Dynamic changes in iris parameters under physiological conditions -development of a predictive model of angle closure risk

Abstract

Purpose : To evaluate changes in anterior chamber (AC) morphology induced by physiological changes between light and dark in eyes of patients with PAC (Primary Angle Closure), PACS (Primary Angle Closure Suspects) and control subjects without ocuar pathology and to identify risk factors associated with primary angle closure using swept-source anterior segment optical coherence tomography (SS-OCT) measurements of the iris.

Methods : Longitudinal prospective study of 39 PAC/PACS subjects and 19 normal controls. Participants underwent gonioscopy and SS-OCT (Tomey Corporation, Nagoya, Japan). Customized software (Tomey Corporation, Nagoya, Japan) was used to measure anterior chamber parameters in dark and light conditions.

Results : The increase in pupil diameter from light to dark was associated with iris volume decrease in all eyes in this study with stronger correlation in control eyes (R²= 0.645) than in PACS eyes (R²= 0.363) and PAC eyes (R²= 0.189). Iris curvature change from light to dark was most pronounced in PACS eyes (mean, 0.034mm; p<0.01) compared to either control (mean, 0.006mm; p<0.09) or PAC eyes (mean 0.013mm; p<0.05). Multivariate regression analysis showed that in control eyes, change in pupil diameter was the only variable significantly associated with change in iris volume (R²= 0.648), while in PACS eyes both pupil diameter and iris curvature were moderately associated with changes in iris volume (R²= 0.397) and no variables showed significant association with iris volume change in PAC eyes (R²= 0.199). In PACS eyes, pupil diameter change from light to dark conditions showed stronger correlation with increase in iridotrabecular contact increase (R²= 0.455) compared to PAC eyes (R²= 0.06).

Conclusions : Proportional decrease of iris volume associated with pupil diameter increase during physiological dilatation is diminished in PACS eyes, compared to controls. Increased iris curvature was more pronounced in PACS eyes under physiological conditions and increase in pupil diameter showed strongest association with increase in iridotrabecular contact in PACS eyes. This study demonstrates a relationship between iris volume and curvature, pupil diameter and iridotrabecular contact, in physiological conditions, in Caucasian patients with occludable angles, which can be used to predict those most at risk of angle closure.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.