The relationship between retinal nerve fiber layer thickness and optic nerve head neuroretinal rim tissue in glaucoma

Purpose: The purpose of this study was to determine the relationship between optical coherence tomography (OCT) measures of retinal nerve fiber layer (RNFL) and neuroretinal rim (NRR) in a nonhuman primate experimental glaucoma model, and in a population of clinical patients.

Methods: For nonhuman primates, normative data were collected from 44 healthy monkeys, and nine animals with unilateral experimental glaucoma that were followed longitudinally. Cross-sectional human subjects data were collected from 89 healthy, 74 glaucoma suspects, and 104 glaucoma patients. Individualized transverse scaling for OCT scans was calculated using a schematic eye that incorporated optical ocular biometry. Custom algorithms were used to quantify RNFL thickness with and without vessels removed, scaled minimum rim width (sMRW), and neural rim volume (NRV).

Results: For the experimental glaucoma group, NRR parameters showed the first changes with increased cumulative IOP. The data for both NRR and RNFL measures were best fit by an exponential rise model (NRV, R2=0.79, P<0.01, sMRW, R2=0.74, P<0.01). The major retinal vascular thickness contribution to the RNFL decreased (0.03 μm/μm, P<0.01) with RNFL loss, but the percent vascular contribution increased (-0.1%/μm, P<0.01) with disease progression. Overall, the findings for the cross-sectional human data were similar to those of the experimental model.

Conclusions: The findings illustrate a nonlinear relationship between NRR and RNFL measures and provide support for the use of multiple OCT scaled morphological measures for the diagnosis and management of primary open angle glaucoma in humans.