Cupping in the Monkey Optic Nerve Transection Model Consists of Prelaminar Tissue Thinning in the Absence of Posterior Laminar Deformation

PURPOSE To use optical coherence tomography (OCT) to test the hypothesis that optic nerve head (ONH) "cupping" in the monkey optic nerve transection (ONT) model does not include posterior laminar deformation. METHODS Five monkeys (aged 5.5-7.8 years) underwent ONH and retinal nerve fiber layer (RNFL) OCT imaging five times at baseline and biweekly following unilateral ONT until euthanization at ∼40% RNFL loss. Retinal nerve fiber layer thickness (RNFLT) and minimum rim width (MRW) were calculated from each pre- and post-ONT imaging session. The anterior lamina cribrosa surface (ALCS) was delineated within baseline and pre-euthanasia data sets. Significant ONT versus control eye pre-euthanasia change in prelaminar tissue thickness (PLTT), MRW, RNFLT, and ALCS depth (ALCSD) was determined using a linear mixed-effects model. Eye-specific change in each parameter exceeded the 95% confidence interval constructed from baseline measurements. RESULTS Animals were euthanized 49 to 51 days post ONT. Overall ONT eye change from baseline was significant for MRW (-26.2%, P = 0.0011), RNFLT (-43.8%, P < 0.0001), PLTT (-23.8%, P = 0.0013), and ALCSD (-20.8%, P = 0.033). All five ONT eyes demonstrated significant eye-specific decreases in MRW (-23.7% to -31.8%) and RNFLT (-39.6% to -49.7%). Four ONT eyes showed significant PLTT thinning (-23.0% to -28.2%). The ALCS was anteriorly displaced in three of the ONT eyes (-25.7% to -39.2%). No ONT eye demonstrated posterior laminar displacement. CONCLUSIONS Seven weeks following surgical ONT in the monkey eye, ONH cupping involves prelaminar and rim tissue thinning without posterior deformation of the lamina cribrosa.