Iris crypts Influence the Dynamic Changes of Iris

Abstract

Purpose : There is increasing evidence that the dynamic response of the iris during pupil dilation plays a crucial role in angle closure. Iris surface features (crypts, furrows and color) were previously reported to be correlated with the anatomical characteristics of the iris. However, the dynamic correlations to these surface features remain unclear. We hypothesized that variation within the surface features may underlie the differential response of the iris during pupil dilation.

Methods : This is a retrospective observational clinical study of 76 Chinese adults aged 50 years and over without ocular diseases. Study participants received eye examination where digital iris photographs were taken and graded for iris crypts and iris furrows following a grading scheme. Iris color was measured objectively, using the Commission Internationale de l’Eclairage (CIE) L* color parameter. Anterior segment was imaged by swept-source optical coherence tomography (Casia SS-1000 OCT, Tomey, Nagoya, Japan) under bright light and dark room conditions. Iris volumes in light and dark conditions were measured with custom semi-automated software and the change in iris volume was quantified. Angle opening distance (AOD) at 750 μm was measured using the built-in SS-OCT software. Associations of the change in iris volume after pupil dilation with underlying iris surface features in right eyes were assessed using linear regression analysis.

Results : In light condition, higher iris crypt grade was associated independently with smaller iris volume (β [change in iris volume in millimeters per crypt grade increment] = -1.10, 95% confidence interval (CI): -1.90 to -0.30; P = 0.008) and greater reduction of iris volume on pupil dilation (β [change in iris volume in millimeters per crypt grade increment] = 0.30, 95%CI: 0.10 to 0.50; P = 0.004), adjusted for age, gender, presence of corneal arcus, pupil size, and AOD. Iris furrows and color were not associated with iris volume in light condition or change in iris volume (all P > 0.05).

Conclusions : Our results are consistent with our hypothesis that eyes with smaller and less iris crypts lose less iris volume on pupil dilation. However, the dynamic responses were not related to either iris furrows or color. These findings highlight the potential role of iris crypts in the reduction of iris volume on pupil dilation, especially in angle closure.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.