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

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.

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.

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.

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.

Widefield OCT enables the quantification of retinal ganglion cell associated loss for the extent of the retina tested by visual fields.