The article “Comparison of the Correlation between Optic Disc Rim Area and Retinal Nerve Fiber Layer Thickness in Glaucoma and Nonarteritic Anterior Ischemic Optic Neuropathy,” by Suh and associates, reported that eyes with nonarteritic anterior ischemic optic neuropathy (n-AION) are well differentiated from open-angle glaucoma eyes by correlations between optic disc rim area and retinal nerve fiber layer thickness (the rim–RNFL correlation), especially in clock-hour sectors.

In this study, eyes with n-AION were determined to be outside the limit on a clock-hour basis when 1 clock-hour sectors or more were outside the 95% prediction interval (PI) for the rim–RNFL correlation of open-angle glaucoma. Recently, we found that eyes with n-AION would better be determined to be above the limit because neuroretinal rim areas in n-AION patients have been reported to be larger than those in glaucoma patients. In addition, n-AION patients would better be determined to be above the limit on a clock-hour basis when they had 2 clock-hour sectors or more above the upper 95% PI of open-angle glaucoma, because the probability that glaucoma eyes are above the upper 95% PI at 2 or more of 9 clock-hour sectors was found to be 2.0% (100 × (1 − 0.975 ⁹ [the probability that all clock hour sectors are below the upper 95% limit] − 0.975 ⁸ × 0.025 × 9 [the probability that 1 clock hour sector is below the upper 95% limit])), which is similar to that found by global area-based analysis (2.5%). The probability that glaucoma eyes are above the upper 95% PI at 1 or more of the 9 clock hour sectors was as high as 20.5% (100 × (1 − 0.975 ⁹ [the probability that all clock hour sectors are below the limit])).

Twenty-two eyes with n-AION had average of 5.8 ± 2.2 clock-hour sectors above the upper 95% PI. When the rim–RNFL correlation of these eyes was analyzed according to the above revised criteria, 95.5% (21/22) were above the upper 95% PI on a clock-hour basis, as compared with 63.6% (14/22) on global area basis ( P = .021, Fisher exact test). Therefore, we conclude that eyes with n-AION are well differentiated from eyes with glaucoma, even using the above revised criteria according to the clock hour-based rim–RNFL correlation.