Nonarteritic Anterior Ischemic Optic Neuropathy: Refractive Error and Its Relationship to Cup/Disc Ratio

Abstract

To investigate refractive error in eyes with nonarteritic anterior ischemic optic neuropathy (NA-AION) and its relationship to cup/disc (C/D) ratio. Cohort study. A total of 608 consecutive patients with NA-AION. At first visit, all patients had a comprehensive ophthalmic evaluation, including recording best-corrected visual acuity, visual fields, anterior segment examination, ophthalmoscopy, and fluorescein fundus angiography. Morphometric measurement of C/D ratio was performed in 65 fellow normal eyes in patients with unilateral NA-AION. Refraction was converted into spherical equivalent for data analysis. The data were analyzed using Pearson correlation, Mantel-Haenszel chi-square test, Cochran-Mantel-Haenszel test, chi-square goodness-of-fit test, and segmented linear regression. Refractive error in NA-AION eyes and any association between refractive error and C/D ratio. Mean age of patients with NA-AION was 60.9 (standard deviation [SD] = 12.6; range 20.5-95.2) years. Median time from onset to refraction was 2 weeks (interquartile range 1-5 weeks). There was a significant association between spherical equivalent and age (P<0.0001). Comparison of refraction in patients with NA-AION who were aged >or=50 years with that of an age-matched general population in the Framingham study cohort showed no significant difference between the 2 groups (P = 0.289). Comparison with the age-matched US population from the 1999-2000 National Health and Nutrition Examination Survey showed a higher proportion of NA-AION eyes with spherical equivalent from -0.5 to 0.5 diopters and a smaller proportion with -3 to <-0.5 and >0.5 to +3 diopters (P<0.001). For horizontal C/D ratio, a higher degree of myopia and higher degree of hyperopia were significantly associated with a larger C/D ratio (P<0.021). A similar pattern was seen for vertical C/D ratio in hyperopia (P = 0.057) but not in myopia (P = 0.428). There was a significant association between spherical equivalent refraction and age (P<0.0001). C/D ratio in persons with NA-AION is significantly smaller than that seen in the general population. Morphometric study in patients with NA-AION showed that a higher degree of myopia and higher degree of hyperopia are significantly associated with a larger C/D ratio. The authors have no proprietary or commercial interest in any materials discussed in this article.