Effect of Pupil Dilation on Angle Metrics Obtained from Spectral-Domain Optical Coherence Tomography (SD-OCT)

Abstract

Purpose: PURPOSE: To evaluate the effect of pupil dilation on anterior chamber angle (ACA) measurements obtained by spectral-domain optical coherence tomography (SD-OCT).

Methods: METHODS: A total of 40 eyes from 20 healthy, normal subjects underwent anterior segment OCT imaging using a Cirrus SD-OCT according to an IRB-approved protocol. For each eye, 5-line raster scans of the inferior angle were performed under 3 pupillary conditions: pupil constricted under standard room lighting, physiologic mydriasis in a darkened room, and after pharmacologic mydriasis. The inferior angle Schwalbe’s line-angle opening distance (SL-AOD) and the Schwalbe’s line-trabecular-iris space area (SL-TISA, measured 500 microns posteriorly from Schwalbe’s line) were computed for each eye and pupillary condition. Measurements were performed by masked certified reading center graders using customized grading software. Differences in measurements between different pupillary conditions were compared.

Results: RESULTS: Among the twenty subjects, 11 were female, and 9 were male. The mean age was 29.8 years and the majority was of Asian-descent (65%). SL-AOD under pupillary constriction to room light measured 0.87 ± 0.31mm, but measured smaller under physiologic mydriasis (0.75 ± 0.29 mm) and larger under pharmacologic mydriasis (0.9 ± 0.38 mm) (P=0.01). Analogously, SL-TISA under pupillary constriction to room light measured 0.33 ± 0.14 mm2, but measured smaller under physiologic mydriasis (0.29 ± 0.13 mm2 ) and larger under pharmacologic mydriasis (0.34 ± 0.17 mm2)(P=0.03). Compared to pupil constriction to light, the mean SL-AOD decreased 0.54 mm and SL-TISA decreased 0.46 mm2 respectively under physiologic mydriasis in the dark (P<0.001). Compared to physiologic mydriasis, the mean SL-AOD increased 0.15 mm and SL-TISA increased 0.05 mm2 respectively after pharmacologic mydriasis(P<0.05).

Conclusions: CONCLUSIONS: Anterior chamber angle metrics differed significantly based on the lighting condition and the state of pupillary dilation. Whereas physiologic mydriasis appeared to make measurements smaller, pharmacologic mydriasis made measurements slightly larger. Accounting for the state of the pupil and standardizing the lighting condition would appear to be of importance for future studies of the angle.

Keywords: 421 anterior segment • 712 shape and contour • 733 topography