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Correlation between posterior capsule opacification and visual function before and after Neodymium: YAG laser posterior capsulotomy
Correlation Between Posterior Capsule Opacification and Visual Function Before and After Neodymium:YAG Laser Posterior Capsulotomy KEN HAYASHI, MD, HIDEYUKI HAYASHI, MD, FUMINORI NAKAO, MD, AND FUMIHIKO HAYASHI, MD
● PURPOSE: To investigate the correlation between visual acuity, contrast sensitivity, and contrast sensitivity with glare source (glare sensitivity), and the degree of posterior capsule opacification (PCO) before and after neodymium:yttrium-aluminum-garnet (Nd:YAG) laser posterior capsulotomy. ● DESIGN: Prospective interventional case series. ● METHODS: Eighty-four patients (90 pseudophakic eyes) scheduled to undergo Nd:YAG laser capsulotomy were recruited. Visual acuity and contrast sensitivity with and without the presence of a circular glare source (using the contrast glare tester) were measured before and after Nd:YAG laser capsulotomy. The PCO density value was measured using a Scheimpflug videophotography system. The visual functions were statistically correlated with the PCO value. ● RESULTS: Before Nd:YAG laser capsulotomy, strong correlation existed between the PCO value and visual acuity (r ⴝ 0.728). Contrast sensitivity and glare sensitivity were also weakly correlated with the PCO value, but the correlation coefficients were smaller than that of visual acuity. After Nd:YAG laser capsulotomy, mean visual acuity, contrast sensitivity, and glare sensitivity at all visual angles improved significantly (P <.0001). After capsulotomy, no significant correlation was found between visual acuity, contrast sensitivity, or glare sensitivity and the PCO value. ● CONCLUSIONS: Before Nd:YAG laser capsulotomy, visual functions correlated significantly with the degree of PCO. Specifically, visual acuity has a stronger associAccepted for publication April 8, 2003. InternetAdvance publication at ajo.com May 22, 2003. From the Hayashi Eye Hospital, (K.H., F.N., F.H.) and the Department of Ophthalmology, School of Medicine, Fukuoka University, Fukuoka, Japan (H.H.). Inquiries to Ken Hayashi, MD, Hayashi Eye Hospital, 4-7-13 Hakataekimae, Hakata-ku, Fukuoka 812-0011, Japan; fax: (⫹81) 92-441-5303; e-mail: [email protected]
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ation with PCO than does contrast sensitivity or glare sensitivity and therefore should be considered to reflect most accurately the degree of PCO. After capsulotomy, these visual functions improve markedly and no longer have a significant correlation with PCO. (Am J Ophthalmol 2003;136:720 –726. © 2003 by Elsevier Inc. All rights reserved.)
P
OSTERIOR CAPSULE OPACIFICATION (PCO) IS THE
most common complication after extracapsular cataract extraction and generally causes a deterioration of visual functions. Earlier studies on neodymium:yttriumaluminum-garnet (Nd:YAG) laser capsulotomy concentrated on measuring high-contrast visual acuity to assess PCO.1–3 More recent studies have shown, however, that PCO significantly disturbs contrast sensitivity, both without and with glare (glare sensitivity), in addition to visual acuity and that all of these visual functions improve significantly after Nd:YAG laser posterior capsulotomy.4 –9 Most of these studies reported a correlation between the improvement of visual acuity, contrast sensitivity, and glare disability after Nd:YAG laser capsulotomy.4 – 6 The other study claimed that the improvement in contrast sensitivity is poorly associated with improvement in visual acuity in patients with good visual acuity, and therefore contrast sensitivity is a more informative test than is visual acuity in the early stages of PCO.7 Furthermore, it is controversial as to whether glare disability is prominent in patients with slight PCO.6,8,9 As the correlation between visual functions and the actual degree of PCO was not addressed in these studies, the most important visual function for assessing visual impairment due to PCO before capsulotomy remains unclear. The purpose of the study described herein was to examine the correlation between the degree of PCO and visual functions before and after Nd:YAG laser capsulotomy. Although visual acuity has a strong correlation with
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0002-9394/03/$30.00 doi:10.1016/S0002-9394(03)00425-2
TABLE 1. Patient Characteristics Characteristic
No. of eyes Age (⫾ SD), years Sex Left/right logMAR visual acuity Prelaser Postlaser
Included Patients
Excluded Patients
90 70.4 ⫾ 9.7 39M/51F 36L/54R
100 72.4 ⫾ 10.7 34M/66F 44L/56R
0.329 ⫾ 0.305 0.052 ⫾ 0.082
0.545 ⫾ 0.600 0.377 ⫾ 0.602
P Value
— .0960* .2322* .6592* .0314† ⬍.0001†
F ⫽ female; logMAR ⫽ logarithm of the minimal angle of resolution; M ⫽ male; SD ⫽ standard deviation. *No statistical significance. † Statistically significant.
FIGURE 1. Mean (ⴞ standard deviation) contrast sensitivity before and after neodymium:yttrium-aluminum-garnet (Nd:YAG) laser capsulotomy. Mean contrast sensitivity improved significantly after Nd:YAG laser capsulotomy at all visual angles (r <.0001).
the degree of PCO, patients in the very early stages of PCO can show impaired contrast sensitivity or marked glare disability despite good visual acuity. Accordingly, we specifically addressed contrast sensitivity and glare sensitivity in patients with relatively good visual acuity who were scheduled to undergo Nd:YAG laser posterior capsulotomy for PCO.
DESIGN THIS STUDY WAS DESIGNED AS A PROSPECTIVE INTERVEN-
tional case series.
METHODS ALL PSEUDOPHAKIC PATIENTS WHO WERE SEQUENTIALLY
scheduled for Nd:YAG laser posterior capsulotomy beVOL. 136, NO. 4
tween January 4 and August 12, 2002 were screened for inclusion in this study. One of the authors (K.H. or F.H.) verified the presence of definite PCO on slit-lamp biomicroscopy and each patient’s complaint of visual impairment and also performed patient screening. Prelaser exclusion criteria were any pathology of the macula or optic nerve, previous history of inflammation, anterior capsule contraction, liquefied aftercataract, or small pupil (⬍6 mm) after mydriasis. Postlaser exclusion criteria were corrected visual acuity of less than 20/40 due to any pathology of unknown cause, pitting of the intraocular lens (IOL) during capsulotomy, media opacities other than PCO, and any difficulties with data collection or analysis. Ninety eyes of 84 patients who met the inclusion criteria were identified and included in the final analysis. The study protocol was approved by the institutional review board, and informed consent was obtained from each patient. After full mydriasis, all patients underwent Nd:YAG laser posterior capsulotomy with a Q-switched Nd:YAG
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FIGURE 2. Mean (ⴞ standard deviation) glare sensitivity before and after neodymium:yttrium-aluminum-garnet (Nd:YAG) laser capsulotomy. Mean glare sensitivity improved significantly after Nd:YAG laser capsulotomy at all visual angles (r <.0001).
are equivalent to visual angles of 6.3, 4.0, 2.5, 1.6, 1.0, and 0.7 degrees at 0.35 m. Contrast sensitivity is calculated as logarithm of inverse value of the contrast threshold. Glare sensitivity was also measured by adding a glare source of 50 cd/m2 around the visual targets. The PCO value of 3.00 ⫻ 0.25 mm area of the central posterior capsule was measured using an axial densitometry of the Scheimpflug videophotography system (EAS-1000; NIDEK, Gamagori, Japan). Measurement procedures for obtaining the PCO value were described previously.10 The area of the Nd:YAG laser capsulotomy opening was also measured using the EAS1000 system. All examinations were performed by experienced ophthalmic technicians who were unaware of the purpose of this study. For statistical analysis, decimal visual acuity was converted to a logarithm of minimal angle of resolution (logMAR) scale. Contrast and glare sensitivities were also converted to the logarithm of inverse values (contrast and glare thresholds). The logMAR visual acuity, contrast sensitivity, glare sensitivity and other continuous variables before and after Nd:YAG laser capsulotomy were compared using the Mann-Whitney U test. Univariate associations between the visual functions and PCO value were evaluated using the Pearson correlation coefficient. Any differences showing a P value of less than .05 were considered to be statistically significant.
TABLE 2. Correlation Coefficients (r) Between LogMAR Visual Acuity and PCO Value and Area of Posterior Capsule Opening
Before Nd:YAG laser capsulotomy Visual acuity vs PCO value Improvement Visual acuity vs PCO value After Nd:YAG laser capsulotomy Visual acuity vs PCO value Visual acuity vs area of Nd:YAG laser opening
Pearson r
P Value
.728
⬍.0001*
.424
.0002*
.031 .065
.7932† .5829†
logMAR ⫽ logarithm of the minimal angle of resolution; Nd: YAG ⫽ neodmymium:yttrium-aluminum-garnet; PCO ⫽ posterior capsule opacification. *Statistically significant. † No statistical significance.
laser (YC-1300; NIDEK, Gamagori, Japan). After topical anesthesia, a contact lens was applied to enhance power density at the level of the posterior capsule. An approximately 4-mm diameter area of the central posterior capsule was then cleared by emitting laser energy on the capsule; energy levels were between 1.0 and 1.5 millijoules. Special care was taken to not pit the IOL optic. As main outcome measures, corrected visual acuity was examined using decimal charts, and contrast sensitivity as well as glare sensitivity was measured using the contrast glare tester (CGT-1000; Takagi Seiko, Nagano, Japan) before and approximately 2 weeks after Nd:YAG laser capsulotomy. The CGT-1000 measures 12-step contrast thresholds using concentric ring-shaped visual targets that 722
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RESULTS A TOTAL OF 190 EYES OF 169 PATIENTS WHO WERE SCHED-
uled for Nd:YAG laser capsulotomy were screened. Before capsulotomy, 60 eyes were excluded because of the presence of various ocular pathologies, 5 because of a previous history of ocular inflammation, 25 because of co-occurOF
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FIGURE 3. Simple correlation between the visual acuity and the posterior capsule opacification (PCO) value before neodymium: yttrium-aluminum-garnet (Nd:YAG) laser capsulotomy. A strong correlation is seen between the logarithm of the minimal angle of resolution visual acuity and the PCO value (Pearson r ⴝ 0.728).
TABLE 3. Correlation Coefficients (r) Between Contrast Sensitivity and PCO Value Before and After Nd:YAG Laser Capsulotomy Visual Angles (Degrees)
6.3 4.0 2.5 1.6 1.0 0.7
Prelaser r
.293 .380 .309 .251 .212 .205
P Value
.0053* .0002* .0032* .0177* .0456* .0543†
Postlaser r
.145 .119 .171 .125 .016 .015
TABLE 4. Correlation Coefficients (r) Between Glare Sensitivity and PCO Value Before and After Nd:YAG Laser Capsulotomy
P Value †
.2200 .3170† .1484† .2939† .8908† .8969†
Visual Angle (Degrees)
Prelaser r
P Value
Postlaser r
P Value
6.3 4.0 2.5 1.6 1.0 0.7
.315 .516 .275 .211 .161 .131
.0030* ⬍.0001* .0108* .0521† .1418† .2332†
.046 .158 .001 .043 .051 .040
.7027† .1822† .9933† .7217† .6707† .7403†
Nd:YAG ⫽ neodymium:yttrium-aluminum-garnet; PCO ⫽ posterior capsule opacification. *Statistically significant. † No statistical significance.
Nd:YAG ⫽ neodymium:yttrium-aluminum-garnet; PCO ⫽ posterior capsule opacification. *Statistically significant. † No statistical significance.
rence of anterior capsule contraction, and 1 because of the presence of liquefied after-cataract. After capsulotomy, two eyes were excluded because of visual acuity worse than 20/40, and seven because of difficulty with data analysis. Accordingly, 90 eyes of 84 patients who met the inclusion criteria were included in the final analysis. Patient demographics of the two groups are shown in Table 1. No significant differences were found in age, sex, the ratio of left and right eyes, and interval between cataract surgery and capsulotomy. Mean prelaser and postolaser visual acuities in the excluded patient group were significantly worse than those in the included patient group. Of the 90 eyes, 33 had a polymethylmethacrylate IOL, 33 had an acrylic IOL, seven had a silicone IOL, and eight had a hydrogel IOL. We could not identify the type of IOL implanted in the other nine eyes, as these patients had
undergone cataract surgery elsewhere. Mean area of the Nd:YAG laser capsulotomy opening was 10.6 ⫾ 4.7 mm2. Mean visual acuity before Nd:YAG capsulotomy was 20/36, whereas that after capsulotomy was 20/22; this improvement was statistically significant (P ⬍.0001). Figures 1 and 2 demonstrate the mean prelaser and postlaser contrast sensitivity and glare sensitivity, respectively. Both mean contrast sensitivity and glare sensitivity improved significantly at all visual angles (P ⬍.0001). Table 2 lists the simple correlation between visual acuity and PCO value and area of the posterior capsule opening. Before capsulotomy, a strong correlation was found between the logMAR visual acuity and PCO value (Pearson r ⫽ 0.728; Figure 3). There was also a significant correlation between improvement in logMAR visual acuity and decrease in PCO value (r ⫽ 0.424). However, after
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TABLE 5. Mean (⫾ SD) Visual Acuity, Contrast Sensitivity, Glare Sensitivity, and PCO Value Before and After Nd:YAG Laser Capsulotomy in Patients Who Have Visual Acuity of 20/25 or Better
LogMAR visual acuity Contrast threshold (degrees) 6.3 4.0 2.5 1.6 1.0 0.7 Glare threshold (degrees) 6.3 4.0 2.5 1.6 1.0 0.7 PCO value (CCT)
Prelaser
Postlaser
P Value
0.060 ⫾ 0.042
0.006 ⫾ 0.025
.0016*
0.022 ⫾ 0.013 0.025 ⫾ 0.013 0.035 ⫾ 0.028 0.062 ⫾ 0.057 0.116 ⫾ 0.244 0.304 ⫾ 0.244
0.014 ⫾ 0.005 0.018 ⫾ 0.008 0.025 ⫾ 0.012 0.116 ⫾ 0.087 0.071 ⫾ 0.042 0.185 ⫾ 0.087
.1047† .1672† .4172† .1811† .0956† .1248†
0.037 ⫾ 0.028 0.043 ⫾ 0.028 0.059 ⫾ 0.046 0.094 ⫾ 0.079 0.201 ⫾ 0.186 0.499 ⫾ 0.731 22.9 ⫾ 12.6
0.025 ⫾ 0.013 0.026 ⫾ 0.013 0.036 ⫾ 0.021 0.055 ⫾ 0.037 0.121 ⫾ 0.107 0.306 ⫾ 0.286 3.7 ⫾ 5.2
.2826† .0757† .1418† .1195† .0688† .1303† ⬍.0001*
CCT ⫽ computer compatible tapes; LogMAR ⫽ logarithm of the minimal angle of resolution; Nd:YAG ⫽ neodymium:yttrium-aluminum-garnet; PCO ⫽ posterior capsule opacification; SD ⫽ standard deviation. *Statistically significant. † No statistical significance.
capsulotomy, no significant correlation was found between the logMAR visual acuity and the PCO value or area of the posterior capsule opening. Table 3 shows the simple correlations between contrast sensitivity and the PCO value before and after Nd:YAG laser capsulotomy. Before capsulotomy, a significant but weak correlation was found between contrast sensitivity and PCO value at visual angles of 6.3, 4.0, 2.5, 1.6, and 1.0 degrees. Pearson correlation coefficients were smaller than that between visual acuity and PCO value. After capsulotomy, no significant correlation was found between contrast sensitivity and PCO value or area of the capsulotomy opening. Table 4 shows the simple correlation between glare sensitivity and PCO value before and after Nd:YAG laser capsulotomy. Before capsulotomy, a moderate to weak correlation was found between glare sensitivity and PCO value at visual angles of 6.3, 4.0, and 2.5 degrees. The correlation coefficients were smaller than that between visual acuity and PCO value. After capsulotomy, no significant correlation was found between glare sensitivity and PCO value or the size of the capsulotomy opening. To assess the impairment in contrast sensitivity and glare sensitivity in patients with PCO who have relatively good visual acuity, 16 eyes with prelaser visual acuity of 20/25 or better were selected. Table 5 shows the mean 724
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TABLE 6. Correlation Coefficients (r) Between Contrast Sensitivity and Glare Sensitivity and PCO Value Before Nd:YAG Laser Capsulotomy in Patients Who Have Visual Acuity of 20/25 or Better Contrast Sensitivity
Glare Sensitivity
Visual Angle (Degrees)
Pearson r
P Value
Pearson r
P Value
6.3 4.0 2.5 1.6 1.0 0.7
.059 .303 .038 .100 .233 .052
.8287* .2538* .8880* .7112* .3847* .8481*
.053 .065 .067 .093 .048 .104
.8453* .8111* .8041* .7329* .8591* .7003*
Nd:YAG ⫽ neodymium:yttrium-aluminum-garnet; PCO ⫽ posterior capsule opacification. *No statistical significance.
visual acuity, contrast sensitivity, glare sensitivity, and PCO value before and after Nd:YAG capsulotomy. The mean visual acuity and PCO value improved significantly after capsulotomy, whereas no significant improvements were observed in contrast sensitivity or glare sensitivity at any visual angles. Furthermore, no significant correlation OF
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was found between contrast sensitivity or glare sensitivity and PCO value before or after capsulotomy (Table 6).
DISCUSSION OUR STUDY HAS DEMONSTRATED THAT VISUAL ACUITY,
contrast sensitivity, and glare sensitivity improve significantly after Nd:YAG laser capsulotomy. The PCO value, as measured using the Scheimpflug videophotogaphy system, also decreased significantly. Furthermore, the improvement in visual acuity was correlated significantly with the decrease in PCO value. These results clearly indicate that the visual functions are disturbed because of PCO and are improved by Nd:YAG laser capsulotomy. Before capsulotomy, visual acuity was strongly correlated with the degree of PCO, and although contrast sensitivity and glare sensitivity at most visual angles also were significantly correlated with PCO, the correlation was weaker than that of visual acuity. These results indicate that visual acuity reflects most relevantly the degree of PCO when patients with various degrees of PCO are included. After capsulotomy, no significant correlation was observed between visual acuity, contrast sensitivity, or glare sensitivity and the degree of PCO. Furthermore, these visual functions had no significant correlation with the area of the Nd:YAG laser capsulotomy opening, which varied considerably in this series. These results thus suggest that even relatively small capsulotomy openings may be sufficient to improve visual function. Most previous studies reported that contrast sensitivity and glare disability improved concomitant with visual acuity after capsulotomy.4 – 6 However, Tan and associates7 reported that the improvement in contrast sensitivity was poorly associated with that in visual acuity and, therefore, that contrast sensitivity testing is more sensitive than is visual acuity in the early stages of PCO. Furthermore, Sunderraj and associates8 also documented that glare disability is prominent in some patients who have good visual acuity. To see whether contrast sensitivity and glare sensitivity are necessarily impaired in the early stages of PCO, we examined these functions in patients with good visual acuity. When we studied patients who had a visual acuity of 20/25 or better, both visual acuity and the PCO value improved significantly after capsulotomy, but contrast sensitivity and glare sensitivity did not show significant improvement. Furthermore, contrast sensitivity and glare sensitivity did not correlate significantly with the PCO value before or after capsulotomy. Although some patients show markedly impaired contrast sensitivity or glare sensitivity despite good visual acuity, our results suggest that this does not hold true for any patients with slight PCO. A plausible explanation for this finding is that PCO generally occludes the entire pupillary area when it has VOL. 136, NO. 4
invaded into the retrolental space and therefore impairs visual acuity from a relatively early stage. Indeed, the pupillary area was entirely and equally covered by PCO in most cases in the present series. It has been reported that posterior subcapsular cataracts and early cataracts are associated with loss of contrast sensitivity and increased glare disability because of intraocular light scatter, despite good visual acuity.11–14 If we examine those eyes in which the pupillary area is only partially or unequally occuluded by very early stage PCO, contrast sensitivity and glare sensitivity may be more impaired than visual acuity.9 In conclusion, high-contrast visual acuity has a stronger association with the degree of PCO than does either contrast sensitivity or glare sensitivity and therefore is the most relevant outcome measure of the degree of PCO. When patients complain of blurred vision and have PCO, visual acuity is thought to be the most reliable measurement. However, in the very early stages of PCO, there are patients who show impaired contrast sensitivity or marked glare disability despite good visual acuity. From these results it is apparent that further study is necessary to examine contrast sensitivity and glare sensitivity in patients who have little or no PCO and who have good visual acuity.
REFERENCES 1. Stark WJ, Worthen D, Holladay JT, Murray G. Neodymium:YAG lasers: an FDA report. Ophthalmology 1985;92: 209 –212. 2. Wasserman EL, Axt JC, Sheets JH. Neodymium:YAG laser posterior capsulotomy. Am Intra-Ocular Implant Soc J 1985; 11:245–248. 3. Weiblinger RP, Spring S. Review of the clinical literature on the use of the Nd:YAG laser for posterior capsulotomy. J Catract Refract Surg 1986;12:162–170. 4. Knighton RW, Slomovic AR, Parrish RK. Glare measurements before and after neodymium-YAG laser capsulotomy. Am J Ophthalmol 1985;100:708 –713. 5. Magno BV, Datiles MB, Lasa MSM, Fajardo MRQ, Caruso RC, Kaiser-Kupfer MI. Evaluation of visual function following neodymium:YAG laser capsulotomy. Ophthalmology 1997;104:1287–1293. 6. Claesson M, Klaren L, Beckman C, Sjorstrand J. Glare and contrast sensitivity before and after Nd:YAG laser capsulotomy. Acta Ophthalmol (Copenh) 1994;72:27–32. 7. Tan JCH, Spalton DJ, Arden GB. The effect of neodymium:YAG capsulotomy on contrast sensitivity and evaluation of methods for its assessment. Ophthalmology 1999;106: 703–709. 8. Sunderraj P, Villada JR, Joyce PW, Watson A. Glare testing in pseudophakes with posterior capsule opacification. Eye 1992;6:411–413. 9. Koch DD, Emery JM, Jardeleza TL, Franklin D. Glare following posterior chamber intraocular lens implantation. J Catract Refract Surg 1986;12:480 –484. 10. Hayashi K, Hayashi H, Nakao F, Hayashi F. Posterior capsule opacification after surgery in patients with diabetes mellitus. Am J Ophthalmol 2002;134:10 –16. 11. Jindra LF, Zemon V. Contrast sensitivity testing: a more
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13. Lasa MSM, Datiles MB, Podgor MJ, Magno BV. Contrast sensitivity and glare sensitivity: association with the type and severity of the cataract. Ophthalmology 1992;99:1045–1049. 14. Adamsons I, Rubin GS, Vitale S, Taylor HR, Stark WJ. The effect of early cataracts on glare and contrast sensitivity: a pilot study. Arch Ophthalmol 1992;110:1081–1086.
complete assessment of vision. J Cataract Refract Surg 1989;15:141–148. 12. Elliot DB, Gilchrist J, Whitaker D. Contrast sensitivity and glare sensitivity changes with three types of cataract morphology: are these techniques necessary in a clinical evaluation of cataract? Ophthalmol Physiol Opt 1989;9:25–30.
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● PURPOSE: To investigate the correlation between visual acuity, contrast sensitivity, and contrast sensitivity with glare source (glare sensitivity), and the degree of posterior capsule opacification (PCO) before and after neodymium:yttrium-aluminum-garnet (Nd:YAG) laser posterior capsulotomy. ● DESIGN: Prospective interventional case series. ● METHODS: Eighty-four patients (90 pseudophakic eyes) scheduled to undergo Nd:YAG laser capsulotomy were recruited. Visual acuity and contrast sensitivity with and without the presence of a circular glare source (using the contrast glare tester) were measured before and after Nd:YAG laser capsulotomy. The PCO density value was measured using a Scheimpflug videophotography system. The visual functions were statistically correlated with the PCO value. ● RESULTS: Before Nd:YAG laser capsulotomy, strong correlation existed between the PCO value and visual acuity (r ⴝ 0.728). Contrast sensitivity and glare sensitivity were also weakly correlated with the PCO value, but the correlation coefficients were smaller than that of visual acuity. After Nd:YAG laser capsulotomy, mean visual acuity, contrast sensitivity, and glare sensitivity at all visual angles improved significantly (P <.0001). After capsulotomy, no significant correlation was found between visual acuity, contrast sensitivity, or glare sensitivity and the PCO value. ● CONCLUSIONS: Before Nd:YAG laser capsulotomy, visual functions correlated significantly with the degree of PCO. Specifically, visual acuity has a stronger associAccepted for publication April 8, 2003. InternetAdvance publication at ajo.com May 22, 2003. From the Hayashi Eye Hospital, (K.H., F.N., F.H.) and the Department of Ophthalmology, School of Medicine, Fukuoka University, Fukuoka, Japan (H.H.). Inquiries to Ken Hayashi, MD, Hayashi Eye Hospital, 4-7-13 Hakataekimae, Hakata-ku, Fukuoka 812-0011, Japan; fax: (⫹81) 92-441-5303; e-mail: [email protected]
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ation with PCO than does contrast sensitivity or glare sensitivity and therefore should be considered to reflect most accurately the degree of PCO. After capsulotomy, these visual functions improve markedly and no longer have a significant correlation with PCO. (Am J Ophthalmol 2003;136:720 –726. © 2003 by Elsevier Inc. All rights reserved.)
P
OSTERIOR CAPSULE OPACIFICATION (PCO) IS THE
most common complication after extracapsular cataract extraction and generally causes a deterioration of visual functions. Earlier studies on neodymium:yttriumaluminum-garnet (Nd:YAG) laser capsulotomy concentrated on measuring high-contrast visual acuity to assess PCO.1–3 More recent studies have shown, however, that PCO significantly disturbs contrast sensitivity, both without and with glare (glare sensitivity), in addition to visual acuity and that all of these visual functions improve significantly after Nd:YAG laser posterior capsulotomy.4 –9 Most of these studies reported a correlation between the improvement of visual acuity, contrast sensitivity, and glare disability after Nd:YAG laser capsulotomy.4 – 6 The other study claimed that the improvement in contrast sensitivity is poorly associated with improvement in visual acuity in patients with good visual acuity, and therefore contrast sensitivity is a more informative test than is visual acuity in the early stages of PCO.7 Furthermore, it is controversial as to whether glare disability is prominent in patients with slight PCO.6,8,9 As the correlation between visual functions and the actual degree of PCO was not addressed in these studies, the most important visual function for assessing visual impairment due to PCO before capsulotomy remains unclear. The purpose of the study described herein was to examine the correlation between the degree of PCO and visual functions before and after Nd:YAG laser capsulotomy. Although visual acuity has a strong correlation with
ELSEVIER INC. ALL
RIGHTS RESERVED.
0002-9394/03/$30.00 doi:10.1016/S0002-9394(03)00425-2
TABLE 1. Patient Characteristics Characteristic
No. of eyes Age (⫾ SD), years Sex Left/right logMAR visual acuity Prelaser Postlaser
Included Patients
Excluded Patients
90 70.4 ⫾ 9.7 39M/51F 36L/54R
100 72.4 ⫾ 10.7 34M/66F 44L/56R
0.329 ⫾ 0.305 0.052 ⫾ 0.082
0.545 ⫾ 0.600 0.377 ⫾ 0.602
P Value
— .0960* .2322* .6592* .0314† ⬍.0001†
F ⫽ female; logMAR ⫽ logarithm of the minimal angle of resolution; M ⫽ male; SD ⫽ standard deviation. *No statistical significance. † Statistically significant.
FIGURE 1. Mean (ⴞ standard deviation) contrast sensitivity before and after neodymium:yttrium-aluminum-garnet (Nd:YAG) laser capsulotomy. Mean contrast sensitivity improved significantly after Nd:YAG laser capsulotomy at all visual angles (r <.0001).
the degree of PCO, patients in the very early stages of PCO can show impaired contrast sensitivity or marked glare disability despite good visual acuity. Accordingly, we specifically addressed contrast sensitivity and glare sensitivity in patients with relatively good visual acuity who were scheduled to undergo Nd:YAG laser posterior capsulotomy for PCO.
DESIGN THIS STUDY WAS DESIGNED AS A PROSPECTIVE INTERVEN-
tional case series.
METHODS ALL PSEUDOPHAKIC PATIENTS WHO WERE SEQUENTIALLY
scheduled for Nd:YAG laser posterior capsulotomy beVOL. 136, NO. 4
tween January 4 and August 12, 2002 were screened for inclusion in this study. One of the authors (K.H. or F.H.) verified the presence of definite PCO on slit-lamp biomicroscopy and each patient’s complaint of visual impairment and also performed patient screening. Prelaser exclusion criteria were any pathology of the macula or optic nerve, previous history of inflammation, anterior capsule contraction, liquefied aftercataract, or small pupil (⬍6 mm) after mydriasis. Postlaser exclusion criteria were corrected visual acuity of less than 20/40 due to any pathology of unknown cause, pitting of the intraocular lens (IOL) during capsulotomy, media opacities other than PCO, and any difficulties with data collection or analysis. Ninety eyes of 84 patients who met the inclusion criteria were identified and included in the final analysis. The study protocol was approved by the institutional review board, and informed consent was obtained from each patient. After full mydriasis, all patients underwent Nd:YAG laser posterior capsulotomy with a Q-switched Nd:YAG
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FIGURE 2. Mean (ⴞ standard deviation) glare sensitivity before and after neodymium:yttrium-aluminum-garnet (Nd:YAG) laser capsulotomy. Mean glare sensitivity improved significantly after Nd:YAG laser capsulotomy at all visual angles (r <.0001).
are equivalent to visual angles of 6.3, 4.0, 2.5, 1.6, 1.0, and 0.7 degrees at 0.35 m. Contrast sensitivity is calculated as logarithm of inverse value of the contrast threshold. Glare sensitivity was also measured by adding a glare source of 50 cd/m2 around the visual targets. The PCO value of 3.00 ⫻ 0.25 mm area of the central posterior capsule was measured using an axial densitometry of the Scheimpflug videophotography system (EAS-1000; NIDEK, Gamagori, Japan). Measurement procedures for obtaining the PCO value were described previously.10 The area of the Nd:YAG laser capsulotomy opening was also measured using the EAS1000 system. All examinations were performed by experienced ophthalmic technicians who were unaware of the purpose of this study. For statistical analysis, decimal visual acuity was converted to a logarithm of minimal angle of resolution (logMAR) scale. Contrast and glare sensitivities were also converted to the logarithm of inverse values (contrast and glare thresholds). The logMAR visual acuity, contrast sensitivity, glare sensitivity and other continuous variables before and after Nd:YAG laser capsulotomy were compared using the Mann-Whitney U test. Univariate associations between the visual functions and PCO value were evaluated using the Pearson correlation coefficient. Any differences showing a P value of less than .05 were considered to be statistically significant.
TABLE 2. Correlation Coefficients (r) Between LogMAR Visual Acuity and PCO Value and Area of Posterior Capsule Opening
Before Nd:YAG laser capsulotomy Visual acuity vs PCO value Improvement Visual acuity vs PCO value After Nd:YAG laser capsulotomy Visual acuity vs PCO value Visual acuity vs area of Nd:YAG laser opening
Pearson r
P Value
.728
⬍.0001*
.424
.0002*
.031 .065
.7932† .5829†
logMAR ⫽ logarithm of the minimal angle of resolution; Nd: YAG ⫽ neodmymium:yttrium-aluminum-garnet; PCO ⫽ posterior capsule opacification. *Statistically significant. † No statistical significance.
laser (YC-1300; NIDEK, Gamagori, Japan). After topical anesthesia, a contact lens was applied to enhance power density at the level of the posterior capsule. An approximately 4-mm diameter area of the central posterior capsule was then cleared by emitting laser energy on the capsule; energy levels were between 1.0 and 1.5 millijoules. Special care was taken to not pit the IOL optic. As main outcome measures, corrected visual acuity was examined using decimal charts, and contrast sensitivity as well as glare sensitivity was measured using the contrast glare tester (CGT-1000; Takagi Seiko, Nagano, Japan) before and approximately 2 weeks after Nd:YAG laser capsulotomy. The CGT-1000 measures 12-step contrast thresholds using concentric ring-shaped visual targets that 722
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RESULTS A TOTAL OF 190 EYES OF 169 PATIENTS WHO WERE SCHED-
uled for Nd:YAG laser capsulotomy were screened. Before capsulotomy, 60 eyes were excluded because of the presence of various ocular pathologies, 5 because of a previous history of ocular inflammation, 25 because of co-occurOF
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FIGURE 3. Simple correlation between the visual acuity and the posterior capsule opacification (PCO) value before neodymium: yttrium-aluminum-garnet (Nd:YAG) laser capsulotomy. A strong correlation is seen between the logarithm of the minimal angle of resolution visual acuity and the PCO value (Pearson r ⴝ 0.728).
TABLE 3. Correlation Coefficients (r) Between Contrast Sensitivity and PCO Value Before and After Nd:YAG Laser Capsulotomy Visual Angles (Degrees)
6.3 4.0 2.5 1.6 1.0 0.7
Prelaser r
.293 .380 .309 .251 .212 .205
P Value
.0053* .0002* .0032* .0177* .0456* .0543†
Postlaser r
.145 .119 .171 .125 .016 .015
TABLE 4. Correlation Coefficients (r) Between Glare Sensitivity and PCO Value Before and After Nd:YAG Laser Capsulotomy
P Value †
.2200 .3170† .1484† .2939† .8908† .8969†
Visual Angle (Degrees)
Prelaser r
P Value
Postlaser r
P Value
6.3 4.0 2.5 1.6 1.0 0.7
.315 .516 .275 .211 .161 .131
.0030* ⬍.0001* .0108* .0521† .1418† .2332†
.046 .158 .001 .043 .051 .040
.7027† .1822† .9933† .7217† .6707† .7403†
Nd:YAG ⫽ neodymium:yttrium-aluminum-garnet; PCO ⫽ posterior capsule opacification. *Statistically significant. † No statistical significance.
Nd:YAG ⫽ neodymium:yttrium-aluminum-garnet; PCO ⫽ posterior capsule opacification. *Statistically significant. † No statistical significance.
rence of anterior capsule contraction, and 1 because of the presence of liquefied after-cataract. After capsulotomy, two eyes were excluded because of visual acuity worse than 20/40, and seven because of difficulty with data analysis. Accordingly, 90 eyes of 84 patients who met the inclusion criteria were included in the final analysis. Patient demographics of the two groups are shown in Table 1. No significant differences were found in age, sex, the ratio of left and right eyes, and interval between cataract surgery and capsulotomy. Mean prelaser and postolaser visual acuities in the excluded patient group were significantly worse than those in the included patient group. Of the 90 eyes, 33 had a polymethylmethacrylate IOL, 33 had an acrylic IOL, seven had a silicone IOL, and eight had a hydrogel IOL. We could not identify the type of IOL implanted in the other nine eyes, as these patients had
undergone cataract surgery elsewhere. Mean area of the Nd:YAG laser capsulotomy opening was 10.6 ⫾ 4.7 mm2. Mean visual acuity before Nd:YAG capsulotomy was 20/36, whereas that after capsulotomy was 20/22; this improvement was statistically significant (P ⬍.0001). Figures 1 and 2 demonstrate the mean prelaser and postlaser contrast sensitivity and glare sensitivity, respectively. Both mean contrast sensitivity and glare sensitivity improved significantly at all visual angles (P ⬍.0001). Table 2 lists the simple correlation between visual acuity and PCO value and area of the posterior capsule opening. Before capsulotomy, a strong correlation was found between the logMAR visual acuity and PCO value (Pearson r ⫽ 0.728; Figure 3). There was also a significant correlation between improvement in logMAR visual acuity and decrease in PCO value (r ⫽ 0.424). However, after
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TABLE 5. Mean (⫾ SD) Visual Acuity, Contrast Sensitivity, Glare Sensitivity, and PCO Value Before and After Nd:YAG Laser Capsulotomy in Patients Who Have Visual Acuity of 20/25 or Better
LogMAR visual acuity Contrast threshold (degrees) 6.3 4.0 2.5 1.6 1.0 0.7 Glare threshold (degrees) 6.3 4.0 2.5 1.6 1.0 0.7 PCO value (CCT)
Prelaser
Postlaser
P Value
0.060 ⫾ 0.042
0.006 ⫾ 0.025
.0016*
0.022 ⫾ 0.013 0.025 ⫾ 0.013 0.035 ⫾ 0.028 0.062 ⫾ 0.057 0.116 ⫾ 0.244 0.304 ⫾ 0.244
0.014 ⫾ 0.005 0.018 ⫾ 0.008 0.025 ⫾ 0.012 0.116 ⫾ 0.087 0.071 ⫾ 0.042 0.185 ⫾ 0.087
.1047† .1672† .4172† .1811† .0956† .1248†
0.037 ⫾ 0.028 0.043 ⫾ 0.028 0.059 ⫾ 0.046 0.094 ⫾ 0.079 0.201 ⫾ 0.186 0.499 ⫾ 0.731 22.9 ⫾ 12.6
0.025 ⫾ 0.013 0.026 ⫾ 0.013 0.036 ⫾ 0.021 0.055 ⫾ 0.037 0.121 ⫾ 0.107 0.306 ⫾ 0.286 3.7 ⫾ 5.2
.2826† .0757† .1418† .1195† .0688† .1303† ⬍.0001*
CCT ⫽ computer compatible tapes; LogMAR ⫽ logarithm of the minimal angle of resolution; Nd:YAG ⫽ neodymium:yttrium-aluminum-garnet; PCO ⫽ posterior capsule opacification; SD ⫽ standard deviation. *Statistically significant. † No statistical significance.
capsulotomy, no significant correlation was found between the logMAR visual acuity and the PCO value or area of the posterior capsule opening. Table 3 shows the simple correlations between contrast sensitivity and the PCO value before and after Nd:YAG laser capsulotomy. Before capsulotomy, a significant but weak correlation was found between contrast sensitivity and PCO value at visual angles of 6.3, 4.0, 2.5, 1.6, and 1.0 degrees. Pearson correlation coefficients were smaller than that between visual acuity and PCO value. After capsulotomy, no significant correlation was found between contrast sensitivity and PCO value or area of the capsulotomy opening. Table 4 shows the simple correlation between glare sensitivity and PCO value before and after Nd:YAG laser capsulotomy. Before capsulotomy, a moderate to weak correlation was found between glare sensitivity and PCO value at visual angles of 6.3, 4.0, and 2.5 degrees. The correlation coefficients were smaller than that between visual acuity and PCO value. After capsulotomy, no significant correlation was found between glare sensitivity and PCO value or the size of the capsulotomy opening. To assess the impairment in contrast sensitivity and glare sensitivity in patients with PCO who have relatively good visual acuity, 16 eyes with prelaser visual acuity of 20/25 or better were selected. Table 5 shows the mean 724
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TABLE 6. Correlation Coefficients (r) Between Contrast Sensitivity and Glare Sensitivity and PCO Value Before Nd:YAG Laser Capsulotomy in Patients Who Have Visual Acuity of 20/25 or Better Contrast Sensitivity
Glare Sensitivity
Visual Angle (Degrees)
Pearson r
P Value
Pearson r
P Value
6.3 4.0 2.5 1.6 1.0 0.7
.059 .303 .038 .100 .233 .052
.8287* .2538* .8880* .7112* .3847* .8481*
.053 .065 .067 .093 .048 .104
.8453* .8111* .8041* .7329* .8591* .7003*
Nd:YAG ⫽ neodymium:yttrium-aluminum-garnet; PCO ⫽ posterior capsule opacification. *No statistical significance.
visual acuity, contrast sensitivity, glare sensitivity, and PCO value before and after Nd:YAG capsulotomy. The mean visual acuity and PCO value improved significantly after capsulotomy, whereas no significant improvements were observed in contrast sensitivity or glare sensitivity at any visual angles. Furthermore, no significant correlation OF
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was found between contrast sensitivity or glare sensitivity and PCO value before or after capsulotomy (Table 6).
DISCUSSION OUR STUDY HAS DEMONSTRATED THAT VISUAL ACUITY,
contrast sensitivity, and glare sensitivity improve significantly after Nd:YAG laser capsulotomy. The PCO value, as measured using the Scheimpflug videophotogaphy system, also decreased significantly. Furthermore, the improvement in visual acuity was correlated significantly with the decrease in PCO value. These results clearly indicate that the visual functions are disturbed because of PCO and are improved by Nd:YAG laser capsulotomy. Before capsulotomy, visual acuity was strongly correlated with the degree of PCO, and although contrast sensitivity and glare sensitivity at most visual angles also were significantly correlated with PCO, the correlation was weaker than that of visual acuity. These results indicate that visual acuity reflects most relevantly the degree of PCO when patients with various degrees of PCO are included. After capsulotomy, no significant correlation was observed between visual acuity, contrast sensitivity, or glare sensitivity and the degree of PCO. Furthermore, these visual functions had no significant correlation with the area of the Nd:YAG laser capsulotomy opening, which varied considerably in this series. These results thus suggest that even relatively small capsulotomy openings may be sufficient to improve visual function. Most previous studies reported that contrast sensitivity and glare disability improved concomitant with visual acuity after capsulotomy.4 – 6 However, Tan and associates7 reported that the improvement in contrast sensitivity was poorly associated with that in visual acuity and, therefore, that contrast sensitivity testing is more sensitive than is visual acuity in the early stages of PCO. Furthermore, Sunderraj and associates8 also documented that glare disability is prominent in some patients who have good visual acuity. To see whether contrast sensitivity and glare sensitivity are necessarily impaired in the early stages of PCO, we examined these functions in patients with good visual acuity. When we studied patients who had a visual acuity of 20/25 or better, both visual acuity and the PCO value improved significantly after capsulotomy, but contrast sensitivity and glare sensitivity did not show significant improvement. Furthermore, contrast sensitivity and glare sensitivity did not correlate significantly with the PCO value before or after capsulotomy. Although some patients show markedly impaired contrast sensitivity or glare sensitivity despite good visual acuity, our results suggest that this does not hold true for any patients with slight PCO. A plausible explanation for this finding is that PCO generally occludes the entire pupillary area when it has VOL. 136, NO. 4
invaded into the retrolental space and therefore impairs visual acuity from a relatively early stage. Indeed, the pupillary area was entirely and equally covered by PCO in most cases in the present series. It has been reported that posterior subcapsular cataracts and early cataracts are associated with loss of contrast sensitivity and increased glare disability because of intraocular light scatter, despite good visual acuity.11–14 If we examine those eyes in which the pupillary area is only partially or unequally occuluded by very early stage PCO, contrast sensitivity and glare sensitivity may be more impaired than visual acuity.9 In conclusion, high-contrast visual acuity has a stronger association with the degree of PCO than does either contrast sensitivity or glare sensitivity and therefore is the most relevant outcome measure of the degree of PCO. When patients complain of blurred vision and have PCO, visual acuity is thought to be the most reliable measurement. However, in the very early stages of PCO, there are patients who show impaired contrast sensitivity or marked glare disability despite good visual acuity. From these results it is apparent that further study is necessary to examine contrast sensitivity and glare sensitivity in patients who have little or no PCO and who have good visual acuity.
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