Relationship Between Iris Surface Features and Angle Width in Asian Eyes

PURPOSE. To examine the associations between iris surface features with anterior chamber angle width in Asian eyes. METHODS. In this prospective cross-sectional study, we recruited 600 subjects from a large population-based study, the Singapore Epidemiology of Eye Diseases (SEED) study. We obtained standardized digital slit-lamp iris photographs and graded the iris crypts (by number and size), furrows (by number and circumferential extent), and color (higher grade denoting darker iris). Vertical and horizontal cross-sections of anterior chamber were imaged using anterior segment optical coherence tomography. Angle opening distance (AOD), angle recess area (ARA), and trabecular-iris space area (TISA) were measured using customized software. Associations of the angle width with the iris surface features in the subject's right eyes were assessed using linear regression analysis. RESULTS. A total of 464 eyes of the 464 subjects (mean age: 57.5 +/- 8.6 years) had complete and gradable data for crypts and color, and 423 eyes had gradable data for furrows. After adjustment for age, sex, ethnicity, pupil size, and corneal arcus, higher crypt grade was independently associated with wider AOD750 (beta [change in angle width per grade higher] = 0.018, P = 0.023), ARA750 (beta = 0.022, P = 0.049), and TISA750 (beta = 0.011, P = 0.019), and darker iris was associated narrower ARA750 (beta = 0.025, P = 0.044) and TISA750 (beta = 0.013, P = 0.011). CONCLUSIONS. Iris surface features, assessed and measured from slit-lamp photographs, correlated well with anterior chamber angle width; irises with more crypts and lighter color were associated with wider angle. These findings may provide another imaging modality to assess angle closure risk based on iris surface features.