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C.I. Zoumalan, M.R. Agarwal, A.A. Sadun; Using optical coherence tomography to map patterns of axonal degeneration in ethambutol–induced optic neuropathy . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2367.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To map and identify the pattern, in vivo, of axonal degeneration in ethambutol–induced optic neuropathy using optical coherence tomography (OCT). Ethambutol (EMB) is an antimycobacterial agent often used in tuberculosis. A serious complication of ethambutol is an optic neuropathy that selectively affects the papillomacular fibers, reducing visual acuity, contrast sensitivity, and color vision. However, early on, when the toxic optic neuropathy is mild and partly reversible, the fundus findings are often subtle and easy to miss. Methods: Two subjects with a history of chronic EMB–induced optic neuropathy and with unresolved visual deficits were administered a full neuro–ophthalmologic examination including visual acuity, color vision, contrast sensitivity, and fundus examination. In addition, OCT (OCT 3000, Humphrey–Zeiss, Dublin, CA) was performed on both eyes of each patient using the retinal nerve fiber layer (RNFL) analysis protocol. OCT interpolates data from 100 points around the optic nerve to effectively map out the RNFL. Results: The results are compared to the calculated average RNFL of normal eyes accumulated from four prior studies using OCT, n=661. In both sets of eyes of both patients, there was an average loss of 79.2% of nerve fiber thickness in the temporal quadrant (Patient A=90.3% loss, Patient B=68.2% loss). There was a combined average loss of 55.8 % loss of fibers from the superior, inferior, and nasal quadrants in both sets of eyes of both patients. Conclusions: The OCT results in these two patients with EMB–induced optic neuropathy show considerable loss especially of the temporal fibers. This is consistent with prior histopathological studies that show predominant loss of parvo–cellular papillomacular axons in toxic or hereditary optic neuropathies. OCT can be a valuable tool in the quantitative analysis of optic neuropathies.
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