Bifocal and Multifocal Contact Lenses

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Bifocal and Multifocal Contact Lenses EDWARD S. BENNETT

CHAPTER OUTLINES

Introduction, 265 How to Achieve Bifocal Vision,  266 Soft Lenses,  266 Preliminary Evaluation and Patient Selection, 266 Presbyopic Contact Lens Options: Single Vision Contact Lenses With Reading Glasses, 269 Monovision, 269 Presbyopic Contact Lens Options: Modified or Enhanced Monovision and Modified Multifocal or Bifocal Lenses,  271 Presbyopic Contact Lens Options: Bifocal/ Multifocal Contact Lens Designs,  271

Introduction Presbyopia, resulting from a gradual decrement in visual function at near, is one of the most prevalent ocular conditions resulting in patient complaints and dissatisfaction in the 40 and older age group. Nevertheless, it also represents an outstanding opportunity for potential contact lens wearers. Presbyopic patients represent the largest growing segment of the population and the largest untapped section of the contact lens market (Bennett & Jurkus 2005): There were 78 million so-called ‘baby boomers’ born in the United States between 1946 and 1964 (Schwartz 1999). ■ Only 3% of presbyopes currently wear some form of presbyopic contact lens correction (Wooley 1998, Rigel & Castellano 1999). This is consistent with a survey that concluded that there has been a significant underprescribing of contact lenses for the correction of presbyopia (Morgan et al. 2011). ■ In the United Kingdom, it has been found that the presbyopic market has greater potential for growth than the normal younger contact lens market (Edwards 1999, Meyler & Veys 1999). ■

The low use of presbyopic contact lenses is most likely the result of several factors (Bennett & Hansen 2004):

General Fitting Considerations,  272 Dispensing the Lenses,  272 Rigid Bifocal and Multifocal Lens Designs, 272 General Points,  279 Translating Designs,  282 Toric Bifocal Designs,  282 Troubleshooting, 282 Patient Education and Follow-Up Care,  285 The Future of Multifocal Lenses,  285 Summary, 286

It is common for patients to be told that bifocal contact lenses are not likely to be successful. ■ Multifocal contact lenses will not be successful if they are never presented as an option to presbyopic patients. ■

(For further information about multifocal contact lens prescribing, see Section 9, Addendum, available at: https:// expertconsult.inkling.com/.) Multifocal and monovision contact lens prescribing increased from 30% of fits in 2003 to 50% in 2010, although after that, it appeared to plateau (Morgan et al. 2016). Increases are likely because: Many baby boomers who have never worn corrective eyewear may choose contact lenses over spectacles because of vanity. ■ Current emerging presbyopes are more active than their predecessors and appear to be more determined to maintain their youthful appearance and active lifestyle. ■ More than 90% of contact lens wearers in the 35- to 55-year-old age category have worn contact lenses for a large period of their lives and are committed to continuing contact lens wear (Edmonds & Reindel 2012). ■

The benefits of multifocal contact lenses compared with spectacles include the following: One can avoid numerous head and gaze requirements associated with spectacle wear during computer use and other activities which require near vision at a level above primary gaze (Vassilieff & Dain 1986, Martin & Dain 1988). ■ Tasks involving numerous dynamic eye movements are more challenging for the multifocal spectacle wearer as a ■

They are often perceived by practitioners as being complicated or challenging to fit, resulting in the selection of easier options such as monovision or single-vision contact lenses in combination with reading glasses and multifocal spectacles (Hansen et al. 2003).

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result of viewing into the varying corrective powers with eye movement (Afanador et al. 1986). ■ Multifocal contact lenses move with the eye, minimising possible problems, as the wearer is typically looking through the lens centre. ■ Progressive addition spectacles can result in distortions in the size and shape of objects whose images extend beyond the limited intermediate and near zones (Diepes & Tameling 1988). The visual freedom that multifocal lenses provide is a powerful benefit, and presbyopic individuals can be among the most satisfied patients. Also, this cohort of patients represents the high end of earnings potential; therefore practice income generated from these patients – and their referrals – can build a contact lens practice. As manufacturing technology continues to improve, success rates increase and both practitioner and consumer confidence continues to grow. The purpose of this chapter is to review important clinical considerations in fitting the presbyope, including patient selection, lens designs, fitting and problem-solving.

History See Section 8, History, available at: https://expertconsult.inkling. com/, for the development of the various designs of lenses.

How to Achieve Bifocal Vision There are two ways to achieve bifocal vision: 1. Translation (see p. 272) refers simply to the shifting upward of the lens during downward gaze to allow the wearer to view through the near optics. These can be annular or concentric, or they can have separate powers similar to a bifocal spectacle lens. 2. Simultaneous or bivision (see p. 271) refers to lens designs in which multiple powers (i.e. near, distance and possibly intermediate) are in front of the eye at the same time. While the patient is looking at a distant object, the light entering the pupil from the near zone forms a very blurred image. The near image blur circle then covers a large area of the retina and is essentially ignored by the lens wearer. These can be: ■ annular or concentric ■ aspheric, where the back surface flattens at a particular rate, generating a gradual increase in plus power away from the centre of the lens. Back surface aspheric multifocal rigid gas permeable (RGP) lenses are popular today due to advances in manufacturing technology that result in better optical quality and the ability to incorporate higher add powers.

Soft Lenses Early soft bifocal or multifocal lenses gave poor optical quality. Manufacturing innovations provide better optical quality, variable add powers and the availability of weekly-to-monthly disposability which: ■ reduces cost to the patient ■ allows for replacement lenses

reduces dry eye–induced complications – more prevalent in the older patient base ■ allows the practitioner to try different lenses on a trial basis for limited time periods in an effort to achieve satisfactory vision. ■

The presbyopic ‘toolbox’ now includes: hydrogel and silicone/hydrogel multifocal lenses daily disposable multifocals in both spherical and toric powers ■ RGP standard and high-add lens designs ■ hyper-oxygen-permeable (Dk) hybrid lenses ■ scleral multifocal designs. ■ ■

Preliminary Evaluation and Patient Selection PHYSIOLOGICAL CHANGES IN THE PRESBYOPIC POPULATION Tear Volume and Quality (see Chapter 5) A reduction in tear volume is the most important change occurring over time. This can result in dry eye symptoms and can impact on contact lens wear. A progressive reduction in tear production results from a reduction in both the goblet cells of the conjunctiva and the mass of the lacrimal glands (Weale 1982). Caution is needed if an extended-wear schedule is prescribed, due to tear physiology and also the thickness of many presbyopic lens designs, making daily wear a preferable option for these patients. Clinical signs of dry eye must be ruled out (Bennett & Jurkus 2005) with careful evaluation of tear film quality and volume, as these are reduced with contact lens wear (Gromacki 2004). The appropriate lens material and lens replacement schedule must also be carefully considered in presbyopic patients. Reduced tear flow results in: increased lens surface deposition blurred vision ■ discomfort ■ possible papillary hypertrophy. ■ ■

Eyelid Tonicity This is reduced, making it challenging for a translating RGP lens to be successful, as these designs depend on lid tonicity to move the lens upward with downward gaze. Crystalline Lens Changes in the crystalline lens can affect the contact lens prescription and best corrected visual acuity. If reduced, the presbyopic contact lens option will result in a further compromise, especially for distance. Pingueculae and Pterygia These can result in a decrease in comfortable lens wear. Dexterity Handling of lenses must be considered since presbyopes find near tasks – such as checking whether the lens is inside out

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– more difficult. Handling tints and lenses that are less ‘floppy’ help with lens insertion.

EXAMINATION PROCEDURES The following procedures are required in addition to those for any new contact lens wearer (see Chapters 6 and 15).

Patient Requirements The primary goals of presbyopic contact lens patients differ from those of pre-presbyopes in various aspects: what they expect from contact lens wear what distance(s) are important to them ■ their occupational/avocational vision require­ments. ■ ■

Several extra details and measurements are needed prior to fitting bifocal lenses.

History and Symptoms (see Chapter 15) ■ History of eye surgery. Cosmetic lid surgery, in particular, can affect RGP translation and aspheric multifocal lens success by causing excessive lifting and superior decentration on blinking. ■ Medication. Check whether the patient is taking any medications that would reduce tear volume. This can include ibuprofen, oestrogen, antihypertensives, tricyclic antidepressants, anticholinergics and the scopolamine patch (Du Toit et al. 2001). ■ Dry eye problems – see ‘Tears’.

Fig. 13.1  Pupil size determination in photopic and scotopic illumination is critical to lens selection. (Courtesy of Dr. Peter Kollbaum.)

A

Tears (see also Chapter 4 and Section 9, Addendum, available at: https://expertconsult.inkling.com/) As tear volume decreases with age, it is especially important to evaluate whether the patient is a good candidate for contact lenses in general. A tear break-up time (TBUT) of: less than 10 seconds indicates that the patient may not be a good candidate (Andres et al. 1987) ■ 6–9 seconds should limit the patient to a daily wear schedule ■ 5 seconds or less typically contraindicates contact lens wear, especially if performed multiple times with a consistently low value (Bennett 2004a). ■

If the patient has blepharitis or meibomian gland dysfunction, tear quality can be reduced, so the condition needs to be managed prior to reassessing tear quality for possible contact lens wear. Tear volume can be assessed either with the Schirmer tear test or with a phenol red thread test (ZoneQuick from Menicon/Allergan), although in routine practice, these are rarely done. In the latter test a value of less than 9 mm of wetting in a 15-second time period should contraindicate contact lens wear (Hamano et al. 1983, Sakamoto et al. 1993).

Pupil Size Pupil size (Fig. 13.1), should be recorded both in room illumination and with the room lights dimmed such that the millimetre rule readings are barely visible. A pupil gauge may be preferable for measuring, and these are available either as a pen-torch (Fig. 13.2) or a card. The presence of a large pupil in normal room illumination (i.e. >5 mm)

B Fig. 13.2  (a) Pupil gauge on a pen-torch. (b) Pupil and corneal diameter gauge on a card.

– although not highly common in the presbyopic population – would contraindicate an aspheric RGP multifocal lens design because of the ghost images and glare the patient would experience under low-illumination conditions. Pupil size is also critical for soft multifocal designs, as almost every design relies on simultaneous vision and is therefore pupil dependent (Cardona & Lopez 2016, Rio et al. 2016). A high intersubject variability was found in pupil diameter, working distance and illumination conditions while conducting the same task. It was concluded that eye-care practitioners should always assess pupil diameter in real-life conditions where possible (Cardona & Lopez 2016).

Lid Position The lid-to-limbus relationship should be observed; in particular, the position of the lower lid and the palpebral aperture

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should be measured. Individuals with a low-positioned lower lid (i.e. >1 mm below the inferior limbus) will not be good candidates for translating RGP lens designs.

Corneal Topography (see also Chapter 8) Whereas keratometry is acceptable in providing an estimate of the paracentral curvature, and thus can assist in selecting the back optic zone radius (BOZR) of the lens to be fitted diagnostically, videokeratography (VKG) does have several benefits: The location of the corneal apex can be determined. ■ A centrally located apex lends itself to aspheric multifocal lens designs. ■ An inferior-positioned apex lends itself to translating designs where an inferior position is desirable (Hansen 1998). ■ Patients with irregular corneas (e.g. keratoconus, trauma, postsurgical) typically are poor candidates for bifocal, multifocal or monovision contact lens correction, with the possible exceptions of hybrid and scleral lens options. ■ Topography also provides information on corneal diameter and pupil size (Norman 2013). ■ Measuring corneal topography over soft lenses can assist in determining where the optics are in relation to the line of sight, which, in turn, may assist in identifying and solving their complaints (Bennett & Henry 2014, Brujic 2016). ■

Visual Status The best candidates for bifocal/multifocal contact lenses should have greater than 1.25 D of myopia or 1.00 D of hyperopia (Josephson & Caffery 1991). Emmetropes or nearemmetropic patients should not be dismissed, however, if they are well-motivated. Even with the advancements in the quality of lens design, if the patient is amblyopic, monovision and soft bifocal contact lens wear are not advisable due to the potential for further compromise in distance vision. Procedures to perform on the potential presbyopic contact lens wearer are summarised in Table 13.1. Hansen et al. (2003) recommend discussing presbyopic options before the patient becomes presbyopic. KEY POINT

A pre-presbyopic high myope who is close to exhibiting presbyopic symptoms (for example, the 40-year-old 6.0 D myope) will experience an increase in accommodative demand when changing to contact lenses and should be advised that a presbyopic contact lens correction may then be necessary.

PATIENT CHARACTERISTICS Personality qualities that have been found to more likely result in success in presbyopic contact lens wear include agreeableness, openness and conscientiousness (Dinardo et al. 2014). Occupational and recreational information required includes: Their goals with the lenses The distance(s) they want to see most clearly – for example:

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Table 13.1  Recommended Examination Procedures for the Potential Presbyopic Contact Lens Patient Case history ■ Medications ■ Surgical history ■ Primary visual requirements and goals ■ Occupational requirements Anatomical/external measurements ■ Pupil size (room illumination/dim illumination) ■ Lid position and tonicity ■ Vertical palpebral aperture ■ Blink rate and quality Tear quality and volume Corneal integrity Keratometry/corneal topography Manifest refraction/best corrected visual acuity

If they use a computer 30% of the time or more in a normal day, then a multifocal lens design would be indicated to help optimise the intermediate vision. Sit the patient in front of a computer to determine the working distance. ■ If critical distance vision is expected, a translating RGP lens should be considered. ■ Perfect vision is not possible at all distances, and some compromise is necessary. Patients not prepared to accept this are not good candidates. ■ A description of the work environment. Excessive wind or dust, poor air quality or prolonged computer use lead to dryness necessitating frequent application of rewetting drops. ■ Do they play sports? ■ A daily disposable soft lens is often the preferred option with these patients. ■ If optimum vision is important, an aspheric, hybrid or scleral multifocal is likely to result in minimal decentration or loss. ■

The goal is to achieve a satisfactory balance between the vision at the distances most important to them (Bennett & Quinn 2014). If patients feel that spectacles interfere in any way with their lifestyle, they are often willing to accept a compromise, if present. The goal of presbyopic contact lens wear should be to satisfy ‘most of the visual needs, most of the time, or essentially to reduce, rather than eliminate the need for supplemental near correction’ (Schwallie 2000, Bennett 2004b). For example, a +1.00 D supplementary spectacle correction may be necessary for reading small print under low illumination for the moderate presbyope, particularly if they have small pupils and are wearing an aspheric multifocal contact lens correction. Fortunately, this is the exception to the rule. However, the practitioner is more likely to be successful and the patient’s confidence maintained if practitioners ‘underpromise and overdeliver’ (Bennett & Hansen 2004). A realistic approach about the time needed to achieve the final fit should be discussed. With all multifocal designs, lens exchange(s) may be necessary, and patients should be informed that the first lens may not be the final lens and that the fit or lens power may need to be fine-tuned at subsequent visits. Increased illumination and magnification can

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Table 13.2  Candidates for Presbyopic Contact Lens Correction High likelihood for success: ■ High need for a distance vision correction ■ Good tear quality and volume (i.e. Tear BUT ≥10 seconds; Zone-Quick* >9 mm) ■ Good ocular health ■ Current contact lens wearer ■ Realistic visual expectations ■ An open, positive and conscientious personality Moderate likelihood for success: ■ Low ametropia ■ Tear BUT between 6–9 seconds ■ New wearer with mild motivation ■ Large pupil size (>5 mm in room illumination, limits design selection) ■ Low lower lid and/or flaccid lids; rules out segmented lens designs Low likelihood for success: ■ Very satisfied spectacle wearer who is unwilling to accept visual compromise ■ Poor tear quality and/or volume (i.e. Tear BUT ≤5 seconds; ≤9 mm Zone-Quick*) ■ Emmetropes ■ Unrealistic expectations ■ Poor hygiene ■ Poor manual dexterity *Zone-Quick phenol red thread test (Menicon/Allergan)

be beneficial, and magnifying apps can help mobile phone users. Candidates suitable for presbyopic contact lens correction are shown in Table 13.2.

Presbyopic Contact Lens Options: Single Vision Contact Lenses With Reading Glasses The use of single-vision lenses (RGP or soft) in combination with reading glasses provides the following benefits (Bennett et al. 2006): good bilateral vision at both distance and near simplicity of fit ■ low cost. ■ ■

The over-spectacles are typically single-power plus lenses but may be a progressive addition, particularly to assist with intermediate correction. In some cases, minimal add powers are used to enhance the reading ability of emerging presbyopes. However, patients with varied near and distance tasks will complain of the inconvenience and poor cosmesis of spectacles. Nevertheless, it is important to present this option to all potential presbyopic contact lens wearers, and some patients will prefer to begin with this option, but they are likely to change to an alternative presbyopic contact lens system later.

Monovision Monovision is an optical means of correction for presbyopia in which one eye is optimally corrected for distance vision and the other eye optimally corrected for near. This is typically accomplished with contact lenses, although monovision

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refractive surgical procedures can also be applied (Jain, Ou, & Azar 2001). The origin of monovision is unclear, although the use of the monocle in the 1800s certainly was an early method of monovision correction. Using a contact lens in this fashion was first attributed to Westsmith in the 1960s (Fonda 1966). The advantages of the monovision system include the following (Bennett & Jurkus 2005, Gasson & Morris 2010): Conventional lenses are used which do not require special lens designs. ■ The professional time required is decreased. ■ It is less expensive to the patient. ■ Thin, non-prism-ballasted lenses are used. ■ Only one lens is changed for current contact lens wearers. ■ The patient can usually determine soon after initiating lens wear if they are going to be successful. ■ Avoidance of many of the symptoms/compromises associated with multifocal contact lenses, including ghost images, reduced contrast sensitivity, and fluctuating vision related to pupil size changes. ■

However, the primary limitation to monovision pertains to concerns about the lack of balanced binocular vision. A literature review by Johannsdottir and Stelmach (2001) indicates that monovision may: stress the visual system impair stereoscopic depth perception ■ affect performance in complex spatial-motor tasks such as driving. ■ ■

PATIENT SELECTION Trying to explain the concept of monovision to a patient can be challenging, and it is often easier to actually demonstrate the system. Cerebral cortex binocular cells have identical receptive fields for detection of size, orientation, motion sensitivity and directionality. The inputs from the two eyes, however, do not produce identical influences on the cortical cells. One eye is dominant (see p. 270 and Michaels 1974, Pearlman 1987). Ninety-five percent of the monovision papers reviewed by Jain, Arora and Azar (1996) had the dominant eye corrected for distance vision. Good and poor candidates for monovision are shown in Table 13.3. Other considerations include: lifestyle motivation ■ visual needs equally distributed between far and near distances (Schwartz 1999) ■ personality – various studies have evaluated personality and psychological factors predictive of successful monovision wear (Josephson et al. 1990, Thompson, Collins, & Hearn 1990, MacAlister & Woods 1991, Du Toit et al. 1998). Cattell’s 16 Personality Factor (16PF) test showed that patients with realistic expectations and the willingness to persevere, the ‘Factor G superego strength score’, could predict monovision success (Du Toit et al. 1998). Adaptable, holistic people with an optimistic attitude towards treatment had high potential for success. Jain et al. (1996) also found that a person’s expectation of self-efficacy, or belief in succeeding, was a predictor of success. ■ ■

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This indicates the dominant eye (Quinn 2007). If the patient reports blurred vision at a distance, regardless of which eye is covered by the plus lens, it is likely that monovision will not be successful.

Table 13.3  Good and Poor Candidates for Monovision Good monovision candidates: ■ Early presbyopes who have a significant refractive error are generally better candidates than emmetropes or previously uncorrected hyperopes and low myopes ■ People who read in positions other than the standard downward gaze, such as office workers, executives, auto mechanics, pharmacists, etc. ■ Current contact lens patients ■ Highly motivated patients; individuals who have realistic expectations and willingness to persevere Poor monovision candidates: ■ Patients with concentrated, specific visual needs ■ Dry eye symptoms or clinical signs ■ Those with high visual demands and expectations (Modified from Bennett, E.S., Jurkus, J.M., 2005. Presbyopic correction. In Bennett, E.S., Weissman, B.A.: Clinical Contact Lens Practice (2nd ed.). Philadelphia: Lippincott Williams & Wilkins: 27-1 to 27-18.)

age – younger presbyopes are more successful than older presbyopes; add powers of +1.00 to +2.00 D are more readily accepted than higher adds (Erickson & McGill 1992, Jain et al. 2001, Shovlin & Eisenberg 2003).

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Schwartz (1996) recommends monovision screening criteria that evaluate: age add power ■ distance prescription ■ prior use of contact lenses ■ motivation ■ pupil size ■ occupational and avocational needs ■ apprehension of handling lenses. ■

The full distance and near powers are generally prescribed. Reducing the add power to minimise the dioptric difference between the two eyes may alter the suppression pattern. Patients with strong sighting preferences have reduced interocular blur suppression and decreased binocular depth of focus. This strong dominance may make it difficult for the patient to learn to ignore the out-of-focus monovision image (Schor & Landsman 1987).

FITTING THE LENSES (FOR LENS FITTING IN MONOVISION, see Section 9, Addendum, available at: https://expertconsult.inkling.com/) Full adaptation to the monovision system can take as long as 8 weeks, with most subjects adapting in 2–3 weeks and about one-half in 1 week (Collins et al. 1994, Jain et al. 1996, Westin et al. 2000). If a patient does not appear to be coping, it may be beneficial to switch the eye powers before discarding the monovision concept, but if the initial acceptance of monovision is lacking, it may not be successful.

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Once the initial screening has been completed, the best predictor of success with monovision is a trial period using the appropriately selected lens powers.

LENS SELECTION AND TYPE The criteria for lens fitting are the same for rigid or soft lenses in monovision, and the lens powers must be carefully selected.

Ocular Dominance Assumptions about dominance can be misleading (Pointer 2001). The patient’s declared writing hand is not necessarily associated with the same sighting or ‘dominant’ eye; nor is the apparently better-sighted eye. If dominance is not tested for and the wrong eye is assumed to be dominant, monovision may ultimately fail. Tests for Ocular Dominance ■ Hole in the hand test – specifically, ask the patient to keep both eyes open and to centre an object, such as a letter on the vision chart, through the opening formed by his linked hands held out at arm’s length (Quinn 1997). The eye that aligns the target in the centre of the opening is the dominant eye. If one eye instinctively closes, this is most likely the nondominant eye. ■ Ask which eye the person uses to sight a camera or telescope. ■ Introduce a +1.00 to +2.00 D plus lens over each eye individually and ask which eye experiences the greater blur.

PROBLEMS WITH MONOVISION Monovision may present some visual challenges. Identifiable visual changes with monovision include a small reduction in high-contrast visual acuity such as reading or viewing a vision chart. There is also a loss of contrast sensitivity function that is proportional to amount of add (Bennett & Jurkus 2005). One of the biggest concerns with monovision is the change in depth perception due to the anisometropic correction. Monocular clues and binocular clues are used to judge depth and distance. The monocular clues are unchanged with monovision. These include: object interposition hiding parts of an object judging the customary object size, colour and clarity of objects ■ lines converging to a vanishing point ■ shadows. ■ ■

Binocularly, although monocular clues for depth perception are present, monovision can reduce stereoacuity. The normal ageing process reduces the mean angle of stereopsis from 20 to 58 arcseconds. Monovision further reduces stereoacuity; stereopsis in monovision ranges from 50 to 113 arcseconds for near; Johannsdottir and Stelmach (2001) found in all the papers they reviewed that stereoacuity was affected adversely. Although there is generally no significant effect on peripheral visual acuity, low-contrast binocular distance acuity may be reduced with monovision. For further information on the visual effects, see Section 9, Addendum, available at: https://expertconsult.inkling.com/.

PATIENT EDUCATION It is possible that a practitioner could be liable for any injury in which a monovision scenario could be a contributing factor

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(Harris & Classe 1988). The report of an aviation accident with a pilot wearing a monovision correction heightened consumer awareness of possible compromise with this form of correction (Nakagawara & Veronneau 2000). The monovision wearer must be particularly aware of the induced vision change and its possible effect on their perception. Patients need to be carefully selected, have a demonstration of vision with monovision and be aware of the adaptation period (Harris and Classe, 1998). Monovision does not tend to improve beyond the initial adaptation period, which, as mentioned previously, can take as long as 8 weeks, and patients should be told not to expect an increase in the quality of their vision after that (Fernandes et al. 2013). Alternative vision correction options should be presented, and the patient should participate in the modality selection. Risks and benefits of correcting the presbyope with all types of lenses must be considered (see also Chapter 31).

Success Despite the compromises present with this modality, monovision is still in common use, although it is not the preferred mode for many practitioners. Internationally, whereas multifocal and monovision lenses accounted for 56% of soft lenses prescribed for individuals 45 years of age or older, the breakdown is 48% multifocal and only 8% monovision (Morgan et al. 2016). Likewise, in the United States, 71% of practitioners rate D multifocals as their preferred correction in presbyopia compared with 19% monovision and 10% overcorrection with reading glasses (Nichols 2016). Jain et al. (1996) in a review of 19 studies found an average success rate of 76%, although other reviews have found 59–67% (Evans 2007). Jain et al. (2001) concluded that visual performance of monovision patients is comparable to that of patients with balanced binocular corrections, provided that the reading add does not exceed +2.50 D, the stimuli are supra-threshold and the illumination is photopic. For a review of monovision, see Evans (2007), and for papers discussing the comparison of monovision and multifocals, see Section 9, Addendum, available at: https:// expertconsult.inkling.com/. Fitting and prescribing guidelines for monovision are provided in Table 13A.1 Section 9, Addendum, available at: https://expertconsult.inkling.com/.

Presbyopic Contact Lens Options: Modified or Enhanced Monovision and Modified Multifocal or Bifocal Lenses Modified monovision combines multifocal optics with single vision or monovision. This combination of spherical and aspheric surfaces is termed an ‘inverse geometry’ design (Gasson & Morris 2010). The lenses are straightforward to fit according to the manufacturer’s instructions, and the aim is to combine minimally compromised acuity at all distances, together with binocular presbyopic correction (Iravani 2002, Shovlin & Eisenberg 2003).

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There are a number of combinations of lenses that can be prescribed to provide modified or enhanced monovision or multifocal vision (Burnett-Hodd 2004). In enhanced monovision contact lenses: ■ The dominant eye is fitted with a single-vision distance lens, and the nondominant eye is fitted with a multifocal contact lens. ■ Occasionally, the dominant eye is fitted with a multifocal lens and the nondominant eye with a near singlevision lens. ■ The dominant eye is fitted with a bifocal lens with full distance correction and a reduced add bifocal, and the nondominant eye wears an undercorrected distance correction with the full addition. ■ For modified multifocal lens fitting (see also p. 271): ■ A full distance correction with a lower addition bifocal is fitted to the dominant eye, and an undercorrection with the full addition is fitted in the other ■ Different multifocal designs are fitted to each eye – usually, distance centre in the dominant eye and a near centre in the nondominant eye (see ‘Biofinity Multifocal Lenses’ on p. 281 and ‘Proclear Multifocal Toric’ on p. 282). ■

Presbyopic Contact Lens Options: Bifocal/multifocal contact lens designs Numerous advancements have been made to improve the success of both RGP and soft lens bifocals. As mentioned previously, a large number of designs are in existence today which can be divided into simultaneous or alternating vision types, although the difference between the two categories appears to have become less distinct. There are several factors important to multifocal/bifocal lens designs, regardless of whether soft or RGP lenses are being fitted.

DEFINITIONS SIMULTANEOUS VISION (OR BIVISION) MULTIFOCAL CONTACT LENSES These are typically defined as lenses that have multiple powers positioned within the pupil at the same time, with light rays from both distance and near targets imaged on the retina. This concept functions on the basis of blur interpretation and/or blur tolerance of superimposed multiple images on the retina which are formed by the various powers of the lens (Benjamin & Borish 1991). The patient will selectively suppress the most blurred images that are not desired for a given visual task. Simultaneous vision lenses are available in both RGP and soft lens materials, but the designs lend themselves much more to soft materials. Those that shift upward or translate (or alternate) often result in only one corrective power in front of the pupil at any one time, and lenses are almost exclusively limited to RGP designs. For true simultaneous vision, the two primary segments must remain within the pupillary boundary in all

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positions of gaze and, to give equally bright images, the distance and near areas the lens should cover nearly equal areas of the pupil. The designs using the simultaneous vision concept are either aspheric or concentric/annular (or target) designs. Aspheric designs have a gradual change of curvature along one surface based on the geometry of conic sections. This rate of flattening (or eccentricity) is much greater than with aspheric single-vision lenses and creates a plus add power effect. KEY POINT

Aspheric designs can be either: • Centre-distance, where the minimum plus power is at the geometric centre and then gradually increases from the centre to the periphery. The eccentricity is located on the posterior surface. • Centre-near, where the maximum plus power is at the geometric centre and then gradually decreases towards the periphery. Concentric or annular lens designs are structured with a small (typically two-thirds to three-quarters the size of the pupil in normal room illumination) annular central zone which, in most designs, provides the distance vision correction, the near correction being ground on a surrounding annulus. Aspheric and concentric centre-distance lenses both gain some additional near power via slight shifting or translating of the lens upward with downward gaze for reading. It is important to note that all three of these ‘simultaneous vision’ lens designs must centre well.

ALTERNATING OR TRANSLATING DESIGNS These designs function where vertical movement or translation results in only one power zone being positioned in front of the pupil (or visual axis) at any one time. Ideally, the distance zone is in front of the pupil when viewing at a distance and in the near zone when viewing at near. These are almost exclusively available as RGP designs because they must translate sufficiently when the patient shifts gaze from one distance to another, and this translation is attained much more easily with rigid lenses than with hydrogels. Essentially there is an intentional shifting of lens position in which separate, discrete images formed by the two power segments in the lens focus on the retina with a change of gaze from distance (up) to near (down) or vice versa. Typically these designs are nonrotating by using a prism ballast construction, sometimes in combination with inferior truncation, which stabilises the lens and allows a smooth translation from the superior distance zone to the inferior near zone when lowering the gaze to read. These nonrotating segmented designs are typically similar to spectacle bifocals. Several types of RGP prism ballast lenses have been developed through the years, including decentred concentric, one-piece segmented, and fused crescent and segmented. Current designs are most commonly crescent or executive style. A number of RGP trifocal translating designs are available, often with either an aspheric or segmented intermediate zone.

General Fitting Considerations Begin by fitting patients who have great potential for success, including: ■ highly motivated individuals ■ existing single-vision contact lens wearers who are entering presbyopia ■ monovision failures. ■ Advise the patient that any blur in vision initially should reduce over time. ■ If possible, provide the patient with lenses in their specific prescription to make their initial experience a more positive one and increase the likelihood of success. This is fairly easy with disposable soft lenses, and for RGP lenses (especially aspheric designs), an empirical lens can be ordered. However, diagnostic fitting of alternating RGP designs is recommended, although with experience, empirical fitting aspheric multifocals can be successful. ■ Have numerous soft and RGP multifocal/bifocal designs available in-office to try. ■ It is not uncommon to prescribe two different lens designs to each eye, especially with soft bifocal lens wearers. ■ Prescribing unequal add powers can help where the patient experiences blur at near but desires little compromise of their distance vision. ■ A ‘modified bifocal’ approach in which one eye is slightly overplussed is also a viable option for the moderate or advanced presbyope who desires better vision for near tasks. ■

Dispensing the Lenses When the patient is first dispensed their lenses, they should be allowed to settle for at least 15–20 minutes before evaluating the fit. ■ Over-refract using trial case lenses or ±0.25–0.50 D flipper lenses, as opposed to a phoropter, to provide a more natural environment. For the same reason, vision should be evaluated binocularly, not monocularly. ■ Have the patient walk around the office and simulate tasks that they perform on a daily basis. This could include looking at a magazine or newspaper, viewing a computer screen, looking outside, etc. They should then determine their level of satisfaction with their vision for the various tasks and identify possible areas of improvement, particularly for those tasks that they perform most frequently and are most important to them. ■ If minimal or no change in prescription is found, reiterate the fact that any blur in their vision initially should reduce over time. ■

Rigid Bifocal and Multifocal Lens Designs There are a number of rigid lens designs available, including higher-add aspheric multifocal designs and segmented alternating designs with an intermediate aspheric correction.

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SIMULTANEOUS VISION RIGID LENSES Although some RGP concentric designs are still in use today, the most common form of rigid simultaneous vision correction is aspheric multifocals. These designs are not strictly simultaneous vision because in order to be successful, they must exhibit some upward shift or translation on downward gaze.

Simultaneous Vision Rigid Lenses – Aspheric Lens Designs Numerous presbyopic designs have an entirely (i.e. not peripheral only) aspheric back surface geometry. The peripheral flattening of the back surface provides a continuously variable near addition. To provide the maximum near addition, a high degree of central curvature steepening or asphericity must be used. This departure from spherical shape is known as eccentricity or ‘e’ factor (for more on the e factor, see Chapter 9). The first designs that were introduced were fitted as much as 0.60 mm (3 dioptres) steeper than ‘K’. These lenses had a very high e value, and some designs are still in use today – for example: VFL 3 lens from Conforma (USA). Quasar Plus from No. 7 (UK), a centre-distance multifocal where the centre is 0.5 mm steeper than the surround. Because of the back surface geometry, the fluorescein pattern shows only slight apical clearance (Fig. 13.3). ■ Many current lens designs have a lower eccentricity. The Aqualine MF from Cantor & Nissel (UK) is fitted 0.05–0.1 mm (0.25–0.50 D) steeper than K. However, as a result of the aspheric geometry and rate of flattening, an alignment or slight central clearance fluorescein pattern will be present (Fig. 13.4).

Fig. 13.4  A low eccentricity value aspheric multifocal lens.

Aspheric multifocal optics

Concentric bifocal optics

■ ■

Many of the laboratories manufacturing back surface aspheric designs can also provide a high-add design, often by adding additional add power to the front surface. For example: Blanchard Contact Lenses of North America has introduced its ‘CSA’ design, which allows for adding more add power in a paracentral ring on the front surface of all three series of its lenses (Fig. 13.5).

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Fig. 13.5  The Essentials CSA Enhancement Multifocal design. The outer ring provides – on the front surface – additional add power such that when the patient looks down, the lens shifts (or translates) upward, and greater near add power is achieved. (Courtesy of Blanchard Contact Lens.)

Reclaim HD Multifocal, available from David Thomas (UK) or Blanchard (USA), is a bi-aspheric lens which allows an increased range of adds, up to +4.00.

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If a back surface only aspheric lens decentres, the corneal topography can alter. Therefore an increasing number of laboratories are introducing front surface (or predominantly front surface) aspheric multifocal designs. Optically the add depends on the pupil size but can provide 0.37 D additional add power measured 2.5 mm away from the optical centre (Caroline 2013). Some designs provide a slight amount of asphericity on the back surface to complement the aspheric power generated on the front surface. They have the added benefit of being fitted essentially ‘on K’ due to the spherical or near-spherical back surface.

Advantages of Aspheric Designs These lenses have a number of advantages (Bennett 2008): Lenses can be fitted empirically (Ames 2001), which allows patients to experience good vision on the initial application. ■ Lenses are simple to fit, allowing for good first-fit success. ■ Lenses are not segmented and do not require prism, in contrast to most alternating vision designs, so the thickness profile is similar or better than conventional single-vision lenses, making it a good first option for the single-vision RGP wearer who has just become presbyopic. ■ If fitted correctly, lenses exhibit little movement and rarely decentre or dislodge, so they can be worn by presbyopic athletes. ■

Fig. 13.3  A high eccentricity value aspheric multifocal lens with a fluorescein pattern similar to a spherical single-vision lens showing slight apical clearance.

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SECTION 4  •  Lens Fitting Modalities

Good intermediate vision is possible because of the progressive addition, which benefits the computer user.

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Disadvantages of Aspheric Designs The problems with aspheric lens designs include: Excessive decentration and/or excessive movement will result in variable and generally unsatisfactory vision at all distances. ■ Insufficient add power. Until recently, high-add presbyopic patients were not good candidates, but the newer designs, which have add power on both front and back surfaces, provide a viable option for the mature presbyope. ■

Where the effective add power cannot be increased, the use of aspheric lenses with different add powers, with the higher add typically on the nondominant eye and a ‘modified multifocal’ approach (see p. 271) in which the dominant eye is also slightly overplussed (e.g. 0.25–0.50 D) for distance, often provides satisfactory vision with little compromise to the distance vision.

Good Candidates for Aspheric Simultaneous Vision RGP Lenses These include: motivated presbyopes who spend, at minimum, 35% of their time at a computer (Hansen 1999), such as accountants, electricians and those involved in mechanical or plumbing responsibilities ■ current RGP wearers ■ soft toric or monovision failures ■ individuals who desire good vision at all distances ■ poor candidates for translating design bifocals ■ those with the following anatomical characteristics: ■ lower lid margin well above or well below the limbus ■ small-to-average pupil size ■ loose lids that will not support prism ballast lenses ■ steep corneal curvatures. ■

The use of a topical anaesthetic at the initial application is beneficial in enhancing the initial experience (Bennett et al. 1998), especially for the neophyte wearer or the presbyope who has been wearing soft lenses (see Chapter 9). ■ The radius is fitted according to the manufacturer’s instructions. ■ If the lens decentres and/or moves too much, steepening the BOZR by 0.10 mm (0.50 D) may solve the problem. Increasing the total diameter (TD) may also help, as may moving to a toric design in against-the-rule cases. ■

SIMULTANEOUS VISION RIGID LENSES – CONCENTRIC (ANNULAR) DESIGNS Concentric designs that are used for simultaneous vision purposes are not in common use today, with translating counterparts more popular. Most designs are centre-distance with a near surround, e.g. Menifocal lens (Menicon). An important parameter to determine prior to fitting this lens design is pupil diameter, which should be measured in dim illumination; the centre-distance annular zone should be made 0.75–1.5 mm smaller than the pupil diameter (Caffery & Josephson 1991, de Carle 1997) (see Table 13.4).

Fitting Menifocal Lenses ■ The use of a diagnostic fitting set is recommended to achieve an optimum fitting relationship (Josephson & Caffery 1988). The key to success with this design is similar to that with aspheric designs: ■ Good centration is achieved (slight superior decentration is preferable to slight inferior decentration). ■ Limited movement, approximately 1 mm, with blinking. Table 13.4  Recommended Diameter of the Distance Portion of Concentric Bifocals as Related to the Pupil Diameter Distance Portion (mm)

Pupil Diameter (mm)

Distance Portion (mm)

4.5

3.20

3.2

2.25

4.4

3.10

3.1

2.20

■

with critical distance vision demands who do not have the motivation for an RGP lens design ■ with larger than normal pupil size due to the aberrations induced, particularly at night ■ with high astigmatism ■ with whom it is difficult to achieve good centration with a corneal lens.

4.3

3.05

3.0

2.10

■

4.2

2.95

2.9

2.05

4.1

2.90

2.8

2.00

4.0

2.80

2.7

1.90

3.9

2.75

2.6

1.85

3.8

2.70

2.5

1.75

Fitting Aspheric Multifocal Lenses As these are thin lenses, the lens material to be prescribed would be similar to a single-vision lens in the practitioner’s preferred material. Otherwise, the author recommends a low-Dk (e.g. 25–50) lens material for myopic patients and a higher-Dk lens material for hyperopic patients.

3.7

2.60

2.4

1.70

3.6

2.55

2.3

1.65

3.5

2.45

2.2

1.55

3.4

2.40

2.1

1.50

3.3

2.30

2.0

1.45

Poor Candidates for Aspheric RGP Simultaneous Vision Lenses These include patients:

A well-centred fitting relationship with minimal movement on blinking is desirable.

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Pupil Diameter (mm)

(With permission from de Carle, J.T., 1997. Bifocal and multifocal contact lenses. In Phillips, A.J., Speedwell, L. Contact Lens Practice (4th ed.) Oxford, ButterworthHeinemann: 540–565.)

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Pupil

Fig. 13.6  A well-fitting concentric bifocal can move up to 1.0 mm and still have all of the distance portion in front of the pupil (shaded). Fig. 13.7  The Tangent Streak bifocal lens (Fused Kontacts of Missouri).

The central zone should cover approximately 50% of the pupil when viewing straight ahead. ■ The lens should be able to move up to 1 mm and still have the distance zone in front of the pupil (de Carle 1997) (Fig. 13.6). ■ When the patient views inferiorly, there should be a slight shift or translation that will assist in providing acceptable near vision. ■

A useful method of evaluating the position of the central zone against the pupil is the zone-check technique (Caffery & Josephson 1991). With an ophthalmoscope held at arm’s length and a +4.00 D hand-held trial lens positioned in front of the patient’s eye, the central zone can be clearly observed and its position and percentage of pupil coverage noted. Less commonly, centre-near lenses have been used that favour near vision due to the decrease in pupil size in bright illumination; conversely, however, they can result in blur at distance during daylight conditions.

Fig. 13.8  The Llevations trifocal design (Tru-Form).

ALTERNATING VISION RIGID LENSES There are two types of alternating (translating) bifocal RGP designs:

Alternating Vision Rigid Lenses – Segmented Lenses Although more complex in design, the most successful bifocal contact lenses from a visual standpoint are the RGP segmented translating designs. For the history of segmented translating lenses, see Section 8, History, available at: https://expertconsult.inkling.com/. Representative Designs With an early limitation being the absence of an intermediate zone, several segmented translating trifocals are available. These include executive bifocal and trifocal (Tangent StreakTM, Fig. 13.7) and trifocal segment (Llevations from Tru-Form Optics – Fig. 13.8), a curved upswept segment (Fig. 13.9), among others. These lenses, via incorporating prism ballast for stability, have a thickness that necessitates a highly oxygen permeable lens material (i.e. typically >50). Advantages of segmented translating or alternating RGP lenses include the following: ■ They have the ability to achieve precise correction and good vision at distance and near unaccompanied by secondary images.

Fig. 13.9  The Solutions Bifocal (X-Cel).

The comfort with these lens designs is usually excellent due to the minimal lens movement on blinking combined with the thin superior edge (Bennett 2005). ■ Both early and advanced presbyopes can be fitted due to the large range of presbyopic adds available. ■

Disadvantages of segmented translating or alternating RGP lenses include the following:

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SECTION 4  •  Lens Fitting Modalities

They are not always straightforward to fit. Lenses are thicker than average, which can cause discomfort, excess lens movement or hypoxia. ■ It may not be possible to achieve sufficient translation with downward gaze. ■ They must be fitted using a fitting set, so the vision of the trial lenses may be poor, and there is a time delay between fitting and issuing lenses. ■ ■

Good Candidates for Segmented Translating or Alternating Vision Lenses These include patients with: the lower lid above, tangent to or ≤1 mm below the limbus spherical or near-spherical myopic or low hypermetropic corrections ■ normal-to-large palpebral fissure sizes ■ normal-to-tight lid tension. ■ ■

Poor Candidates for Segmented Translating or Alternating Vision Lenses These include patients with: high hypermetropia because of the increased thickness of the prism-ballasted plus lenses ■ loose lids, as they may not be able to maintain proper alignment of the thicker inferior edge on the lower lid margin with downward gaze ■ a lower lid ≥1 mm below the lower limbus, as the lens does not tend to translate enough to allow the near zone to cover the pupil sufficiently. ■

Fitting Segmented Translating or Alternating RGP Lenses ■ The goal of these prism-ballasted segmented designs is for the inferior portion of the lens to rest on or near the lower lid such that the lens is pushed upward or translates with downward gaze. ■ A diagnostic fitting set is useful but not essential. To accurately assess the seg position and translation, these typically have an average TD and seg height and an intermediate amount of prism (typically 2 prism diopters base down). ■ Fit slightly flatter than ‘K’ such that the lens rests on or near the lower lid during distance gaze and the seg line is positioned at or slightly below the lower pupil margin. In general, all plus power and prism-ballasted lenses, due to their anterior centre of gravity, tend to decentre inferiorly when fitted with a BOZR flatter than ‘K’. ■ The lens must decentre (translate) 2 mm or more upward on downward gaze to position a sufficient portion of the near zone in front of the pupil while performing near tasks and with its lower edge supported by the lower lid margin. With the patient fixating straight ahead, the lens should lift up 1–2 mm on blinking and then quickly drop back to the lower position. ■ Ensure that the superior lens edge is overlapping the pupil in dim illumination (Yager 2002), especially with patients who have borderline low lower lid positions.

Assess the relationship of lower lid to limbus with a biomicroscope for accuracy. If the lower lid is slightly below the lower limbus (e.g. 0.1–0.9 mm), a larger than average TD and seg height are indicated to provide sufficient pupil coverage during distance gaze and satisfactory near vision with downward gaze. ■ Have the patient look straight ahead when evaluating the position of the seg line. The seg line should be positioned at – or slightly below – the lower pupil margin such that the movement of the lens with the blink will not move the seg more than 1 mm into the pupillary zone. For trifocal designs, the intermediate optics should be positioned such that they are located over the inferior pupil area. If too high, even the simple act of smiling can raise the seg position, which will interfere with distance vision, an important consideration when driving. ■ The seg height can be performed using a slit-lamp or a digital photograph. ■ To evaluate lens translation: ■ Lift the patient’s upper lid, have them look down and note the upward shift of the lens whilst viewing with a slit-lamp (Fig. 13.10). Most of the near zone should then be in front of the pupil on downward gaze and viewing with a biomicroscope, the seg line should, at minimum, bisect the pupil as the patient is viewing inferiorly. ■ Use a direct ophthalmoscope (Quinn 2001). Dim the room lights and stand at arm’s length from the patient. Add plus power in the ophthalmoscope until the edge of the pupil is focused in the red reflex. ■ Ask the patient to maintain fixation in straight-ahead gaze and then blink. The seg line should be observed to rise into the pupil zone immediately following the blink and then drop quickly. If the seg remains in the pupil for a prolonged period, the patient is likely to complain of distance blur (see ‘Troubleshooting’ below). ■

Fig. 13.10  Good translation. (Courtesy of Firestone Optics.)

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277

Fig. 13.12  Excessive rotation of a segmented translating lens design fit steeper than ‘K’.

Table 13.5  Troubleshooting Gas Permeable (Gp) Translating Bifocal Lens Designs Problem

Management Options

Excessive rotation

1. Flatten BOZR 0.1 mm if with-the-rule cyl 2. Steepen BOZR 0.1 mm if against-therule cyl 3. Offset prism if upswept lower lid; order prism at 105 degrees (right eye) and 75 degrees (left eye)

Superior decentration

1. Increase prism by 0.50 Δ 2. Flatten BOZR by 0.1 mm 3. Thin the apex of the lens edge

Poor translation

1. Flatten BOZR 0.1 mm or flatten peripheral curve 2. Increase prism or truncation 3. Change to another lens design due to flaccid lower lid

Poor distance vision

1. Superior decentration: increase prism by 0.50 Δ 2. Inadequate pupil coverage: increase TD ≥0.5 mm 3. If seg height into pupil: reduce seg height

Poor near vision

1. Poor lens translation: manage as indicated above 2. Excessive rotation: manage as indicated above 3. Too low seg height: increase seg height 4. Patient is dropping head, not eyes, to read: educate patient appropriately

Poor intermediate vision

1. Over-spectacles for intermediate distance 2. Select a GP translating lens design with an intermediate correction

Fig. 13.11  The lower edge of a truncated prism-ballasted lens should not be straight, as shown in (a), but curved to match the line of the lower lid, as shown in (b).

Provide the patient with a near card (or appropriate reading material). When viewed straight ahead, the reading material should be blurred. As patients gradually lower the reading material, it should become clear as it enters their normal reading position and distance (Edwards 1999). If the reading material remains blurred, a higher seg height will be necessary.

■

Truncation, in addition to prism ballast, assists in both the stability of the lens on the eye and also with translation. It is not commonly used, as the upper lid exerts the major influence in lens translation by pulling the lens upward during downward gaze (Borish & Perrigin 1985, Borish 1986). If the lens is truncated, the truncation should contour the lower lid (de Carle 1997) (Fig. 13.11). Similarly, if the lower lid is upswept or the lens tends to rotate excessively, it can result in blur at distance (and possibly at near as well); the segment can be offset relative to the prism base–apex line to correct for this. The LARS acronym (Left Add, Right Subtract) can be used to align the truncation with the lower lid (if truncated) or to align any rotated segmented translating design (Davis 2003).

Troubleshooting (see Table 13.5) ■ Excessive rotation with a blink. This is often the result of a BOZR that is too steep (Fig. 13.12). As with a hyperopic spherical lens, a steeper BOZR can assist in promoting centration and, likewise, in enabling a greater upper lid torquing effect on the upper edge with the blink. Flattening the base curve radius by 0.1 mm can allow the lens to fall more quickly to the lower lid and not be prone to the rotational effects of the upper lid (Bennett & Luk 2001). If necessary, increasing the amount of prism ballast may also help. ■ Insufficient or absent translation (Fig. 13.13). This may be resolved by increasing the amount of edge clearance to

allow the lens edge to exhibit more contact with the lower lid. This can be accomplished by selecting a flatter BOZR or flattening the peripheral curve radius. If the lens is still not translating, it is likely to be due to a flaccid lower lid, which may worsen with age. ■ Excessive movement with a blink (Fig. 13.14). If the lens rises too high on blinking: ■ Increase the prism (Bennett & Luk 2001, Yager 2002). ■ Flatten the BOZR. ■ Thin the upper edge. ■ Poor vision at varying distances – see Table 13.5.

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SECTION 4  •  Lens Fitting Modalities

Fig. 13.13  A segmented translating lens exhibiting poor translation.

Fig. 13.14  A segmented translating lens design which is lifted too much with the blink.

Fig. 13.15  The Expert Progressive empirically designed GP multifocal. (Courtesy of Art Optical.)

Poor intermediate vision. A common problem with segmented translating designs is the absence of an intermediate correction for the advanced presbyope. As well as trifocal designs, the Expert Progressive from Art Optical and Essilor can be designed empirically if all of the recommended anatomical information is provided (Fig. 13.15).

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Alternating Vision Rigid Lenses – Annular/Concentric KEY POINT

Annular or concentric alternating bifocals are front surface concentric designs which are constructed with a larger centre-distance zone than simultaneous vision designs.

13  •  Bifocal and Multifocal Contact Lenses

These ‘target’ bifocals translate with near gaze to shift the concentric near zone in front of the pupil. They typically have a 3–5 mm central distance zone which is decentred superiorly, with prism and truncation often present to prevent lens rotation and to facilitate translation on eye movement. A fitting set is useful, but the lenses can be fitted empirically, ensuring that the optic zone is large enough based on pupil size to ensure good distance vision. Lenses are often fitted slightly flatter than ‘K’, especially with prism-ballasted designs, in which the inferior edge should position close to or adjacent to the inferior lid, similar to segmented designs. Representative Designs.  The Mandell Seamless Bifocal (Con-Cise) provides an aspheric transition zone between the distance and near annular zones. It is a front surface concentric design with central distance zone diameters ranging from 3.0 to 3.8 mm and an average TD of 9.8 mm (Mandell 2002, Davis 2003, Bennett 2004c); it is actually only slightly thicker than single-vision lens designs. A well-centred fitting relationship is desirable. The Menifocal Z (Menicon) is a concentric aspheric design with a central distance area, a transition zone and a peripheral reading zone. This design has the benefits of potentially good vision at all distances as well as a hyper-Dk lens material. It is fitted 0–0.05 flatter than flattest K to give adequate translation from distance to near portions. Advantages of Annular/Concentric Alternating Vision Designs ■ It is possible to achieve precise correction and good vision at distance and near unaccompanied by secondary images. ■ High success rate is found in patients with appropriate ocular anatomy. Disadvantages of Annular/Concentric Alternating Vision Designs ■ Precise measurements are essential. ■ Increased centre thickness is required with prism ballast, although the translating concentric designs are the thinnest of the prism ballast bifocals. ■ The distance zone must be large enough to minimise distance flare, which may be difficult with small pupils. ■ Image jump, due to prismatic effects resulting from the bicentric construction of these lenses, can result in patient problems when shifting gaze. Good Candidates for Annular/Concentric Alternating Vision Lenses.  Those patients with: a lower lid margin tangent to, slightly above or no more than 1 mm below the limbus ■ an 8.5 mm or larger palpebral aperture (vertical fissure size) ■ normal (not loose) lid tension ■ myopic/low hyperopic refractive errors. ■

SOFT BIFOCAL/MULTIFOCAL LENS DESIGNS The initial hydrogel multifocal and bifocal lens designs were developed in the 1970s, typically duplicating PMMA lens

279

designs. The early results were not encouraging, as little research had been performed with these designs, which were custom-made, expensive and had a high percentage of failures (see Section 8, History, available at: https://expertconsult. inkling.com/).

General Points Numerous improvements in both lens design and disposability have resulted in greater use and success with soft lenses than in the past. Perhaps the most important change has been the availability of these designs in disposable and frequent-replacement modalities. Although these designs utilise the simultaneous vision principle, the ability to vary the design – between eyes – to optimise vision at various distances can be helpful. Patients can trial lenses for limited time periods while the practitioner adjusts the design to optimise both the fitting and vision. Motivation is important, particularly if they are motivated to avoid or minimise spectacle wear. Existing soft lens wearers are more likely to accept further slight vision compromise with a presbyopic lens design (Soni et al. 2003), but patients must be advised of this in advance. As with all presbyopic patients interested in contact lenses, establish the primary goals required with these lenses. Discuss vision at different distances and have them rate the importance of each task: distance – driving at night intermediate – computer work, playing music ■ near – reading, mobile phone use, etc. ■ ■

As discussed earlier, patients should be advised that the goal with their vision is to achieve a balance between difference tasks (which sounds more positive than using the word compromise). A useful tool for lens design and fitting is the Multifocal Simulator from Specialeyes (Davis 2016). A centre-near or centre-distance design can be specified, and it considers add power and pupil size in helping to determine what central zone size will optimise vision (Fig. 13.16). Many of the fitting considerations mentioned with RGP designs also pertain to soft presbyopic lenses, but there are some additional points: Soft lens multifocal designs often have the benefit of being fitted from inventory, either with or close to the indicated lens powers for a given patient. This then allows the patient and practitioner to assess the likely final result. ■ Evaluating pupil size carefully and prescribing optical zone sizes based on the pupil diameter can significantly improve patient success with soft multifocal lenses (Lampa et al. 2016). ■ With astigmatism of less than 1.00 DC, the spherical equivalent power is recommended. ■ Use a trial frame and flipper or hand-held trial lenses, not a phoropter, for refining vision. ■ Good illumination with real-world materials is necessary when assessing near vision. ■ It is commonly acceptable to have less than 6/6 (20/20) vision, especially at near, so resist the temptation to jump from design to design. ■ Ensure that patients know that an adaptation period is essential, so their vision will be least optimal on application ■

280

SECTION 4  •  Lens Fitting Modalities

Fig. 13.16  The SpecialEyes Multifocal Simulator. (Courtesy of Robert Davis, OD.)

and should improve over a minimum of a 1-week adaptation period. If after that the lenses are not meeting their visual goals, a change in design or power can be made. Often this power change is only 0.25 D, which can make a significant difference to the presbyopic patient. ■ It is important for the practitioner to have several different soft multifocal lens designs available to be able to try different lens types and adds in each eye. ■ Performing topography over a soft multifocal can determine the difference between the centre of the pupil and the central ring of the topographic image as it is centred over the patient’s line of sight (Davis 2016).

GOOD CANDIDATES FOR SOFT MULTIFOCAL LENSES

high astigmatic errors. A limited range of disposable toric multifocal lenses is available, and custom-made soft toric multifocal designs are much more expensive.

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LENS DESIGNS Lenses can be centre-distance or centre-near and either aspheric or concentric, although most are concentric.

Centre-Distance Lenses This design has a central distance zone surrounded by an annular near zone. Advantage of centre-distance lenses: The quality of distance vision is good in high illumination with subsequent pupil constriction.

■

These include patients with: single-vision soft lenses who have emerged into presbyopia monovision that they are dissatisfied with ■ low or no astigmatism ■ no critical distance vision demand ■ a high intermediate vision demand, e.g. those working at a computer much of the day. ■ ■

POOR CANDIDATES FOR SOFT MULTIFOCAL LENSES These include: patients who cannot accept some vision compromise emmetropes or near-emmetropes who are likely to be dissatisfied with the visual compromise ■ high-hypermetropes who may risk hypoxic complications even with silicone hydrogel ■ individuals with small pupils (i.e. ≤3 mm in normal room illumination) who may not obtain satisfactory vision at distance (if near-centre design) or at near (if centre-distance design) ■ ■

Disadvantage of centre-distance lenses: The primary limitation is the effect on near vision for an individual working in high-illumination (small pupil) environment (Caffery & Josephson 1991); therefore centre-near designs tend to predominate today.

■

Representative Designs ■ The Acuvue Oasys for Presbyopia (Johnson & Johnson) is a silicone hydrogel centre-distance concentric design incorporating alternating aspheric zones of power (Fig. 13.24). These zones allow for less pupil dependence, as the design combines the concentric zones with asphericity in an attempt to achieve a balanced visual outcome (Watanabe 2010). It is available in low-, mid-, and highadd powers. ■ The Proclear EP from CooperVision is specifically targeted towards the emerging presbyope and has a central distance zone with a surrounding progressive aspheric zone for intermediate and near vision. This option, using the Proclear material, is a useful option for the early presbyope experiencing dry eyes. The design is similar to the Proclear and Biofinity ‘D’ lens (see below).

13  •  Bifocal and Multifocal Contact Lenses

LO ADD +1.25 D

MED ADD +1.50 D to +2.00 D

281

HI ADD >+2.00 D

Fig. 13.17  Air Optix Aqua Multifocal. (Courtesy of Alcon.)

Centre-Near Lenses In these the reading zone is central with a surrounding distance zone, and vision is optimised in mesopic or scotopic conditions with the larger pupil. Conversely, under high illumination (e.g. reading), the pupil constricts as a response to light and convergence, and near vision is optimised. Advantage of centre-near lenses: better near vision in high illumination with constricted pupils ■ greater choice of lenses available.

Near

■

Disadvantage of centre-near lenses: poorer distance vision in bright illumination when the pupil constricts.

■

Representative Designs ■ The Air Optix Aqua Multifocal (Alcon) is a centre-near bi-aspheric silicone hydrogel lens with three add ranges. It aims to compensate for the patient’s loss of accommodation by extending the depth of focus in an effort to optimise vision at both distance and near (Fig. 13.17). ■ The Bausch & Lomb Ultra for Presbyopia multifocal lens is based on their PureVision2 Multifocal but with a different base curve and diameter and in a thinner edge design. This is a centre-near three-zone design with a power profile that demonstrates a consistent amount of add power across the range of distance lens powers (Fig. 13.18). MoistureSeal® technology is used to minimise dehydration, and there are two add powers in a monthly-replacement silicone hydrogel material. ■ 1-day Acuvue Moist Multifocal is an aspheric centrenear design hydrogel lens. The optic zone is smaller for hypermetropic corrections and larger for myopic ones and is available in three add powers (Low – maximum +1.25; Medium – maximum +1.75; High – maximum +2.50). Representative Design The Biofinity Multifocal (CooperVision) is a silicone hydrogel monthly lens. A centre-distance (D) lens, which transitions through an aspheric intermediate to an outer near zone, is placed on the dominant eye. A centre-near (N) lens, which transitions through an aspheric intermediate to a spherical peripheral distance zone, is placed on the nondominant eye

Intermediate

Distance Fig. 13.18  Ultra for Presbyopia. (Courtesy of Bausch & Lomb.)

(Iravani 2002, Quinn 2002b, Wan 2003) (Fig. 13.19). Visual summation then usually occurs, providing acceptable vision at all distances under binocular conditions. The central zone sizes are different between the D lens (2.3 mm) and N lens (1.7 mm) to emphasise the visual performance between each zone. It is available in one TD and BOZR, +1.50 D, +2.00 D and +2.50 D add powers. In a multicentre study, on average, patients required 0.12 D greater add power with the Frequency 55 Multifocal (similar to Biofinity Multifocal) nondominant lens compared with their spectacles (Iravani 2002). Patients should be warned that possible shadowing and ghost images may be present for the first week or so (Wan 2003). Changes in lens power can be expected in 20–40% of the patients at the first follow-up visit, and approximately half may benefit from the use of different add powers (Daniels & Cottam 2002).

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SECTION 4  •  Lens Fitting Modalities

Biofinity design

Table 13.6  Suggested Lenses to Use for Each Eye Depending on Reading Add Add

Dominant Eye

Non-Dominant Eye

Distance vision (spherical central zone)

+1.00

D

D

+1.50

D

D

Intermediate vision (progressive zone)

+2.00

D

N

+2.50

D

N

Near vision (spherical zone)

D, centre-distance lens; N, centre-near lens. (Courtesy of CooperVision). Lens edge D lens

Toric Bifocal Designs A limitation to the aforementioned lens designs is the correction of astigmatism. Although incorporating toric optics onto a multifocal design (or vice versa) could further compromise vision, this is a viable option for the motivated astigmatic presbyope who either is not a good RGP candidate or does not desire this option. They have been found to provide acceptable distance and near vision without compromising stereopsis (Madrid-Costa et al. 2012).

Near vision (spherical central zone) Intermediate vision (progressive zone) Distance vision (spherical zone) Lens edge N lens Fig. 13.19  Biofinity Multifocal EW. (Courtesy of CooperVision.)

Fitting Guide Fitting is much the same whether fitting centre-near or modified monovision. It is always advisable to start with a new refraction. Determine the spherical equivalent and with the patient wearing the prescription in the trial frame with both eyes open, keep adding +0.25 DS trial lenses to obtain maximum plus power for distance. ■ Establish which eye is the dominant eye by blurring each eye with +1.00 DS and asking the patient which is more comfortable. ■ Give the minimum near add that the patient is comfortable to accept, preferably using the patient’s own reading matter such as their mobile or cell phone. ■ Calculate the prescription, allowing for back vertex distance if necessary. ■ The manufacturer’s guide will suggest which lens to choose for each eye. Table 13.6 shows CooperVision’s suggested lenses for the Biofinity multifocal. ■ After inserting the lenses, allow the recommended adaptation time period in-office to establish the patient’s initial visual perception; the patient should walk around the office and perform customary daily tasks (Pal 2016). ■ Optimise the vision preferably using −0.25 DS in the dominant eye (distance) and +0.25 DS in the nondominant eye (near). ■

Representative Design ■ The Proclear multifocal toric (CooperVision) material (62% omafilcon) is known for representing a viable option for dry eye individuals. It uses the modified monovision ‘D’ and ‘N’ designs (Fig. 13.20) and is available with up to 5.75 D cylinder powers. Many laboratories are able to custom-make silicone hydrogel materials for toric multifocal designs.

■

Translating Designs See Section 8, History, available at: https://expertconsult. inkling.com/.

Troubleshooting Always adhere to the manufacturer’s recommended guidelines. ■ Generally the following applies: ■ Poor distance vision – add minus power in 0.25 D steps to the dominant eye only and/or decrease the add in the dominant eye (Bennett & Henry 2013). ■ Poor near vision – add plus power in 0.25 D steps to the nondominant eye and/or increase the add power. ■ Poor distance and near – address the distance problem first. ■ Check monocular acuities to determine which lens may need to be altered, then recheck the visual acuity with an over-refraction at both distance and near. ■ Finally reconfirm the dominant eye in case an error had been made initially. ■ If vision still is not acceptable, try a different lens design in one or both eyes. ■

Hybrid Multifocals Hybrid designs incorporate a rigid lens centre and a soft surrounding skirt (see Chapters 9 and 20 and http:// synergeyes.com). The potential benefit of these designs is

283

13  •  Bifocal and Multifocal Contact Lenses

3 mm progressive centre near add zone

9:00

Distance asphere

GP/Soft Skirt Hyperbond®

3:00

7.0 mm posterior optic zone SoftCushion® Outer Landing Zone

8.5 mm GP diameter

D lens

SiHy Soft Skirt Fig. 13.21  Duette Progressive multifocal. (Courtesy of SynergEyes.) 9:00

3:00

Poor Candidates for Multifocal Hybrid Contact Lenses.  The following are unlikely to benefit from these lenses: severe dry eye or ocular surface disease dry eye symptoms with all soft contact lenses ■ lenticular astigmatism ■ patients with very high expectations for vision ■ patients unmotivated to try a different lens modality. ■ ■

N lens Fig. 13.20  The Proclear multifocal toric. The purple zones pertain to distance correction and the blue zones to near correction. (Courtesy of CooperVision)

the vision associated with rigid lens optics and the initial comfort associated with soft lenses. Representative Design.  The Duette Progressive multifocal (SynergEyes) has a rigid 8.5 mm central RGP section with 84 Dk and a 14.5 mm silicone hydrogel skirt with 130 Dk. As these lenses do not translate on the eye, a centre-near design is used. Three separate add powers are available in an aspheric design that gradually increases in distance power away from the centre (Fig. 13.21). There are seven BOZR ranging from 7.1 to 8.3 mm and three soft lens skirt curve radii. Soft lens multipurpose and hydrogen peroxide care systems are recommended for lens care. Good Candidates for Multifocal Hybrid Contact Lenses.  The ability to correct astigmatism, utilise RGP lens optics and have the good initial comfort results in many potential candidates for this option (Bennett et al. 2015), including: astigmatic presbyopes soft multifocal patients seeking to eliminate their reading glasses ■ soft multifocal patients with astigmatism ■ soft toric monovision patients who want better near vision ■ patients desiring better overall vision ■ patients wishing to try the latest technology. ■ ■

Fitting Guide ■ Lenses can be fitted from a diagnostic fitting set. ■ They more commonly are fitted empirically by sending the following information to the laboratory: ■ refraction ■ keratometry ■ add power ■ dominant eye. ■ The goal is to have mild apical clearance with about 100 microns of initial clearance and ultimately about 30–60 microns after 10 minutes or more. ■ Choose the flattest soft skirt curve that provides comfort, centration and good movement (Quinn 2013). ■ Review at a follow-up visit 2 weeks later to allow adequate time for them to adapt to the lenses. Troubleshooting (see Bennett et al. 2015) ■ Decreased wear time or tight lenses – hybrid lenses should exhibit movement similar to a soft lens. If the lens is not moving on blinking, a flatter skirt radius should be selected. If the patient is already in the flattest skirt radius, a flatter BOZR should be used. ■ Distance vision unacceptable – because of the centre-near design, the distance power is typically −0.50 to −1.50 D more than the manifest refraction. If this is not the case, the BOZR should be adjusted to fall within this range. ■ Lens dryness – change the care system to a hydrogen peroxide system. A flatter skirt curve radius may help, or if

284

SECTION 4  •  Lens Fitting Modalities

the flattest skirt curve is being worn, changing to a flatter BOZR. The recommended replacement frequency of 6 months and the greater cost compared with a conventional RGP lens can be a problem for some patients.

dry eye symptoms or experience with contact lens dryness ■ post-refractive surgery patients with irregular topography. ■

Poor Candidates for Scleral Multifocal Contact Lenses Those patients: with high visual expectations with significant vision loss, with or without corneal scarring ■ unwilling to try a new lens modality, especially if there is a learning curve with lens handling ■ desiring a contact lens correction immediately. ■

SCLERAL MULTIFOCALS (see Chapter 14) An emerging area of popularity is the use of scleral lenses for individuals with healthy eyes. Several scleral multifocal designs have been introduced in recent years, and it is becoming a niche product in the presbyopic contact lens toolbox (Barnett 2015). Like hybrid multifocals, scleral designs do not translate; therefore the great majority are centre-near designs. The patient should first be fitted with single-vision distance lenses and, once an optimum fit and power and add power have been achieved, this information given to the laboratory. The fitting, problem-solving and care guidelines are identical to those for the conventional scleral lens wearer. A representative design is the Digiform15 Near-Center Bifocal from TruForm Optics (Fig. 13.22).

Advantages of Scleral Multifocals ■ The ability to correct astigmatism ■ Rigid lens optics ■ Good initial comfort ■ The optimum option for presbyopic patients with ocular surface disease. Disadvantages of Scleral Multifocals ■ They can be difficult to insert without a bubble. ■ Some patients find they can’t wear them for more than a few hours. ■ They have a higher cost than other designs. ■ The fitting and troubleshooting process is longer. Good Candidates for Scleral Multifocal Contact Lenses (Messer et al. 2015) These include: normal corneas irregular astigmatism

■ ■

Fig. 13.22  Fluorescein pattern of a TruForm Scleral Lens. (Courtesy of TruForm Optics.)

■

POST-REFRACTIVE SURGERY AND KERATOPLASTY Several lens designs have been introduced for the postrefractive surgery patient who is now becoming presbyopic. These typically consist of a front surface aspheric rigid multifocal in combination with a reverse geometry back surface to align an oblate cornea. The Refractive Surgery Specific (RSS) design of the Reclaim multifocal lens (Blanchard) is a reverse geometry, aberration-controlled front surface aspheric multifocal lens which has an effective centre-distance zone. It can be used after both refractive surgery and penetrating keratoplasty where the graft tissue is flatter than the periphery. The lens should show good centration, minimum central clearance and stable vision (Fig. 13.23). The standard diameter is 10.5 mm, and it is available with an add of up to +4.00. The lens can be fitted from a fitting set or by sending the topography scans taken pre- and post-refractive surgery.

SUCCESS RATES AND QUALITY OF VISION A typical success rate of 75–90% is found with gas permeable multifocal and bifocal lens designs (Remba 1988, Meter et al. 1990, Byrnes & Cannella 1999, Woods et al. 1999, Lieblein 2000, Van Dzid 2004). One study claimed a success rate of 100% after one month of lens wear (Gromacki et al. 2003). Woods et al. (2015) compared subjective and objective visual performance using the Air Optix Aqua Multifocal lenses with monovision. They found that high- and low-contrast acuities and also near tasks were better with monovision. However, participants rated multifocals better for focus changing when

Fig. 13.23  The Reclaim RSS lens. (Courtesy of Blanchard Contact Lens.)

13  •  Bifocal and Multifocal Contact Lenses

285

Table 13.7  Factors to Consider in the Decision-Making Process Lens Type

DV

NV

IMV

Astig Corr.

Initial Comfort

Inventory/ Emp Fitting

Cost

Care/Handling

Soft MFs (freq. replac)

G/Acc

G/Acc

G/Acc

Poor

Great

Yes

$$

Good

Soft MFs (dailies)

G/Acc

G/Acc

G/Acc

Poor

Great

Yes

$$$$

Great

Soft toric MFs

Acc

Acc

Acc

Acc

Great

No*

$$$$

Good

Aspheric GP MFs

Gr/G

Gr/G/Acc

Gr/G

Great

Acc

Yes

$$

Good

Seg BIF GP MFs

Gr

Gr/G

P

Gr

Acc

No**

$$

G

Seg TRI GP MFs

Gr

Gr/G

Gr/G

Gr

Acc

No**

$$$

G

Hybrid MFs

Gr/G

Gr/G

Gr/G

Gr

Gr/G

Both***

$$$

G/Acc

Scleral MFs

G

Gr

G

Gr

Gr

No

$$$$

Acc

Monovision

G/Acc

G/Acc

Acc/P

P

Gr

Yes

$

G

(Soft)

(Soft)

Gr

Acc

(GP)

(GP)

*Trial lenses in the proper prescription can be ordered in some cases. **This is true for all but one design. ***Diagnostic fitting has been recommended, but company is changing towards empirical. Gr = Great G = Good Acc = Acceptable P = Poor DV, Distance vision; GP, gas permeable; MF, multifocal; NV, near vision; IMV, intermediate vision. (With permission from Bennett, E.S., Quinn, T.G., 2014. Multifocal lens decision-making 101. Contact Lens Spectrum 29 (4), 30–38.)

driving. Eighty-eight percent of participants achieved an acceptable result with either one or both of these options. Sivardeen et al. (2016) compared four popular soft multifocal lens designs to monovision and found that, visually, the multifocal designs outperformed monovision. However, Woods et al. (2009) showed that low-contrast near vision in early presbyopes was better with monovision low-addition multifocals, but multifocals were the preferred option for distance tasks (Woods et al. 2009). Rajagopalan et al. (2006), comparing the quality of vision of wearers of progressive addition spectacle lenses (PALs), monovision lenses, soft multifocal lenses and aspheric RGP multifocal lenses, found that the RGP wearers exhibited similar quality of vision results to the PAL wearers; soft multifocal lens wearers were third, and monovision wearers exhibited the poorest performance. It is evident that patients need to be carefully screened prior to selecting the specific presbyopic contact lens option that is best for them. A summary of the decisionmaking process is provided in Table 13.7 (Bennett & Quinn 2014).

from friends and relatives. In addition, these individuals need to be closely monitored for possible complications that may arise from the ageing eye.

Patient Education and Follow-Up Care (see Chapters 16 and 17)

Corneal aberrations and pupil diameter have been found to be the primary subject-dependent variables influencing quality of vision, so these factors are likely to be addressed in future designs (Rio et al. 2016). Manufacturers will be able to make more custom designs that take into consideration soft lens decentration, for example, with the nasal sclera being more elevated than the temporal sclera (Lampa 2016); decentring the optical centre nasally can result in improved visual

Presbyopic patients, especially new contact lens wearers, need to be thoroughly educated regarding correct lens care and handling (see Chapters 6 and 15). First-time wearers may have been exposed to negative experiences/complications

CARE AND HANDLING For the first-time wearer, it is important that the patient leave the office feeling confident in the handling of their lenses. Presbyopic contact lens patients should be regularly monitored, preferably every 6 months with emphasis on possible dryness-related problems. Patients unable to wear daily disposable lenses may benefit from a hydrogen peroxide care system. In addition to routine checks, keratometry/corneal topography and refraction should be performed, particularly with patients wearing the thicker bifocal designs, in which undesirable curvature and hypoxic and refractive changes may occur.

The Future of Multifocal Lenses

286

SECTION 4  •  Lens Fitting Modalities

performance (Brujic 2016). There is much interest in contact lenses that can actually ‘accommodate’ for different distances. The first step in that direction is a novel contact lens which extends the depth of focus by deliberate manipulation of higher-order spherical aberrations. Research has concluded that this design, when compared to a commercially available soft multifocal, provides better intermediate and near vision performance without compromising distance vision (Tilia, Bakaraju et al. 2016, Tilia, Murno et al. 2016). Finally, electronic accommodating lenses may well be the way of the future (see also Chapter 27).

Summary Fitting the presbyopic patient with contact lenses can be a challenging process, but often it is not nearly as complicated as perceived. It is important to be realistic with every patient, informing each that visual compromises may be present compared with single- vision lenses and spectacles. Likewise, the fees as well as the amount of potential chair time need to be communicated. They should also be informed that the goal of presbyopic contact lens fitting is to reduce, rather than eliminate, the need for supplemental near correction even though in most cases the latter will not be necessary. Certainly this process is made easier if patients are informed of the contact lens options prior to reaching presbyopia. If the patient has been adequately informed and demonstrates sufficient motivation, then success is likely with high patient satisfaction resulting. Presbyopic patients represent the most untapped segment of the potential contact lens wearing population, and yet, as this chapter hopefully emphasises, multifocals are not particularly challenging to fit and are likely to be successful. Patients deserve the opportunity to be informed and, if motivated, fitted with the appropriate lenses. Certainly, with the ever-increasing percentage of the population becoming presbyopic, and refractive surgery meeting the needs of only a very small number of individuals in this age group, it makes good sense to present the contact lens option to all presbyopic patients in eye-care practice today.

Acknowledgement The editors would like to thank Judith Morris for her helpful comments on the European lenses mentioned in this chapter.

References Afanador, A.J., Aitsebaomo, P., Gerstman, D.R., 1986. Eye and head contribution to gaze at near through multifocals: The usable field of view. Am. J. Optom. Physiol. Opt. 63, 187–192. Ames, K., 2001. Fitting the presbyope with gas permeable contact lenses. Contact Lens Spectrum 16 (10), 42–45. Andres, S., Henriques, A., Garcia, M.L., et al., 1987. Factors of the precorneal fluid break-up time (BUT) and tolerance of contact lenses. Int. Contact Lens Clin. 14, 81–120. Barnett, M., 2015. Multifocal scleral lenses. Contact Lens Spectrum 30 (12), 26–31. Benjamin, W.J., Borish, I.M., 1991. Physiology of aging and its influence on the contact lens prescription. J. Am. Optom. Assoc. 62 (10), 743–752. Bennett, E.S., 2004a. Patient selection, evaluation, and consultation. In: Bennett, E.S., Hom, M.M. (Eds.), Manual of Gas Permeable Contact Lenses, second ed. Elsevier Publ, St. Louis, pp. 58–85. Bennett, E.S., 2004b. Guide to fitting GP multifocals and bifocals: Part 1. Rev. Contact Lenses May, 15.

Bennett, E.S., 2004c. Guide to fitting GP multifocals and bifocals: Part 4. Rev. Contact Lenses October, 14. Bennett, E.S., 2005. Researching gas permeable multifocals. Contact Lens Spectrum 20 (2), 21. Bennett, E.S., 2008. Contact lens correction of presbyopia. Clin. Exp. Optom. 91 (3), 265–278. Bennett, E.S., Dinardo, A., Woo, S.L., 2015. Can we solve the presbyopia dilemma? Presented at the Global Specialty Lens Symposium, Las Vegas, NV. Bennett, E.S., Hansen, D., 2004. Presbyopia: Gas-permeable bifocal fitting and problem-solving. In: Bennett, E.S., Hom, M.M. (Eds.), Manual of Gas Permeable Contact Lenses, second ed. Elsevier Science, St. Louis, pp. 324–356. Bennett, E.S., Henry, V.A., 2013. Multifocal contact lens update. Lecture presented at the Annual Meeting of the American Academy of Optometry, Seattle, WA. Bennett, E.S., Henry, V.A., 2014. Bifocal contact lenses. In: Bennett, E.S., Henry, V.A. (Eds.), Clinical Manual of Contact Lenses, fourth ed. Lippincott Williams & Wilkins, Philadelphia, pp. 395–434. Bennett, E.S., Jurkus, J.M., 2005. Presbyopic correction. In: Bennett, E.S., Weissman, B.A. (Eds.), Clinical Contact Lens Practice, second ed. Lippincott Williams & Wilkins, Philadelphia, pp. 27-1–27-18. Bennett, E.S., Luk, B., 2001. Rigid gas permeable bifocal contact lenses: an update. Optom. Today 34–36. Bennett, E.S., Quinn, T.G., 2014. Multifocal lens decision-making 101. Contact Lens Spectrum 29 (4), 30–38. Bennett, E.S., Smythe, J., Henry, V.A., et al., 1998. The effect of topical anesthetic use on the initial patient satisfaction and overall success with rigid gas permeable contact lenses. Optom. Vis. Sci. 75, 800–805. Bennett, E.S., Weissman, B.A., Remba, M.J., 2006. Contact lenses and the elderly patient. In: Rosenbloom, A.A., Morgan, M.M. (Eds.), Vision and Aging, third ed. Elsevier Publ., St. Louis, MO, pp. 215–240. Borish, I.M., 1986. Presbyopia. In: Bennett, E.S., Grohe, R.M. (Eds.), Rigid Gas-Permeable Contact Lenses. Professional Press, New York, pp. 385–414. Borish, I.M., Perrigin, D.M., 1985. Observations of bifocal contact lenses. Int. Eyecare 1 (3), 241–248. Brujic, M., 2016. Effects of line of sight on patients vision. Presented at the Global Specialty Lens Symposium. Las Vegas, NV. Burnett-Hodd, N., 2004. Contact lens correction for presbyopia. Optom. Today 44–51. Byrnes, S.P., Cannella, A., 1999. An in-office evaluation of a multifocal RGP lens design. Contact Lens Spectrum 14 (11), 29–33. Caffery, B.E., Josephson, J.E., 1991. Rigid bifocal lens correction. In: Bennett, E.S., Weissman, B.A. (Eds.), Clinical Contact Lens Practice. JB Lippincott, Philadelphia, pp. 42-1–42-12. Cardona, G., Lopez, S., 2016. Pupil diameter, working distance and illumination during habitual tasks. Implications for simultaneous vision contact lenses for presbyopia. J. Optom. 9 (2), 78–84. Caroline, P., 2013. Personal communication. Collins, M., Bruce, A., Thompson, B., 1994. Adaptation to monovision. Int. Contact Lens Clin. 21, 218–224. Daniels, K., Cottam, L., 2002. Independent clinical evaluation of inverse geometry multifocal for presbyopic correction. Presented at the Annual Meeting of the American Academy of Optometry, San Diego, CA, Dec., 2002. Davis, R., 2003. Pinpoint success with GP multifocal lenses. Contact Lens Spectrum 18 (10). Davis, R.L., 2016. Determining multifocal parameters for a better fit. Rev. Optom. 153 (8), 50–56. de Carle, J.T., 1997. Bifocal and multifocal contact lenses. In: Phillips, A.J., Speedwell, L. (Eds.), Contact Lens Practice, fourth ed. ButterworthHeinemann, Oxford, pp. 540–565. Diepes, H., Tameling, A., 1988. Comparative investigations of progressive lenses. Am. J. Optom. Physiol. Opt. 65, 571–579. Dinardo, A., Fosso, T., Norman, C., et al., 2014. Common factors in multifocal lens success. Paper presented at the Global Specialty Lens Symposium, Las Vegas, Nevada. Du Toit, R., Ferreira, J.T., Nel, Z.J., 1998. Visual and nonvisual variables implicated in monovision wear. Optom. Vis. Sci. 75, 119–125. Du Toit, R., Situ, P., Simpson, T., et al., 2001. The effects of six months of contact lens wear on the tear film, ocular surfaces, and symptoms of presbyopes. Optom. Vis. Sci. 78, 455–462. Dzid, J.M., 2004. A successful hybrid. Optom. Management 39 (10), 84. Edmonds, F., Reindel, W., 2012. As cited in Tan J: Contact Lens Optics for Presbyopia http://www.siliconehydrogels.org/editorial_jackie_tan.asp. Accessed January, 2012.

13  •  Bifocal and Multifocal Contact Lenses Edwards, K., 1999. Contact lens problem-solving: Bifocal contact lenses. Optician 218, 26–32. Eggink, F.A.G.J., Pinkers, A.J.L.G., DeGraaf, R., 1990. Visual acuity and contrast sensitivity with Diffrax contact lenses. Contact Lens J. 18 (2), 37–39. Erickson, P., McGill, E.C., 1992. Role of visual acuity, stereoacuity, and ocular dominance in monovision patient success. Optom. Vis. Sci. 69, 761–764. Evans, B.J., 2007. Monovision: a review. Ophthalmol. Physiol. Opt. 27, 417–439. Fernandes, P.R.B., Neves, H.I.F., Lope-Ferreira, D.P., et al., 2013. Adaptation to multifocal and monovision contact lens correction. Optom. Vis. Sci. 90 (3), 228–235. Fonda, G., 1966. Trans Ophthalmologic Society of Australia XXV. 46–50. Gasson, A., Morris, J., 2010. Lenses for presbyopia. In: Gasson, A., Morris, J. (Eds.), The Contact Lens Manual: A Practical Fitting Guide, fourth ed. Butterworth Heinemann, Oxford, pp. 277–293. Gromacki, S.J., 2004. Preventing contact lens challenges for presbyopes. Contact Lens Spectrum 19 (8), S2–S7. Gromacki, S.J., Badowski, L., Wicker, D., et al., 2003. A clinical study of an RGP multifocal contact lens. Contact Lens Spectrum 18 (4), 36–41. Hamano, H., et al., 1983. A new method of measuring tears. CLAO J. 9, 281–289. Hansen, D., Baker, R., Bennett, E.S., 2003. Why today’s GP designs are easier to fit. Rev. Optom. 140, 43–46. Hansen, D.W., 1998. Mapping the way to successful bifocal RGP selection. Contact Lens Spectrum 13 (3). Hansen, D.W., 1999. Advanced multifocal fitting and management. Contact Lens Spectrum 14 (8), 25–33. Harris, M.G., Classe, J.G., 1988. Clinicolegal considerations of monovision. J. Am. Optom. Assoc. 59, 491–495. Iravani, N., 2002. New multifocal offers best of both worlds. Contact Lens Spectrum 17, 9. Jain, S., Arora, I., Azar, D.T., 1996. Success of monovision in presbyopes: Review of the literature and potential applications to refractive surgery. Surv. Ophthalmol. 40, 491–499. Jain, S., Ou, R., Azar, D.T., 2001. Monovision outcomes in presbyopic individuals after refractive surgery. Ophthalmology 108, 1430–1433. Johannsdottir, K.R., Stelmach, L.B., 2001. Monovision: a review of the scientific literature. Optom. Vis. Sci. 78, 646–651. Josephson, J.E., Caffery, B.E., 1988. Tips on fitting and evaluating the Alges® bifocal contact lens. Contact Lens Forum 13 (6), 33–34. Josephson, J.E., Erickson, P., Back, A., et al., 1990. Monovision. J. Am. Optom. Assoc. 61, 820–826. Lampa, M., 2016. New findings in scleral shape. Presented at the Global Specialty Lens Symposium. Las Vegas, NV. Lampa, M., Davis, R., Becherer, P.D., et al., 2016. Pupil diameter and variable multifocal zone sizes related to success. Presented at the Global Specialty Lens Symposium. Las Vegas, NV. Lieblein, J.S., 2000. Fitting success with multifocal contact lenses. Contact Lens Spectrum 15 (3), 50–51. MacAlister, G.O., Woods, C.A., 1991. Monovision versus RGP translating bifocals. J. Br. Contact Lens Assoc. 14, 173–178. Madrid-Costa, D., Tomas, E., Ferrer-Blasco, T., et al., 2012. Visual performance of a multifocal toric soft contact lens. Optom. Vis. Sci. 89 (11), 1627–1635. Mandell, R.B., 2002. A new concept in GP bifocal contact lenses. Contact Lens Spectrum 17 (10). Martin, D.K., Dain, S.J., 1988. Postural modifications of VDU operators wearing bifocal spectacles. Appl. Ergon. 19, 293–300. Messer, B.M., Woo, S.L., Bennett, E.S., 2015. Presbyopic lens patient management and troubleshooting. Contact Lens Spectrum 30 (3), 20–23, 25–28. Meyler, J., Veys, J., 1999. A new pupil-intelligent design for presbyopic correction. Optician 217, 18–23. Michaels, D.D., 1974. Ocular Dominance. Surv. Ophthalmol. 17, 151–163. Morgan, P.B., Efron, N., Woods, C.A., 2011. International contact lens prescribing survey consortium. Clin. Exp. Optom. 94 (1), 87–92. Morgan, P.B., Woods, C.A., Tranoudis, J.G., et al., 2016. International Contact Lens Prescribing in 2015. Contact Lens Spectrum 31 (1), 24–29. Nakagawara, V.B., Veronneau, S.J.H., 2000. Monovision contact lens use in the aviation environment: a report of a contact lens-related aircraft accident. Optometry 71 (6), 390–395. Nichols, J.J., 2016. Contact lenses 2015. Contact Lens Spectrum 31 (1), 18–23, 55.

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Norman, C., 2013. Where do we go from here? Contact Lens Spectrum 28 (1), 17. Pal, S., 2016. Use education and empathy to connect with presbyopes. Rev. Optom. 153 (8), 34–38. Pearlman, A., 1987. The central visual pathways. In: Moses, R.A., Hart, W.M. (Eds.), Adler’s Physiology of the Eye: Clinical Application. CV Mosby, St. Louis, MO, pp. 583–618. Pointer, J.S., 2001. Sighting dominance, handedness, and visual acuity preference: three mutually exclusive modalities? Ophthalmic Physiol. Opt. 21, 117–126. Quinn, T.G., 1997. Identifying the presbyopic contact lens candidate. Contact Lens Spectrum 12 (9), 3s–6s. Quinn, T.G., 2001. Translating bifocals into success. Contact Lens Spectrum 16 (3). Quinn, T.G., 2002a. The monovision vs. multifocal debate. Contact Lens Spectrum 17 (11). Quinn, T.G., 2002b. Making sense of frequent replacement soft multifocals. Contact Lens Spectrum 17 (3). Quinn, T.G., 2007. The role of ocular dominance in presbyopic lens correction. Contact Lens Spectrum 22 (1), 48. Quinn, T.G., 2013. A logical approach to multifocal contact lens fitting. Contact Lens Spectrum 28 (3), 20–25, 31. Rajagopalan, A.S., Bennett, E.S., Lakshminarayanan, V., et al., 2006. Visual performance of subjects wearing presbyopic contact lenses. Optom. Vis. Sci. 83 (8), 611–615. Remba, M.J., 1988. The Tangent Streak rigid gas permeable bifocal contact lens. J. Am. Optom. Assoc. 59 (3), 212–216. Rigel, L.E., Castellano, C.F., 1999. How to fit today’s soft bifocal contact lenses. Optom. Today 7 (Suppl.), 45–51. Rio, D., Woog, K., Legras, R., 2016. Effect of age, decentration, aberrations and pupil size on subjective image quality with concentric bifocal optics. Ophthalmic Physiol. Opt. 36 (4), 411–420. Sakamoto, R., Bennett, E.S., Henry, V.A., et al., 1993. The phenol red thread test: a cross-cultural study. Invest. Ophthalmol. Vis. Sci. 34, 3510–3514. Schor, C., Landsman, L., 1987. Ocular dominance and the interocular suppression of blur in monovision. Am. J. Optom. Physiol. Opt. 64, 723–730. Schwallie, J., 2000. Multifocal contact lenses: a valuable alternative for your presbyopic patient. Contact Lens Spectrum 15 (12). Schwartz, C.A., 1996. Presbyopia: Monovision. In: Schwartz, C.A. (Ed.), Specialty Contact Lenses: A Fitter’s Guide, first ed. W.B. Saunders Company, pp. 85–93. Schwartz, C.A., 1999. Portrait of a presbyope in 1999. Optom. Today Suppl, 5–7. Shovlin, J.P., Eisenberg, J.S., 2003. Monovision vs. multifocal: which would you choose? Rev. Optom. 140, 36–38. Sivardeen, A., Laughton, D., Wolffsohn, J.S., 2016. Randomized crossover trial of silicone hydrogel presbyopic contact lenses. Optom. Vis. Sci. 93 (2), 141–149. Soni, P.S., Patel, R., Carlson, R.S., 2003. Is binocular contrast sensitivity at distance compromised with multifocal soft contact lenses used to correct presbyopia? Optom. Vis. Sci. 80 (7), 505–514. Thompson, B., Collins, M.J., Hearn, G., 1990. Clinician interpersonal communication skills and contact lens wearers’ motivation, satisfaction and compliance. Optom. Vis. Sci. 67, 673–678. Tilia, D., Bakaraju, R.C., Chung, J., et al., 2016. Short-term visual performance of novel extended depth-of-focus contact lenses. Optom. Vis. Sci. 93 (4), 435–444. Tilia, D., Murno, A., Chung, J., et al., 2016. Short-term comparison between extended depth-of-focus prototype contact lenses and a commercially available center-near multifocal. J. Optom. May 6. Van Meter, W.S., Gussler, J.R., Litteral, G., 1990. Clinical evaluation of three bifocal contact lenses. CLAO J. 16 (3), 203–207. Vassilieff, A., Dain, S., 1986. Bifocal wearing and VDU operation: A review and graphical analysis. Appl. Ergon. 17, 82–86. Wan, L., 2003. Take some frustration out of multifocal fitting. Contact Lens Spectrum 18 (9), 42–44. Watanabe, R.K., 2010. Design characteristics of two new soft multifocals. Contact Lens Spectrum 25 (2), 18. Weale, R.A., 1982. A Biography of the Eye: Development, Age, and Growth. HK Lewis, London. Westin, E., Wick, B., Harrist, R.B., 2000. Factors influencing success of monovision contact lens fitting: survey of contact lens diplomates. Optometry 71, 757–763.

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Woods, C., Ruston, D., Hough, T., et al., 1999. Clinical performance of an innovative back surface multifocal contact lens in correcting presbyopia. CLAO J. 25 (3), 176–181. Woods, J., Woods, C.A., Fonn, D., 2009. Early symptomatic presbyopes – what correction modality works best? Eye Contact Lens 35 (5), 221–226. Woods, J., Woods, C., Fonn, D., 2015. Visual performance of a multifocal contact lens versus monovision in established presbyopes. Optom. Vis. Sci. 92 (2), 175–182.

Wooley, S., 1998. Doctor, do I need to give up my contact lenses just because I need bifocals? Optom. Today 6, 40–42. Yager, J., 2002. Pearls for fitting the presbyopic patient. Rev. Contact Lenses Sept. 28–32.