Biometric Evaluation of Anterior Chamber Changes after Physiologic Pupil Dilation Using Pentacam and Anterior Segment Optical Coherence Tomography

Abstract

We evaluated changes in anterior chamber (AC) morphology and iris volume induced by physiological mydriasis in fellow eyes of acute angle-closure patients, and age-, sex-, and central AC depth-matched primary angle-closure suspects (PACS). In our study, 21 fellow eyes of patients with acute angle closure; 40 age-, sex-, and central AC depth-matched PACS eyes; and 40 age- and sex-matched normal open-angle eyes were imaged using a Pentacam and anterior segment optical coherence tomography (AS-OCT) under light conditions, and after 5 minutes of darkness using AS-OCT. Iris volume was estimated using AS-OCT and a customized image-processing software. Central AC depth, corneal curvature, axial length, and lens thickness did not differ significantly between the PACS and fellow eyes. When going from light to dark, angle opening distance at 500 μm decreased significantly more in fellow eyes than in PACS (-68% vs. -52%, P < 0.001). When going from light to dark, the mean iris volume increased significantly in the fellow eyes (from 45.34 ± 2.1 to 47.68 ± 3.2 mm(3), P < 0.01), whereas it decreased significantly in most PACS eyes (from 45.01 ± 2.2 to 42.11 ± 2.3 mm(3), P < 0.01), and in all open-angle eyes (from 44.68 ± 1.16 to 41.67 ± 1.20 mm(3), P < 0.01). Based on multivariate analysis, significant predictors of angle narrowing under darkness (relative change in angle-opening distance 500) were fellow eyes compared to PACS (β = -2.98, SE = 0.249, P = 0.005) and higher iris volume increase with pupil dilation (β = -3.146, SE = 0.432, P = 0.015). Under dark conditions, angles of fellow eyes closed dramatically more than did those of PACS. Iris volume increase per millimeter of pupil dilation is an independent predictor of angle narrowing in darkness.