Purpose: Although previous studies have examined the risk of bilaterality of nonarteritic ischemic optic neuropathy (NAION), none have compared extensively the extent of visual loss between fellow eyes. The authors examined cases of bilateral NAION to determine the extent of vision loss in the second eye compared with that in the first eye. Methods: Thirty- one cases of bilateral NAION were reviewed. Variables included age, gender, and the presence of comorbid disease. Visual function was assessed by Snellen visual acuity, color vision, and pattern and mean deviation of the visual fields. Results: No correlation was detected between the extent or pattern of visual loss in fellow eyes. No significant difference in visual function existed between first and second eyes for the patients overall. Patients who retained better visual function in the second eye were significantly older than those who retained better visual function in the first eye (visual acuity, P = 0.0005; color vision, P = 0.07; mean deviation, P = 0.02). In patients older than 50 years of age (25 of 31 cases), the second eye had significantly better visual acuity (P = 0.04) and less Humphrey visual field mean deviation (P = 0.04) than the first eye. Conclusion: Visual function in the second eye correlated poorly with that of the first eye. Older patients with bilateral NAION retained better visual function in the second eye than in the first eye. For younger patients, the extent of visual loss in the second eye could not be predicted based on the visual loss in the first eye.
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