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 mu m (IT750) and 2000 mu m (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.