Optic Nerve Head Deformation in Glaucoma: A Prospective Analysis of Optic Nerve Head Surface and Lamina Cribrosa Surface Displacement

Abstract

Purpose To evaluate long-term, longitudinal displacement of the optic nerve head (ONH) and anterior lamina cribrosa surfaces in glaucoma patients imaged with spectral-domain optical coherence tomography (SD OCT). Design Prospective study. Participants A total of 173 eyes of 108 subjects (88 with glaucoma and 20 normal subjects) followed for a mean of 5.3 years. Methods The optic disc was imaged with SD OCT at approximately 4-month intervals, and the ONH surface depth (ONHSD), anterior lamina cribrosa surface depth (ALCSD), and prelaminar tissue thickness (PTT) were measured. The reproducibility coefficients of ONHSD, ALCSD, and PTT were calculated from 2 baseline measurements of the glaucoma group. Change in ONHSD/ALCSD/PTT was confirmed when the differences between the first baseline and the latest 2 consecutive follow-up visits were greater than the corresponding reproducibility coefficient. Factors associated with ONHSD and ALCSD changes were identified with linear mixed modeling. Main Outcome Measures Proportion of eyes with ONHSD/ALCSD change. Results Within the glaucoma group, 23.9% (33 eyes) had confirmed ONHSD change (15.2% with posterior and 8.7% with anterior displacement) and 24.6% (34 eyes) had confirmed ALCSD change (12.3% with posterior and 12.3% with anterior displacement). Some 9.4% (13 eyes) showed a decrease in PTT, and 2.2% (3 eyes) showed an increase in PTT. The specificity for detection of ONHSD/ALCSD/PTT change was 91.4% (95% confidence interval [CI], 77.6-97.0), 82.9% (95% CI, 67.3-91.9), and 94.3% (95% CI, 81.4-98.4), respectively. There were no significant differences in the proportion of eyes with visual field progression or history of filtration surgery between the groups with anterior and posterior displacement of ONH/anterior laminar surfaces (P ≥ 0.678). For each millimeter of mercury increase in the average intraocular pressure (IOP) during follow-up, the ONH and anterior laminar surfaces displaced posteriorly by 1.6 μm and 2.0 μm, respectively. An older age was associated with a decrease in magnitude of posterior displacement of the ONH and anterior laminar surfaces (P ≤ 0.009). Conclusions The ONH and anterior laminar surfaces displaced not only posteriorly but also anteriorly (with reference to Bruch's membrane opening) in a significant portion of glaucoma patients. The magnitude of change was related to age and the averaged IOP during follow-up.