Purpose
To investigate the long-term effect of surface light scattering and glistenings of various intraocular lenses (IOLs) on visual function and optical aberrations after cataract surgery.
Design
Case-control study.
Methods
Thirty-five eyes that underwent implantation of a hydrophobic acrylic, silicone, or polymethyl methacrylate (PMMA) IOL more than 10 years ago were recruited. The scattering light intensity of the surface and internal matrix of the optic was measured using Scheimpflug photography. Visual acuity (VA) was measured using VA charts, and contrast VA and that with glare (glare VA) were examined using a contrast sensitivity tester. Ocular higher-order aberrations (HOAs) were measured using a Hartmann-Shack aberrometer.
Results
Mean scattering light intensity of the surface and internal matrix of the optic was significantly higher in the acrylic group than in the silicone and PMMA groups ( P < .0001). Mean uncorrected VA, photopic and mesopic contrast VA and glare VA, and HOAs did not differ significantly among groups, although mean corrected VA in the acrylic group was significantly better than that in the other groups ( P = .0023). Scattering light intensity of the surface and internal matrix did not correlate with VA, contrast VA, or glare VA, and did not correlate with ocular and internal optic HOAs in the acrylic group.
Conclusions
At more than 10 years postoperatively, visual function, including contrast sensitivity, and ocular HOAs were comparable among eyes that received acrylic, silicone, and PMMA IOLs. Surface scattering and glistenings with the acrylic IOLs were not significantly correlated with visual function and optical aberrations.
Since the introduction of the first model of AcrySof intraocular lens (IOL) in 1994, hydrophobic acrylic IOL have become the most popular IOL used after cataract extraction. The reason is mainly that the incidence of postoperative complications, including posterior capsule opacification (PCO), is lower with the acrylic IOL than with IOLs made of other materials. In the early stage after implantation, however, small bright particle formations called glistenings were found in the optic of the acrylic IOL. Although studies showed that glistenings occur with any material and design of the IOL, the hydrophobic acrylic IOL has the greater degree of glistenings. More recently, light scattering was also noted on the surface of the acrylic IOL in the late stage after implantation. Both phenomena depend on the formation of microvacuoles containing water in the optic, although the sizes of the vacuoles differ.
Controversy remains, however, as to whether glistenings and surface light scattering deteriorate visual function. Dhaliwal and associates and Gunenc and associates reported that glistenings significantly impair visual acuity (VA) or contrast sensitivity, whereas other studies reported no glistenings-related decrease in visual function. Furthermore, a middle-term study by Miyata and associates did not find a significant visual impairment attributable to surface light scattering. In contrast, Matsusima and associates reported that surface scattering of extracted acrylic IOLs decreased the percentage of light transmission by approximately 4%. Because the degree of surface scattering gradually increases for many years, the long-term effect of surface scattering on visual function remains a concern.
The purpose of the present study was to assess the long-term effect of glistenings and surface scattering on visual function in eyes that underwent implantation of a hydrophobic acrylic IOL, and to examine the relationship between glistenings as well as surface scattering and visual function. To strictly evaluate the effects of these phenomena on visual function, eyes that received a silicone or polymethyl methacrylate (PMMA) IOL served as controls.
Methods
Patients
Thirty-five eyes that had undergone phacoemulsification with implantation of either a hydrophobic acrylic, silicone, or PMMA IOL more than 10 years ago were planned to be enrolled in each IOL group. For patient enrollment, a clinical research coordinator screened the medical records of patients who had participated in some randomized clinical trials performed at Hayashi Eye Hospital more than 10 years ago. Inclusion criteria were: 1) eyes that had uneventful surgery; 2) eyes that had complete in-the-bag implantation; 3) eyes that showed corrected VA of 20/25 or better several days after cataract surgery; 4) eyes with no comorbidity of the cornea, vitreous, macula, or optic nerve; 5) eyes with no history of inflammation or other surgery; and 6) no anticipated difficulties with analysis or examination. Eligible patients who met the criteria were sequentially called by the clinical research coordinator and asked to undergo examinations. Screening and patient enrollment were continued until 35 eyes were included in each of the 3 IOL groups. All enrolled eyes were scheduled to undergo examinations of visual function, Scheimpflug photography, and wavefront aberrations. All implanted IOLs were 6.0-mm round optic spherical IOLs. In the acrylic group, all 35 eyes received a 3-piece AcrySof IOL with PMMA haptics (MA60BM; Alcon Laboratories, Fort Worth, Texas, USA) through a 4.1-mm straight corneoscleral incision. In the silicone group, 18 eyes received a SI30NB and 17 received a SI40NB (Abbot Medical Optics, Santa Ana, California, USA) through a 3.0- or 3.5-mm corneoscleral or clear corneal incision. The SI30NB and SI40NB have silicone optic and rigid polypropylene loops. In the PMMA group, 16 eyes received a MZ60BD (Alcon Laboratories), 17 received a UV25T or UV22 (Menicon, Nagoya, Japan), and 2 received a UV60SB (Menicon) through a 6.0-mm frown incision. The MA60BD and UV60SB were single-piece PMMA IOLs, and the UV25T and UV22 were 3-piece PMMA IOLs with rigid polyimide loops. Informed consent was obtained from all patients. The Supplemental Figure (available at AJO.com ) illustrates the patient enrollment method employed.
Surgical Procedure
All surgeries were performed by a single surgeon (K.H.) using almost the same surgical procedure as described previously. First, a continuous curvilinear capsulorrhexis measuring approximately 5.5 mm in diameter was accomplished using a 25-gauge bent needle through a side port. After continuous capsulorrhexis, a corneoscleral or clear corneal incision was made horizontally for phacoemulsification. A 3.5-mm straight corneoscleral incision was made for implantation of the acrylic and silicone IOLs using a diamond knife and a diamond crescent knife, while a 2.5-mm clear corneal incision was made for implantation of silicone IOL using a stainless steel keratome. For implantation of the PMMA IOLs, a 5.0-mm frown incision with a chord length of 6.5 mm was made using a diamond knife and crescent knife. After hydrodissection, endocapsular phacoemulsification of the nucleus and aspiration of the residual cortex were carried out. Using a stainless keratome, the wound was enlarged to a 3.0, 3.5, 4.1, or 6.0 mm for implantation of the IOL. The lens capsule was inflated with 1% sodium hyaluronate (Healon; Abbot Medical Optics), after which an IOL was implanted. The acrylic IOL was folded and grasped with the Buratto II acrylic IOL implant forceps (Asico, Westmont, Illinois, USA) at room temperature, and placed into the capsular bag through a 4.1-mm incision. The silicone IOL was folded and grasped with the Universal II silicone IOL forceps (Rhein Medical, Tampa, Florida, USA) at room temperature, and inserted into the capsular bag through a 3.0- or 3.5-mm incision. The PMMA IOL was grasped and inserted using a Shepard IOL forceps through a 6.0-mm incision. After IOL insertion, the viscoelastic material was thoroughly evacuated. No suture was placed in any case.
Main Outcome Measures
All enrolled patients were examined for the intensity of scattering light of the optic surface and inner optic of IOLs measured using Scheimpflug photography, corrected distance VA, examination of slit-lamp biomicroscopy and fundoscopy, contrast VA with and without glare, ocular and corneal wavefront aberrations, refractive status, keratometric cylinder, and pupillary diameter. The refractive spherical power as well as cylindrical power and axis were examined using an autorefractometer (KR-7100; Topcon, Tokyo, Japan); the manifest spherical equivalent value was determined as the spherical power plus half the cylindrical power. Best-corrected distance VA was examined using decimal charts and converted to a logarithm of minimal angle of resolution (logMAR) scale for statistical analysis. Pupillary diameter was measured using a Colvard pupillometer (Oasis Medical, Glendora, California, USA). Two physicians (M.Y., K.Y.) determined the grade of the glistenings according to the method described by Miyata and associates, and evaluated the presence of PCO and other ocular comorbidities. When a clinically significant PCO was found, a neodymium–yttrium-aluminum-garnet (Nd:YAG) laser posterior capsulotomy was performed before examination. Careful attention was paid to damage the optics by the Nd:YAG laser shots.
The scattering light intensity of the anterior optic surface, internal matrix of the optic, and the PCO density value was determined with a previously described method using the Scheimpflug photography system (EAS-1000; Nidek, Gamagori, Japan). In brief, the examiner first obtained a Scheimpflug slit image of the IOL at the 0-degree, 45-degree, 90-degree, and 135-degree meridians after full mydriasis. The highest-quality image was then transferred to an image analysis computer and the average scattering light intensity of the central 3.00 × 0.25-mm area in the anterior optic surface as well as in the posterior capsule, and in the internal matrix of the optic, was measured using the axial densitometry of the computer. The scattering light intensity was expressed in computer-compatible tape steps: the scattering light intensity obtained by densitometry was stratified to range from 0 to 255 (256 steps). The scattering light intensity of the 4 meridians was averaged, and the resultant values of the anterior optic surface and internal matrix of the optic were considered to represent the surface light scattering and glistenings, respectively. In addition, the PCO density value in 1 cross-sectional image was determined by subtracting the scattering light intensity of the anterior optic surface area from that of the posterior capsule area. The PCO values of the 4 meridians were then averaged and considered to represent the PCO value.
Contrast VA and that in the presence of glare (glare VA) under photopic and mesopic conditions were examined after best distance correction using the Contrast Sensitivity Accurate Tester (CAT-2000; Menicon, Nagoya, Japan). This device measures logMAR corrected distance VA, with a range from 1.0 to −0.1, using visual targets with 5 contrast levels (100%, 25%, 10%, 5%, and 2.5%) under photopic and mesopic conditions. Measurement under photopic conditions was performed with chart lighting of 100 cd/m 2 , and that under mesopic conditions with chart lighting of 2 cd/m 2 . For measurement of glare VA, a 200-lux glare source was located in the periphery at 20 degrees around the visual axis.
Ocular wavefront aberrations were determined using the Hartmann-Shack wavefront analyzer, and corneal wavefront aberrations were determined using the videokeratography, both of which are incorporated in the Topcon KR-1W. The details of this apparatus were described previously. After full mydriasis, analysis was conducted by measuring the central 4.0 and 6.0 mm using the aperture. The root mean square (RMS) of the third-order Zernike coefficients was used to represent coma-like aberrations, and that of the fourth-order coefficients was used to represent spherical-like aberrations. Total HOA was defined as the sum of the RMS of the third- to sixth-order coefficients. In addition, assuming a simple eye model, wavefront aberrations of the internal optics were obtained by direct subtraction of the corneal aberrations from the ocular aberrations. Examination of slit-lamp biomicroscopy and ocular fundus was performed by the 2 ophthalmologists, and other measurements were performed by 4 experienced ophthalmic technicians unaware of the purpose of the study.
Statistical Analysis
The scattering light intensity of the optic surface and internal matrix of the optic; the PCO value; uncorrected and corrected distance VA; contrast VA and glare VA; ocular and internal optic HOAs; pupillary diameter; and other continuous variables among the acrylic, silicone, and PMMA IOL groups were compared using the Kruskal-Wallis test. Categorical variables were compared among the 3 groups using the χ 2 goodness-of-fit test. When a statistically significant difference was detected among the 3 groups, the difference between each pair of groups was further compared using the Mann-Whitney U test for continuous variables and the χ 2 test for discrete variables with the Bonferroni correction for multiple comparisons. Simple correlation between the scattering light intensity of the optic surface and internal matrix of the optic and corrected VA and contrast VA as well as glare VA, and between the intensity and HOAs, was examined using the Pearson simple correlation analysis. The incidence of eyes that required an Nd:YAG laser capsulotomy was compared between groups using the Kaplan-Meier survival analysis. Any differences with a P value of less than .05 were considered to be statistically significant.
Results
Of the 105 patients originally enrolled, 3 patients in the silicone group did not undergo all of the examinations because of scheduling conflicts. Accordingly, 35 eyes in the acrylic group, 32 in the silicone group, and 35 in the PMMA group remained for analysis. Patients and examiners were unaware as to which IOL material was implanted in each eye. Because the investigator that performed the data analysis, who also performed the cataract surgery, did not participate in any examination, patient assignment was kept concealed until all of the data were collected.
The mean age of the patients at the time of examination (± standard deviation [SD]) was 75.4 ± 7.7 years; there were 29 men and 73 women. The patient characteristics of the 3 groups are shown in Table 1 . The 3 groups were not different in sex, ratio of the left to right eyes, manifest spherical equivalent value, pupillary diameter, or time interval between surgery and examination. The mean age at the time of surgery and examination was significantly different among the 3 groups ( P ≤ .0025); the PMMA group was significantly younger than the acrylic and silicone groups ( P ≤ .0080).
| Characteristic Value | Acrylic Group | Silicone Group | PMMA Group | P Value |
|---|---|---|---|---|
| Age at the time of surgery (years) | 62.6 ± 5.8 | 65.5 ± 5.6 | 58.5 ± 9.5 | .0024 a |
| Age at the time of examination (years) | 75.2 ± 6.0 | 79.1 ± 9.5 | 72.1 ± 9.5 | .0012 a |
| Sex (male/female) | 11/24 | 5/27 | 13/22 | .1327 |
| Left/right | 18/17 | 15/17 | 18/17 | .9130 |
| SE (D) b | −1.80 ± 1.10 | −0.98 ± 1.07 | −1.50 ± 1.32 | .2010 |
| Pupillary diameter (mm) c | 3.16 ± 0.45 | 3.03 ± 0.54 | 3.01 ± 0.77 | .5698 |
| Decentration of IOL (mm) | 0.17 ± 0.09 | 0.16 ± 0.09 | 0.18 ± 0.16 | .7437 |
| IOL tilt (degrees) | 1.14 ± 0.39 | 0.98 ± 0.48 | 1.22 ± 1.14 | .3064 |
| Interval between surgery and examination (y) | 12.7 ± 1.3 | 13.5 ± 1.3 | 13.6 ± 1.8 | .0613 |
a Statistically significant difference.
b Manifest spherical equivalent value.
Sixty eyes had already undergone an Nd:YAG laser posterior capsulotomy before enrollment in this study, and extensive pits or cracks were not found in the optic of all eyes. The physicians identified clinically significant PCO in 6 eyes, and these eyes underwent an Nd:YAG laser capsulotomy before examination. Accordingly, the mean PCO value after capsulotomy measured using the Scheimpflug photography was 4.6 ± 11.6 computer compatible tape steps (CCT) in the acrylic group, 3.0 ± 5.2 CCT in the silicone group, and 4.2 ± 7.4 CCT in the PMMA group; there was no significant difference in the PCO value between the 3 groups ( P = .9048). Furthermore, extensive pits or cracks attributable to the Nd:YAG laser shots were not observed in the optic of these eyes, which may account for the fact that mean corrected distance VA, contrast VA and glare VA, and ocular or internal optic HOAs after capsulotomy were comparable to or better than those before capsulotomy.
The mean intensity of scattering light of both the optic surface and internal matrix of the optic in the acrylic group was significantly greater than that in the silicone and PMMA group ( P < .0001; Figure 1 ) . The mean grade of glistenings determined by the physician was 0.89 ± 0.83 in the acrylic group, 0.78 ± 0.55 in the silicone group, and 0.40 ± 0.55 in the PMMA group; the mean grade in the acrylic and silicone groups was significantly greater than in the PMMA group ( P ≤ .0054). The mean decentration length and tilt angle was not significantly different between the 3 groups ( P ≥ .3065). Extensive pits or cracks attributable to the Nd:YAG laser shots were not observed in the optics of any eyes.
Mean uncorrected distance VA was not significantly different ( P = .5804; Table 2 ), while corrected distance VA was significantly different among the 3 groups ( P = .0023); mean corrected VA in the acrylic group was significantly better than that in the silicone group ( P = .0003). Contrast VA ( Figure 2 ) and glare VA ( Figure 3 ) under photopic conditions were not significantly different among the 3 groups. Mesopic contrast VA at 100%, 25%, and 10% contrast and mesopic glare VA at 100% and 25% contrast were not significantly different. In this series, because mesopic contrast VA at 5% and 2.5% and mesopic glare VA at 10%, 5%, and 2.5% were below the detectable limit in most eyes of all groups, a statistical comparison was not performed for these contrasts. When we assumed a decimal contrast VA and glare VA of 0.2 under photopic conditions at 100%, 25%, and 10% contrast visual targets to be a clinically meaningful difference between the 3 groups using the Kruskal-Wallis test, the statistical powers were calculated to be more than 84%. Additionally, when we assumed a decimal contrast VA and glare VA of 0.1 at the other visual targets to be a clinically meaningful of difference, the statistical powers were calculated to be more than 80%.
| Acrylic Group | Silicone Group | PMMA Group | P Value | |
|---|---|---|---|---|
| Uncorrected VA | 20/42 (0.54 ± 0.50) | 20/35 (0.36 ± 0.37) | 20/40 (0.39 ± 0.33) | .5804 |
| Corrected VA | 20/19 (−0.01 ± 0.05) | 20/21 (0.04 ± 0.07) | 20/20 (0.00 ± 0.06) | .0023 a |
a Mean corrected distance VA in the acrylic group was significantly better than that in the silicone group ( P = .0003).
For a 4-mm pupil, the mean ocular, corneal, and internal optic total HOAs; third-order coma-like aberrations; and fourth-order spherical-like aberrations were not significantly different among the 3 groups ( P ≥ .2307; Figure 4 ) . Six of 6 eyes that underwent Nd:YAG laser posterior capsulotomy showed improved ocular HOAs in all eyes. When we assumed total HOAs, third-order aberrations, and fourth-order aberrations of 0.05 μm to be a clinically meaningful magnitude of difference between the 3 groups, the statistical powers were calculated to be more than 88%.
The data for simple correlation analyses between the scattering light intensity of optic surface or internal matrix of the optic and visual function and between the scattering light intensity and HOAs in the acrylic group are shown in Table 3 . Scattering light intensity of optic surface and internal matrix of the optic was not significantly correlated with corrected VA, nor with contrast VA as well as glare VA, under photopic and mesopic conditions ( P ≥ .3820; Table 3 ). The scattering light intensity did not significantly correlate with total HOAs, coma-like aberrations, and spherical-like aberrations of the eye, cornea, and internal optics ( P ≥ .2040; Table 3 ). The scatterplots of the correlation between the scattering light intensity of the optic surface or internal matrix of the optic and the low-contrast VA at 10% contrast and between the scattering light intensity and ocular HOAs showed no significant correlation ( Figure 5 ) .
| Correlation Coefficient | P Value | Correlation Coefficient | P Value | ||
|---|---|---|---|---|---|
| Scattering light intensity of optic surface | |||||
| CDVA | 0.003 | .9849 | — | — | |
| Photopic contrast VA | Photopic glare VA | ||||
| 100% contrast | 0.019 | .9156 | 100% contrast | 0.152 | .3820 |
| 25% contrast | 0.030 | .8642 | 25% contrast | 0.147 | .3995 |
| 10% contrast | 0.014 | .9346 | 10% contrast | 0.087 | .6208 |
| 5% contrast | 0.051 | .7708 | 5% contrast | 0.132 | .4491 |
| 2.5% contrast | 0.001 | .9933 | 2.5% contrast | 0.099 | .5720 |
| Mesopic contrast VA | Mesopic glare VA | ||||
| 100% contrast | 0.124 | .4770 | 100% contrast | 0.105 | .5479 |
| 25% contrast | 0.127 | .4656 | 25% contrast | 0.058 | .7391 |
| 10% contrast | 0.090 | .6054 | 10% contrast | — | — |
| Scattering light intensity of internal matrix of the optic | |||||
| CDVA | 0.090 | .6056 | — | — | |
| Photopic contrast VA | Photopic glare VA | ||||
| 100% contrast | 0.164 | .3475 | 100% contrast | 0.219 | .2056 |
| 25% contrast | 0.175 | .3144 | 25% contrast | 0.219 | .2069 |
| 10% contrast | 0.143 | .4122 | 10% contrast | 0.015 | .9335 |
| 5% contrast | 0.065 | .7099 | 5% contrast | 0.048 | .7848 |
| 2.5% contrast | 0.016 | .9283 | 2.5% contrast | 0.054 | .7591 |
| Mesopic contrast VA | Mesopic glare VA | ||||
| 100% contrast | 0.169 | .3321 | 100% contrast | 0.011 | .9497 |
| 25% contrast | 0.013 | .9422 | 25% contrast | 0.030 | .8633 |
| 10% contrast | 0.106 | .5432 | 10% contrast | — | — |
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