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C.I. Zoumalan, A.A. Sadun; OCT Can Identify Reversible Nerve–fiber Layer Changes in a Patient With Ethambutol–induced Mitochondrial Pptic Neuropathy . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4275.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To map and identify reversible nerve–fiber layer (NFL) swelling in ethambutol (EMB)–induced optic neuropathy using optical coherence tomography (OCT). A serious complication of ethambutol is a toxic mitochondrial optic neuropathy that produces impairment in visual acuity, contrast sensitivity, and color vision in as many as 6% of patients. OCT has shown NFL swellings in LHON, an irreversible genetic mitochondrial optic neuropathy. However, deficits in EMB–induced optic neuropathy may be reversible. Methods: One subject with a history of EMB–induced optic neuropathy was administered a full neuro–ophthalmologic examination including visual acuity, color vision, contrast sensitivity, fundus examination, visual fields testing, and OCT at three separate visits. These three visits occurred at two, five, and eight months after EMB discontinuation. OCT was performed on both eyes of the subject using the retinal nerve fiber layer (RNFL) analysis protocol on the three visits. Results: OCT quantified a significant increase in NFL thickness in the inferior quadrant of the right eye (201µm thickness, or 298% increase in thickness) on the second visit than seen on the first visit (91µm). This corresponded well with the presentation of new–onset right–hemisphere superior visual field defects in the subject’s right eye on the same visit (MD = –9.0 +/– 6.24, p<.01). However, at the third visit, there was a notable decrease in the NFL thickness in the subject’s inferior quadrant (162 µm, or a 19% decrease in thickness) when compared to the second visit. Additionally, there was a concurrent improvement in the subject’s superior visual field defect when compared to the second visit (MD=–5.4 +/– 3.29, p<.01). Conclusions: We are able to identify and quantify, for the first time, reversible NFL changes in a patient with EMB–induced optic neuropathy using OCT. There is evidence of reversible axonal swelling in the peripheral RNFL, which is occupied by axons of larger caliber than found in the macula. These axons contain a larger percentage of magno–cellular fibers that subserve motion stereopsis, depth perception, and low–contrast sensitivity. These larger axons seem to have a greater capacity for compensation for mitochondrial injury. OCT can be a valuable tool in the quantitative analysis of optic neuropathies.
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