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J. K. Thomas, M. J. Smarr, L. N. Johnson; A Comparison of the Clinical Characteristics of Ethambutol Optic Neuropathy and Amiodarone Associated Optic Neuropathy. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2485.
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Ethambutol and amiodarone are medications which may cause a toxic optic neuropathy. This study compares the clinical manifestations of ethambutol optic neuropathy (EON) with amiodarone optic neuropathy (AON).
An OVID English literature search from 1966 to 2006 was performed to identify cases of EON. Visual loss onset, presenting and final visual acuity, visual field defect, and color vision loss were ascertained. Visual function in EON was compared with the clinical manifestations of AON identified in the world literature by one of the authors (Johnson et al, 2004).
There were 65 cases (63% male, 37% female) of EON and 55 cases (87% male, 13% female) of AON. The mean age was 49 years for EON and 62 years for AON. The median time interval to development of EON was 4.8 months (and 90% within 12 months) after commencing ethambutol use, and 4.0 months (with 88% occurring within 12 months) for AON after initiating amiodarone use. EON presented with insidious onset of visual loss in 40 (62%) cases and sudden onset in 25 (38%) cases. Correspondingly, AON presented with insidious onset of visual loss in 26 (47%) cases, sudden onset in 22 (40%) cases, and was asymptomatic in 7 (13%) cases. The median visual acuity at presentation for EON was 20/200 (range, 20/20 to no light perception), and the median final visual acuity following discontinuation of ethambutol was 20/50 (54% improved, 35% no change, 11% worsened). For AON, the median visual acuity at presentation was 20/30 (range, 20/15 to light perception), and visual acuity improved in 40%, worsened in 10%, and had no change in 50%. The most common visual field defect in EON was bilateral central/centrocecal/paracentral scotoma (64%). For AON, arcuate or altitudinal scotomas were found in 45% cases, and central/centrocecal scotomas in 15% cases. Color vision loss was identified in 75% of EON cases and 40% of AON cases. Optic nerve pallor (atrophy) occurred in 26% of EON cases and 32% AON cases.
Ethambutol optic neuropathy has features in common with amiodarone optic neuropathy, in particular, median onset of visual loss beginning at approximately 4 months after initiating medication use, male preponderance, insidious onset, rate of color vision loss, and rate of visual acuity improvement. The visual field loss of EON is more often central/centrocecal scotoma, in contrast with AON being more often arcuate/altitudinal scotoma.
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