To assess the impact of laser peripheral iridotomy (LPI) on forward-scatter of light and subjective visual symptoms and to identify LPI parameters influencing these phenomena.
Cohort study derived from a randomized trial, using an external control group.
Chinese subjects initially aged 50 or older and 70 years or younger with bilateral narrow angles undergoing LPI in 1 eye selected at random, and age- and gender-matched controls.
Eighteen months after laser, LPI-treated subjects underwent digital iris photography and photogrammetry to characterize the size and location of the LPI, Lens Opacity Classification System III cataract grading, and measurement of retinal straylight (C-Quant; OCULUS, Wetzlar, Germany) in the treated and untreated eyes and completed a visual symptoms questionnaire. Controls answered the questionnaire and underwent straylight measurement and (in a random one-sixth sample) cataract grading.
Main Outcome Measures
Retinal straylight levels and subjective visual symptoms.
Among 230 LPI-treated subjects (121 [58.8%] with LPI totally covered by the lid, 43 [19.8%] with LPI partly covered by the lid, 53 [24.4%] with LPI uncovered by the lid), 217 (94.3%) completed all testing, as did 250 (93.3%) of 268 controls. Age, gender, and prevalence of visual symptoms did not differ between treated subjects and controls, although nuclear (P<0.01) and cortical (P = 0.03) cataract were less common among controls. Neither presenting visual acuity nor straylight score differed between the treated and untreated eyes among all treated persons, nor among those (n = 96) with LPI partially or totally uncovered. Prevalence of subjective glare did not differ significantly between participants with totally covered LPI (6.61%; 95% confidence interval [CI], 3.39%–12.5%), partially covered LPI (11.6%; 95% CI, 5.07%–24.5%), or totally uncovered LPI (9.43%; 95% CI, 4.10%–10.3%). In regression models, only worse cortical cataract grade (P = 0.01) was associated significantly with straylight score, and no predictors were associated with subjective glare. None of the LPI size or location parameters were associated with straylight or subjective symptoms.
These results suggests that LPI is safe regarding measures of straylight and visual symptoms. This randomized design provides strong evidence that treatment programs for narrow angles would be unlikely to result in important medium-termvisual disability.
Proprietary or commercial disclosure may be found after the references.
Glaucoma is the second most common cause of blindness worldwide, affecting an estimated 60.5 million people in 2010, of whom 8.4 million were blind.1
Angle-closure glaucoma is 3 to 4 times as likely to be associated with blindness at the time of diagnosis compared with the open-angle form of the disease.2
The prevalence of glaucoma is expected to rise steeply as the world’s population continues to age.1
Laser peripheral iridotomy (LPI) often is used to achieve 1 or more of 3 related clinical goals in the treatment of angle closure: to reduce the risk of future acute attacks of glaucoma resulting from pupillary block, to lower intraocular pressure (IOP), or to promote configurational changes in the angle that may lessen the risk of formation of peripheral anterior synechiae and progression to chronic angle-closure glaucoma.3
Various visual symptoms
have been reported after LPI, including monocular blurring, shadows, ghost images, lines, glare, haloes, and spots.4
Spaeth et al5
reported visual symptoms
after LPI in 9% of eyes with completely covered LPI, in 26% with partially covered LPI, and 17.5% with fully exposed LPIs. Other authors4
have suggested that fully exposed and fully covered LPIs are less prone to visual
disturbances compared with those that are partially covered.
A large, randomized trial currently is underway in China to establish the efficacy of LPI treatment for narrow angles in reducing risk of IOP elevation, formation of peripheral anterior synechiae, and occurrence of acute attacks of angle-closure glaucoma.8
Given the importance of glaucoma as a cause of blindness in China,2
there is much interest in large-scale programs to screen for and treat patients with narrow angles, if the efficacy of early LPI can be established. An important prerequisite for such programs is a better understanding of the incidence of visually significant complications associated with treatment, as well as treatment parameters that minimize such side effects. Large-scale mobilization for LPI treatment likely will depend on such knowledge.
This article reports a convenience sample of patients from the Zhongshan Angle-Closure Prevention (ZAP) Trial, and a set of age- and gender-matched controls. All ZAP participants underwent LPI in 1 eye chosen at random and slit-lamp cataract grading, and those participating in the current study also underwent photographic documentation of the size and location of the LPI and measurement of retinal straylight11
in the treated and untreated eyes. Control subjects underwent straylight
measurement and (in a random sample) cataract grading, and both treated subjects and controls were asked aboutsymptoms
of glare or other visual
phenomena. The objectives of the current report were: (1) to assess the impact of LPI on glare by comparing measured retinal straylight
in treated and untreated eyes of subjects receiving unilateral LPI and by comparing the prevalence of subjective reports of glare symptoms
and other visual
phenomena among treated subjects and matched controls; and (2) to identify treatment parameters, including size and location of the LPI, associated with lower incidence of visual symptoms
and smaller retinal straylight
values, while adjusting for potential confounders such as cataract.
Patients and Methods
The full protocol for the ZAP Trial and the protocol for additional photographs and testing for the current study were reviewed separately and were approved by both the Ethics Committee of the Zhongshan Ophthalmic Center, Guangzhou, China, and the institutional review board of the Johns Hopkins Medical Institutions, Baltimore, Maryland. All subjects gave written informed consent for participation in the study, and the tenets of the World Medical Association’s Declaration of Helsinki were followed throughout.
Recruitment and Procedures for Laser Peripheral Iridotomy and Cataract Grading in the Zhongshan Angle-Closure Prevention Trial
The protocol for the ZAP Trial has been described elsewhere in detail8
and is summarized here for reference. Subjects 50 years of age and older and 70 years of age and younger with best-corrected vision of 6/12 or better and 6 or more clock hours of angle circumference in which the pigmented trabecular meshwork was not visible in both eyes by static gonioscopy were recruited from an urban district in Guangzhou, Southern China. Guangzhou is China’s third-largest city, with a population of 12.8 million in 2010, and has one of the highest mean gross domestic products in the country at $13 111 in 2009. A total of 10 083 persons meeting the age requirements underwent screening to identify eligible subjects. Recruitment was by means of flyers and television advertisements offering free eye examinations. Subjects were assigned to receive LPI in 1 eye selected at random. Exclusion criteria included severe health problems or the presence in either eye of any peripheral anterior synechiae, glaucomatous optic neuropathy, media opacity precluding LPI, clinical evidence of a prior acute attack of angle-closure glaucoma, prior intraocular surgery, penetrating ocular injury, IOP of more than 21 mmHg, or a rise in IOP of more than 15 mmHg after dilation or dark prone testing.
Presenting visual acuity was measured separately for each eye using an Early Treatment Diabetic Retinopathy Study logarithm of the minimum angle of resolution E chart (Precision Vision, Villa Park, IL). Best-corrected acuity after subjective refraction by an optometrist was measured for all subjects with presenting visual acuity worse than 6/12 in either eye.
All ZAP Trial subjects underwent an LPI in 1 eye at random, 15 minutes after pretreatment with brimonidine purite 0.15% and pilocarpine 2%. The LPI was carried out by a recently trained junior doctor with the use of an Abraham lens (Ocular Instruments, Bellevue, WA). A neodymium:yttrium–aluminum–garnet laser (Visulas YAG III; Carl Zeiss Meditec, Dublin, CA) with an initial setting of 1.5 J was used to create a patent iridotomy of at least 200 μm in diameter. No laser pretreatment was used. Wherever possible, the LPI was placed in a crypt or other area where the iris appeared thinnest and was positioned beneath the superior lid. The IOP was checked 1 hour after completion of the procedure, with pressure-lowering treatment administered as needed according to a predefined protocol. Dexamethasone drops were used hourly during the day for 24 hours after surgery and then 4 times daily for 1 week.
At 2 weeks and 6, 18, 30, and 42 months after LPI treatment, all ZAP Trial subjects underwent cataract grading using the Lens Opacity Classification System III (LOCS III)12
at the slit lamp after pharmacologic dilation of the pupil and with reference to standard photographs. Grading was carried out by 3 trained graders who underwent an initial period of standardization and additional training sessions by 1 of the investigators (N.C.) over the course of the study. Treated subjects in the current study were recruited from the ZAP Trial and underwent all testing reported here at the 18-month examination in the ZAP Trial.
Selection of Controls
Age- (within 5 years) and gender-matched controls were selected from among spouses and relatives of patients seeking treatment at the Cataract Service at the Zhongshan Ophthalmic Center (n = 129); from among patients recruited initially for the ZAP Trial and meeting all study criteria except for narrow angles (n = 66); and from outreach visits to retirement facilities in Guangzhou (n = 73) to supplement the number of older controls. All controls were subject to the same exclusion criteria as outline above for participants in the ZAP Trial and underwent measurement of visual acuity and assessment of retinalstraylight and subjective visual symptoms (see below) according to the same protocol as treated subjects. In addition, a randomly selected one-sixth sample (n = 43) of controls underwent cataract grading using the LOCS III system at the slit lamp after dilation of the pupil.
Iris Photographs and Photogrammetry
Digital slit-lamp photography of the iris (SL-D7; Topcon, Tokyo, Japan) was carried out on the treated eye of each ZAP Trial subject using diffuse illumination of the cornea at the lowest illumination setting to avoid miosis of the pupil and changes in lid position in response to photophobia. A single photograph was obtained of a field including the subject’s upper and lower lids in their normal position, and whatever portion of the iris was visible between them, with the eye in primary gaze. A millimeter ruler, glued to the end of a tongue depressor held perpendicular to the floor, was held next to, but not touching, the eye in the same plane as the iris when the picture was obtained (Fig 1
). A second picture at the same illumination and magnification was obtained with the eye looking downward in reading position. A third picture was obtained with the patient’s upper lid retracted superiorly with the photographer’s index finger, such that the limbus at both 6 and 12 o’clock was visible clearly.
Photographs showing the methodology for measuring the distance from laser peripheral iridotomy (LPI) center to the lid margin. The first column shows 2 eyes in forward gaze with the lid in normal position: in (A) the LPI is fully uncovered by the lid, and in (B), it is fully covered. The second column displays the LPI (outlined in white) with the eyelid manually raised by the investigator. The third column shows the image with lid raised overlaid on the image with the lid in normal position, at 80% opacity. Images were aligned using the center of the pupil as a reference point. The smallest circle then was drawn that had its center at the center of the LPI and would still contact the lid margin in normal position: above the LPI in (A) and below the LPI in (B). The distance from LPI center to the eyelid is represented by the circle’s radius.
The digital image files were exported to a desktop computer, and Photoshop CS3 Extended (version 10.0.1; Adobe Systems, Inc., San Jose, CA) was used to measure the area, circumference, and vertical and horizontal diameter of the LPI; the shortest distances from the center of the LPI to the limbus, lower margin of the upper lid, and pupil center in millimeters; and the angle created by a line extending from the center of the pupil to the center of the LPI and a line normal to the floor, in degrees (this latter value was expressed as clock hours during analysis). The image of the millimeter ruler in each file and the Set Measurement Scale command in Photoshop was used to set the scale in pixels per millimeter. The measurement of LPIs covered by the lid was carried out by superimposing the image with the lid in normal position over that with the lid retracted manually, with the former at 80% opacity (Fig 1
). The absolute value of the shortest distance from the center of the LPI to the lid margin was used in all calculations. In addition, 2 graders (X.Y., M.P.) categorized the LPI in each image with the lids in normal position as being completely covered by the lid, partially covered by the lid, or completely uncovered by the lid.
Measurement of Retinal Straylight and Subjective Visual Symptoms
All treated subjects and controls were asked about glare symptoms
using 2 validated questions from the National Eye Institute Refractive Error Quality of Life Instrument, version 1.0,14
which had been translated into the Mandarin and Cantonese dialects of Chinese. In addition, all subjects were asked specifically about the presence or absence of any of the following visual
phenomena, as described by Spaeth et al5
: shadows, ghost images, lines, glare, haloes, and spots. A positive response to either the National Eye Institute Refractive Error Quality of Life Instrument glare questions or the question about other visual
phenomena was considered to be evidence of a subjective visual
All LPI-treated participants and controls next underwent testing of retinal straylight
levels in both eyes (C-Quant; OCULUS, Wetzlar, Germany). The methodology and rationale for the use of this machine has been described in detail elsewhere.15
A forced-choice protocol is used to estimate levels of forward-scattered (“stray”) light striking the retina with reference to light of a standard intensity as an objective measure of glare. The nontested eye is patched, and a trial lens 2 diopters (D) more hyperopic than the patient’s distance prescription is placed over the tested eye if the subject’s distance acuity is worse than 6/60 (no study subjects actually met this standard for refractive correction during testing). The eye to be tested was placed close to the eye piece, maintaining a minimal distance, and subjects were asked to compare 2 half fields in the center of the field, indicating which one was flickering more strongly. The test required an average of 3 to 4 minutes for both eyes. Tests flagged as unreliable by the machine were repeated for a total of up to 3 times per eye, and subjects were excluded if a reliable test could not be obtained in 1 or more eyes. On the basis of previous published studies,15
including some 20 000 measurements, it was decided to exclude subjects with a straylight
score of less than 0.5 log (degrees2
/steradian) in either eye, assuming these to be erroneous measurements, because values in this range are unlikely to represent genuine, physiologically meaningful results.
Data analyses were performed using the Stata statistical software package (Stata Corporation, College Station, TX). All continuous data were presented in the form of mean±standard deviation, statistical tests were 2-sided, and the level of significance was set at 0.05. Differences in qualitative and categorical data between groups were compared using the chi-square test. The association between various independent variables and the 2 principal study outcomes (presence of subjective glare symptoms and straylight score as a continuous variable) was analyzed by logistic and linear regression models, respectively.
Among 230 subjects recruited from the ZAP Trial, 217 (94.3%) were able to complete reliable straylight
testing in both eyes, and all (100%) completed the questionnaire, iris photography, and cataract grading. Among 268 controls, all (100%) completed the questionnaire and 250 (93.3%) completed straylight
testing. Those not completing testing included 3 ZAP Trial subjects and 0 controls excluded on the basis of straylight
scores of less than 0.5 log (degrees2
/steradian) on 3 successive tests in both eyes. The mean age and gender distribution did not differ between those completing straylight
testing and those unable to do so for either treated subjects or controls. Among 43 control subjects (17.2%) selected at random to undergo slit-lamp cataract grading, all (100%) completed grading. The 217 LPI-treated subjects and 250 age- and gender-matched controls with complete data form the basis for all remaining analyses except where indicated. There were no statistically significant differences between LPI-treated persons and controls with regard to age, gender, or subjective report of glare orvisual
phenomena (Table 1
Table 1. Comparison of Characteristics of Subjects Undergoing Laser Peripheral Iridotomy and Age- and Gender-Matched Controls
The LOCS III cataract grades differed significantly comparing the treated eyes of ZAP Trial subjects and right eyes of controls for nuclear opalescence (treated subjects, 84 [38.7%] ≥3.0 on a scale of 0–5; controls, 3 [7.0%]; P<0.01) and cortical cataract (treated subjects, 37 [20.7%] ≥2.5 on a scale of 0–5; controls: 3 [7.0%]; P = 0.03), but not posterior subcapsular cataract (no treated subjects or controls with grade ≥2.0 on a scale of 0–5; P = not significant).
describes the size, location, and position relative to the lid of LPIs among 217 ZAP Trial subjects. A total of 121 subjects (55.8%) had LPIs that were totally covered by the lid, based on iris photographs with the lid in normal position, whereas 43 (19.8%) were partially covered and 53 (24.4%) were uncovered (Table 2
). The mean ± standard deviationstraylight
scores for eyes with totally covered, partially covered, and totally uncovered LPIs were 1.28±0.31, 1.20±0.21, and 1.24±0 .21 log (degrees2
/steradian), respectively. (A higher score indicates more straylight
or glare.) The mean straylight
score for eyes with totally covered LPIs did not differ significantly from that for eyes with LPIs that were partially covered (P
>0.3) or totally uncovered (P
>0.3). Among subjects with totally covered, partially covered, and totally uncovered LPIs, 6.61% (n = 8), 11.6% (n = 5), and 9.43% (n = 5), respectively, reported glare or other visual
phenomena. These proportions did not differ significantly from one another.
Table 2. Characteristics of Laser Peripheral Iridotomy (LPI) Procedures among Treated Subjects
*An LPI at exactly 3:00 or 9:00 would be at 90 degrees; an LPI at exactly 12:00 would be at 0 degrees.
Neither the mean presenting logarithm of the minimum angle of resolution visual
= 0.18, paired t
test) nor the meanstraylight
= 0.77, paired t
test) differed between the treated and untreated eyes of all ZAP subjects, nor did the meanvisual
= 0.28, paired t
test) or straylight
= 0.19, paired t
test) differ when comparing only the treated and untreated eyes of 96 subjects with partially or totally uncovered LPIs (Fig 2
; Table 3
). Mean visual
acuity was better andstraylight
scores were higher (more glare) among controls versus treated subjects, whether all 217 subjects (visual
= 0.004) or only the 96 subjects with partially or totally uncovered LPIs (visual
scores, both P
<0.001) were considered (Table 3
). These differences remained when adjusting for LOCS III cataract grade (data not shown).
Table 3. Characteristics of Eyes Treated with Laser Peripheral Iridotomy (LPI) Compared with Untreated Eyes of Subjects and Right Eyes of Controls
logMAR = logarithm of the minimum angle of resolution; SD = standard deviation.
Higher logMAR visual
acuity and lower straylight
scores are better.
Separate multivariate regression models were created for the 2 main study outcomes: straylight
score (treated eye for ZAP Trial subjects and right eye for controls) and answering yes to the question about glare or visual
phenomena. In univariate analyses, older age (P
= 0.03) and worse cortical cataract grade (P
= 0.003) were associated significantly with higherstraylight
score, and none of the potential predictors was associated significantly with a report of glare or visual
phenomena (Table 4
). In multivariate analyses, only a greater cortical cataract grade (P
= 0.01) was associated with higher straylight
score, and there were no significant predictors of subjective glare symptoms
. Neither presenting visual
acuity, gender, grades for other types of cataract, nor any of the parameters describing size or location of the LPI was significantly predictive of eitherstraylight
score or subjective glare report. The LPI parameters analyzed included: LPI vertical and horizontal diameter, circumference, and area; LPI distance to the pupil center, limbus, and lid margin; and LPI location expressed as clock hour and as totally covered versus partially or totally uncovered by the lid (Table 4
Table 4. Multiple Regression Models of Potential Predictors of a Positive Subjective Symptom Report of Glare (Logistic Regression) and of Straylight Score (Linear Regression)
LPI = laser peripheral iridotomy; VA = visual acuity.
Boldface values indicate statistical significance at the P<0.05.
No evidence of a significant increase in retinal straylight
or subjective symptoms
of glare or other visual
phenomena associated with LPI were found in the current study. Measured levels of straylight
did not differ between the treated and untreated eyes of ZAP Trial subjects, and the prevalence of visual symptoms
did not differ between ZAP Trial subjects and controls. Although there have been case reports of patients with new visual symptoms
such as monocular diplopia and blurred vision arising immediately after LPI,4
the finding that such phenomena are rare is consistent with previous large studies of glare and LPI. Murphy and Trope4
described vision symptoms
among 2.7% of persons undergoing LPI, well below the background rate of such phenomena observed among controls in the current study (10.0%). Spaeth et al5
actually found a higher prevalence of visual symptoms
among 100 controls matched for age, gender, and presenting vision (66%) than among 93 patients having undergone LPI in 1 or both eyes (15%). Although many of the excess symptoms
among control patients were the result of nonspecific problems with blurred vision and glare, there was little evidence for visual
phenomena that were specific to treatment with LPI: 4 subjects in each group reported ghost images and crescents, and only 1 treated subject indicated seeing a line, a phenomenon that has been described as typical of post-LPI vision symptoms
Also, no consistent evidence was found of any association between objective measures of retinal straylight
or subjective glare on the one hand and position of the LPI relative to the lid margin or other ocular landmarks, such as the limbus or pupil, on the other. This is contrary to the finding in studies by Spaeth et al5
and Murphy and Trope4
of more common visualsymptoms
among LPIs that were partially covered by the lid (as opposed to fully covered or fully uncovered). However, it is in agreement with the results of Weintraub and Berke,16
who found no association between lid position and visual symptoms
after LPI. Discrepancies between the current and previous reports, all of which have included largely subjects of European descent, may be the result of fewer glare symptoms
among Chinese subjects in the current study because of their more heavily pigmented irides17
(although Spaeth et al5
reported that iris color was not a predictor of visual symptoms
in that study). Alternatively, the current cases were recruited at 18 months after their LPI, whereas those in the Spaeth et al5
study, for example, were recruited as soon as 1 month after surgery. It is possible that earlier examination in the present cohort might have detected more visual symptoms
or a clearer association between visual
phenomena and lid position. Cases in the current study represented a wide variety of LPI locations (Table 1
), with one quarter of LPIs between 9 and 10 o’clock or between 2 and 3 o’clock, and nearly half (96/217; 44%) partially or fully uncovered by the lid.
The finding that a number of parameters describing the size of the LPI were unassociated with either objective or subjective measures of glare is consistent with the report by Spaeth et al,5
although the current study based measurements on photogrammetry of digitized images, whereas Spaeth et al characterized LPIs into small, medium, and large based on observations at the slit lamp. All LPIs in the ZAP Trial were carried out by a junior doctor after 2 weeks of training8
to mimic better the conditions under which LPI likely would be performed in large, rural programs. Perhaps as a consequence there was substantial variation in the size of LPIs observed in the current study (Table 1
). It does not seem likely that an association between LPI size and glare outcomes was missed because of high uniformity of LPIs in the ZAP Trial.
The C-Quant device has been described in a recent review as potentially superior to other glare tests discussed, such as the Brightness Acuity Tester.19
This is in distinction to reviews of earlier glare testing devices, which conclude generally that they performed poorly and did not predict glare symptoms
The principal of straylight
testing as used in the C-Quant device has been found to be repeatable and sensitive.23
Beckman et al24
reported a correlation between straylight
testing and subjective measures of patients’ glare symptoms
using questionnaires, although a difference between the meanstraylight
scores of subjects with and without subjective glare symptoms
was not found among either the ZAP Trial subjects (P
= 0.24) or controls (P
= 0.15). The finding that straylight
as measured with the C-Quant device correlated most strongly with cortical cataract grade is consistent with clinical observations and the available literature.25
A high proportion of both ZAP subjects and controls (>90%) also were able to complete testing with the device.
To assess visual symptoms
that may be associated with LPI, questions related to glare from a previously validated instrument13
translated into Chinese were used, supplemented with descriptions of specific phenomena reported by Spaeth et al5
to be associated with LPI in that large series. No distinction between more general glare phenomena and those such as lines that may be more typical for LPI was made, in view of Spaeth et al having reported a significant overlap in visualsymptoms
between treated subjects and controls.
The strengths of the current study include its large size (the largest series describing visual
phenomena and glare in LPI patients and matched controls yet reported); the randomized, prospective design allowing the comparison of treated and untreated eyes in the same subject; objective measurement both of retinal straylight
and of various LPI parameters with digital images and photogrammetry; assessment of cataract as another potential determinant of glare, using a well-validated instrument12
; long-term follow-up; and testing in an ethnic group with a high burden of narrow angles, for whom the results of this study are highly relevant.
Weaknesses of the study also must be acknowledged. Controls differed in important ways (better presenting visual
acuity but higher straylight
scores) from ZAP Trial participants, and because of the limited examination protocol for controls, the factors underlying these differences cannot be explained fully. Despite the use of 2 different measures of glare, subjective and objective, a precise figure for prevalence of the phenomenon in this cohort cannot be given, and thus, for example, calculations of the number of persons who would be likely to experience significant vision problems in large screening programs cannot be made. The possibility that differences in culture, lifestyle, questionnaire used, daily activities, or a combination thereof may reduce the comparability of rates of subjective symptoms
of glare between this cohort and Western cohorts reported previously in the literature cannot be excluded. The National Eye Institute Refractive Error Quality of Life Instrument that was used14
has not, to the best of the authors’ knowledge, been validated in the Chinese language. Patients were examined well after LPI treatment, and thus the possibility of a higher prevalence of more short-term symptoms
cannot be ruled out. Finally, the power and length of follow-up of the current substudy of the ZAP Trial is not sufficient to assess the prevalence and severity of other potential complications of LPI, such as lens opacity. Monitoring for such complications is underway in the ongoing ZAP Trial.
Nonetheless, this study has clear relevance for potential programs to screen and treat narrow angles in China. If the ZAP Trial and other trials do in fact demonstrate that early treatment with LPI substantially reduces the risk of vision-threatening complications of narrow angles, the current study suggests that such treatment, even in the hands of a junior physician with relatively modest training, is unlikely to be associated with a significant burden of glare or other vision symptoms. This study of cataract after LPI, another potentially important complication, is ongoing in the ZAP Trial.
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- Glaucoma in China: how big is the problem? . . Br J Ophthalmol . 2001;85:1277–1282
- Peripheral iridotomy for angle-closure glaucoma . . In: Shaarawy TM , Sherwood MB , Hitchings RA , Crowston JG editor. Glaucoma (Surgical Management) . vol. 2: Shanghai, China: Saunders Elsevier; 2009;p. 61–70
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- Ocular media clarity and straylight . . In: Dartt DA , Besharse JC , Dana R editor.Encyclopedia of the Eye . vol. 3: London: Academic; 2010;p. 173–183
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- LOCS III examination at the slit lamp, do settings matter? . . Ophthalmic Epidemiol .2003;10:259–266
- Psychometric properties of the National Eye Institute-Refractive Error Quality of Life Instrument . Ophthalmology . 2003;110:2292–2301
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- Dependence of intraocular straylight on pigmentation and light transmission through the ocular wall . . Vision Res . 1991;31:1361–1367
- Grading of iris color with an extended photographic reference set . . J Optom .2008;1:36–40
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