Influence on visual function of forward light scattering associated with subsurface nanoglistenings in intraocular lenses

ARTICLE

Influence on visual function of forward light scattering associated with subsurface nanoglistenings in intraocular lenses Simone Beheregaray, MD, Toshiya Yamamoto, MD, Takahiro Hiraoka, MD, PhD, Tetsuro Oshika, MD, PhD

PURPOSE: To quantitatively assess the impact of subsurface nanoglistenings on forward light scattering and visual function. SETTING: University of Tsukuba, Tsukuba, Japan. DESIGN: Case-control study. METHODS: Eyes with subsurface nanoglistenings and increased intraocular lens (IOL) surface light scattering and control eyes without subsurface nanoglistenings were evaluated. Forward light scattering was assessed with a double-pass device (Optical Quality Analysis System II) using the objective scatter index (OSI) as a quantitative parameter. Backward light scattering in the IOL surface was evaluated using Scheimpflug imaging (EAS-1000). The contrast sensitivity function was assessed as the area under the log contrast sensitivity function (AULCSF) measured with the Optec 6500 device. Correlations between the OSI, visual function, age, time after surgery, IOL power, and backward light scattering were analyzed. RESULTS: In the study group, logMAR corrected distance visual acuity (CDVA) ranged from
0.176 to 0.045 (
0.06 G 0.07 [SD]); no patient had a CDVA worse than 20/25. The OSI was significantly higher than in the control group (PZ.0074) and correlated with CDVA (PZ.0021), AULCSF photopic without glare (PZ.0002) and with glare (P<.0001), and AULCSF mesopic without glare (PZ.0038) and with glare (PZ.0008). Multivariate analysis showed OSI was the only variable that correlated with CDVA and contrast sensitivity with glare. The OSI and age correlated with contrast sensitivity without glare (P<.05). CONCLUSIONS: Eyes with subsurface nanoglistenings had increased forward light scattering but no deterioration in CDVA. Increases in forward light scattering correlated with reductions in visual acuity and contrast sensitivity, although both remained within their normal range. Financial Disclosures: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2014; -:-–- Q 2014 ASCRS and ESCRS

It is well-known that some intraocular lenses (IOLs) develop a slightly white opacified appearance with time that occurs as a result of an increase of light scattering on their surface.1–3 Previously referred to as whitening by some researchers,4,5 this phenomenon is caused by infiltration of small aggregates of water molecules originating from the aqueous humor in nanovacuoles close to the IOL surface,1,4,6 and it was recently recognized as subsurface nanoglistenings.6 It is important to recognize the distinction between glistenings and subsurface nanoglistenings. Q 2014 ASCRS and ESCRS Published by Elsevier Inc.

Glistenings are bigger microvacuoles filled with fluid that range in size from 1 to 20 mm; unlike subsurface nanoglistenings, they are located throughout the thickness of the IOL optic. The density of glistenings can be graded at the slitlamp, and the number and size of glistenings can be evaluated by analyzing digital images.7–10 In contrast, in subsurface nanoglistenings, cryogenic focused ion beam scanning electron microscopy images identified vacuoles smaller than 200 nm situated 120 mm or less from the IOL surface.6 The whitish IOL appearance can be observed on 0886-3350/$ - see front matter http://dx.doi.org/10.1016/j.jcrs.2013.10.047

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slitlamp examination by directing the light in a 30-degree or greater angle. Increased light scattering can also be assessed using a Scheimpflug imaging system, which captures the amount of backward light scattering on the IOL surface.1,2 Different types of light scattering exist, and the characteristics depend on several elements including wavelength of light, and the size, shape, and density of the particles. In subsurface nanoglistenings, the particle is smaller than the wavelength of incident light; thus, Rayleigh scattering is induced and shorter wavelengths are more scattered.11 The effects of light scattering in eyes can be divided into backward and forward. Backward light scattering is the light scattered out of the eye toward the light source; therefore, it can be observed during slitlamp examination. Forward light scattering, or intraocular light scattering, is composed of the light scattered toward the retina. Thus, it can reduce visual acuity, impair contrast, and induce glare.12 Although subsurface nanoglistenings increase the intensity of backward light scattering, most studies report that subsurface nanoglistenings do not adversely influence visual function.2,4,13,14 Nonetheless, the exact influence of subsurface nanoglistenings on forward light scattering and visual function has not been explored in detail. This study aimed to quantify forward light scattering in eyes with acrylic spherical IOLs with increased surface light scattering caused by subsurface nanoglistenings and compare it with that in eyes with acrylic aspheric IOLs with no subsurface nanoglistenings. This study also evaluated the impact of forward light scattering on the visual function of patients with subsurface nanoglistenings.

Submitted: August 14, 2013. Final revision submitted: October 15, 2013. Accepted: October 30, 2013. From the Department of Ophthalmology (Beheregaray, Hiraoka, Oshika), Faculty of Medicine, University of Tsukuba, Tsukuba, and Ushiku Aiwa General Hospital (Yamamoto), Ushiku, Ibaraki, Japan. Presented at the 116th Annual Meeting of the Japanese Ophthalmological Society, Tokyo, Japan, April 2012, the XXX Congress of the European Society of Cataract and Refractive Surgeons, Milan, Italy, September 2012, and [email protected] and Societ
a Italiana Cellule Staminali e Superficie Oculare, Sienna, Italy, June 2013. Corresponding author: Simone Beheregaray, MD, Department of Ophthalmology, Faculty of Medicine, University of Tsukuba, Tennoudai 1-1-1, Tsukuba Ibaraki 305-8575, Japan. E-mail: [email protected].

PATIENTS AND METHODS This study was performed at the University of Tsukuba Hospital between December 2010 and June 2013. An institutional review board approved the study, and all patients provided informed consent. The practices and research adhered to the tenets of the Declaration of Helsinki. Patients who had phacoemulsification and implantation of spherical acrylic Acrysof IOLs (models SA60AT, SN60AT, MA60AC, MA60BM, Alcon Laboratories, Inc.) were evaluated to verify the presence of increased surface light scattering resulting from subsurface nanoglistenings (study group). Two ophthalmologists made the diagnosis of subsurface nanoglistenings by observing the IOL appearance at the slitlamp and by identifying increased backward light scattering in the anterior IOL surface using a Scheimpflug system (EAS-1000, Nidek Co., Ltd.). Only eyes with backward light scattering in the anterior IOL surface higher than 20 computer-compatible tape (CCT) units were included in the study group. Patients with aspheric acrylic Acrysof SN60WF IOL, acrylic iSert 251 IOL, or acrylic iSert 255 IOL (Hoya Corp.) with backward light scattering in the anterior IOL surface of 20 CCT units or smaller were selected for the control group. All IOLs in this study were hydrophobic. Individuals with ocular surface pathology, posterior capsule opacification, retinal disease, optical nerve pathology, neurological disorders, or a condition that could affect contrast sensitivity were excluded. The following parameters were evaluated: age, IOL power, time after surgery, forward light scattering, backward light scattering in the anterior IOL surface, visual acuity, and contrast sensitivity. Distance visual acuity was measured with a Landolt chart at 5 m. The Optec 6500 system (Stereo Optical Co., Inc.) was used to evaluate contrast sensitivity under photopic conditions (85 candelas [cd]/m2) and mesopic conditions (3.0 cd/m2) with and without glare light (1 lux for night and 10 lux for day). This system evaluates 5 spatial frequencies (1.5, 3.0, 6.0, 12.0, and 18.0 cycles per degree). Each spatial frequency has 9 circular sine-wave grating charts showing a progressive decrease of 0.15 log in contrast. Patients were asked to identify the directions of the bars of each patch until the first mistaken identification. The area under the log contrast sensitivity function (AULCSF) was calculated and used for the analyses. The Optical Quality Analysis System II (Visiometrics) was used to quantify forward light scattering. The device uses a double-pass method in which an image of a point source object is projected onto the retina. After retinal reflection and double pass through the ocular media, the image is recorded by an infrared video camera. The equipment evaluates the forward light scattering through the objective scatter index (OSI). Using the double-pass image that arises from the light diffused by the eye, the system calculates the OSI as the ratio between the amount of energy recorded in an eccentric area and the amount obtained closer to the center. The artificial exit pupil diameter in the system was set at 4.0 mm. Spherical errors between
8.0 diopters (D) and C6.0 D were corrected by the instrument's optometer, and astigmatism was corrected by a cylindrical lens placed in front of the eye. The degree of light scattering was classified as normal (OSI !1), low (OSI R1 to !2), moderate (OSI R2 to !5), and high (OSI R5).15,16 To evaluate backward light scattering, the IOLs were photographed under mydriasis using the Scheimpflug system with 200 watt-seconds of light and an 8.0 mm slit length at

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Table 1. Demographic and clinical data by group. Study Group (n Z 42) Parameter Age (y) Time after surgery (y) UDVA (logMAR) CDVA (logMAR) AULCSF photopic no glare AULCSF mesopic no glare AULCSF photopic with glare AULCSF mesopic with glare OSI Anterior surface BLS (CCT units) IOL power (D)

Control Group (n Z 17)

Mean G SD

Min

Max

Mean G SD

Min

Max

P Value

69.8 G 7.3 6.48 G 2.80 0.352 G 0.363
0.061 G 0.066 1.574 G 0.321 1.209 G 0.398 1.603 G 0.369 0.999 G 0.434 2.3 G 1.2 66.99 G 33.17 19.1 G 4.2

55 1.41
0.176
0.176 0.864 0.490 0.498 0 0.9 23.00 6.5

85 12.89 1.301 0.045 2.159 1.986 2.128 1.756 5.9 124.75 25.5

70.2 G 7.0 0.59 G 0.69 0.272 G 0.321
0.052 G 0.051 1.624 G 0.255 1.283 G 0.360 1.695 G 0.288 1.048 G 0.474 1.6 G 0.8 7.51 G 4.82 19.8 G 2.8

62 0.02
0.079
0.176 1.108 0.581 1.108 0 0.7 0.50 16.0

87 2.57 1.000 0 2.080 1.744 2.103 1.657 3.7 19.00 25.0

.8671* !.0001*,† .4767* .7172* .8083* .5095z .3613z .6978z .0076*,† !.0001*,† .8605*

AULCSF Z area under the log contrast sensitivity function; BLS Z backward light scattering; CCT Z computer-compatible tape; CDVA Z corrected distance visual acuity; IOL Z intraocular lens; OSI Z objective scatter index; UDVA Z uncorrected distance visual acuity *Mann-Whitney test † P!.05 z Unpaired t test

angles of 0 degree, 45 degrees, 90 degrees, and 135 degrees. The density of light scattering in each degree angle was measured in the central 3.0 mm  0.25 mm area of the anterior IOL surface. Backward light scattering was defined as the mean density of light obtained from the 4 studied angles, and those values were calculated for the anterior IOL surface. Results were shown in CCT units, which is a measure of the intensity of scattered light that ranges from 0 (black) to 255 (white).

Statistical Analysis The mean G standard deviation (SD) values were calculated for all parameters. The unpaired t test and Mann-Whitney test were used to assess differences between patients. A simple test analysis using the Pearson coefficient (r) was used to identify correlations between the OSI and other parameters. Multiple regression analysis was used to assess the relationship between visual function and several parameters. The objective variables were the corrected distance visual acuity (CDVA), photopic contrast sensitivity with and without glare, and mesopic contrast sensitivity with and without glare. Independent variables were age, period after surgery, anterior IOL surface backward light scattering, IOL power, and OSI values. Tests were considered statistically significant when the P value was less than 0.05. Graphpad Instat statistical software (Graphpad Software, Inc.) was used for the analysis.

RESULTS Forty-two eyes of 33 patients with subsurface nanoglistenings (study group) and 17 control eyes of 14 patients were evaluated. The backward light scattering in the anterior IOL surface, OSI, and time after surgery were significantly higher in the study group than in the control group (P!.0001, PZ.0076, and P!.0001, respectively). All patients had a CDVA better than

0.9 (decimal), indicating that no patient had poor visual acuity as a result of the subsurface nanoglistenings. Table 1 shows the demographic and clinical data in the study group and control group. In the study group, the time elapsed after surgery was statistically significantly longer and photopic contrast sensitivity with glare was statistically significantly lower in eyes with a 3-piece IOL than in eyes with a 1-piece IOL. Table 2 shows the demographic and clinical data according to IOL type in the study group. In the control group, the only statistically significant difference between eyes with the Acrysof SN60WF IOL (8 eyes of 8 patients) and eyes with the iSert 251 IOL or iSert 255 IOL (9 eyes of 6 patients) was in uncorrected distance visual acuity (UDVA), with better results in eyes with 1 of the latter 2 IOLs (PZ.0382). Table 3 shows the demographic and clinical data according to IOL type in the control group.

Forward Light Scattering In the study group, forward light scattering was normal in 2 eyes (5%), low in 20 eyes (48%), moderate in 17 eyes (40%), and high in 3 eyes (7%). In the control group, forward light scattering was normal in 3 eyes (18%), low in 9 eyes (53%), and moderate in 5 eyes (29%); no eye in that group had high forward light scattering. The OSI had significant correlations with the CDVA (r Z 0.4615, PZ.0021), AULCSF photopic without glare (r Z
0.5459, PZ.0002), AULCSF photopic with glare (r Z
0.5651, P!.0001), AULCSF mesopic without glare (r Z
0.4367, PZ.0038), and AULCSF mesopic with

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Table 2. Demographic and clinical data in the study group by IOL type. 3-Piece IOL†

1-Piece IOL* Parameter Age (y) Time after surgery (y) UDVA (logMAR) CDVA (logMAR) AULCSF photopic no glare AULCSF mesopic no glare AULCSF photopic with glare AULCSF mesopic with glare OSI Anterior surface BLS (CCT units) IOL power (D)

Mean G SD

Min

Max

Mean G SD

Min

Max

P Value

69.2 G 7.6 5.68 G 2.49 0.377 G 0.399
0.066 G 0.060 1.634 G 0.295 1.264 G 0.405 1.697 G 0.287 1.075 G 0.421 2.0 G 1.0 67.63 G 31.91 18.4 G 4.6

55 1.41
0.176
0.176 0.936 0.490 1.036 0 0.9 23.00 6.5

85 12.52 1.301 0.046 2.159 1.986 2.128 1.756 4.8 118.75 25.5

71.4 G 6.7 8.74 G 2.32 0.283 G 0.234
0.048 G 0.082 1.405 G 0.345 1.056 G 0.348 1.338 G 0.452 0.784 G 0.413 3.1 G 1.6 70.82 G 37.88 21.2 G 1.4

59 6.22
0.079
0.176 0.864 0.511 0.498 0 1.1 26.00 19.0

82 12.89 0.699 0.045 2.031 1.723 2.110 1.458 5.9 124.75 23.0

.6367z .0011x,{ .4669{ .4908z .0553z .1383{ .0041x,{ .0548{ .0671z .6268z .1059z

AULCSF Z area under the log contrast sensitivity function; BLS Z backward light scattering; CCT Z computer-compatible tape; CDVA Z corrected distance visual acuity; IOL Z intraocular lens; OSI Z objective scatter index; UDVA Z uncorrected distance visual acuity *SN60AT (n Z 4); SA60AT (n Z 27) † MA60AC (n Z 6); MA60BM (nZ 5) z Mann-Whitney test x P!.05 { Unpaired t test

glare (r Z
0.4965, PZ.0008) (Figures 1 to 5). The OSI had no significant correlation with age, time after surgery, UDVA, IOL power, or backward light scattering in the anterior IOL surface. In the control group, the OSI had no significant correlation with any parameter. Visual Function According to multivariate analysis, in the study group the OSI was the only variable that correlated with CDVA (t Z 3.147, PZ.0033) and with contrast

sensitivity with glare under photopic conditions and mesopic conditions (t Z 3.310, PZ.0021 and t Z 2.616, PZ.0129, respectively). The OSI and age correlated with contrast sensitivity without glare under photopic conditions (t Z 3.214, PZ.0028 and t Z 2.254, PZ.0304, respectively) and mesopic conditions (t Z 2.188, PZ.0352 and t Z 2.161, PZ.0374, respectively). In the control group, the only correlation was between age and photopic contrast sensitivity with glare (t Z 3.008, PZ.0119).

Table 3. Demographic and clinical data in the control group by IOL type. SN60WF IOL (n Z 8) Parameter Age (y) Time after surgery (y) UDVA (logMAR) CDVA (logMAR) AULCSF photopic no glare AULCSF mesopic no glare AULCSF photopic with glare AULCSF mesopic with glare OSI Anterior surface BLS (CCT units) IOL power (D)

251 IOL (n Z 4) and 255 IOL (n Z 5)

Mean G SD

Min

Max

Mean G SD

Min

Max

P Value

69.2 G 7.7 0.89 G 0.84 0.403 G 0.347
0.052 G 0.064 1.672 G 0.322 1.247 G 0.300 1.727 G 0.356 1.004 G 0.456 1.6 G 0.6 8.31 G 6.83 19.1 G 2.7

62 0.10 0.046
0.176 1.108 0.975 1.108 0.144 1.0 0.50 16.0

87 2.59 1.000 0 2.080 1.744 2.103 1.479 2.4 19.00 23.5

71.0 G 6.7 0.32 G 0.38 0.155 G 0.262
0.053 G 0.040 1.581 G 0.187 1.315 G 0.422 1.666 G 0.229 1.088 G 0.513 1.5 G 1.0 6.81 G 2.11 20.4 G 2.9

62 0.02
0.079
0.079 1.281 0.581 1.323 0 0.7 4.00 16.5

78 1.16 0.824 0 1.797 1.730 2.019 1.657 3.7 10.00 25.0

.6303* .0927* .0382*,† .8059* .4807z .7117z .6741z .7280z .5000* .5657x .3451z

AULCSF Z area under the log contrast sensitivity function; BLS Z backward light scattering; CCT Z computer-compatible tape; CDVA Z corrected distance visual acuity; IOL Z intraocular lens; OSI Z objective scatter index; UDVA Z uncorrected distance visual acuity *Mann-Whitney test † P!.05 z Unpaired t test x Unpaired t test with Welch correction

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Figure 1. Correlation between OSI and CDVA (CDVA Z corrected distance visual acuity; OSI Z objective scatter index).

Figure 2. Correlation between OSI and photopic contrast sensitivity with no glare (AULCSF Z area under the log contrast sensitivity function; OSI Z objective scatter index).

DISCUSSION The increased light scattering in subsurface nanoglistenings is caused by water phase separation close to the IOL surface.1,4,6 Although it has been suggested that protein films and inorganic deposits found on the IOL could be responsible for increased surface light scattering,17 a recent study6 found that these components were not important in hydrophobic acrylic IOLs; the water hydration dependent mechanism was the predominant cause. Increased surface light scattering caused by subsurface nanoglistenings has been observed in different types of IOLs, such as poly(methyl methacrylate) and silicone. However, most studies focus on hydrophobic acrylic IOLs. Miyata et al.2 found increased surface scatter in acrylic IOLs compared with silicone IOLs during the 3 years after surgery. In a study by Hayashi et al.,13 surface and inner optic light scattering were stronger in hydrophobic acrylic IOLs. Kawai et al.18 performed accelerated deterioration tests on hydrophobic acrylic and hydrophilic acrylic IOLs

and found that transparency remained better when the water content of the IOL was higher. The amount of intraocular light scattering varies among eyes according to their health status; therefore, visual function can be affected to different extents. In young healthy eyes, the impact of forward light scattering is not relevant. On the other hand, increased forward light scattering causing visual impairment is especially important in eyes with cataract.19 Because forward light scattering is directed toward the retina and might influence the quality of vision, it is useful to study the degree of forward light scattering induced in patients with subsurface nanoglistenings. As several studies1,2,5,14 have shown, the incidence and the intensity of subsurface nanoglistenings tend to increase with time; it is important to recognize the possible effects on the visual function. Observation and diagnosis of increased light scattering due to subsurface nanoglistenings on slitlamp examination might vary according to the examiner. Although it is possible to measure the intensity of backward light scattering in the anterior IOL surface, no

Figure 3. Correlation between OSI and photopic contrast sensitivity with glare (AULCSF Z area under the log contrast sensitivity function; OSI Z objective scatter index).

Figure 4. Correlation between OSI and mesopic contrast sensitivity with no glare (AULCSF Z area under the log contrast sensitivity function; OSI Z objective scatter index).

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Figure 5. Correlation between OSI and mesopic contrast sensitivity with glare (AULCSF Z area under the log contrast sensitivity function; OSI Z objective scatter index).

objective value has been established that can indicate on its own whether a patient presents with subsurface nanoglistenings or not. In a study by Ong et al.,6 the mean surface light scattering was 5.0 G 5.6 CCT units after protein removal and drying in cadaver eye IOLs and in clinically explanted IOLs and 4.2 G 2.2 CCT units in finished-goods inventory-control IOLs. In a study of the effects of increased surface light scattering by Miyata et al.,14 the backward light scattering in the anterior IOL surface was 63.3 G 48.8 CCT units in the study group with Acrysof IOLs and 16.5 G 2.2 CCT units in the control group with Sensar AR40 or AR40e hydrophobic acrylic IOLs (Abbott Medical Optics, Inc.). Based on these reports, our study group comprised eyes that presented with backward light scattering in the anterior IOL surface of higher than 20 CCT units. To fulfill the inclusion criteria for the control group, we selected eyes with backward light scattering in the anterior IOL surface of 20 CCT units or lower. Ideally, we would have included eyes with the same IOL models as in the study group; however, because backward light scattering in the anterior IOL surface tends to increase with time and newer IOL models are being used in our patients, we could not form a control group with the same IOLs. To our knowledge, this is the first study quantifying forward light scattering and showing its influence on the visual function of patients presenting with subsurface nanoglistenings. Findings in previous studies15,20 suggest that normal OSI values in healthy eyes are lower than 1.0. In our study, the mean OSI value was significantly higher in the study group (2.3 G 1.2) than in the control group (1.6 G 0.8). The percentage of cases with moderate and high degrees of forward light scattering was higher in the study group, while the percentage of normal levels was lower than in the control group. In both groups, almost all patients had an OSI greater than 1.0, indicating that most had higher forward light scattering than in

normal eyes. Nanavaty et al.21 studied forward light scattering in different models of hydrophobic IOLs with at least a 3-month postoperative period; the mean OSI value was 1.6 G 1.0 for Acrysof SN60WF IOLs and 1.8 G 1.4 for Acrysof SN60AT IOLs. On the other hand, in vitro tests performed to study light scatter generated in IOLs showed lower straylight scatter values than in healthy human donor lenses of different ages.22 Nanavaty et al.21 also performed in vitro experiments and found clinically insignificant forward light scattering in hydrophilic and hydrophobic IOLs than in a young eye, a normal aged eye, and an eye with cataract. Recently, a new technique to measure forward light scattering of IOLs was reported.23 The authors showed that although the forward light scattering was increased in artificially aged IOLs in comparison with new IOLs, the increase was within G1 SD of the value in the normal population. Indeed, infrared light penetrates more than visible light; thus, the amount of forward light scattering measured with the doublepass system used in our study might have increased the actual effect of retinal scatter.20 This does not, however, invalidate the data in our study or the importance of performing this type of study in vivo. In addition to the double-pass image technique, there are other ways to estimate forward light scattering in the eyes; these include psychophysical approaches or the analysis of Hartmann-Shack images.24 The C-Quant straylight meter (Oculus Optikger€ate GmbH), for example, is based on a compensation comparison method, which has been described in detail25 and used in studies that report repeatable and reliable results.25,26 Briefly, during the examination, the patient indicates which half of the disk-shaped test field is flickering the most by pressing a button; thus, neural factors are also involved in the assessment. On the other hand, measurements of forward light scattering acquired with the Optical Quality Analysis System II double-pass system do not rely on the patient's response, which could be an advantage over the C-Quant device, especially in elderly patients or individuals with neurological conditions. Measurements obtained with the double-pass system used in the current study have also shown good repeatability.16 With the C-Quant straylight meter, the intraocular scatter value is derived from a psychometric function and is expressed in log units, while with the Optical Quality Analysis System II intraocular scatter is indicated by the OSI, which is a ratio between the amount of light in an eccentric area of the point-spread function (PSF) within 12 and 20 minutes of arc (arcmin) and the amount obtained closer to the center of the PSF, a circular area of 1 arcmin from the central peak. Although forward light scattering did not cause severe deterioration in visual function, we found that

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increases in forward light scattering in the study group led to decreases in CDVA and contrast sensitivity, although both remained within their normal range; no such correlation was observed in the control group. Many studies of subsurface nanoglistenings focused on backward light scattering, and most found no relationship to visual function. A study comparing light scattering in different IOL types showed no differences in visual function between IOLs in the third postoperative year.2 Hayashi et al.13 evaluated patients after 10 years of phacoemulsification with IOL implantation and found no relationship between surface light scattering and visual acuity or contrast sensitivity. Matsushima et al.4 concluded that subsurface nanoglistenings had only minor effects on visual function. On the other hand, there are suggestions that subsurface nanoglistenings might affect visual function. A study by Yoshida et al.27 found that severe subsurface nanoglistenings significantly decreased light transmission in the visible range and impaired visual function. Also, although Miyata et al.14 found no correlation between subsurface nanoglistenings and changes in CDVA, several cases with higher backward light scattering in the IOL surface had decreased visual acuity. We found no relationship between forward light scattering and backward light scattering, reinforcing the concept that in complex biological media it is usually not feasible to infer the quantity of forward light scattering from the quantity of backward light scattering.19 As mentioned, light scattering is influenced by different factors (eg, wavelength; shape, size, and density of the particles) that affect the resultant angular distribution of light scatter. Variation in these parameters in association with multiple light scatter inside the eye may contribute to the lack of association between forward light scattering and backward light scattering. In our study, photopic contrast sensitivity with glare was significantly lower in eyes with 3-piece IOLs than in eyes with 1-piece IOLs; however, the period that elapsed after surgery and the number of eyes were different between the 2 subgroups, which could explain our findings. In a study by van Gaalen et al.,28 the C-Quant straylight meter detected a significant increase in straylight measurements in pseudophakic eyes with dilated pupils compared with natural pupils, which could be explained by the smaller capsulorhexis in relation to the pupil size in dilated eyes. In our study, to record forward light scattering, we examined all patients under mydriasis and set the artificial pupil diameter of the Optical Quality Analysis System II to 4.0 mm, which is closer to the natural size. Thus, considering the actual pupil size, we might have underestimated the scattering values under mesopic conditions or overestimated them in the photopic scenario. Also, all capsulorhexes were larger than

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4.0 mm in diameter and there were no cases of contraction of capsulorhexis opening on slitlamp examination. As mentioned, we had to recruit patients with spherical IOLs for the study group and aspheric IOLs for the control group. Although this might have been a confounding factor, studies29,30 have found no significant differences in straylight measurements of the C-Quant meter between spherical IOLs and aspheric IOLs. In the current study, we mainly focused on the evaluation of subsurface nanoglistenings and did not evaluate the degree of the glistenings. Colin and Orignac8 used the C-Quant straylight meter to evaluate the relationship between glistenings and light scattering in healthy eyes. Reliable straylight data was obtained in 53 of 97 eyes; the mean log values were 1.2 G 0.2 for grade 0 glistenings (21 eyes), 1.2 G 0.2 for grade 1 (17 eyes), and 1.3 G 0.2 for grade 2 (15 eyes). No significant association was found between straylight and the grade of the glistenings. Thus, it is likely that the presence of glistenings had no influence on our results. As a final consideration, our control group was relatively small. In conclusion, this study evaluated the effect of forward light scattering, measured using a double-pass technique, on the visual function in eyes with increased surface light scattering due to subsurface nanoglistenings. Eyes presenting with subsurface nanoglistenings had increased forward light scattering values compared with control eyes. Although forward light scattering associated with subsurface nanoglistenings did not deteriorate visual function, it appeared to correlate with reductions in visual acuity and contrast sensitivity, although both remained within their normal range. WHAT WAS KNOWN  Subsurface nanoglistenings of Acrysof hydrophobic acrylic IOLs increase the intensity of backward light scattering; however, the in vivo influence on forward light scattering and visual function is not well understood.  Most studies report that subsurface nanoglistenings do not adversely influence visual function. WHAT THIS PAPER ADDS  Quantification of forward light scattering in vivo using a double-pass instrument found that eyes with increased surface light scattering in their IOLs due to subsurface nanoglistenings had significantly higher forward light scattering than in control eyes with low surface scattering in the IOL.  Forward light scattering in eyes with subsurface nanoglistenings did not deteriorate visual acuity; however, increases in forward light scattering correlated with reductions in the visual function, although it remained within normal limits.

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FORWARD LIGHT SCATTERING AND SUBSURFACE NANOGLISTENINGS ON IOLS

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J CATARACT REFRACT SURG - VOL -, - 2014

First author: Simone Beheregaray, MD Department of Ophthalmology, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan