Retinal Nerve Fiber Layer Thickness/Minimum Rim Width Ratio Differentiates Glaucoma From Other Optic Neuropathies

Abstract

Précis: Global peripapillary retinal nerve fiber layer thickness (pRNFL)/Bruch membrane opening–minimum rim width (BMO–MRW) ratio is an objective and effective parameter to separate glaucomatous optic neuropathies (GONs) from nonGONs (NGONs). Purpose: This study was undertaken to evaluate the diagnostic capability of the pRNFL/ BMO–MRW ratio to differentiate GONs from NGONs. Patients and Methods: This retrospective study included patients with an optic neuropathy (ON), visual loss for>6 months and a confirmed single etiology. pRNFL thickness and BMO–MRW were measured with spectral-domain optical coherence tomography (Spectralis, Heidelberg Engineering, Heidelberg, Germany). The diagnostic accuracies of pRNFL, BMO–MRW and the global pRNFL/BMO–MRW ratio were evaluated with the areas under receiver operating characteristics curves. Results: One eye each from 171 patients was investigated: 50 primary open angle glaucomas, 15 normal pressure glaucomas, 50 optic neuritises, 15 nonarteritic anterior ischemic ONs, 24 compressive ONs, 10 dominant optic atrophies, and 7 nutritional ONs. The global pRNFL/BMO–MRW ratio had the highest area under receiver operating characteristics curve [0.97 vs. 0.92; P=0.01]. It was able to distinguish between GONs and NGONs with a cutoff value of 0.34. Increased mean deviation of the visual field-defect severity was associated with a higher ratio for GONs and a lower ratio for NGONs. Conclusion: Compared with NGONs and for the same degree of pRNFL thinning, lower BMO– MRW was found to be a specific marker of glaucoma, reflecting the neuroglial architecture changes within the optic nerve head typical of glaucoma and supporting fundamental pathophysiological differences.