Mingguang He

Lens Vault, Thickness, and Position in Chinese Subjects with Angle Closure

PURPOSE To investigate the association of lens parameters-specifically, lens vault (LV), lens thickness (LT), and lens position (LP)-with angle closure. DESIGN Prospective, comparative study. PARTICIPANTS One hundred two Chinese subjects with angle closure (consisting of primary angle closure, primary angle-closure glaucoma, and previous acute primary angle closure) attending a glaucoma clinic and 176 normal Chinese subjects with open angles and no evidence of glaucoma recruited from an ongoing population-based cross-sectional study. METHODS All participants underwent gonioscopy and anterior-segment optical coherence tomography (AS OCT; Carl Zeiss Meditec, Dublin, CA). Customized software was used to measure LV, defined as the perpendicular distance between the anterior pole of the crystalline lens and the horizontal line joining the 2 scleral spurs, on horizontal AS OCT scans. A-scan biometry (US-800; Nidek Co, Ltd, Tokyo, Japan) was used to measures LT and to calculate LP (defined as anterior chamber depth [ACD] +1/2 LT) and relative LP (RLP; defined as LP/axial length [AL]). MAIN OUTCOME MEASURES Lens parameters and angle closure. RESULTS Significant differences between angle-closure and normal eyes were found for LV (901±265 vs. 316±272 μm; P<0.001), LT (4.20±0.92 vs. 3.90±0.73 mm; P = 0.01), LT-to-AL ratio (0.18±0.04 vs. 0.16±0.03; P<0.001), ACD (2.66±0.37 vs. 2.95±0.37 mm; P<0.001), and AL (22.86±0.93 vs. 23.92±1.37 mm; P<0.001), but no significant differences were found for LP (4.76±0.51 vs. 4.90±0.54 mm; P = 0.34) or RLP (0.21±0.02 vs. 0.20±0.02; P = 0.14). After adjusting for age, gender, ACD, LT, and RLP, increased LV was associated significantly with angle closure (odds ratio [OR], 48.1; 95% confidence interval [CI], 12.8-181.3, comparing lowest to highest quartile), but no association was found for LT (OR, 1.78; 95% CI, 0.76-4.16), LP (OR, 1.94; 95% CI, 0.59-6.31), or RLP (OR, 2.08; 95% CI, 0.66-6.57). There was low correlation between LV and LT (Pearsons correlation coefficient [PCC], 0.17), between LV and RLP (PCC, 0.08), or between LV and LP (PCC, 0.2). CONCLUSIONS Eyes with angle closure have thicker lenses with greater LV compared with normal eyes. The LV, which represents the anterior portion of the lens, is a novel parameter independently associated with angle closure after adjusting for age, gender, ACD, and LT.

Effect of Time Spent Outdoors at School on the Development of Myopia Among Children in China: A Randomized Clinical Trial

IMPORTANCE Myopia has reached epidemic levels in parts of East and Southeast Asia. However, there is no effective intervention to prevent the development of myopia. OBJECTIVE To assess the efficacy of increasing time spent outdoors at school in preventing incident myopia. DESIGN, SETTING, AND PARTICIPANTS Cluster randomized trial of children in grade 1 from 12 primary schools in Guangzhou, China, conducted between October 2010 and October 2013. INTERVENTIONS For 6 intervention schools (n = 952 students), 1 additional 40-minute class of outdoor activities was added to each school day, and parents were encouraged to engage their children in outdoor activities after school hours, especially during weekends and holidays. Children and parents in the 6 control schools (n = 951 students) continued their usual pattern of activity. MAIN OUTCOMES AND MEASURES The primary outcome measure was the 3-year cumulative incidence rate of myopia (defined using the Refractive Error Study in Children spherical equivalent refractive error standard of ≤-0.5 diopters [D]) among the students without established myopia at baseline. Secondary outcome measures were changes in spherical equivalent refraction and axial length among all students, analyzed using mixed linear models and intention-to-treat principles. Data from the right eyes were used for the analysis. RESULTS There were 952 children in the intervention group and 951 in the control group with a mean (SD) age of 6.6 (0.34) years. The cumulative incidence rate of myopia was 30.4% in the intervention group (259 incident cases among 853 eligible participants) and 39.5% (287 incident cases among 726 eligible participants) in the control group (difference of -9.1% [95% CI, -14.1% to -4.1%]; P < .001). There was also a significant difference in the 3-year change in spherical equivalent refraction for the intervention group (-1.42 D) compared with the control group (-1.59 D) (difference of 0.17 D [95% CI, 0.01 to 0.33 D]; P = .04). Elongation of axial length was not significantly different between the intervention group (0.95 mm) and the control group (0.98 mm) (difference of -0.03 mm [95% CI, -0.07 to 0.003 mm]; P = .07). CONCLUSIONS AND RELEVANCE Among 6-year-old children in Guangzhou, China, the addition of 40 minutes of outdoor activity at school compared with usual activity resulted in a reduced incidence rate of myopia over the next 3 years. Further studies are needed to assess long-term follow-up of these children and the generalizability of these findings. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00848900.

A survey of blindness and cataract surgery in Doumen County, China.

PURPOSE To assess blindness prevalence and that caused specifically by cataract in rural southern China. DESIGN Population-based, cross-sectional study. PARTICIPANTS A total of 5342 persons older than 50 years of age. METHODS Visual acuity and eye examinations were performed in the summer of 1997 in a random sample of villages in Doumen County. Differences in blindness prevalence associated with age, gender, and education were explored using logistic regression. The survey was preceded by a pilot study in which operational methods were refined and quality assurance measures were performed. MAIN OUTCOME MEASURES Distance visual acuity and lens status. RESULTS Bilateral blindness (presenting visual acuity < 0.10) was found in 4.37% (95% confidence interval, 3.67%-5.06%). Blindness was associated with increasing age (P < 0.001) and with the lack of education (P < 0.01). Cataract was the principal cause of blindness in at least one eye in 61.5% of blind people, with refractive error responsible for another 10%. An estimated 40% of the cataract blind were operated on; surgical coverage was lowest among the elderly, women, and those without schooling, although not at statistically significant levels. CONCLUSIONS Despite the increased attention given to eye care in Doumen County, blindness remains a major public health problem. Cataract surgery is reaching fewer than half of those who could benefit from it.

Iris cross-sectional area decreases with pupil dilation and its dynamic behavior is a risk factor in angle closure.

PurposeTo estimate the change in iris cross-sectional (CS) area with pupil dilation using anterior segment optical coherence tomography comparing eyes with angle closure (AC) to open angle glaucoma (OAG). MethodsSixty-five patients from the Wilmer Glaucoma service, 36 with definite or suspected OAG and 29 with definite or suspected AC, underwent anterior segment optical coherence tomography imaging under 3 conditions (pupil constriction to light, physiologic dilation in the dark, and after pharmacologic dilation). The nasal and temporal iris CS areas were measured with custom software, 3 times in each of 4 meridians. The principal outcome variables were iris CS area and change in iris CS area/mm pupil diameter change. The relation of these parameters to potential variables that would influence iris area was estimated by multivariate regression. ResultsCS area was smaller in eyes with larger pupil diameter, those that had undergone trabeculectomy, and those of European-derived persons (P<0.05 for all in a univariate analysis). In a multivariate model with CS area as the dependent variable, larger pupil diameter (with a 0.19 mm2 decrease in CS area for each 1 mm of pupil enlargement, P=0.0002), and trabeculectomy remained significant factors. In a second multivariate model, AC irides had less change in CS area/mm pupil enlargement than OAG or OAG suspects (P=0.01). Change in iris CS area was essentially complete in 5 seconds (n=10 eyes). ConclusionsThe iris loses nearly half its volume from a pupil diameter of 3 to 7 mm, probably by eliminating extracellular fluid. Smaller iris CS area change with physiologic pupil dilation is a potential risk factor for AC. Dynamic iris CS area change deserves testing as a prospective indicator of AC.

Quantitative Iris Parameters and Association with Narrow Angles

PURPOSE To investigate the relationship between quantitative iris parameters (iris curvature [I-Curv], iris area [I-Area], and iris thickness) and the presence of narrow angles. DESIGN Cross-sectional, community-based study. PARTICIPANTS We recruited 2047 subjects >50 years old without ophthalmic symptoms from a community clinic in Singapore. METHODS All subjects underwent gonioscopy and anterior segment optical coherence tomography (AS-OCT) under dark conditions. An eye was considered to have narrow angles if the posterior pigmented trabecular meshwork was not visible for >/=180 degrees on nonindentation gonioscopy with the eye in the primary position. Customized software was used on horizontal AS-OCT scans to measure I-Curv, I-Area, and iris thickness 750 mum (IT750) and 2000 mum (IT2000) from the scleral spur. The average of both temporal and nasal measured values of the right eye was used for analysis. MAIN OUTCOME MEASURES The association between iris parameters and narrow angles on gonioscopy. RESULTS Iris parameters from 1465 eyes (71.6%) were available for analysis. Of these, 315 subjects (21.5%) had narrow angles. The mean I-Curv (0.366 vs 0.259 mm; P<0.020), IT750 (0.476 vs 0.453 mm; P<0.001), and IT2000 (0.491 vs 0.482 mm; P = 0.010) were greater in persons with than without narrow angles. After adjusting for age, gender, anterior chamber depth, axial length, and pupil size, the greater I-Curv, I-Area, IT750, and IT2000 were significantly associated with narrow angles (odds ratio [OR] 2.5 and 95% confidence interval [CI], 1.3-5.1; OR, 2.7 and 95% CI, 1.6-4.8; OR, 2.6 and 95% CI, 1.6-4.1; OR, 2.7 and 95% CI, 1.5-4.7, comparing 4th with 1st quartile for each parameter, respectively). In stratified analysis, women and subjects aged >/=60 years had stronger associations for most iris parameters with narrow angles than men and younger subjects. CONCLUSIONS Quantitative iris parameters (I-Curv, I-Area, and iris thickness) are independently associated with narrow angles, particularly in women and older subjects. These data provide further insights into the pathogenesis of angle closure in Singaporeans. FINANCIAL DISCLOSURE(S) Proprietary or commercial disclosure may be found after the references.

Quantitative analysis of anterior segment optical coherence tomography images : the Zhongshan Angle Assessment Program

Aim: To describe a new image analysis method and software for anterior chamber images obtained by the anterior-segment optical coherence tomography (AS-OCT) and to assess its intraobserver and interobserver measurement reproducibility. Methods: Twenty 8-bit greyscale 600×300 AS-OCT images with apparent wide angles and 20 images with apparent narrow angles were consecutively selected from a database. Two glaucoma fellowship-trained ophthalmologists used proprietary image analysis software to analyse the images twice. Algorithms defined the borders and curvatures of anterior chamber (AC) structures and measured AC parameters using scleral spur location as the only observer input. The intraobserver and interobserver reproducibility of scleral spur location and angle parameters was calculated in terms of limits of agreement (LOA; mean of differences±1.96SD of differences) and coefficient of variation (CV; SD of differences/overall mean). Results: The analysis software successfully measured all parameters in all images. When the same image was assessed twice by the same grader, the mean differences ranged from 0 to 0.010 mm in linear measurements and 0.001 to 0.006 mm2 in angle area measurements. LOA tended to be greater in the wider angles. The upper and lower limit values of LOAs were approximately 1/5 to 1/4 of the overall mean. Measurements between two graders had a higher variance. Reproducibility in terms of CV was better in wide angles when compared with narrow angles. The reproducibility of scleral spur placement between observers was poorer in narrow angles (p = 0.001). About 50% of the interobserver variance in angle-area measurements was attributable to the variance of scleral spur placement, while this proportion was only 10–20% in linear measurements. Conclusions: Determination of angle parameters using semiautomated software leads to variability in measurement. Variability increases when more than one observer identifies the scleral spur. Variability differs in narrow and open angles, and so including both types is essential when evaluating angle-assessment software. A fully automated analysis and higher image resolution would likely improve quantification of Visante AS-OCT images.

Angle-closure glaucoma in East Asian and European people. Different diseases?

In contrast to the pattern of disease in Europeans, primary angle closure has a higher prevalence and tends to be asymptomatic in East Asians. The higher prevalence is attributed to differences in anterior chamber and angle anatomy. Several studies suggest that central anterior chamber depth is shallower in East Asians than in Europeans, although this is not universally accepted. It is debated whether pupil block is the predominant mechanism of angle closure in Asian people. Meaningful comparison between studies is currently hindered by differences in patient selection, examination technique, and case definition; however, the major scientific deficiency is the paucity of prospective followup data to give an insight into natural history of the disease. This review examines the data on prevalence, risk factors, and mechanism of angle closure. Special consideration is given to limitations of methodology in research to date, with the intention of developing more robust data in future studies.

The worldwide epidemic of diabetic retinopathy.

Diabetic retinopathy (DR), a major microvascular complication of diabetes, has a significant impact on the worlds health systems. Globally, the number of people with DR will grow from 126.6 million in 2010 to 191.0 million by 2030, and we estimate that the number with vision-threatening diabetic retinopathy (VTDR) will increase from 37.3 million to 56.3 million, if prompt action is not taken. Despite growing evidence documenting the effectiveness of routine DR screening and early treatment, DR frequently leads to poor visual functioning and represents the leading cause of blindness in working-age populations. DR has been neglected in health-care research and planning in many low-income countries, where access to trained eye-care professionals and tertiary eye-care services may be inadequate. Demand for, as well as, supply of services may be a problem. Rates of compliance with diabetes medications and annual eye examinations may be low, the reasons for which are multifactorial. Innovative and comprehensive approaches are needed to reduce the risk of vision loss by prompt diagnosis and early treatment of VTDR.

Anterior Chamber Angle Assessment Techniques

Angle-closure glaucoma is a leading cause of irreversible blindness. Diagnosis and treatment are intricately related to angle assessment techniques. This article reviews the literature on angle assessment and provides recommendations about optimal techniques based on the published evidence. Specifically, we review gonioscopy, ultrasound biomicroscopy, and anterior segment optical coherence tomography, all of which can be used to assess the anterior chamber angle directly. In addition, we discuss surrogate approaches to measuring the angle configuration, including limbal anterior chamber depth measurement, scanning peripheral anterior chamber depth measurement, and Scheimpflug photography.

Prevalence of myopia in urban and rural children in mainland China.

It has been well recognized that myopia more likely affects East Asians, particularly the Japanese and Chinese population. Although some studies have reported the prevalence of myopia in children living in mainland China, most of these studies are based on subjects with unknown representativeness, non-uniform definition, and measurement methods. A higher prevalence of myopia in urban settings, compared with rural settings, has been consistently suggested in several studies. This article intends to review the available data on the prevalence of myopia in Chinese children living in China; particular consideration is given to the evidence of urban–rural differences and their implications.