scrolling was roughly equivalent to the words passing across the
These elements explored the effect that distraction, or visual crowding or clutter, can have on recognition of text and patterns. Particularly in modern societies, the average person is subject to a huge number and variety of visual stimuli: television, computer games, signage, advertisements on billboards, artificial lighting, etc. Each of these forms of media typically present complex and highly-detailed images, sometimes making it more difficult to focus on and interpret the most pertinent information in the subject’s visual field. In some situations, this type of distraction can be dangerous: when driving, for example, rapid recognition of road signs and other vehicles helps prevent accidents. The connection between defocus and the effect of visual clutter is generally poorly understood, but a study by Ho et al. [15] showed that older patients with poorer VA did worse than younger patients in a visual search task when visual clutter was introduced [16]. Earlier work [17,18] also showed the effect that crowding and noise has on the ability to recognize letters quickly. It was therefore postulated that artificially introducing clutter into a visual target might allow “revealing” of information to the patient when their vision is corrected. Fig. 7 shows a line of text surrounded by visual clutter. The clutter itself is designed to somewhat match the characteristics of
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
5
surrounded by bright circles reminiscent of artificial lights. In both cases, it was hypothesized that poorer VA makes it more difficult for the visual system to separate the semantic content (i.e. the words) from the background compared with not having visual clutter at all, and thus making it more challenging for the patient to read. It is well understood that contrast discrimination of the human eye varies with the difference in modulation of different signals. This can be considered to be a form of visual overstimulation: high-contrast elements can essentially “drown out” weaker lowcontrast elements in the field of view. Building on the understanding from the John Lennon illusion, a number of visual elements were created, of which a typical example is shown in Fig. 9. Highcontrast visual patterns are overlaid onto a lower-contrast texture or image. If the patient is uncorrected, the high-contrast pattern becomes blurred and is more difficult to detect, revealing the lowcontrast pattern underneath. However, in this case the reverse
Fig. 6. Text in motion.
Fig. 7. Text surrounded by visual clutter.
the text itself, in terms of colour, contrast, and directionality. The edges of letters were softened to limit the ability of the visual system to detect letter edges. Fig. 8 shows another embodiment that seeks to imitate a night-time driving scene, using text
Fig. 8. Text surrounded by visual clutter (night-time variant).
Fig. 9. (a) High contrast pattern overlaid on low contrast image. (b) The low contrast image without the high contrast pattern.
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
6
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
Fig. 10. High-frequency image of a smiling woman overlaid onto a low-frequency image of a calm-faced woman.
would be preferred: namely that correction of defocus would reveal the more interesting pattern (or John Lennon’s face).
Fig. 11. Two words composed from gratings stacked atop each other (contrast increased for publication).
4.3. Pattern recognition In order to make sense of the world around us, our visual system relies heavily on pattern recognition. This can be made very apparent in some images, where a seemingly random collection of blobs suddenly takes on meaning. This effect is very abrupt (sometimes categorized as a Gestalt shift), and once the visual system “sees” the new image, it becomes impossible to contradict it. Fig. 10 shows an example of an image where a high frequency image of a smiling woman is overlaid on a low-frequency image of the same woman with a neutral expression. This builds on the success of the “Dr Angry and Mr Smile” illusion, and is taking advantage of the visual system's ability (and in fact propensity) to detect faces. Faces and their expressions also have an emotional and social meaning for the viewer, which adds relevance and interest to the image. It works as already described in the explanation of the “Dr Angry and Mr Smile” illusion, where the high-frequency features that show the smiling face are only visible once refractive error is fully corrected (i.e. including low amounts of astigmatism).
Fig. 12 takes inspiration from standard contrast sensitivity test charts. Round targets are arranged in rows and columns across a grey background. Each target contains a grating with a particular spatial frequency between 10–60 cyc/deg at a fixed contrast (0.2) and at a random orientation (but biased towards horizontal and vertical). Regardless of the VA of the viewer, some of the targets will be unresolvable. For uncorrected patients, even small amounts of defocus will cause some of the targets to disappear. In any image of high enough resolution and viewed from a far enough distance, elements of the image become impossible to see since they fall beyond the threshold of contrast detection. These are typically the finest details: fine hairs, subtle textures, small text, etc. Fig. 13 shows an example image containing some of these
4.4. Contrast sensitivity As already discussed, contrast sensitivity is one of the bestunderstood and widely researched performance indicators of visual quality. While it has underpinned some of the visual elements already discussed, elements that relied solely or heavily on contrast detection were investigated separately. Fig.11 shows two words, composed from high-frequency gratings (30 cycles per degree) with a simulated contrast ratio of 0.2. Each of the gratings is oriented differently from the other: one at 0 degrees, and one at 90 degrees. For typical “with-the-rule” or “against-therule” astigmats, one of the two words will appear sharper and more readable than the other. The grey colour of the background is precisely the median value of the darkest black and lightest white contained in the grating: when the grating is blurred due to defocus its average colour will match that of the background, making it disappear. The choice of words can be altered to create interesting phrases that change their meaning as more words become visible.
Fig. 12. Random array of gratings (contrast increased for publication).
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
7
Fig. 13. High-frequency, detailed image. Fig. 15. Final target scene in a cultural setting. The arrows annotate different elements in the image referred to earlier in the text. (A) Text in perspective (see Fig. 14). (B) Text with visual clutter (see Fig. 6). (C) High-frequency details (see Fig. 13). (D) Faces.
described above were chosen for further development. Each was rated on the criteria described above: was the effect noticeable, engaging, and important? In each case, this was determined through a combination of qualitative subjective assessment (using subjects with astigmatism in the range 0.75–1.25 DC, or with astigmatism induced using trial frames, n = 3) and with insights from earlier research. The ratings are given in Table 1. High-frequency detail clearly provided a high degree of impact for viewers across all three criteria, as did text in perspective. Text in motion also scored
Fig. 14. Simulated row of shops in perspective with signage.
details. Several such images were optimized so that the finest and richest details in the image were unresolvable to patients with small refractive errors (between 20 and 30 cyc/deg). These images had a range of features across different contrasts and types of pattern, from geometric to highly random. Fig. 14 shows a simulated row of shops with signage in perspective. Each shop front has signage that becomes smaller as the shop moves further back into the image. This image essentially encodes optotypes from the Snellen chart into an image that is more familiar and can be more easily related to by patients than the standard chart. Ideally, the signs in the image would be optimized so that the majority of the text is equivalent to a grating between 20 and 30 cycles per degree (assuming an optotype, e.g. “E”, is representable as 2.5 cycles of a grating). A wide range of sizes helps to capture a wider number of patient prescriptions. Perspective allows us to modulate the vertical and horizontal frequencies independently for particular orientations of astigmatism. 5. Selecting elements for the final scenes It will be apparent that none of the images presented so far fulfil all the set criteria: while several of the images present effects which are certainly noticeable, it is much more difficult to argue that they are engaging, or indeed important. To achieve this, each of the elements required further development before they could be combined into a final image. To avoid over-complicating the final image and in order to ensure a better result, four of the nine elements in Figs. 5–14
Fig. 16. Final target scene in a retail setting. For the meaning of annotations, see Fig. 15. Table 1 Ratings of each of the nine explored visual elements. Items with asterisks were incorporated into the final scenes. Element
Noticeable
Important
Engaging
Total
High-frequency detail* Text in motion Array of gratings Facial expressions* Text in perspective* Text with distraction* High-contrast patterns Gratings and text Rotating grating
6 5 4 4 4 3 3 3 2
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
8
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
highly, but since it requires a digital display it was felt to be impractical for the final hand-held tool. Digital application of the scenes could be considered in subsequent phases of development. While array of gratings also scored highly, there was a lack of relevance and importance in rating overall visual quality, so it was dismissed. 6. Clinical study A clinical study was performed to evaluate the scenes, visual features and viewing distance that demonstrate the most visual improvement and to determine if the demonstration is clinically useful in subjects with low astigmatism. This was an open label, single arm, multi-site, one-visit, bilateral, non-dispensing study. Subjects were astigmats aged between 18 and 39 years of age. Subjects’ vertex corrected spherical distance refraction was between 1.00 D and 5.00 D, with refractive cylinders between 0.75 DC and 1.00 DC in each eye. All were habitual soft spherical or toric contact lens wearers and had a best corrected VA of 6/7.5 + 3 or better in each eye. Subjects had “normal” eyes i.e. no chronic disease, routine use of ophthalmic medication, or active infections. Each scene was printed for viewing at 50 cm (hand-held; “near”) and 1.8 m (poster; “far”), such that the angular size remained constant. Room illumination was controlled with a minimum of 400 lux across all sites. Subject’s best spherical equivalent correction was determined by subjective spherical refraction. Subject was given an explanation what astigmatism was and the purpose of the study. Subjects’ wore their spherical equivalent correction with daily disposable, hydrogel contact lenses (etafilcon A) binocularly. This demonstrated the vision without their astigmatism corrected. When a specially designed trial lens that incorporated +0.25 DS compensation with 0.75 DC power was placed in front of the subjects’ eyes, this simulated their vision when wearing contact lenses with astigmatism correction. The trial lens used in this study incorporated +0.25 DS compensation with 0.75 DC power, based on the expectation that the best sphere refraction would be approximately 0.25 DS more than the sphere component of the sphero-cylinder refraction to keep equivalent sphere shift less than 0.13 D with and without the flipper. The +0.25 DS sphere compensation was used rather than +0.37 DS (perfect compensation) due to the 0.25 D steps of contact lens products. Therefore, the trial lens had +0.25 D in one meridian and 0.50 D in another meridian 90 degrees apart. When the lenses were rotated to match the subjective best spherocylindrical refraction axis, it gave a prescription power of “+0.25/0.75 subject’s axis”. While looking at the scenes, trial lenses were introduced and then removed so visual differences could be evaluated. The order of presenting the scenes was randomised while the order of viewing distances was static such that assessed scenes in near and then far distance. A questionnaire was conducted to assess the preferred scene, features and viewing distance that showed the greatest visual benefit(s), and whether the introduction of the cylinder affected their subjective vision performance. They were also asked whether they would be likely to try or recommend toric soft contact lenses, based on the scene demonstration. Additionally, the ECPs completed a post-study qualitative interview on ease of use and the potential impact of the scenes on toric soft contact lens prescribing. The plan was to enrol approximately 70 subjects with an aim to complete at least 60. Sample size calculation was based on the result of previous (unpublished) work (n = 46) that indicated 90% of subjects found the demonstration of astigmatism with a similar trial lens useful. Assuming 90% of targeted population experience vision improvement using the trial lens, and assuming more than
75% of the subject would experience vision improvement with the trial lens, at least 60 subjects was needed to achieve the hypothesis test (i.e. correctly reject the primary null hypothesis) with a minimum of 80% power based on one sample binomial exact test using 2-sided with alpha = 0.05 (SAS Proc Power was used). Considering the 15% dropout rate, the enrolment goal was 70 subjects. All data summaries and statistical analyses were performed using the SAS software Version 9.3 (SAS Institute, Cary, NC). Efficacy variables were analysed for all subjects who completed the study per protocol and safety variables were summarized for all subjects who received the study article. 7. Primary endpoint The primary endpoint was the proportion of subjects experiencing overall visual improvement when viewing both scenes at both distances with astigmatism correction. Subjects rated the statement, “When I looked with the astigmatic correction, I experienced overall visual improvement”, using a five-level agreement scale (agree strongly, agree somewhat, neither agree nor disagree, disagree and disagree strongly). These five responses were categorised into a binary outcome, where “agree strongly” and “agree somewhat” were assigned the value 1 (visual improvement) and the other responses were assigned the value 0 (no visual improvement). The null and alternative hypotheses were: H0 : p 0:75; Ha : p > 0:75;where p was the expected proportion of subjects who experienced overall visual improvement with astigmatism corrected under H0. For the primary variable, an exact binomial 95% CI was constructed with a significance level of a = 0.05. If the lower bound of the CI was greater than 0.75, then it was concluded that the astigmatism correction effectively demonstrated the improvement of the vision quality for low cylinder astigmats. This primary analysis was conducted with an overall type I error rate of 5%. 8. Secondary endpoints The secondary endpoints were the proportions of subjects experiencing visual improvement for each scene–distance combination. For each scene–distance combination, subjects were asked to choose which one of five responses (much better, slightly better, no difference, slightly worse and much worse) best described how they felt about their vision. These five responses were categorized into the binary outcome; the top two responses (“much better” and “slightly better”) were assigned the value 1 (visual improvement) and the rest of the responses were assigned the value 0 (no visual improvement). This binary outcome was analysed using a generalized estimating equation (GEE) model with logit as the link function. The model included age, sequence of presenting the images, period, scene, viewing distance and the interaction between scene and viewing distance as fixed factors. An unstructured covariance structure was used to model the correlation between measurements within the same subject and viewing distance across the images. The proportions of subjects who experience visual improvement were estimated with 95% confidence intervals for each scene–distance combination. A simulated-based method was employed to adjust type I error for multiple comparisons 9. Results 9.1. Creating real-world images Each element was individually rated as being somewhat engaging, noticeable, and important, but the aim was to enhance
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
each of these by combining the elements together into a final image, or target. Two “real-world” scenes were created, and to allow maximum flexibility these scenes were created digitally in 3D architectural software (CAD). In order to make best use of this medium, industry experts in architectural visualisation were involved to help plan and design the final targets (Ciaran Ryan Ltd., London, UK). This helped to ensure that the final scenes had a high level of realism and were visually appealing, while maintaining the principles that underpin the original visual elements. To transfer the elements into the final scenes, a series of tools were developed that provided a common design language, translating the underlying scientific concepts into a set of rules to be followed when making the scenes. These tools were different for each of the visual elements, and are described in the following sections.
9
in adverts or signage that vie for the viewer’s attention on the high street or in the shopping mall. By incorporating these images into billboards, adverts, and other signage, these elements were added to the scenes in a way that appeared natural. 9.5. Faces Initially, the “Dr Angry, Mr Smile”-type image was developed into more realistic and higher-definition faces to use in the final scene. However, reactions to these faces were predominantly negative: informal testing showed that the faces appeared unnatural both before and after correction. The approach was therefore simplified, instead using a particular size of face in the final image that in testing showed the biggest difference in recognition before and after correction. At 1.8 m, this size was 3–4 cm from the chin to the top of the head.
9.2. Text in perspective 10. Final targets Optotypes in the range 20–30 cyc/deg were determined to be most likely to become unreadable for low cylinder defocus. Using a spreadsheet in Microsoft Excel, a simple tool was created where, given a piece of text (such as a car license plate) and the desired VA required to read the text, the tool calculated the distance from the viewer and the height of the text in CAD space. This allowed elements of text in the CAD environment to be created quickly that, when printed and viewed at a set distance, would have the desired cycles per degree, and hence the desired visibility. A more sophisticated version of the tool also allowed alteration of the angle of the text relative to the viewer in CAD-space and calculated the resulting cycles per degree of the printed text. This meant there was complete freedom in how text in the images was positioned, enabling the creation of scenes that were more realistic and looked natural. A future version of this tool might support customization of the images. For example an ECP might add their practice name onto a shop front in the scene. 9.3. High-frequency detail From earlier results, geometric patterns and fine lines in images were determined to be the most likely to become difficult to see when defocus was increased, particularly at relatively low contrasts (<0.5). This is likely due to their similarity to grating patterns— breaks or discontinuities in the pattern could be resolved with hyperacuity. Repetitive geometric textures are relatively uncommon in natural scenes, but are prevalent in cityscapes: brickwork, windows, pavements, etc. Setting both of the scenes in city environments allowed natural-looking textures on buildings to be used that revealed higher level of detail when vision was corrected. The range of line widths that became difficult to resolve for uncorrected patients were specified, which at 1.8 m distant corresponded to line widths between 0.5 mm (30 cyc/deg) and 0.2 mm (60 cyc/deg). Using these as a guideline, Ciaran Ryan Ltd., created a number of textures for building facades and pavements that had line widths falling predominantly in this range. 9.4. Text with distraction Two different hypotheses for text with distraction were explored. In the first, it was supposed that text would become more difficult to read because it became less easily distinguishable from its background. This was the mechanism behind the effect already mentioned and shown in Fig. 5. While effective, it was concluded that visually the images looked too artificial and could not be incorporated into a final scene. The second hypothesis was based primarily on the effect depicted in Fig. 7. These kinds of images are much more commonplace in the real world, particularly
The two scenes were both city scenes, one a “cultural scene”, and the other a “retail scene” (Figs. 15 and 16). Both scenes contained the same visual elements, but contrasted each other in several ways. The cultural scene was lighter, and had a particular focus on informative signage (such as way finding signs). The perspective in the cultural scene is also weaker than the retail scene, where one can “see farther” down the street into the distance. In both scenes, the virtual camera has been placed at eyelevel, giving the impression that it is the view one would have standing in the scene. The objects and lighting were also carefully chosen to provide realism and variety in both images. The rationale for using street scenes brings us back to the original criteria. Street environments are familiar to most people and are therefore very relevant. Often, it is also important that signage can be seen clearly so that the viewer can navigate easily or read adverts. These scenes are typically engaging as well: the variety of textures, colours, and text draws the attention of the viewer and are rich in detail. To test noticeability, the final scenes were presented to n = 4 subjects with varying levels of astigmatism (0.75–1.25 DC). The subject was then asked to apply (and remove) correction of their astigmatism with trial lenses. These subjective tests are being followed up by a more comprehensive trial (to be described in a forthcoming publication). Preliminary reactions showed some promising trends. In particular, patients reacted strongly to the higher detail visible in the scene after correction. Several patients also noted details that only became visible after correction, particularly signage text. Encouragingly, patients also found it easier to relate to the improvement in their VA to something understandable, such as being able to “see further” down the street, rather than “my vision is 20/20”. Two formats of the final scene were created. A poster version was printed on standard A0-sized paper to be viewed at 1.8 m. A second, hand-held version was printed on standard A4 paper to be viewed as 0.5 m. These formats were chosen to be mindful of the constraints in a typical ECP’s practice: wall-space is generally limited, so the choice of a poster or handheld version gives the ECP more flexibility. It should also be straightforward to adapt the handheld scene to other similar formats, e.g. in a magazine. The scenes might also be adapted to large digital screens suitable for viewing at a distance, or perhaps tablet computers suitable for viewing close up. 10.1. Clinical study results A total of 74 binocular astigmatic subjects were enrolled and completed the study (mean age 28 5.8 years, range 18–39);
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
10
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
Fig. 17. Proportion of subjects reporting visual improvement when viewing the scenes with astigmatic correction, overall and for each scene–distance combination (n = 74).
thirty-nine subjects habitually wore toric soft contact lenses with the remainder wearing spherical soft lenses. The majority of subjects (91.9%; 95% CI: 83.2, 97.0) reported an overall visual improvement viewing the scenes with correction for low levels of astigmatism (Figs. 17 and 18). For both scenes viewed at the far distance of 1.8 m, visual improvement was noted (94.0% (95% CI: 81.91, 98.19) experienced improvement with the daytime/ courtyard scene; 91.6% (95% CI: 78.20, 97.07) for the night-time/ street scene). When looking at scene preference, 46% preferred the night-time/street scene, 42% the daytime/courtyard scene and 12% had no preference. For preferred viewing distance, 60% chose the 1.8 m testing distance, 24% chose 50 cm and 16% had no preference. “Text in Perspective” and “Text with Distraction” features demonstrated the most visual improvement in both scenes (Fig. 18). The vast majority of subjects (96%) believed the scenes
would be helpful when considering the benefit of toric soft contact lenses (Fig. 19). The qualitative interview was conducted with 11 US ECPs, with all finding the scenes extremely easy to use. They felt it could reduce chair time with toric soft fitting, thereby increasing their likelihood to prescribe these lenses. Practitioners felt the key patients to target would be spherical CL wearers and new CL fits, and that using the scene addressed barriers often cited in fitting low astigmats with toric soft contact lenses, such as time to explain the benefits of toric lenses and the ability to effectively demonstrate the visual benefits of a low cylinder toric lens. 11. Discussion This is a new approach to vision assessment for patients with low levels of astigmatism and has resulted in two final scenes,
% of subjects visual improvement with asgmac correcon when viewing scenes
100 90 80
Text in Perspecve
72.1
70 60
Text with Distracon
50 41.4
Face
40 30 20
23.4
High Frequency Detail
18 15.3
10
10.4
7.7 7.2
0 Dayme Courtyard
Nighme Downtown
Fig. 18. Visual improvement with scene visual features (n = 74).
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
100
11
96 93.2
90
85.1
80
% of subjects agree
70 60 50 40 30 20 10 0 Recommend toric lenses to others
Likelihood to try toric lenses
Helpfulness to try toric lenses vs. non-toric lenses
Fig. 19. Subjective impressions of from subject post-fit questionnaire (n = 74).
designed to better demonstrate the benefits of correcting cylinder powers. The method was grounded in an understanding of fundamental vision science and an exploration of perceptual effects, creating scenes that did not just change noticeably for patients after correction (as with e.g. a Snellen chart), but also engaged them, and showed them how the correction can be important in their day-to-day lives. The combination of these three aspects is critical in distinguishing these scenes from typical VA tests. The Snellen chart, for example, appeals to a rational mentality: the scenes, by contrast, are designed to appeal to patients on both a rational and an emotional level. Setting the test in a scene familiar to the patient (and also culturally relevant) that is engaging and evokes the sense of being out in the real world helps to achieve this, and makes connecting with and understanding the real-world benefit more intuitive and immediate. While it is true that the scenes have been designed to highlight the difference between corrected and uncorrected astigmatism, this does not make them biased in the sense that they over-emphasize the effects: the elements in the images can all be found in the real world, and the images bring them into the ECP’s consulting room. The complexity of the scenes with several elements also allows patients to discover the benefits for themselves, and particularly what the patient could be “missing-out” on by not correcting their astigmatism. This puts a stronger focus on assessment of visual quality, as opposed to just VA. The scenes also have the potential to change how ECPs interact with patients. The tools can be used in many different ways with patients, both in the choice of format, as well as how the patient is guided through the image. The poster tool requires more wall space, but its sheer size makes it quite visually arresting, and helps transform the perhaps sterile environment of the clinic into one that is more inviting, comfortable, and familiar. Conversely, the handheld version needs far less space, and allows the patient to hold and control the scenes themselves. Some ECPs may take their patient
from the consulting room to a bigger room or to view outside the differences in vision performance with trial lenses; however, this is not always possible due to time and/or space, and could introduce more variability with different conditions and contrast, hence the scenes allow demonstration of realistic everyday images that can be used in the consulting room. In most cases, guidance from the ECP will be minimal; selfdiscovery is typically a more satisfying experience than being told what to look at by someone else, and people will discover and respond to elements in the image differently. It also puts the patient in control, rather than the clinician, particularly when it the target is used with the hand-held correction tool. This empowerment will stimulate better dialog between patients and ECPs, and help patients to reach a better understanding of their vision correction options and how they will impact vision quality. The method outlined is not limited to creating static images—it can naturally be extended to different image formats, as well as other media such as video (particularly using modern, highresolution displays). It is not limited to low astigmats (who were the original target of this work); presbyopes could also use the scenes to assess vision quality. A clinical trial of the scenes showed encouraging results, and the scenes were generally well liked and accepted by both ECPs and patients. The majority of low astigmatic subjects experienced overall visual improvement when viewing both scenes at distance and near and found the scenes demonstrated the benefits of astigmatic correction. Although the 1.8m testing distance demonstrated greater visual improvement, the hand held version was still found to be impactful, and may be more practical to use than the distance poster in some ECPs’ consulting rooms. Also, whilst originally developed for use with low astigmats, the scenes could also be impactful for demonstrating the benefits of astigmatic correction with patients with higher levels of uncorrected cylinders. The choice to fully correct astigmatism is a decision between the patient and their ECP, and is not always chosen by patients with
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
small refractive errors (particularly low cylinder) in the ‘non-real world’ consulting room environment. The scenes have the potential to revolutionize how ECPs interact with patients and fundamentally change how, in a clinical setting, patients perceive the vision quality benefits of correcting low levels of astigmatism. Acknowledgement This research project was funded by Johnson & Johnson Vision Care, Inc. Johnson & Johnson Vision Care are developing the scenes for use in practice. References [1] G. Young, A. Sulley, C. Hunt, Prevalence of astigmatism in relation to soft contact lens fitting, Eye Contact Lens 37 (2011) 20–25. [2] (b) A. Sulley, G. Young, K.O. Lorenz, C. Hunt, Clinical evaluation of fitting toric soft contact lenses to current non-users, Ophthalmic Physiol. Opt. 33 (2013) 94–103Johnson & Johnson Vision Care Data on file 2015; Internal Analysis based on independent third party data. Disposable toric soft fits in UK Jan–Dec 2014. [3] S.K. West, G.S. Rubin, A.T. Broman, B. Munoz, K. Bandeen-Roche, K. Turano, How does visual impairment affect performance on tasks of everyday life? The see project, Arch. Ophthalmol. 120 (2002) 774–780. [4] A.L. Coleman, F. Yu, E. Keeler, C.M. Mangione, Treatment of uncorrected refractive error improves vision-specific quality of life, J. Am. Geriatr. Soc. 54 (2006) 883–890.
[5] B.S. Chu, J.M. Wood, M.J. Collins, The effect of presbyopic vision corrections on nighttime driving performance, Invest. Ophthalmol. Vis. Sci. 51 (2010) 4861– 4866. [6] J.M. Wood, R.A. Tyrrell, A. Chaparro, R.P. Marszalek, T.P. Carberry, B.S. Chu, Even moderate visual impairments degrade drivers’ ability to see pedestrians at night, Invest. Ophthalmol. Vis. Sci. 53 (2012) 2586–2592. [8] D.A. Atchison, R.L. Woods, A. Bradley, Predicting the effects of optical defocus on human contrast sensitivity, J. Opt. Soc. Am. A 15 (1998) 2536–2544. [9] G. Smith, Relation between spherical refractive error and visual acuity, Opt. Vis. Sci. 68 (1991) 591–598. [10] L. Remón, M. Tornel, W.D. Furlan, Visual acuity in simple myopic astigmatism: influence of cylinder Axis, Opt. Vis. Sci. 83 (2006) 311–315. [11] G. Westheimer, Editorial visual acuity and hyperacuity, Invest. Ophthalmol. Vis. Sci. 14 (1975) 570–572. [12] H. Brom, A. Kooijman, L. Blanksma, G. Rij, Measurement of visual acuity with two different charts; a comparison of results and repeatability in patients with cataract, Doc. Ophthalmol. 90 (1995) 61–66. [13] P.G. Schyns, A. Oliva, Dr. Angry and Mr. Smile: when categorization flexibly modifies the perception of faces in rapid visual presentations, Cognition 69 (1999) 243–265. [14] P.G.J. Barten, Contrast Sensitivity of the Human Eye, SPIE Press, Washington, 1999. [15] G. Ho, C.T. Scialfa, J.K. Caird, T. Graw, Visual search for traffic signs: the effects of clutter, luminance, and aging, Hum. Factors 43 (2001) 194–207. [16] B. Eriksen, C. Eriksen, Effects of noise letters upon the identification of a target letter in a nonsearch task, Percept. Psychophys. 16 (1974) 143–149. [17] M.C. Flom, F.W. Weymouth, D. Kahneman, Visual resolution and contour interaction, J. Opt. Soc. Am. 53 (1963) 1026–1032.
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
Contact Lens and Anterior Eye xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Contact Lens and Anterior Eye journal homepage: www.elsevier.com/locate/clae
Demonstrating correction of low levels of astigmatism with realistic scenes Andy Miltona,* , Michael Murphyb , Ben Rosea , Giovanna Olivaresc , Borm Kim Littlec, Charis Lauc , Anna Sulleyd a
Innovia Technology Ltd., Cambridge UK Proxama, Norwich, UK Johnson & Johnson Vision Care, Inc., Jacksonville, FL, USA d Johnson & Johnson Vision Care, Wokingham, UK b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 18 March 2015 Received in revised form 26 June 2015 Accepted 16 July 2015
Purpose and Method: Modern standard visual acuity tests are primarily designed as diagnostic tools for use during subjective refraction and normally bear little relation to real-world situations. We have developed a methodology to create realistic rendered scenes that demonstrate potential vision improvement in a relevant and engaging way. Low-cylindrical refractive error can be made more noticeable by optimizing the contrast and spatial frequencies, and by testing four different visual perception skills: motion tracking, pattern recognition, visual clutter differentiation and contrast sensitivity. Using a 1.00 DC lens during iteration, we created a range of still and video scenes before optimizing to a selection 3-D rendered street scenes. These were assessed on everyday relevance, emotional and visual engagement and sensitivity to refractive correction for low-cylinder astigmats (0.75–1.00 DC, n = 74) wearing best spherical equivalent correction and then with astigmatism corrected. Results and Conclusions: The most promising visual elements involved or combined optimized textures, distracting patterns behind text, faces at a distance, and oblique text. 91.9% of subjects (95% CI: 83.2, 97.0) reported an overall visual improvement when viewing the images with astigmatic correction, and 96% found the images helpful to determine which type of contact lens to use. Our method, which combines visual science with design thinking, takes a new approach to creating vision tests. The resultant test scenes can be used to improve patient interaction and help low cylinder astigmats see relevant, every-day benefits in correcting low levels (0.75 & 1.00 DC) of astigmatism. ã 2015 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
Keywords: Subjective refraction Toric Low-cylinder Correction assessment Relevance
1. Introduction Routine patient visual acuity (VA) tests used during subjective refraction typically bear little relation to real life. Take, for example, the Snellen chart. While this tool is essential for eye care professionals (ECPs) in assessing VA, for the patient, the appearance of the chart is not something they will often come across in daily life. The outcome of such an assessment can also be difficult for patients to understand—the common benchmark and term heard by patients of “20/20 vision”, for example, might make some kind of sense when explained, but it can be difficult for the patient to visualise what these numbers mean. Sitting in an ECP practice, how should one visualise 6 m? Or understand what difference a
* Corresponding author. E-mail address: [email protected] (A. Milton).
refractive error of 1.00 D makes to daily tasks, like reading or driving? There is a significant gap between the artificial visual experience in the ECP’s consulting room and its static nature, and the real benefits of improved vision quality in the patient’s day-today life. The difficulty for the patient becomes more apparent at small refractive errors. In particular, patients with low levels of astigmatism (1.00 DC) may opt not to correct their astigmatism at all when using contact lenses, perhaps due to a true lack of comparison beyond artificial acuity tests, or by the ECP not demonstrating the vision performance benefit over spherical contact lenses. Despite the prevalence of clinically significant astigmatism (0.75 D) in at least one eye of 47% [1], industry figures in 2014 showed that only 21% of soft contact lenses sold in the UK were toric designs [2]. This suggests that there is still room for improvement, even for astigmats using spherical lenses as opposed to torics [3]. Several studies have also shown the impact that proper optical correction can have on everyday life [4,5]. Other
http://dx.doi.org/10.1016/j.clae.2015.07.004 1367-0484/ ã 2015 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
2
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
studies have shown that even moderate visual impairments degrade drivers’ ability to see pedestrians at night—even a relatively modest amount of refractive blur, equivalent to 20/ 40 vision, meant that drivers responded to pedestrians at a 3.6 shorter distance [6]. This highlights the need for patients to use full refractive error correction, whether using spectacles or contact lenses. The purpose of this work was to develop a methodology for creating a novel visual assessment test – or visual “target” – that highlighted improvements to visual performance with cylinder correction. Visual elements in a scene that are particularly sensitive to refractive error were designed to demonstrate the benefits of full vision correction in a way that is more engaging, noticeable and important for the patient. 2. Methods The steps of the development method are depicted in the flowchart (Fig. 1) and are described in this section. 3. Exploration of vision optics and perception The effect of refractive error on the patient’s ability to resolve different visual elements is well documented [8]. One example is contrast sensitivity: take a one-dimensional sinusoidal grating (Fig. 2) projected onto the retina. The visual system’s ability to discriminate troughs and peaks of the light level depends on both the frequency of the light pattern (typically measured in cycles per degree) and the amplitude (or modulation, i.e. the difference in light level between troughs and peaks). Typically, a healthy corrected visual system can discriminate up to around 40 cycles per degree (LogMAR 0.10), but this is reduced as optical defocus increases [9,10]. Another example is the patient’s ability to resolve optotypes, even at high contrasts. Typically, a corrected visual system can resolve optotypes up to around 30 cycles per degree (LogMAR = 0.00), but increasing optical defocus by 1.00 D reduces this typically to less than 20 cycles per degree (LogMAR > 0.18). More precisely, given sphere (S) and cylinder (C) defocus at an axis a, the blurring strength |u| is given by qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi C C C juj ¼ M2 þ J 20 þ J245 ; M ¼ S þ ; J ¼ cos2a; J45 ¼ sin2a 2 2 2 M represents the equivalent defocus, J0 the vertical/horizontal astigmatism, and J45 the oblique astigmatism.
Fig. 2. One-dimensional sinusoidal grating.
Remón et al. [10] found empirically [11] that for a standard Snellen letter chart, the relationship between the blur strength |u| and VA was best fit by the linear equation LogMAR = 0.28|u| 0.08. So, even relatively small amounts of defocus can lead to measurable differences in VA. Using these equations we can predict the change in logMAR expected by 0.75 diopters of astigmatism. For |u| = 0, logMAR = 0.08. For |u| = 0.375 (0.75 D uncorrected cylinder), logMAR = 0.025. So DlogMAR = 0.1, equivalent to about 1 line on a VA chart, is the predicted loss in monocular high contrast acuity for 0.75 D of uncorrected astigmatism. In both cases, optical defocus causes a “blurring” of visual elements as they pass through the eye and are projected against the retina. However, while the eye optically limits the resolution of visual elements, the visual system is sometimes able to compensate for missing information. One well documented example is hyperacuity [12], where the alignment of two lines can be resolved with up to ten times better accuracy than VA typically allows. Other learning effects are also known to influence VA results, particularly in the case of optotypes [13]. These effects highlight the role of perception in vision to make sense of the world around us. Visual illusions play on these effects to great success, fooling the visual system in ways that surprise and engage. In the development of the scene, a number of different visual illusions were explored, and two illusions were of particular interest. Fig. 3 shows an example of the “Dr Angry and Mr Smile” illusion [14], of which the “Einstein/Monroe” illusion is a variant. In this image, low spatial frequencies are used to create the image of a calm face, while a high-spatial-frequency image of an angry face is superimposed over the top. When the image is placed at a far enough distance (or the viewer’s optical defocus is high enough),
Fig. 1. Flowchart highlighting main activities carried out in the scene development.
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
3
Fig. 3. Dr Angry and Mr Smile illusion. A high frequency angry face is superimposed over a low frequency calm face. Reprinted with permission from Elsevier [14].
the high-frequency angry face cannot be resolved fully by the viewer’s visual system, leading them to only see the low-frequency calm face. After bringing the image closer (or after optical correction), the high-frequency image becomes resolvable. Importantly, the change is binary: compared to standard VA tests that normally present a sliding scale, most visual illusions present only two options, making the change more noticeable. This takes advantage of the contrast sensitivity function to reveal the highfrequency image only when the visual system is able to detect it. Fig. 4 is an example of the “John Lennon” illusion. Here, a dark grey outline of a face (in the original, John Lennon’s) is placed onto a slightly lighter grey background. Overlaid on top is a hard grating of black lines at a relatively high frequency. At distance (or with defocus), the grating becomes blurred, allowing the face underneath to become visible. As the viewer moves closer (or is corrected), the grating becomes visible. Since the grating has a much higher contrast than the underlying face image it becomes impossible to see the face. This effect is a result of both contrast sensitivity and contrast discrimination [15], where the eye is unable to detect two different signals (the high-frequency grating and the low-frequency face) because of their different modulation (or contrast). It is worth noting that this effect is inverted: ideally a visual element provides a benefit when the patient is properly corrected, but in this case the face becomes visible when uncorrected. In addition to existing knowledge on VA and the exploration of visual illusions, aspects of the patient’s life where vision is also impaired were also considered. For example, driving at night, one is often confronted with very high contrast from sources of light in darkness, which can serve to distract or dazzle the driver. This can be made worse when driving in poor weather, such as rain. Typical city and town scenes were also investigated, picking out elements that exhibit high contrasts, complex textures, or embed important information for the viewer. Moving media was also considered: many patients are exposed daily to TV images which show moving text (such as a news channel ticker tape). The effect of defocus on patients in these types of environment is relatively unknown, but it is precisely in these environments, particularly activities such as driving, where improved vision is most important for the patient. 4. Prototyping visual elements Given this understanding, the goal was to create a number of visual elements that create an engaging, noticeable, and important
difference to patients with small refractive error (particularly astigmats with cylindrical error 1.00 DC) when their vision is corrected. “Engaging” means that the element is able to hold the attention of the viewer and encourages them to interact with it and further explore it. “Noticeable” means that the viewer perceives a clear difference in the element before and after correction, ideally binary, in the sense that something that was completely invisible before is suddenly made visible. The meaning of “important” is more difficult to quantify: different things are important to different people. In general, this is classified as something relevant to the viewer (e.g. recognizable, familiar, or meaningful) but also where it makes a real difference in the viewer's life; for example, the ability to do something better or more safely (such as driving a car, or working with machinery). By combining all three, it could create a “wow” moment for the patient that is quick and intuitive; this is covered further in the discussion. The primary focus at this stage was noticeability, and four broad areas were explored whose effect could make a noticeable difference: motion tracking, visual overstimulation, pattern recognition, and contrast sensitivity. Note that with some of the elements discussed below these areas overlap, particularly with contrast sensitivity. In many of these elements, gratings are referred to with particular frequencies measured in cycles per degree, as well as computed contrast, which is a measure of the amplitude of the grating. The computed contrast is given by ratio of the difference in brightness between the lightest and darkest colours in the grating with the maximum possible brightness (white colour). In each case, low cylinder astigmats (1.00 DC) were particularly targeted. 4.1. Motion tracking Moving visual elements pose problems for the visual system. In general, moving elements are harder to recognize and provide less time for the visual system to process them before they move outside the eye’s foveal vision, requiring constant movement of the eye. Two particular elements were looked at: rotating gratings, and text in motion. Fig. 5 shows a snapshot of a rotating grating. The animation consists of two letters, placed next to one another, which are created from a masked grating (35 cycles per degree, simulated contrast ratio 0.2). The edges of the letter forms are blurred to prevent artefacts caused by the visual system’s ability to detect
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
4
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
Fig. 5. Snapshot of a rotating grating (contrast increased for publication).
screen at a typical reading speed of 1–200 wpm. This suggests the predominant effect is the astigmatic blur increasing the time required for the brain to recognise each letter and word, rather than difficulties in the eyes tracking the words due to their angular speed across the field of vision. The optimal speed for the test is when the brain can keep up reading the text without astigmatic blur, but not with astigmatic blur, creating a clear and binary distinction. Using names also has the advantage that learning effects can also be partly bypassed, particularly for unusual names that the patient might not be familiar with. This kind of animation will be recognizable to the patient from film credits, but scrolling the text in other directions could be reminiscent of ticker-tape text on news channels. 4.2. Visual clutter
Fig. 4. (a) John Lennon illusion. A man’s face with glasses with low contrast is set behind a high contrast grating. (b) The man’s face with increased contrast without the high contrast grating.
edges, and the black cross acts as a fiducial marker to allow the eye to properly accommodate and bring the plane of the animation into focus. The gratings for each word rotate around the centre of each letter. Each word “flashes” as the grating becomes alternately aligned and anti-aligned to the principle axis of the astigmatism. The speed of rotation was not especially critical for the effect; it should give a perceptible pulsing effect (so not too fast), but the patient should not have to wait too long for each cycle. A rotation rate of around 1 Hz worked well. Fig. 6 shows a snapshot of text in motion. This animation scrolls a list of names, much like film credits, within a rectangular area. At a threshold rate of scrolling, viewing the animation with a small amount of astigmatic blur (0.75 DC) of any axis produced a noticeable difference to the ease of reading. This threshold rate of scrolling was roughly equivalent to the words passing across the
These elements explored the effect that distraction, or visual crowding or clutter, can have on recognition of text and patterns. Particularly in modern societies, the average person is subject to a huge number and variety of visual stimuli: television, computer games, signage, advertisements on billboards, artificial lighting, etc. Each of these forms of media typically present complex and highly-detailed images, sometimes making it more difficult to focus on and interpret the most pertinent information in the subject’s visual field. In some situations, this type of distraction can be dangerous: when driving, for example, rapid recognition of road signs and other vehicles helps prevent accidents. The connection between defocus and the effect of visual clutter is generally poorly understood, but a study by Ho et al. [15] showed that older patients with poorer VA did worse than younger patients in a visual search task when visual clutter was introduced [16]. Earlier work [17,18] also showed the effect that crowding and noise has on the ability to recognize letters quickly. It was therefore postulated that artificially introducing clutter into a visual target might allow “revealing” of information to the patient when their vision is corrected. Fig. 7 shows a line of text surrounded by visual clutter. The clutter itself is designed to somewhat match the characteristics of
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
5
surrounded by bright circles reminiscent of artificial lights. In both cases, it was hypothesized that poorer VA makes it more difficult for the visual system to separate the semantic content (i.e. the words) from the background compared with not having visual clutter at all, and thus making it more challenging for the patient to read. It is well understood that contrast discrimination of the human eye varies with the difference in modulation of different signals. This can be considered to be a form of visual overstimulation: high-contrast elements can essentially “drown out” weaker lowcontrast elements in the field of view. Building on the understanding from the John Lennon illusion, a number of visual elements were created, of which a typical example is shown in Fig. 9. Highcontrast visual patterns are overlaid onto a lower-contrast texture or image. If the patient is uncorrected, the high-contrast pattern becomes blurred and is more difficult to detect, revealing the lowcontrast pattern underneath. However, in this case the reverse
Fig. 6. Text in motion.
Fig. 7. Text surrounded by visual clutter.
the text itself, in terms of colour, contrast, and directionality. The edges of letters were softened to limit the ability of the visual system to detect letter edges. Fig. 8 shows another embodiment that seeks to imitate a night-time driving scene, using text
Fig. 8. Text surrounded by visual clutter (night-time variant).
Fig. 9. (a) High contrast pattern overlaid on low contrast image. (b) The low contrast image without the high contrast pattern.
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
6
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
Fig. 10. High-frequency image of a smiling woman overlaid onto a low-frequency image of a calm-faced woman.
would be preferred: namely that correction of defocus would reveal the more interesting pattern (or John Lennon’s face).
Fig. 11. Two words composed from gratings stacked atop each other (contrast increased for publication).
4.3. Pattern recognition In order to make sense of the world around us, our visual system relies heavily on pattern recognition. This can be made very apparent in some images, where a seemingly random collection of blobs suddenly takes on meaning. This effect is very abrupt (sometimes categorized as a Gestalt shift), and once the visual system “sees” the new image, it becomes impossible to contradict it. Fig. 10 shows an example of an image where a high frequency image of a smiling woman is overlaid on a low-frequency image of the same woman with a neutral expression. This builds on the success of the “Dr Angry and Mr Smile” illusion, and is taking advantage of the visual system's ability (and in fact propensity) to detect faces. Faces and their expressions also have an emotional and social meaning for the viewer, which adds relevance and interest to the image. It works as already described in the explanation of the “Dr Angry and Mr Smile” illusion, where the high-frequency features that show the smiling face are only visible once refractive error is fully corrected (i.e. including low amounts of astigmatism).
Fig. 12 takes inspiration from standard contrast sensitivity test charts. Round targets are arranged in rows and columns across a grey background. Each target contains a grating with a particular spatial frequency between 10–60 cyc/deg at a fixed contrast (0.2) and at a random orientation (but biased towards horizontal and vertical). Regardless of the VA of the viewer, some of the targets will be unresolvable. For uncorrected patients, even small amounts of defocus will cause some of the targets to disappear. In any image of high enough resolution and viewed from a far enough distance, elements of the image become impossible to see since they fall beyond the threshold of contrast detection. These are typically the finest details: fine hairs, subtle textures, small text, etc. Fig. 13 shows an example image containing some of these
4.4. Contrast sensitivity As already discussed, contrast sensitivity is one of the bestunderstood and widely researched performance indicators of visual quality. While it has underpinned some of the visual elements already discussed, elements that relied solely or heavily on contrast detection were investigated separately. Fig.11 shows two words, composed from high-frequency gratings (30 cycles per degree) with a simulated contrast ratio of 0.2. Each of the gratings is oriented differently from the other: one at 0 degrees, and one at 90 degrees. For typical “with-the-rule” or “against-therule” astigmats, one of the two words will appear sharper and more readable than the other. The grey colour of the background is precisely the median value of the darkest black and lightest white contained in the grating: when the grating is blurred due to defocus its average colour will match that of the background, making it disappear. The choice of words can be altered to create interesting phrases that change their meaning as more words become visible.
Fig. 12. Random array of gratings (contrast increased for publication).
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
7
Fig. 13. High-frequency, detailed image. Fig. 15. Final target scene in a cultural setting. The arrows annotate different elements in the image referred to earlier in the text. (A) Text in perspective (see Fig. 14). (B) Text with visual clutter (see Fig. 6). (C) High-frequency details (see Fig. 13). (D) Faces.
described above were chosen for further development. Each was rated on the criteria described above: was the effect noticeable, engaging, and important? In each case, this was determined through a combination of qualitative subjective assessment (using subjects with astigmatism in the range 0.75–1.25 DC, or with astigmatism induced using trial frames, n = 3) and with insights from earlier research. The ratings are given in Table 1. High-frequency detail clearly provided a high degree of impact for viewers across all three criteria, as did text in perspective. Text in motion also scored
Fig. 14. Simulated row of shops in perspective with signage.
details. Several such images were optimized so that the finest and richest details in the image were unresolvable to patients with small refractive errors (between 20 and 30 cyc/deg). These images had a range of features across different contrasts and types of pattern, from geometric to highly random. Fig. 14 shows a simulated row of shops with signage in perspective. Each shop front has signage that becomes smaller as the shop moves further back into the image. This image essentially encodes optotypes from the Snellen chart into an image that is more familiar and can be more easily related to by patients than the standard chart. Ideally, the signs in the image would be optimized so that the majority of the text is equivalent to a grating between 20 and 30 cycles per degree (assuming an optotype, e.g. “E”, is representable as 2.5 cycles of a grating). A wide range of sizes helps to capture a wider number of patient prescriptions. Perspective allows us to modulate the vertical and horizontal frequencies independently for particular orientations of astigmatism. 5. Selecting elements for the final scenes It will be apparent that none of the images presented so far fulfil all the set criteria: while several of the images present effects which are certainly noticeable, it is much more difficult to argue that they are engaging, or indeed important. To achieve this, each of the elements required further development before they could be combined into a final image. To avoid over-complicating the final image and in order to ensure a better result, four of the nine elements in Figs. 5–14
Fig. 16. Final target scene in a retail setting. For the meaning of annotations, see Fig. 15. Table 1 Ratings of each of the nine explored visual elements. Items with asterisks were incorporated into the final scenes. Element
Noticeable
Important
Engaging
Total
High-frequency detail* Text in motion Array of gratings Facial expressions* Text in perspective* Text with distraction* High-contrast patterns Gratings and text Rotating grating
6 5 4 4 4 3 3 3 2
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
8
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
highly, but since it requires a digital display it was felt to be impractical for the final hand-held tool. Digital application of the scenes could be considered in subsequent phases of development. While array of gratings also scored highly, there was a lack of relevance and importance in rating overall visual quality, so it was dismissed. 6. Clinical study A clinical study was performed to evaluate the scenes, visual features and viewing distance that demonstrate the most visual improvement and to determine if the demonstration is clinically useful in subjects with low astigmatism. This was an open label, single arm, multi-site, one-visit, bilateral, non-dispensing study. Subjects were astigmats aged between 18 and 39 years of age. Subjects’ vertex corrected spherical distance refraction was between 1.00 D and 5.00 D, with refractive cylinders between 0.75 DC and 1.00 DC in each eye. All were habitual soft spherical or toric contact lens wearers and had a best corrected VA of 6/7.5 + 3 or better in each eye. Subjects had “normal” eyes i.e. no chronic disease, routine use of ophthalmic medication, or active infections. Each scene was printed for viewing at 50 cm (hand-held; “near”) and 1.8 m (poster; “far”), such that the angular size remained constant. Room illumination was controlled with a minimum of 400 lux across all sites. Subject’s best spherical equivalent correction was determined by subjective spherical refraction. Subject was given an explanation what astigmatism was and the purpose of the study. Subjects’ wore their spherical equivalent correction with daily disposable, hydrogel contact lenses (etafilcon A) binocularly. This demonstrated the vision without their astigmatism corrected. When a specially designed trial lens that incorporated +0.25 DS compensation with 0.75 DC power was placed in front of the subjects’ eyes, this simulated their vision when wearing contact lenses with astigmatism correction. The trial lens used in this study incorporated +0.25 DS compensation with 0.75 DC power, based on the expectation that the best sphere refraction would be approximately 0.25 DS more than the sphere component of the sphero-cylinder refraction to keep equivalent sphere shift less than 0.13 D with and without the flipper. The +0.25 DS sphere compensation was used rather than +0.37 DS (perfect compensation) due to the 0.25 D steps of contact lens products. Therefore, the trial lens had +0.25 D in one meridian and 0.50 D in another meridian 90 degrees apart. When the lenses were rotated to match the subjective best spherocylindrical refraction axis, it gave a prescription power of “+0.25/0.75 subject’s axis”. While looking at the scenes, trial lenses were introduced and then removed so visual differences could be evaluated. The order of presenting the scenes was randomised while the order of viewing distances was static such that assessed scenes in near and then far distance. A questionnaire was conducted to assess the preferred scene, features and viewing distance that showed the greatest visual benefit(s), and whether the introduction of the cylinder affected their subjective vision performance. They were also asked whether they would be likely to try or recommend toric soft contact lenses, based on the scene demonstration. Additionally, the ECPs completed a post-study qualitative interview on ease of use and the potential impact of the scenes on toric soft contact lens prescribing. The plan was to enrol approximately 70 subjects with an aim to complete at least 60. Sample size calculation was based on the result of previous (unpublished) work (n = 46) that indicated 90% of subjects found the demonstration of astigmatism with a similar trial lens useful. Assuming 90% of targeted population experience vision improvement using the trial lens, and assuming more than
75% of the subject would experience vision improvement with the trial lens, at least 60 subjects was needed to achieve the hypothesis test (i.e. correctly reject the primary null hypothesis) with a minimum of 80% power based on one sample binomial exact test using 2-sided with alpha = 0.05 (SAS Proc Power was used). Considering the 15% dropout rate, the enrolment goal was 70 subjects. All data summaries and statistical analyses were performed using the SAS software Version 9.3 (SAS Institute, Cary, NC). Efficacy variables were analysed for all subjects who completed the study per protocol and safety variables were summarized for all subjects who received the study article. 7. Primary endpoint The primary endpoint was the proportion of subjects experiencing overall visual improvement when viewing both scenes at both distances with astigmatism correction. Subjects rated the statement, “When I looked with the astigmatic correction, I experienced overall visual improvement”, using a five-level agreement scale (agree strongly, agree somewhat, neither agree nor disagree, disagree and disagree strongly). These five responses were categorised into a binary outcome, where “agree strongly” and “agree somewhat” were assigned the value 1 (visual improvement) and the other responses were assigned the value 0 (no visual improvement). The null and alternative hypotheses were: H0 : p 0:75; Ha : p > 0:75;where p was the expected proportion of subjects who experienced overall visual improvement with astigmatism corrected under H0. For the primary variable, an exact binomial 95% CI was constructed with a significance level of a = 0.05. If the lower bound of the CI was greater than 0.75, then it was concluded that the astigmatism correction effectively demonstrated the improvement of the vision quality for low cylinder astigmats. This primary analysis was conducted with an overall type I error rate of 5%. 8. Secondary endpoints The secondary endpoints were the proportions of subjects experiencing visual improvement for each scene–distance combination. For each scene–distance combination, subjects were asked to choose which one of five responses (much better, slightly better, no difference, slightly worse and much worse) best described how they felt about their vision. These five responses were categorized into the binary outcome; the top two responses (“much better” and “slightly better”) were assigned the value 1 (visual improvement) and the rest of the responses were assigned the value 0 (no visual improvement). This binary outcome was analysed using a generalized estimating equation (GEE) model with logit as the link function. The model included age, sequence of presenting the images, period, scene, viewing distance and the interaction between scene and viewing distance as fixed factors. An unstructured covariance structure was used to model the correlation between measurements within the same subject and viewing distance across the images. The proportions of subjects who experience visual improvement were estimated with 95% confidence intervals for each scene–distance combination. A simulated-based method was employed to adjust type I error for multiple comparisons 9. Results 9.1. Creating real-world images Each element was individually rated as being somewhat engaging, noticeable, and important, but the aim was to enhance
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
each of these by combining the elements together into a final image, or target. Two “real-world” scenes were created, and to allow maximum flexibility these scenes were created digitally in 3D architectural software (CAD). In order to make best use of this medium, industry experts in architectural visualisation were involved to help plan and design the final targets (Ciaran Ryan Ltd., London, UK). This helped to ensure that the final scenes had a high level of realism and were visually appealing, while maintaining the principles that underpin the original visual elements. To transfer the elements into the final scenes, a series of tools were developed that provided a common design language, translating the underlying scientific concepts into a set of rules to be followed when making the scenes. These tools were different for each of the visual elements, and are described in the following sections.
9
in adverts or signage that vie for the viewer’s attention on the high street or in the shopping mall. By incorporating these images into billboards, adverts, and other signage, these elements were added to the scenes in a way that appeared natural. 9.5. Faces Initially, the “Dr Angry, Mr Smile”-type image was developed into more realistic and higher-definition faces to use in the final scene. However, reactions to these faces were predominantly negative: informal testing showed that the faces appeared unnatural both before and after correction. The approach was therefore simplified, instead using a particular size of face in the final image that in testing showed the biggest difference in recognition before and after correction. At 1.8 m, this size was 3–4 cm from the chin to the top of the head.
9.2. Text in perspective 10. Final targets Optotypes in the range 20–30 cyc/deg were determined to be most likely to become unreadable for low cylinder defocus. Using a spreadsheet in Microsoft Excel, a simple tool was created where, given a piece of text (such as a car license plate) and the desired VA required to read the text, the tool calculated the distance from the viewer and the height of the text in CAD space. This allowed elements of text in the CAD environment to be created quickly that, when printed and viewed at a set distance, would have the desired cycles per degree, and hence the desired visibility. A more sophisticated version of the tool also allowed alteration of the angle of the text relative to the viewer in CAD-space and calculated the resulting cycles per degree of the printed text. This meant there was complete freedom in how text in the images was positioned, enabling the creation of scenes that were more realistic and looked natural. A future version of this tool might support customization of the images. For example an ECP might add their practice name onto a shop front in the scene. 9.3. High-frequency detail From earlier results, geometric patterns and fine lines in images were determined to be the most likely to become difficult to see when defocus was increased, particularly at relatively low contrasts (<0.5). This is likely due to their similarity to grating patterns— breaks or discontinuities in the pattern could be resolved with hyperacuity. Repetitive geometric textures are relatively uncommon in natural scenes, but are prevalent in cityscapes: brickwork, windows, pavements, etc. Setting both of the scenes in city environments allowed natural-looking textures on buildings to be used that revealed higher level of detail when vision was corrected. The range of line widths that became difficult to resolve for uncorrected patients were specified, which at 1.8 m distant corresponded to line widths between 0.5 mm (30 cyc/deg) and 0.2 mm (60 cyc/deg). Using these as a guideline, Ciaran Ryan Ltd., created a number of textures for building facades and pavements that had line widths falling predominantly in this range. 9.4. Text with distraction Two different hypotheses for text with distraction were explored. In the first, it was supposed that text would become more difficult to read because it became less easily distinguishable from its background. This was the mechanism behind the effect already mentioned and shown in Fig. 5. While effective, it was concluded that visually the images looked too artificial and could not be incorporated into a final scene. The second hypothesis was based primarily on the effect depicted in Fig. 7. These kinds of images are much more commonplace in the real world, particularly
The two scenes were both city scenes, one a “cultural scene”, and the other a “retail scene” (Figs. 15 and 16). Both scenes contained the same visual elements, but contrasted each other in several ways. The cultural scene was lighter, and had a particular focus on informative signage (such as way finding signs). The perspective in the cultural scene is also weaker than the retail scene, where one can “see farther” down the street into the distance. In both scenes, the virtual camera has been placed at eyelevel, giving the impression that it is the view one would have standing in the scene. The objects and lighting were also carefully chosen to provide realism and variety in both images. The rationale for using street scenes brings us back to the original criteria. Street environments are familiar to most people and are therefore very relevant. Often, it is also important that signage can be seen clearly so that the viewer can navigate easily or read adverts. These scenes are typically engaging as well: the variety of textures, colours, and text draws the attention of the viewer and are rich in detail. To test noticeability, the final scenes were presented to n = 4 subjects with varying levels of astigmatism (0.75–1.25 DC). The subject was then asked to apply (and remove) correction of their astigmatism with trial lenses. These subjective tests are being followed up by a more comprehensive trial (to be described in a forthcoming publication). Preliminary reactions showed some promising trends. In particular, patients reacted strongly to the higher detail visible in the scene after correction. Several patients also noted details that only became visible after correction, particularly signage text. Encouragingly, patients also found it easier to relate to the improvement in their VA to something understandable, such as being able to “see further” down the street, rather than “my vision is 20/20”. Two formats of the final scene were created. A poster version was printed on standard A0-sized paper to be viewed at 1.8 m. A second, hand-held version was printed on standard A4 paper to be viewed as 0.5 m. These formats were chosen to be mindful of the constraints in a typical ECP’s practice: wall-space is generally limited, so the choice of a poster or handheld version gives the ECP more flexibility. It should also be straightforward to adapt the handheld scene to other similar formats, e.g. in a magazine. The scenes might also be adapted to large digital screens suitable for viewing at a distance, or perhaps tablet computers suitable for viewing close up. 10.1. Clinical study results A total of 74 binocular astigmatic subjects were enrolled and completed the study (mean age 28 5.8 years, range 18–39);
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
10
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
Fig. 17. Proportion of subjects reporting visual improvement when viewing the scenes with astigmatic correction, overall and for each scene–distance combination (n = 74).
thirty-nine subjects habitually wore toric soft contact lenses with the remainder wearing spherical soft lenses. The majority of subjects (91.9%; 95% CI: 83.2, 97.0) reported an overall visual improvement viewing the scenes with correction for low levels of astigmatism (Figs. 17 and 18). For both scenes viewed at the far distance of 1.8 m, visual improvement was noted (94.0% (95% CI: 81.91, 98.19) experienced improvement with the daytime/ courtyard scene; 91.6% (95% CI: 78.20, 97.07) for the night-time/ street scene). When looking at scene preference, 46% preferred the night-time/street scene, 42% the daytime/courtyard scene and 12% had no preference. For preferred viewing distance, 60% chose the 1.8 m testing distance, 24% chose 50 cm and 16% had no preference. “Text in Perspective” and “Text with Distraction” features demonstrated the most visual improvement in both scenes (Fig. 18). The vast majority of subjects (96%) believed the scenes
would be helpful when considering the benefit of toric soft contact lenses (Fig. 19). The qualitative interview was conducted with 11 US ECPs, with all finding the scenes extremely easy to use. They felt it could reduce chair time with toric soft fitting, thereby increasing their likelihood to prescribe these lenses. Practitioners felt the key patients to target would be spherical CL wearers and new CL fits, and that using the scene addressed barriers often cited in fitting low astigmats with toric soft contact lenses, such as time to explain the benefits of toric lenses and the ability to effectively demonstrate the visual benefits of a low cylinder toric lens. 11. Discussion This is a new approach to vision assessment for patients with low levels of astigmatism and has resulted in two final scenes,
% of subjects visual improvement with asgmac correcon when viewing scenes
100 90 80
Text in Perspecve
72.1
70 60
Text with Distracon
50 41.4
Face
40 30 20
23.4
High Frequency Detail
18 15.3
10
10.4
7.7 7.2
0 Dayme Courtyard
Nighme Downtown
Fig. 18. Visual improvement with scene visual features (n = 74).
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
100
11
96 93.2
90
85.1
80
% of subjects agree
70 60 50 40 30 20 10 0 Recommend toric lenses to others
Likelihood to try toric lenses
Helpfulness to try toric lenses vs. non-toric lenses
Fig. 19. Subjective impressions of from subject post-fit questionnaire (n = 74).
designed to better demonstrate the benefits of correcting cylinder powers. The method was grounded in an understanding of fundamental vision science and an exploration of perceptual effects, creating scenes that did not just change noticeably for patients after correction (as with e.g. a Snellen chart), but also engaged them, and showed them how the correction can be important in their day-to-day lives. The combination of these three aspects is critical in distinguishing these scenes from typical VA tests. The Snellen chart, for example, appeals to a rational mentality: the scenes, by contrast, are designed to appeal to patients on both a rational and an emotional level. Setting the test in a scene familiar to the patient (and also culturally relevant) that is engaging and evokes the sense of being out in the real world helps to achieve this, and makes connecting with and understanding the real-world benefit more intuitive and immediate. While it is true that the scenes have been designed to highlight the difference between corrected and uncorrected astigmatism, this does not make them biased in the sense that they over-emphasize the effects: the elements in the images can all be found in the real world, and the images bring them into the ECP’s consulting room. The complexity of the scenes with several elements also allows patients to discover the benefits for themselves, and particularly what the patient could be “missing-out” on by not correcting their astigmatism. This puts a stronger focus on assessment of visual quality, as opposed to just VA. The scenes also have the potential to change how ECPs interact with patients. The tools can be used in many different ways with patients, both in the choice of format, as well as how the patient is guided through the image. The poster tool requires more wall space, but its sheer size makes it quite visually arresting, and helps transform the perhaps sterile environment of the clinic into one that is more inviting, comfortable, and familiar. Conversely, the handheld version needs far less space, and allows the patient to hold and control the scenes themselves. Some ECPs may take their patient
from the consulting room to a bigger room or to view outside the differences in vision performance with trial lenses; however, this is not always possible due to time and/or space, and could introduce more variability with different conditions and contrast, hence the scenes allow demonstration of realistic everyday images that can be used in the consulting room. In most cases, guidance from the ECP will be minimal; selfdiscovery is typically a more satisfying experience than being told what to look at by someone else, and people will discover and respond to elements in the image differently. It also puts the patient in control, rather than the clinician, particularly when it the target is used with the hand-held correction tool. This empowerment will stimulate better dialog between patients and ECPs, and help patients to reach a better understanding of their vision correction options and how they will impact vision quality. The method outlined is not limited to creating static images—it can naturally be extended to different image formats, as well as other media such as video (particularly using modern, highresolution displays). It is not limited to low astigmats (who were the original target of this work); presbyopes could also use the scenes to assess vision quality. A clinical trial of the scenes showed encouraging results, and the scenes were generally well liked and accepted by both ECPs and patients. The majority of low astigmatic subjects experienced overall visual improvement when viewing both scenes at distance and near and found the scenes demonstrated the benefits of astigmatic correction. Although the 1.8m testing distance demonstrated greater visual improvement, the hand held version was still found to be impactful, and may be more practical to use than the distance poster in some ECPs’ consulting rooms. Also, whilst originally developed for use with low astigmats, the scenes could also be impactful for demonstrating the benefits of astigmatic correction with patients with higher levels of uncorrected cylinders. The choice to fully correct astigmatism is a decision between the patient and their ECP, and is not always chosen by patients with
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004
G Model CLAE 832 No. of Pages 12
12
A. Milton et al. / Contact Lens & Anterior Eye xxx (2015) xxx–xxx
small refractive errors (particularly low cylinder) in the ‘non-real world’ consulting room environment. The scenes have the potential to revolutionize how ECPs interact with patients and fundamentally change how, in a clinical setting, patients perceive the vision quality benefits of correcting low levels of astigmatism. Acknowledgement This research project was funded by Johnson & Johnson Vision Care, Inc. Johnson & Johnson Vision Care are developing the scenes for use in practice. References [1] G. Young, A. Sulley, C. Hunt, Prevalence of astigmatism in relation to soft contact lens fitting, Eye Contact Lens 37 (2011) 20–25. [2] (b) A. Sulley, G. Young, K.O. Lorenz, C. Hunt, Clinical evaluation of fitting toric soft contact lenses to current non-users, Ophthalmic Physiol. Opt. 33 (2013) 94–103Johnson & Johnson Vision Care Data on file 2015; Internal Analysis based on independent third party data. Disposable toric soft fits in UK Jan–Dec 2014. [3] S.K. West, G.S. Rubin, A.T. Broman, B. Munoz, K. Bandeen-Roche, K. Turano, How does visual impairment affect performance on tasks of everyday life? The see project, Arch. Ophthalmol. 120 (2002) 774–780. [4] A.L. Coleman, F. Yu, E. Keeler, C.M. Mangione, Treatment of uncorrected refractive error improves vision-specific quality of life, J. Am. Geriatr. Soc. 54 (2006) 883–890.
[5] B.S. Chu, J.M. Wood, M.J. Collins, The effect of presbyopic vision corrections on nighttime driving performance, Invest. Ophthalmol. Vis. Sci. 51 (2010) 4861– 4866. [6] J.M. Wood, R.A. Tyrrell, A. Chaparro, R.P. Marszalek, T.P. Carberry, B.S. Chu, Even moderate visual impairments degrade drivers’ ability to see pedestrians at night, Invest. Ophthalmol. Vis. Sci. 53 (2012) 2586–2592. [8] D.A. Atchison, R.L. Woods, A. Bradley, Predicting the effects of optical defocus on human contrast sensitivity, J. Opt. Soc. Am. A 15 (1998) 2536–2544. [9] G. Smith, Relation between spherical refractive error and visual acuity, Opt. Vis. Sci. 68 (1991) 591–598. [10] L. Remón, M. Tornel, W.D. Furlan, Visual acuity in simple myopic astigmatism: influence of cylinder Axis, Opt. Vis. Sci. 83 (2006) 311–315. [11] G. Westheimer, Editorial visual acuity and hyperacuity, Invest. Ophthalmol. Vis. Sci. 14 (1975) 570–572. [12] H. Brom, A. Kooijman, L. Blanksma, G. Rij, Measurement of visual acuity with two different charts; a comparison of results and repeatability in patients with cataract, Doc. Ophthalmol. 90 (1995) 61–66. [13] P.G. Schyns, A. Oliva, Dr. Angry and Mr. Smile: when categorization flexibly modifies the perception of faces in rapid visual presentations, Cognition 69 (1999) 243–265. [14] P.G.J. Barten, Contrast Sensitivity of the Human Eye, SPIE Press, Washington, 1999. [15] G. Ho, C.T. Scialfa, J.K. Caird, T. Graw, Visual search for traffic signs: the effects of clutter, luminance, and aging, Hum. Factors 43 (2001) 194–207. [16] B. Eriksen, C. Eriksen, Effects of noise letters upon the identification of a target letter in a nonsearch task, Percept. Psychophys. 16 (1974) 143–149. [17] M.C. Flom, F.W. Weymouth, D. Kahneman, Visual resolution and contour interaction, J. Opt. Soc. Am. 53 (1963) 1026–1032.
Please cite this article in press as: A. Milton, et al., Demonstrating correction of low levels of astigmatism with realistic scenes, Contact Lens & Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.07.004