Detection of Disease Progression Using Widefield Optical Coherence Tomography in the Nonhuman Primate Experimental Glaucoma Model

Purpose: To determine whether there is detectable thinning of the ganglion cell inner plexiform layer (GCIPL) and retinal nerve fiber layer (RNFL) across all eccentricities of a 55° × 45° widefield optical coherence tomography (OCT) scan in the nonhuman primate experimental glaucoma model. Methods: Eight rhesus monkeys (Macaca mulatta) with unilateral experimental glaucoma were monitored longitudinally using widefield OCT. GCIPL and RNFL thickness maps were generated, and longitudinal disease changes were quantified using Z-score maps with 1° × 1° super pixel granularity. For validation, the correspondence between GCIPL volume (mm3) and histologically determined retinal ganglion cell (RGC) counts was determined for 1 mm retinal samples in four longitudinally monitored animals and three additional animals from a separate study. Results: The Z-score maps from follow-up scan sessions demonstrated significant RNFL thinning across the retina, whereas GCIPL thinning was limited to the central 12° in eyes with experimental glaucoma. For the five eccentricities sampled for histology, GCIPL volume was a predictor of RGC counts (F = 44.14, P < 0.01). The linear mixed-effects model, which included eccentricity and disease state, accounted for a substantial portion of the variance (R2 = 0.72). For locations 12.7° and greater, the GCIPL is at a floor in healthy eyes as illustrated by the clustering of disease and control data. Conclusions: Widefield imaging has the potential to quantitatively monitor RNFL wedge defects across a 55° scanned region. GCIPL thickness is a valuable measure of local RGC content in the macular region, but its value for monitoring disease in the periphery is less significant. Translational Relevance: Widefield OCT enables the quantification of retinal ganglion cell associated loss for the extent of the retina tested by visual fields.