Glaucoma Detection using the GDx Nerve Fiber Analyzer and the Retinal Thickness Analyzer (RTA)

Abstract

Purpose

To compare the ability of the nerve fiber analyzer (GDx) and the retinal thickness analyzer (RTA) to discriminate between glaucomatous and healthy eyes.

Methods

Thirty-seven glaucoma patients (early to moderate severity) and 34 healthy controls were included. Glaucoma patients were defined as those with two repeatable abnormal visual fields by automated perimetry within 1 year. All subjects were examined with a GDx scanning laser polarimeter and RTA. Twelve GDx retinal nerve fiber layer parameters and 12 RTA optic disk topography parameters were obtained. GDx and RTA measurements were compared between both experimental groups using t-tests. Areas under the receiver operating characteristic curves (AUROC) for discriminating between healthy and glaucomatous eyes using GDx and RTA parameters were calculated and compared, and sensitivities at ≥80% and≥95% specificity were reported.

Results

Statistically significant differences between glaucomatous and healthy eyes were found for most GDx and RTA parameters. For GDx, the parameter with the largest AUROC for discriminating between healthy and glaucomatous eyes was the number (AUROC = 0.91, sensitivity = 85% at specificity = 84%, sensitivity = 73% at specificity = 95%). For RTA, the parameter with the largest AUROC was mean cup depth (AUROC = 0.79, sensitivity = 61% at specificity = 82%, sensitivity = 33% at specificity = 95%). The AUROC for the GDx number was significantly larger than the AUROC for RTA mean cup depth (p<0.05).

Conclusions

GDX showed better discrimination and better sensitivities at fixed specificities than RTA. The currently available RTA optic disk analysis software likely cannot replace GDx RNFL analysis software for successful glaucoma diagnosis.