Quantitative analysis of iris changes after physiologic and pharmacologic mydriasis in a rural Chinese population.

Purpose: To estimate and compare the change in iris cross-sectional area (IA) and iris volume (IV) following physiologic and pharmacologic pupil dilation in primary angle closure suspects (PACS) and normal subjects.

Methods: Anterior segment-optical coherence tomography (AS-OCT) measurements in light, dark, and following pharmacologic dilation were obtained on 186 PACS and 224 normal subjects examined during the 5-year follow-up of the Handan Eye Study. Iris cross-sectional area, IV, and other biometric parameters calculated using the Zhongshan angle assessment program in the right eyes of all subjects were analyzed.

Results: The mean IA and IV decreased in dark compared with light and after pharmacologic dilation in both PACS and normal eyes. This change was statistically significant in normal eyes: light versus pharmacologic dilation for IA (P = 0.038) and for IV, both light versus dark (P = 0.031) and light versus pharmacologic dilation (P = 0.012). A longer axial length (P = 0.028) and a greater change in pupil diameter (PD) (P < 0.001) were associated with a larger decrease of IA for the light to dark comparison. A diagnosis of normal eyes (P = 0.011), larger PD in dark (P = 0.001), and a larger change in PD (P = 0.001) were associated with a larger decrease of IV from light to dark.

Conclusions: The differences in iris behavior between PACS and normal rural Chinese subjects following physiologic or pharmacologic pupillary dilation may help provide insights into the pathogenesis of angle closure.