Dynamic Analysis of Dark-light Changes of the Anterior Chamber Angle With Anterior Segment OCT

Abstract

Purpose:: To describe the use of anterior segment optical coherence tomography (OCT) in studying the dynamic dark-light changes of the anterior chamber angle.

Methods:: Thirty-seven normal subjects with open angles on dark room gonioscopy grading and 18 subjects with narrow angles were analyzed. The dynamic dark-light changes of the anterior chamber angle were captured with real-time video recording. The angle opening distance (AOD 500) of the nasal angle and the pupil diameter in each of the representative serial images were measured. Linear regression analysis was performed to investigate the association between AOD 500 and pupil diameter. Demographic and biometry measurements associated with the AOD difference (AOD 500 _(light) - AOD 500 _(dark)) were analyzed with univariate and multivariate regression models.

Results:: The AOD 500 measured in the light in the open angle and the narrow angle groups were 689 ± 334µm and 265 ± 78µm, respectively. These values were significantly higher than those measured in the dark (488 ± 269µm and 119 ± 82µm, respectively, both with p<0.001). The range of the AOD difference (AOD 500 _(light) - AOD 500 _(dark)) was 13µm to 817µm with an average of 180µm. Multivariate regression analysis identified a positive correlation between anterior chamber depth and AOD difference after adjusting for age. Forty-seven eyes showed high correlation between AOD and pupil size (correlation coefficient ranged between -0.73 and -0.99, median = -0.93) whereas four eyes demonstrated no association. Four eyes in the narrow angle group showed appositional angle closure in the dark.

Conclusions:: The dynamic dark-light changes of the anterior chamber angle can be imaged and analyzed with anterior segment OCT. While the angle width, in general, decreased linearly with increasing pupil size, the differences of the angle width measured in the dark and in the light vary substantially among individuals. Our findings demonstrate the importance of standardizing the light condition in the evaluation of anterior chamber angle configuration.

Keywords: anterior segment • imaging/image analysis: clinical • image processing