Retinal Ganglion Cell Content Underlying Standard Automated Perimetry Size I to V Visual Sensitivities in the Non-Human Primate Experimental Glaucoma Model.

PURPOSE

To determine the relationship between visual sensitivities from white-on-white Goldmann size I to V stimuli and the underlying retinal ganglion cell (RGC) content in the non-human primate (NHP) experimental glaucoma model.

METHODS

Normative data were collected from 13 NHPs. Unilateral experimental glaucoma was induced in seven animals with the least variable fields who were monitored using optical coherence tomography and 30-2 full-threshold standard automated perimetry (SAP). At varying endpoints, animals were euthanized followed by perfusion fixation, and 1-mm retinal punches were obtained from 34 corresponding SAP locations. RGCs were immunolabeled with an antibody against an RNA-binding protein (RBPMS) marker and imaged using confocal microscopy. RGC counts from each location were then related to visual sensitivities for each stimulus size, after accounting for ocular magnification.

RESULTS

At the endpoint, the circumpapillary retinal nerve fiber layer thickness for experimental glaucoma eyes ranged from 47 to 113 µm. RGC density in control eyes was greatest for the 4.24° sample (18,024 ± 6869 cells/mm2) and decreased with eccentricity. Visual sensitivity at each tested location followed that predicted by spatial summation, with the critical area increasing with eccentricity (slope = 0.0036, R2 = 0.44). The relationship between RGC counts and visual sensitivity was described using a two-line fit, where the intercept of the first segment and hinge points were dependent on eccentricity.

CONCLUSIONS

In NHPs, SAP visual thresholds are related to the underlying RGCs. The resulting spatial summation based structure-function model can be used to estimate RGC content from any standard white-on-white stimulus size.