Hydrophobic acrylic intraocular lenses (IOLs) have become prevalent since the advent of small-incision cataract surgeries, possibly due to the reduced occurrence of posterior capsule opacification and calcification compared with IOLs made of other materials.1 However, glistenings and surface light scattering have been mainly reported in association with hydrophobic acrylic IOLs, specifically AcrySof IOLs (Alcon Laboratories, Inc., Fort Worth, TX).2 Glistenings are defined as sparkling bright spots under slit-lamp examination and surface light scattering is described as pronounced dense whitening on the surface of IOLs under slit-lamp microscopy and Scheimpflug photography.3 Thus far, the specific mechanisms of both phenomena remain obscure. The leading theory regarding lens glistening formation is fluid-filled microvacuoles aggregating within the IOL optic,4 whereas surface light scattering has been primarily associated with long-term phase separation water near the IOL surface.5
However, controversy surrounds the question of whether the visual performance of pseudophakic eyes is impaired by glistenings and surface light scattering. Visual performance, such as contrast sensitivity, was reported to be influenced by glistenings in some studies.2,6 Moreover, some case series have reported IOL exchange due to blurred images caused by severe glistenings or surface light scattering,7 which is similar to our clinical experience.
Meanwhile, to our knowledge, relationships between both phenomena and other objective visual function tests, such as point spread function (PSF), have seldom been reported in a clinical setting. The aim of the current study was to determine the effect of IOL glistenings and surface light scattering on visual performance and optical quality. To achieve this, visual acuity and contrast sensitivity were used to evaluate the subjective visual performance of patients. Objective optic characteristics, such as straylight, aberrations, PSF, and modulation transfer function (MTF), were also investigated.
Patients and Methods
Study Design and Patients
Our study comprised eligible patients who underwent standard phacoemulsification and IOL implantation at Zhongshan Ophthalmic Center, Guangzhou, China, between January 2005 and December 2011, and had routine ophthalmic examinations for at least 5 years postoperatively. All surgeries were performed using the same standard surgical procedure with a well-centered continuous curvilinear capsulorhexis (approximately 5-mm). IOLs implanted were either AcrySof SA60AT (Alcon Laboratories, Inc.) or Sensar AR40e (Johnson & Johnson Vision, Santa Ana, CA). Both IOLs have similar characteristics, including posterior square-edged design, a 13-mm overall diameter, a 6-mm spherical optic, and hydrophobic acrylic material.8
Participants with ocular pathologies that limited visual outcomes, previous intraocular surgery, and noticeable postoperative complications, such as posterior capsule opacification and significant IOL decentration (> 1 mm) and tilt (> 5°)9 were excluded. Eyes with postoperative corrected distance visual acuity (CDVA) worse than 0.1 logMAR (Snellen equivalent 20/25) were also excluded.
A single investigator (MW), who was masked to the visual testing results, assessed the incidence of glistenings and/or surface light scattering phenomena of the IOL optic after pupil dilation under slit-lamp–adapted anterior segmental photography (BX900; Haag-Streit AG, Bern, Switzerland) with a 30° angle. This investigator recorded the absence or presence of glistenings or surface light scattering (Figure A, available in the online version of this article) and allocated eyes into the following groups: glistenings, surface light scattering, and control (IOLs without the former two phenomena).
Examples of the (A) intraocular lens (IOL) glistenings, (B) surface light scattering, and (C) control groups (IOL without the former two phenomena. (E–G) Higher magnification of the selected areas (square boxes with yellow line) of the images shown above. Image (original magnification ×25) acquisition was performed using a slit lamp (BX900; Haag-Streit AG, Bern, Switzerland).
All study procedures were performed in accordance with the tenets of the Declaration of Helsinki and were approved by the Ethics Committee of the Zhongshan Ophthalmic Center. The purpose and methods of the study were explained to all participants before written informed consent was obtained.
The follow-up examinations included uncorrected distance visual acuity (UDVA) and CDVA using a retro-illuminated Snellen chart with tumbling-E optotypes (Precision Vision, La Salle, IL) with a working distance of 5 meters under photopic conditions. Measurements were transformed to logMAR units for statistical analysis. Refractive status was tested by non-cycloplegic autorefraction (AR8900; Topcon Corporation, Tokyo, Japan). Intraocular pressure was measured with a non-contact tonometer (model Tx-F full auto non-contact tonometer; Canon, Tokyo, Japan). Slit-lamp biomicroscopy and funduscopy were performed to identify possible preexisting ocular pathology after pupil dilation. The retro-illumination images were loaded into a program (POCOman, Kings College London, United Kingdom) to quantify the degree of posterior capsule opacification.8 The degrees of IOL decentration and tilt were measured using a Pentacam system (Oculus Optikgeräte GmbH, Wetzlar, Germany) and analyzed by Image-pro plus 6.0 software as previously described.10 IOL power was obtained from patient discharge summaries. In addition, any Nd:YAG laser capsulotomy history was recorded.
A contrast glare tester (Takagi CGT-1000; Takagi Seiko, Tokyo, Japan) was used to examine contrast sensitivity with and without glare after all patients were informed about its specific purpose. A monocular contrast sensitivity test was conducted with optimal corrected vision. The target rings at six different visual angles were 6.3°, 4.0°, 2.5°, 1.6°, 1.0°, and 0.7°, corresponding to cycles per degree (cpd) of 1.0, 1.7, 2.6, 4.2, 6.6, and 10.4, ranging from low to high spatial frequencies.11 The examination results were automatically printed on a graph.
Straylight measurement with undilated pupils and corrected vision took place with a C-Quant straylight meter (Oculus Optikgeräte GmbH) as previously described.12 Intraocular straylight values are presented in log scale (straylight parameter) [log(s)]. In addition, the C-quant measurements included the reliability and quality parameters Esd and Q. According to the device instruction manual, measurements with Esd < 0.08 and Q > 0.5 were considered acceptable and recorded in this study.
Higher order aberrations (HOAs) analysis was performed with the Optical Path Difference (OPD)-III scan refractive power/corneal analyzer system (NIDEK Co. Ltd., Gamagori, Japan), which uses dynamic skiascopy-based ocular aberrometry and Placido-disk corneal topography to collect optical data. The parameters of this study analyzed for a 5-mm pupil included the root mean square (RMS) of HOAs (Zni) (3 ≤ n ≤ 6), spherical aberration (Z40), coma (Z31 and Z3−1), and trefoil (Z32 and Z3−2) after pupil dilation. Intraocular aberrations were calculated automatically by subtracting corneal aberrations from total ocular aberrations. Additionally, PSF and MTF values were calculated based on the total HOAs. PSF was expressed as Strehl ratio values and the mean MTF value, which was previously described and was calculated in a logarithmic plot for subsequent analysis.13
Statistical analysis was performed using SPSS software (version 20.0; IBM Corporation, Armonk, NY). Data are presented as mean ± standard deviation. Variables were examined for normal distribution with the Shapiro–Wilk test. For quantitative normal data, statistical tests including analysis of variance with least significant difference post-hoc comparison were implemented. Furthermore, Kruskal–Wallis tests were used to compare non-normal data and Dunn–Bonferroni tests for post-hoc comparisons were performed to determine differences between specific groups. Categorical variables were compared using chi-square tests. A P value of .05 or less was considered statistically significant.
Of the 117 patients, 140 pseudophakic eyes were examined in this study. No postoperative complications were recorded and all IOLs were well centered. SA60AT IOLs were implanted in 98 eyes and AR40e IOLs were implanted in 42 eyes. According to the slit-lamp examination, glistenings and surface light scattering phenomena were only observed in SA60AT IOLs, whereas AR40e IOLs were phenomenon free. Hence, 42 eyes with AR40e IOLs served as controls in our study, whereas patients in both the glistenings and surface light scattering groups were implanted with SA60AT IOLs. The glistenings group comprised 65 eyes with definite bright spots inside the IOL optic and the surface light scattering group comprised 33 eyes with membrane-like whitening of the IOL surface alone.
The median postoperative follow-up time was 85.11 ± 19.73 (mean ± SD) months (range: 60 to 168 months). Patient characteristics of the three groups are shown in Table A (available in the online version of this article). There were no significant differences among the three groups.
The visual and refractive outcomes for IOL-based procedures of all patients are presented in Figure 1 and Table B (available in the online version of this article) describes the UDVA and CDVA of the three groups in more detail. No significant differences were found among the three groups. In addition, 9 eyes had already undergone Nd:YAG laser posterior capsulotomy before participation in this study. Extensive pits or cracks attributable to Nd:YAG laser shots were not observed in the optic of any eye.
Standard graphs for refractive outcomes for intraocular lens–based procedures. (A) Uncorrected distance visual acuity (UDVA); (B) UDVA vs corrected distance visual acuity (CDVA); (C) spherical equivalent refraction accuracy; (D) postoperative refractive cylinder. D = diopters
Mean Postoperative UDVA and CDVA
Contrast sensitivity results are shown in Figure 2. Under glare testing condition, no statistical between-group differences were detected in contrast sensitivity at any spatial frequency. Under testing condition without glare, significant differences in contrast sensitivity among the three groups were found at low, medium, and high spatial frequencies (6.3°, P < .001; 4.0°, P = .027; 1.6°, P = .004; 1°, P = .008). Dunn–Bonferroni tests for post-hoc comparisons revealed that contrast sensitivity at low, medium, and high frequencies were lower in the glistenings group compared with those in the control group (6.3°, P = .004; 4.0°, P = .022; 1.6°, P = .003; 1°, P = .006). However, a significant difference was only detected at a low frequency (6.3°, P = .001) between the surface light scattering and control groups, and no additional significant differences between the glistenings and surface light scattering groups were found.
Contrast sensitivity curves of the three groups. Contrast sensitivity gradually decreased as the visual angle increased. (A) Under glare testing conditions, no significant differences were found among the three groups. (B) Under testing condition without glare, the contrast sensitivity values of the glistenings group were lower than those of the control group at large, intermediate, and small visual angles (6.3°, P = .004; 4.0°, P = .022; 1.6°, P = .003; 1°, P = .006). However, a significant difference between the surface light scattering group and control group was only found at a low frequency (large visual angles, 6.3°, P = .001).
The mean log (straylight parameter) values were 1.53 ± 0.16, 1.43 ± 0.17, and 1.39 ± 0.14 for the glistenings, surface light scattering, and control groups, respectively, which revealed a significant difference (P < .001). After multiple comparisons with least significant difference, straylight values of the glistenings group were significantly increased compared with those of the surface light scattering and control groups (glistenings vs surface light scattering group, P = .006; glistenings vs control group, P < .001), whereas these values were not significantly different between the latter two groups (P = .259). A more descriptive representation of intraocular straylight values is presented in Figure 3.
Mean straylight values of the three groups. Pseudophakic eyes with glistenings had statistically significant higher straylight values than the surface light scattering group and control group, whereas no significant difference was found between the two latter groups.
As shown in Table 1, HOAs and spherical aberration were significantly different among the three groups. Post-hoc comparison tests revealed that spherical aberration was significantly higher in the glistenings and surface light scattering groups than those in the control group (glistenings vs control group: P < .001; surface light scattering group vs control group: P = .001). No significant difference was found between the former two groups (P = .973). Furthermore, significant differences were found for the Strehl ratio among the three groups. Post-hoc comparisons demonstrated that the Strehl ratio values were significantly lower in the glistenings and surface light scattering groups (glistenings vs control group: P = .004; surface light scattering group vs control group: P = .046) than those in the control group, whereas no differences were found between the former two groups (P > .05). Figure 4 shows the magnitude of change in PSF in the three groups.
Wavefront Data and Strehl Ratio of Intraocular Lens in Different Groups
Change in the point spread function (PSF) for the (A) glistenings, (B) surface light scattering, and (C) control groups. The magnitude of PSF obtained from the former two groups appears to increase significantly compared with that from the control group.
Additionally, MTF values were significantly different at 5 (P = .008), 10 (P = .020), and 15 (P = .022) cpd. Dunn–Bonferroni's post-hoc test revealed that the control group performed better than the glistenings group did at 5 (P = .012), 10 (P = .023), and 15 (P = .032) cpd. However, for mean MTF values, a significant difference between the surface light scattering and control groups was only found at 5 cpd (P = .037, Figure B, available in the online version of this article). In addition, MTF values of the glistenings group were not significantly different from those of the surface light scattering group at any spatial frequency.
Modulation transfer function (MTF) curve of the intraocular lenses obtained from the three groups at different spatial frequencies. MTF values of the control group were higher than that of the glistenings group at 5, 10, and 15 cpd. However, a significant difference between the surface light scattering and control groups was only found at 5 cpd.
Both glistenings and surface light scattering are commonly observed in hydrophobic IOLs. AcrySof SA60AT IOLs, which are used prevalently for IOL implantation worldwide, have high occurrence of the two phenomena, which has been reported in several studies.3,14 However, hydrophobic AR40e IOLs rarely present the former two phenomena, as previous studies described.8,15 Our results also show more glistenings and surface light scattering in the SA60AT IOL than in the AR40e IOL. To our knowledge, both phenomena minimally impair visual acuity4,16 but have a negative impact on other visual functions and thus decrease visual quality to some degree.2,6 This study focuses mainly on the subjective visual performance and objective optical quality of patients at least 5 years postoperatively in whom IOL glistenings and/or surface light scattering had developed, and it is a supplement and extension of some previous studies.
First, our data demonstrate that glistenings and surface light scattering have little effect on postoperative visual acuity, which is consistent with previous reports.1,2,4,16
In terms of contrast sensitivity under glare testing, no significant difference was found among the three groups, which is likely due to a veiling glare across the screen, decreasing the contrast of the target and the background and thus inducing reduced contrast sensitivity even in normal IOLs.17 For contrast sensitivity without glare testing, our results suggest that surface light scattering impairs postoperative contrast sensitivity only at low frequencies. However, glistenings influence contrast sensitivity at low, intermediate, and high spatial frequencies, which is consistent with previous findings,2 and indicates that contrast sensitivity decreased to a larger degree in patients with IOL glistenings.
Straylight is an objective indicator of assessing the optical quality, which is defined as the light deviating from the original route to the retina due to uneven refractive media, and is strongly influenced by IOL opacification.18 In the current study, the mean stray-light value of the glistenings group was higher than that of the surface light scattering and control groups; however, there was no significant difference between the latter two groups. These findings agree with previous studies that glistenings induce more apparent ocular scattering than surface light scattering.18,19
In this study, the significant difference of spherical aberration partly resulted from the two different IOL models in the groups and the aberrometer used for analysis. Automated skiascopy used infrared light and the sampling rate of the OPD-III scan may still limit to capture the actual change of spherical aberration caused by the glistening or surface light scattering; nevertheless, the OPD-III scan exhibited favorable applicability and repeatability for the aberration measurement, as published literature described.20,21 Schweitzer et al.22 also suggested that severe glistenings increase the values of spherical aberration, which is consistent with our results. Additionally, we supposed that a distortion of a simulated point source of light tends to be enhanced with the presence of both phenomena, which has been presented now by the difference in PSF and MTF values among groups. Our results are in agreement with previous research in mathematical model eyes,6,23 and to some extent provide further clinical evidence that objective visual quality was prone to be compromised by glistenings and surface light scattering. To our best knowledge, our study was the first to evaluate PSF and MTF of IOLs in conjunction with glistenings or surface light scattering in patients. However, more kinds of aberrometers are needed to further verify these findings.
Another limitation was that our study failed to grade the phenomena and correlate the findings along with the intensity of the phenomena in current study. Although several authors proposed to quantify these phenomena using Scheimpflug image analysis, this method has limitations and is not widely used.23,24 Future studies with more precise assessment methods to grade phenomenon and larger sample sizes are needed to confirm the current findings.
This study demonstrates that both subjective and objective visual quality are prone to be compromised by IOL glistenings and surface light scattering. Our findings are helpful to further understand the reason for IOL exchange in healthy eyes with severe glistenings or surface light scattering that are associated with symptoms of poor visual performance. Considering the rapidly increasing use of foldable IOLs, we emphasize the need for continued testing and examination of new IOL biomaterials to prevent or delay the process of glistenings and surface light scattering.
- Hayashi K, Hirata A, Yoshida M, Yoshimura K, Hayashi H. Long-term effect of surface light scattering and glistenings of intraocular lenses on visual function. Am J Ophthalmol. 2012;154:240–251.e2. doi:10.1016/j.ajo.2012.03.011 [CrossRef]
- Xi L, Liu Y, Zhao F, Chen C, Cheng B. Analysis of glistenings in hydrophobic acrylic intraocular lenses on visual performance. Int J Ophthalmol. 2014;7:446–451.
- Werner L. Glistenings and surface light scattering in intraocular lenses. J Cataract Refract Surg. 2010;36:1398–1420. doi:10.1016/j.jcrs.2010.06.003 [CrossRef]
- Rønbeck M, Behndig A, Taube M, Koivula A, Kugelberg M. Comparison of glistenings in intraocular lenses with three different materials: 12-year follow-up. Acta Ophthalmol. 2013;91:66–70. doi:10.1111/j.1755-3768.2011.02277.x [CrossRef]
- Ong MD, Callaghan TA, Pei R, Karakelle M. Etiology of surface light scattering on hydrophobic acrylic intraocular lenses. J Cataract Refract Surg. 2012;38:1833–1844. doi:10.1016/j.jcrs.2012.05.043 [CrossRef]
- DeHoog E, Doraiswamy A. Evaluation of loss in optical quality of multifocal intraocular lenses with glistenings. J Cataract Refract Surg. 2016;42:606–612. doi:10.1016/j.jcrs.2015.10.071 [CrossRef]
- Matsushima H, Nagata M, Katsuki Y, et al. Decreased visual acuity resulting from glistening and sub-surface nano-glistening formation in intraocular lenses: a retrospective analysis of 5 cases. Saudi J Ophthalmol. 2015;29:259–263. doi:10.1016/j.sjopt.2015.07.001 [CrossRef]
- Chang A, Behndig A, Ronbeck M, Kugelberg M. Comparison of posterior capsule opacification and glistenings with 2 hydrophobic acrylic intraocular lenses: 5- to 7-year follow-up. J Cataract Refract Surg. 2013;39:694–698. doi:10.1016/j.jcrs.2012.11.032 [CrossRef]
- Ale JB. Intraocular lens tilt and decentration: a concern for contemporary IOL designs. Nepal J Ophthalmol. 2011;3:68–77.
- Zhang R, Song H, Tang X. Comparison of tilt, decentration and visual quality of two different one-piece designed aspheric intraocular lens after surgery [article in Chinese]. Chin J Pract Ophthalmol. 2014;32:419–423.
- Puell MC, Benítez-del-Castillo JM, Martínez-de-la-Casa J, et al. Contrast sensitivity and disability glare in patients with dry eye. Acta Ophthalmol Scand. 2006;84:527–531. doi:10.1111/j.1600-0420.2006.00671.x [CrossRef]
- Franssen L, Coppens JE, van den Berg TJ. Compensation comparison method for assessment of retinal straylight. Invest Ophthalmol Vis Sci. 2006;47:768–776. doi:10.1167/iovs.05-0690 [CrossRef]
- Santhiago MR, Netto MV, Barreto J Jr, Gomes BA, Oliveira CD, Kara-Junior N. Optical quality in eyes implanted with aspheric and spherical intraocular lenses assessed by NIDEK OPD-Scan: a randomized, bilateral, clinical trial. J Refract Surg. 2011;27:287–292. doi:10.3928/1081597X-20100714-01 [CrossRef]
- Chang A, Kugelberg M. Glistenings 9 years after phacoemulsification in hydrophobic and hydrophilic acrylic intraocular lenses. J Cataract Refract Surg. 2015;41:1199–1204. doi:10.1016/j.jcrs.2014.09.038 [CrossRef]
- Miyata K, Honbo M, Otani S, Nejima R, Minami K. Effect on visual acuity of increased surface light scattering in intraocular lenses. J Cataract Refract Surg. 2012;38:221–226. doi:10.1016/j.jcrs.2011.08.042 [CrossRef]
- Moreno-Montañes J, Alvarez A, Rodríguez-Conde R, Fernández-Hortelano A. Clinical factors related to the frequency and intensity of glistenings in AcrySof intraocular lenses. J Cataract Refract Surg. 2003;29:1980–1984. doi:10.1016/S0886-3350(03)00136-6 [CrossRef]
- Pesudovs K. Takagi Glare Tester CGT-1000 for contrast sensitivity and glare testing in normal individuals and cataract patients. J Refract Surg. 2007;23:492–498.
- Labuz G, Reus NJ, van den Berg TJ. Comparison of ocular stray-light after implantation of multifocal intraocular lenses. J Cataract Refract Surg. 2016;42:618–625. doi:10.1016/j.jcrs.2016.02.022 [CrossRef]
- Henriksen BS, Kinard K, Olson RJ. Effect of intraocular lens glistening size on visual quality. J Cataract Refract Surg. 2015;41:1190–1198. doi:10.1016/j.jcrs.2014.09.051 [CrossRef]
- Ferreira TB, Almeida A. Comparison of the visual outcomes and OPD-scan results of AMO Tecnis toric and Alcon Acrysof IQ toric intraocular lenses. J Refract Surg. 2012;28:551–555. doi:10.3928/1081597X-20120703-03 [CrossRef]
- Buscemi P, Fujieda M, Bains HS. Clinical outcomes using the NAVEX platform. Ophthalmol Clin North Am. 2004;17:183–189. doi:10.1016/j.ohc.2004.02.005 [CrossRef]
- Schweitzer C, Orignac I, Praud D, Chatoux O, Colin J. Glistening in glaucomatous eyes: visual performances and risk factors. Acta Ophthalmol. 2014;92:529–534. doi:10.1111/aos.12276 [CrossRef]
- DeHoog E, Doraiswamy A. Evaluation of the impact of light scatter from glistenings in pseudophakic eyes. J Cataract Refract Surg. 2014;40:95–103. doi:10.1016/j.jcrs.2013.10.018 [CrossRef]
- Mackool RJ, Colin J. Limitations of Scheimpflug photography in quantifying glistenings. J Cataract Refract Surg. 2009;35:1480–1481. doi:10.1016/j.jcrs.2009.03.044 [CrossRef]
Wavefront Data and Strehl Ratio of Intraocular Lens in Different Groupsa
|Parameter (5-mm Pupil)||Glistenings Group (n = 65)||Surface Light Scattering Group (n = 33)||Control Group (n = 42)||P|
|HOAs (μm)||0.50 ± 0.24||0.45 ± 0.13||0.41 ± 0.20||.032b|
|Spherical aberration||0.15 ± 0.07||0.15 ± 0.06||0.09 ± 0.06||< .001b|
|Coma||0.16 ± 0.10||0.14 ± 0.06||0.13 ± 0.07||.408|
|Trefoil||0.37 ± 0.26||0.32 ± 0.16||0.28 ± 0.22||.066|
|Strehl ratio||0.04 ± 0.02||0.04 ± 0.02||0.06 ± 0.03||.004b|
|Parameter||Glistenings Group (n = 65)||Surface Light Scattering Group (n = 33)||Control Group (n = 42)||Pb|
|Female||29 (45%)||16 (48%)||20 (48%)||.920|
|Age (y)||71.09 ± 6.27||71.24 ± 9.49||70.29 ± 7.53||.822|
|Follow-up time (mo)||87.88 ± 19.57||86.55 ± 25.24||79.71 ± 13.47||.095|
|SE (D)||−0.07 ± 0.73||−0.18 ± 0.93||−0.14 ± 0.54||.786|
|Mean IOL power (D)||19.67 ± 2.41||19.58 ± 2.59||19.86 ± 2.51||.850|
|Decentration of IOL (mm)||0.16 ± 0.07||0.14 ± 0.07||0.15 ± 0.08||.120|
|IOL tilt (degrees)||1.25 ± 0.40||1.24 ± 0.51||1.35 ± 0.55||.440|
|PCO value||0.11 ± 0.19||0.10 ± 0.18||0.17 ± 0.26||.647|
Mean Postoperative UDVA and CDVAa
|Parameter||Glistenings Group (n = 65)||Surface Light Scattering Group (n = 33)||Control Group (n = 42)||Pb|
|UDVA (logMAR)||0.11 ± 0.15||0.12 ± 0.14||0.06 ± 0.12||.212|
|CDVA (logMAR)||−0.03 ± 0.08||−0.05 ± 0.08||−0.07 ± 0.08||.108|