Case series: Superficial plexus en face may aid distinction of retinal nerve fiber layer loss from diabetic retinal ischemia versus glaucoma

SIGNIFICANCE In normal tension glaucoma suspects with diabetes, inspection of superficial plexus capillary dropout patterns on optical coherence tomography–angiography (OCT-A) may help differentiate retinal nerve fiber layer (RNFL) and ganglion cell loss due to retinal ischemia from glaucoma. PURPOSE This study aimed to demonstrate that the pattern and degree of capillary bed dropout in early glaucoma appear different on OCT-A superficial plexus en-face slabs compared with retinal ischemia. RNFL loss associated with retinal ischemia in diabetic patients may be explained and accounted for by overlying the RNFL deviation map on a superficial plexus en-face montage. CASE REPORTS Three middle-aged White men with diabetes mellitus showed cup-to-disc ratios of approximately 0.7 and RNFL and ganglion thinning. Each patient had several Cirrus OCT and OCT-A scans taken of the posterior pole. The OCT-A en-face images demonstrated specific patterns of superficial capillary dropout. The appearance of superficial plexus capillary dropout in one case of glaucoma is contrasted against two cases of retinal ischemia. CONCLUSIONS Early glaucoma appears to be associated with incomplete capillary bed dropout that extends from macular regions to the disc in a wedge- or arc-shaped pattern. Diabetic retinal ischemia appears to be associated with well-defined patchy and polygonal pockets of complete capillary bed obliteration that may not extend back to the disc. If an RNFL deviation map is superimposed over the superficial plexus en-face montage, areas of RNFL loss may correlate with and thus be well accounted for by areas of retinal ischemia in cases with RNFL thinning likely from ischemia. This approach may supplement inspection of OCT B-scans for focal retinal thinning when trying to differentiate RNFL and ganglion cell loss from retinal ischemia versus glaucoma in patients with diabetes. Formal research studies are needed to validate our observations and proposed use of OCT-A together with OCT in these patients.