Abstract
PURPOSE: To determine whether a structure-function model developed for normal age-related losses of retinal ganglion cells also models the retinal ganglion cell losses in glaucomatous optic neuropathy. METHODS: The model to relate age-related loss of retinal nerve fiber layer thickness and reduced sensitivity for standard automated perimetry was evaluated with data from 30 glaucoma patients and 40 normal individuals. Perimetry thresholds were translated into separate retinal ganglion cell body estimates for test locations in the superior and inferior visual fields. The retinal nerve fiber layer thickness from optical coherence tomography was also divided into regions representing the superior and inferior hemifields to obtain estimates of the axons in each hemifield. The 2 estimates of retinal ganglion cell populations were compared for corresponding regions. RESULTS: Agreement between neural estimates was good for normal individuals and patients with early glaucomatous damage. Results for individuals with advanced glaucoma showed disparities between neural estimates that were proportional to the stage of disease. A correction factor for the stage of disease was introduced for the derivation of ganglion cell populations from the nerve fiber layer measurements, which produced agreement between the optical coherence tomography and perimetric estimates for all patients. CONCLUSIONS: The modified structure-function model provided well-correlated relationships between the subjective measures of visual sensitivity and the objective measures of retinal nerve fiber layer thickness when parameters for the patient's age and the severity of the disease were included. The results suggest constitutive relationships between structure and function for the full spectrum of normal-to-advanced glaucomatous neuropathy.