Change in Iris Cross-Sectional Area With Pupil Dilation: Comparison Between Angle- Closure and Open Angle Eyes

Abstract

Purpose: : To compare the change in iris cross-sectional (CS) area with pupil dilation using anterior segment optical coherence tomography (ASOCT) in eyes with angle closure, compared to open angles

Methods: : This comparative study examined 107 subjects diagnosed to have angle-closure (consisting of 57 eyes with chronic primary angle closure glaucoma [PACG], 50 eyes with chronic primary angle closure [PAC], and 50 fellow eyes of acute angle closure) and 40 control subjects (20 normal and 20 with primary open angle glaucoma). All participants underwent gonioscopy and ASOCT (Visante, Carl Zeiss Meditec, Dublin, CA) imaged along the 180, 45 and 135 degree meridians simultaneously for each eye in the light and repeated again in the dark. The iris CS -area and pupil diameter were measured with custom software (Zhongshan Angle Assessment Program, Guangzhou, China). Analysis of co-variance (ANCOVA) was used to analyze for differences between groups for the change in mean iris CS-area from light to dark.

Results: : In the dark, mean iris CS-area was smaller with larger pupil diameters for all groups, decreasing by 0.30 mm² for every mm increase in pupil diameter (p<0.01). On multivariate analysis, mean CS-Area in the dark was associated with pupil diameter (ß= -0.33; p<0.001) and axial length (ß= 0.13; p=0.03) but not with age, sex or anterior chamber (AC) width. When comparing light and dark measurements, the change in mean iris CS-area was least for fellow eyes of acute angle closure (0.43 mm² [standard error 0.10], p=0.04, ANCOVA), followed by PAC/PACG eyes (0.61mm²[0.10], p=0.16) compared to controls eyes (0.91mm² [0.13]), after adjusting for age, gender, pupil diameter in dark, AC depth, AC width, axial length, central corneal thickness and intraocular pressure.

Conclusions: : In the dark, iris CS-area was smaller with larger pupil diameter. When illumination was changed from light to dark, fellow eyes of acute angle closure eyes had the least change in mean iris CS-area compared to chronic PAC/PACG and control eyes. Such differences in iris dynamics may contribute to acute angle closure.

Keywords: imaging/image analysis: clinical • iris • clinical (human) or epidemiologic studies: risk factor assessment