Cataract Progression after Prophylactic Laser Peripheral Iridotomy Potential Implications for the Prevention of Glaucoma Blindness Laurence S. Lim, MBBS,1 Rahat Husain, MRCOphth,1,2 Gus Gazzard, FRCOphth,1,2 Steve K. L. Seah, FRCS(Ed), FRCOphth,1 Tin Aung, PhD, FRCS(Ed)1,3 Purpose: To evaluate changes in lens opacity in the first year after prophylactic laser peripheral iridotomy (LPI) performed in fellow eyes of subjects with acute primary angle closure (APAC). Design: Prospective observational case series. Participants: Sixty Asian subjects with unilateral APAC. Methods: All fellow eyes underwent prophylactic LPI within the first week of presentation, followed by 1 week of topical steroids. The degree of lens opacity was graded at the slit-lamp examination using the Lens Opacity Classification System III (LOCS III) with standard color photographs as the reference for grading of lens opacity. This was performed 2 weeks, 4 months, and 12 months after LPI. Progression in lens opacity was defined as an increase in LOCS III grade by 2 or more units in any lens region. Main Outcome Measures: Lens Opacity Classification Sytem III grades in nuclear, cortical, and posterior subcapsular (PSC) regions. Results: Most patients were Chinese (85%) and female (63.3%), with an average age of 61.5 ⫾ 10.6 years. The mean baseline LOCS grades in the nuclear, cortical, and PSC regions were 3.58 ⫾ 0.74, 0.57 ⫾ 1.08, and 0.23 ⫾ 0.72, respectively. With 12 months of follow-up, 14 of the 60 eyes (23.3%; 95% confidence interval, 16.9 –29.7%) showed significant progression in any lens region. Progression in the nuclear, cortical, and PSC regions was documented in 5%, 6.7%, and 16.7% of cases, respectively. By use of logistic regression, the following factors were not found to be significant for cataract progression in any lens region: age, race, gender, history of hypertension or diabetes, presence of peripheral anterior synechiae or angle width at baseline, and total laser energy delivered. Conclusions: In fellow eyes of APAC, prophylactic LPI is complicated by significant cataract progression, mainly in the posterior subcapsular region. These findings may have implications for the role of prophylactic LPI in the prevention of angle-closure blindness. Ophthalmology 2005;112:1355–1359 © 2005 by the American Academy of Ophthalmology.
Primary angle-closure glaucoma (PACG) is a major cause of blindness and accounts for nearly half of the estimated 67 million people afflicted with glaucoma worldwide. Acute primary angle closure (APAC) is a potentially blinding presentation of PACG. The incidence of APAC seems to be particularly high in East Asia.1 The focus of therapy in APAC has been the relief of pupil block, either by surgical iridectomy or laser peripheral iridotomy (LPI). The concept of APAC as a disease with a predisposition to bilaterality2 Originally received: January 8, 2005. Accepted: February 27, 2005. Manuscript no. 2005-19. 1 Singapore National Eye Centre, Singapore. 2 Institute of Ophthalmology, London, United Kingdom. 3 National University of Singapore, Singapore. Correspondence to Dr Tin Aung, Glaucoma Department, Singapore National Eye Centre, 11 Third Hospital Avenue, Singapore 168751. E-mail:
[email protected]. © 2005 by the American Academy of Ophthalmology Published by Elsevier Inc.
led to the recommendation by Chandler3 that iridectomies be performed prophylactically in the fellow eye, a practice that has since become accepted as the standard of care.4 Changes in the angle configuration after LPI have been reported in Mongolian eyes with early angle closure.5 A median increase of 2 Shaffer grades was documented 1 to 3 years after LPI, and LPI was effective in preventing a rise in intraocular pressure (IOP) in 97% of eyes in the short term. However, once glaucomatous optic neuropathy associated with peripheral anterior synechiae (PAS) had occurred, LPI alone was less effective in controlling IOP.5 These findings suggest that treatment with LPI may arrest the progression of angle closure only if the procedure is done early enough, such as in eyes with narrow angles before the onset of PAS or glaucomatous damage. Because many PACG cases worldwide originate from countries where access to eye care is limited, a simple technique like LPI performed prophylactically for eyes with narrow angles is an attractive ISSN 0161-6420/05/$–see front matter doi:10.1016/j.ophtha.2005.02.026
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Ophthalmology Volume 112, Number 8, August 2005 proposition for the prevention of angle-closure blindness. However, such a procedure must not be associated with significant complications. Accelerated cataractogenesis after LPI has previously been proposed as a possible postoperative cause of decreased visual acuity,6 but no prospective study has, as yet, assessed cataract progression directly. Our study aimed to address this issue by using the Lens Opacity Classification System III (LOCS III) cataract grading system to give an objective measure of cataract progression after prophylactic laser iridotomy performed in asymptomatic fellow eyes of APAC subjects.
assessment.9 Subjects who underwent cataract surgery during the follow-up period were excluded from the analysis. At each visit, logarithm of the minimum angle of resolution (logMAR) visual acuity, IOP measurement, slit-lamp examination, and gonioscopy were also performed. The drainage angle was graded according to Shaffer’s convention10 in each quadrant. Under this convention, the angle width is graded “4” for wide open with the ciliary body being visible, and “0” represents a state where no angle structures are visible. The average angle width was calculated by adding the Shaffer grade in each quadrant and dividing by 4. Indentation gonioscopy was used to detect PAS, and the number of clock hours of PAS was recorded.
Statistical Analysis
Patients and Methods Subjects with unilateral APAC were recruited for the study. Written informed consent was obtained from all subjects, and the study had the approval of the Ethics Committee of the Singapore National Eye Centre and was performed in accordance with the tenets of the Declaration of Helsinki. Demographic characteristics, medical history, and ophthalmic data related to the APAC episode (such as laterality of affected eye, visual acuity, and presenting IOP) were recorded. Cases of APAC were defined by the following criteria: 1. Presence of at least 2 of the following symptoms: ocular or periocular pain, nausea and/or vomiting, and an antecedent history of intermittent blurring of vision with haloes. 2. Presenting IOP of ⬎28 mmHg (as measured by Goldmann applanation tonometry) and the presence of at least 3 of the following signs: conjunctival injection, corneal epithelial edema, mid-dilated unreactive pupil, and shallow anterior chamber. Cases of secondary angle closure such as lens subluxation or iris neovascularization were excluded. On presentation, APAC cases were initially managed by medical therapy to reduce the IOP. Once the acute episode had resolved with reduction of IOP and improved corneal clarity, sequential LPI7 was performed, usually within 24 to 48 hours of presentation. Prophylactic LPI was performed in fellow eyes of all cases within the first week of presentation. After LPI, all subjects received topical steroids 4 to 6 times a day for 1 week. The total amount of argon laser energy administered to each eye was calculated by multiplying the power (in watts) by the exposure length (in seconds) and the number of shots required. The total neodymium:yttrium–aluminum– garnet laser energy was determined by multiplying the energy setting per shot (in millijoules) by the number of shots. The total laser energy was then taken as the sum of the argon and neodymium:yttrium– aluminum– garnet energies. In fellow eyes, a total of 3 lens evaluations over a 1-year period were performed by 1 of 2 observers who were blinded to previous examinations: 2 weeks, 4 months, and 12 months after LPI. The degree of lens opacity was graded at slit-lamp examination with the subjects’ pupils fully dilated. The LOCS III standard color photographs were used as the reference for grading, and the grading nomenclature of nuclear color, nuclear opalescence, and cortical and posterior subcapsular (PSC) cataract was adopted.8 Grading was based on objective measures of color, density, and area, and each lens was assigned an integer grade with values from 0 to 6 (0 –7 in the case of nuclear opalescence). For nuclear cataracts, a composite score calculated from the average of the nuclear opalescence and nuclear color readings was taken. Progression in lens opacity was defined as an increase in LOCS grade by 2 or more units in any lens region from the week 2 baseline
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Normality assumptions for angle parameters were checked with the Kolmogorov–Smirnov 1-sample test. Comparisons between the affected and fellow eyes were assessed by the 2-sample test when normality assumption was satisfied; otherwise, the equivalent Mann–Whitney U test was applied. The paired t test (or the equivalent no parametric Wilcoxon signed rank test) was used to compare angle parameters between time points within the affected and fellow eyes. Multivariate analysis was performed by use of logistic regression to determine risk factors for lens opacity progression. The following variables were chosen as covariates on the basis that they were either known or potential risk factors: age, race, gender, history of hypertension or diabetes, angle width and presence of PAS at baseline, and total argon and yttrium–aluminum– garnet laser energy delivered. Statistical significance was assumed at the P⬍0.05 level.
Results A total of 90 subjects were recruited into the study and underwent the baseline examination. Of these, 5 subjects underwent cataract surgery during the study period and were excluded from analysis, and 25 subjects were lost to follow-up, leaving 60 subjects who completed 12 months of follow-up. The demographics of the 60 subjects are presented in Table 1. Most of the subjects were Chinese (85%) and female (63.3%), with an average age of 61.5 ⫾ 10.6 years. Table 1. Demographic Features of Study Subjects with Acute Primary Angle Closure Who Underwent Prophylactic Laser Peripheral Iridotomy Demographic Feature Gender Male Female Race Chinese Malay Indian Other Age (yrs) Mean ⫾ SD Range Median Laterality of affected eye Right Left SD ⫽ standard deviation.
No. of Subjects (n ⴝ 60) 22 (36.7%) 38 (63.3%) 51 (85%) 6 (10%) 2 (3.3%) 1 (17%) 61.5 ⫾ 10.6 35–99 62 23 (38%) 37 (62%)
Lim et al 䡠 Cataract Progression after Prophylactic Laser Peripheral Iridotomy Table 2. Baseline Ocular Parameters of Fellow Eyes of Study Subjects with Acute Primary Angle Closure 2 Weeks after Prophylactic Laser Peripheral Iridotomy Mean ⴞ Standard Deviation
Ocular Parameter LOCS III score Nuclear cataract score Cortical cataract score PSC cataract score Number of clock hours of peripheral anterior synechiae Average angle width (mean Shaffer grade) Intraocular pressure (mmHg) Mean axial length (mm) Mean anterior chamber depth (mm) Visual acuity (logMAR)
3.58 ⫾ 0.74 0.57 ⫾ 1.08 0.23 ⫾ 0.72 1.80 ⫾ 3.08 0.85 ⫾ 0.84 15.1 ⫾ 5.78 21.92 ⫾ 0.88 2.06 ⫾ 0.27 0.24 ⫾ 0.46
LOCS III ⫽ Lens Opacity Classification System III; logMAR ⫽ logarithm of the minimum angle of resolution; PSC ⫽ posterior subcapsular.
Table 4. Logistic Regression of Risk Factors for Cataract Progression (in any Region) after Prophylactic Laser Peripheral Iridotomy in Fellow Eyes of Subjects with Acute Primary Angle Closure
Age ⬎60 yrs Male gender Chinese race History of hypertension History of diabetes mellitus Presence of peripheral anterior synechiae at baseline Average angle width (mean Shaffer grade) at baseline ⱕ2 Total laser energy for laser peripheral iridotomy ⬎3 J
Odds Ratio
95% Confidence Interval
P Value
0.82 2.07 0.55 1.12 0.51 0.59
0.25–2.73 0.61–6.97 0.12–2.56 0.26–4.88 0.06–4.66 0.18–1.96
0.74 0.24 0.45 0.88 0.55 0.39
1.96
0.48–8.04
0.35
2.48
0.43–14.34
0.28
J ⫽ joules.
The baseline ophthalmic parameters are summarized in Table 2. The average angle width was 0.85 ⫾ 0.84, and the mean number of clock hours of PAS was 1.80 ⫾ 3.08. There were no cases of plateau iris. At presentation, the mean LOCS III grades in the nuclear, cortical, and PSC regions were 3.58 ⫾ 0.74, 0.57 ⫾ 1.08, and 0.23 ⫾ 0.72, respectively. Over 12 months of follow-up, 14 of the 60 eyes (23.3 ⫾ 3.3%, 95% confidence interval, 16.9 –29.7%) showed significant progression in any lens region (i.e., an increase in LOCS III score of 2 or more). Three of 60 (5%) cases showed progression in the nuclear region, 4 of 60 (6.7%) in the cortical region, and 10 of 60 (16.7%) in the PSC region. Three subjects (5%) showed progression in more than 1 region. The degree of lens opacity noted in the PSC region at baseline, month 4, and month 12 was 0.23 ⫾ 0.72, 0.33 ⫾ 0.99, and 0.75 ⫾ 1.49 (P⬍0.01), respectively. The baseline characteristics of the eyes that did and did not develop significant cataract progression are shown in Table 3. There were no significant differences detected between the 2 groups in any of the baseline parameters examined. Over the 12 months, the angle width and IOP remained the same, and the extent of PAS did not progress in eyes that had significant cataract progression develop. In eyes that showed significant progression of cataract, the change in visual acuity between baseline and month 12 was 0.11 ⫾ 0.32, which corresponds to a loss of roughly 1 line of Snellen Table 3. Baseline Characteristics of Eyes That Did and Did Not Develop Significant Cataract Progression (Defined as an Increase in Lens Opacity Classification System Score of 2 or More in Any Region) after Prophylactic Laser Peripheral Iridotomy
Average angle width (mean Shaffer grade) Extent of peripheral anterior synechiae (number of clock hours) Intraocular pressure (mmHg) Visual acuity (logMAR)
Significant Cataract Progression
No Significant Cataract Progression
P Value
0.9 ⫾ 1.2
0.8 ⫾ 0.8
0.87
2.0 ⫾ 3.2
1.7 ⫾ 3.1
0.78
14.9 ⫾ 2.5 0.26 ⫾ 0.52
20.5 ⫾ 10.7 0.24 ⫾ 0.45
0.06 0.84
logMAR ⫽ logarithm of the minimum angle of resolution.
visual acuity. In all, there were 22 subjects (36.7%) who lost 1 or more lines of Snellen acuity and 13 subjects (21.7%) who lost 2 or more lines. There were no cases of persistent corneal edema or retinal pathology detected that might otherwise account for the change in visual acuity. Eyes that did not have significant cataract progression develop had no change in visual acuity over 12 months (change in visual acuity ⫽ 0.02 ⫾ 0.21; P ⫽ 0.48). An analysis of potential risk factors for cataract progression in any lens region was conducted by use of a logistic regression model (Table 4). None of the factors analyzed was found to be significant.
Discussion Prior studies on the risk of cataract formation after iridectomy or LPI have used visual acuity as a surrogate marker of cataract progression. Reviews by Quigley6 and Robin and Pollack11 on the long-term safety of laser iridotomy have shown some visual loss presumptively attributed to cataract when followed up for 1.8 and 5 years, respectively. A recent study on an Asian population by Hsiao et al12 reported reduced visual acuity 6 months after LPI in 2.1% of cases, and this was, again, largely attributed to cataract formation. As far as we are aware, no study has as yet provided direct and objective evidence of cataract progression after LPI. Our study has shown that significant cataract progression can occur after LPI performed prophylactically in the fellow eyes of subjects with APAC. With 12 months of follow-up, 14 of the 60 eyes (23.3 ⫾ 3.3%) showed significant progression in any lens region. Progression in the nuclear, cortical, and PSC regions was documented in 5%, 6.7%, and 16.7% of cases, respectively. These are alarmingly high rates of cataract progression for a procedure that is widely regarded as relatively harmless and is performed prophylactically in many patients with narrow angles to prevent angle-closure glaucoma. By studying only asymptomatic fellow eyes in this study, the confounding element introduced by an acute angle-closure event was avoided. The angle characteristics and IOP in eyes with cataract progres-
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Ophthalmology Volume 112, Number 8, August 2005 sion also did not show any change over time to indicate a chronic angle-closure disease process. These factors are, thus, unlikely to have contributed significantly to the development of cataracts in our study population. Eyes in which significant cataract progression occurred were associated with a decrease in visual acuity of approximately 0.1 logMAR, corresponding to a loss of roughly 1 line of Snellen visual acuity. In contrast, eyes without significant cataract progression maintained essentially unchanged visual acuities. There was no significant increase in corneal edema or anterior chamber activity after LPI, and no cases of persistent corneal edema or post-LPI inflammatory activity were noted. Retinal pathology was also not detected, indicating that injury to other ocular structures from the LPI was unlikely to account for the deterioration in visual acuity. There were 22 subjects (36.7%) who lost 1 or more lines of Snellen acuity and 13 subjects (21.7%) who lost 2 or more lines. This loss occurred over 1 year, in contrast to the corresponding rates reported by Robin and Pollack11 (47% over 4 –5 years) and Quigley6 (15% over 2 years) over a longer study period. The cataract progression that occurred after prophylactic LPI is, thus, visually significant, which probably reflects the high proportion of PSC cataracts. Because ours was a middle-aged to elderly population, natural aging of the lens may have contributed to the progression in lens opacities found. Few longitudinal studies on the rate of senile cataract progression are available for comparison, and none exist for Asian eyes. The Barbados Eye Studies (BDES), conducted in a population of African origin, reported cataract progression rates in terms of an increase in cataract grading by ⱖ2 units.9 With 4 years of follow-up, progression was noted in the nuclear, cortical, and PSC regions in 2.2%, 14.5%, and 3.2% of subjects, respectively. The corresponding rates in our study over 1 year were 5%, 6.7%, and 16.7%, respectively. Of note is that the BDES used the LOCS II scale, which has been suggested to overestimate cataract grade compared with the LOCS III because of its ordinal nature.9 The higher progression rates that we found would, thus, be even more significant. The period of follow-up in our study was also much shorter than in the BDES. In addition, the profile of cataract progression by region in our study differs significantly from that in the BDES population. Using a different definition of cataract incidence as an increase in LOCS score by ⱖ2 units in eyes with baseline scores ⬍2 units, the corresponding rates in the BDES over 4 years were 9.2%, 22.2%, and 3.3% for nuclear, cortical, and PSC opacities,9 whereas the figures from the Longitudinal Study of Cataract after 5 years of follow-up were 8%, 7.7%, and 4.3%, respectively.13,14 In contrast, the incidence over 1 year calculated using this criterion in our study population was 0%, 8.2%, and 18.9%, respectively, demonstrating a marked preponderance of progression of PSC opacities. We were unable to uncover any factors that might otherwise account for the cataract progression. A review of the literature identified steroid use, diabetes mellitus, and hypertension as risk factors for cataract progression, in particular PSC cataract formation.15,16 In our study population, there were no cases that received prolonged steroids after LPI. Hypertension and diabetes mellitus were not found to
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be correlated with cataract development. Higher doses of laser energy were also not a risk factor for cataract progression, which suggests that direct injury to the lens by the laser is not responsible for the changes seen. Instead, alterations in the physiology of the eye induced by the LPI are postulated to be the cause of cataract progression. Several studies have demonstrated elevations in transforming growth factor- and other cytokines in the aqueous in the early post-LPI period,17,18 and transforming growth factor- is known to be a key mediator in the pathogenesis of PSCs in animal studies.19 –21 Because elevations in inflammatory mediators may be transient, it is possible that long-term changes in the aqueous may also underlie cataract progression. The aqueous contains transforming growth factor- inhibitory factors22 such as alpha2-macroglobulin, and decreased levels of these, perhaps through altered aqueous dynamics, may predispose the lens to cataract formation. Our study has some limitations. The main limitation of this study was the absence of a control group to evaluate cataract progression in untreated eyes. The grading of lens opacity by the LOCS III grading system is not truly objective and may be affected by interobserver and intraobserver variability. Because the study was focused on only the fellow eyes of APAC patients, these eyes may not be representative of other patients with asymptomatic angle closure, and the possibility of previous subclinical angleclosure episodes in these eyes cannot be ruled out. Similarly, it may be unfair to apply these findings to the population in general. The sample size was also relatively small, and this may have limited our ability to determine risk factors for cataract progression. Finally, because the study population was Asian (predominantly Chinese), it is not known whether the results could be applied to other racial groups. In conclusion, our study has shown that LPI performed as a prophylactic procedure in fellow eyes of APAC is associated with a high rate of development of visually significant cataracts. Unlike senile cataracts, the predisposition to progression of lens opacity in the posterior subcapsular region seems to be particularly strong. Although we do not dispute the importance of performing LPI in fellow eyes of APAC to prevent an acute attack,23 we believe our findings may have potential implications for the role of prophylactic LPI in the prevention of angle-closure blindness. Performing LPI in eyes with asymptomatic narrow angles (without glaucomatous optic nerve damage, PAS, or raised IOP) to prevent PACG may cause further morbidity from cataract. Further studies are needed to evaluate the safety of LPI before the procedure can be advocated in this situation.
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