Stereoscopic Analysis of Optic Nerve Head Parameters in Primary Open Angle Glaucoma: The Glaucoma Stereo Analysis Study

Purpose: The Glaucoma Stereo Analysis Study (GSAS), a cross sectional multicenter collaborative study, used a stereo fundus camera to assess various morphological parameters of the optic nerve head (ONH) in glaucoma patients and investigated the relationships between these parameters and patient characteristics. Subjects and Methods: The study included 187 eyes of 187 subjects with primary open angle glaucoma or normal tension glaucoma (male: female = 100: 87, age = 61 +/- 9 years). Stereo pairs of ONH photographs were made with a stereo fundus camera (nonmyd WX). ONH morphological parameters were calculated with prototype analysis software. In addition to 35 standard parameters, we defined three novel parameters: disc tilt angle, rim decentering, and the absolute value of rim decentering. The correlation between each parameter and patient characteristics was analyzed with Spearman's rank correlation coefficient. Results: Patient characteristics included refractive error of -3.38 +/- 3.75 diopters, intraocular pressure (IOP) of 13.6 +/- 2.6 mmHg, and visual field mean deviation (MD) of -4.71 +/- 3.26 dB. Representative ONH parameters included a horizontal disc width of 1.66 +/- 0.28 mm, vertical disc width of 1.86 +/- 0.23 mm, disc area of 2.42 +/- 0.63 mm(2), cup area of 1.45 +/- 0.57 mm(2), and cup volume of 0.31 +/- 0.22 mm(3). Correlation analysis revealed significant negative associations between vertical cup-to-disc ratio (0.82 +/- 0.08) and MD (r = -0.40, P<0.01) and between disc tilt angle (10.5 +/- 12.5 degrees) and refractive error (r = -0.36, P<0.01). Seventy-five percent of the eyes had a positive value for rim decentering (0.30 +/- 0.42), indicating that rim thinning manifested more often as an inferior lesion than a superior lesion. Conclusion: We used stereoscopic analysis to establish a database of ONH parameters, which may facilitate future studies of glaucomatous changes in ONH morphology.