Asymmetry Analysis of Macular Inner Retinal Layers for Glaucoma Diagnosis

Purpose To determine if asymmetry in thickness of the retinal nerve fiber layer (RNFL), ganglion cell layer, ganglion cell complex, and total retina between upper and lower macula halves can predict glaucoma. Design Retrospective case-control series. Methods One hundred twenty-two eyes of 122 patients (30 normal eyes and 30 preperimetric, 31 early, and 31 advanced glaucoma eyes) were studied. The RNFL, ganglion cell layer, ganglion cell complex, and total retina were segmented and measured on 10 vertical B-scans over a 30 × 15 degree macular area. The equation asymmetry index =|log 10 (lower hemiretinal thickness/upper hemiretinal thickness)| was used to calculate asymmetry indices for 8 pairs of upper and lower 0.5-mm segments equidistant from the fovea on each scan. Areas under the receiver operating characteristic curve (AROCs) for mean thickness and mean asymmetry index of 10 B-scans were compared. Results The overlap in values for normal and glaucomatous eyes was minimal for the ganglion cell layer asymmetry index. Thickness parameters decreased with the severity of glaucoma, whereas asymmetry indices did not. AROCs for thickness measurements tended to increase with increasing glaucoma severity (preperimetric, 0.746–0.808; early, 0.842–0.940; advanced, 0.943–0.995), whereas AROCs for asymmetry indices did not have distinct ranges according to glaucoma severity (advanced, 0.819–0.996; early, 0.861–0.998; preperimetric, 0.773–0.994). The AROC for the ganglion cell layer asymmetry index remained almost perfect regardless of glaucoma severity (0.994–0.998). Conclusions Macular retinal layer thickness asymmetry indices, particularly for the ganglion cell layer, show promise as early indicators of glaucomatous retinal damage.