Decreased retinal nerve fibre layer thickness detected by optical coherence tomography in patients with ethambutol-induced optic neuropathy

Baylor College of Medicine, Houston, Texas, United States
British Journal of Ophthalmology (Impact Factor: 2.98). 08/2007; 91(7):895-7. DOI: 10.1136/bjo.2006.113118
Source: PubMed


It is difficult to assess the degree of optic nerve damage in patients with ethambutol-induced optic neuropathy, especially just after the onset of visual loss, when the optic disc typically looks normal.
To evaluate changes in retinal nerve fibre layer thickness (RNFLT) using optical coherence tomography (OCT) in patients with optic neuropathy within 3 months of cessation of ethambutol treatment.
A retrospective observational case series from a single neuro-ophthalmology practice.
8 patients with a history of ethambutol-induced optic neuropathy were examined within 3 months after stopping ethambutol treatment. All patients underwent a neuro-ophthalmologic examination, including visual acuity, colour vision, visual fields and funduscopy. OCT was performed on both eyes of each patient using the retinal nerve fibre layer analysis protocol.
The interval between cessation of ethambutol treatment and the initial visit ranged from 1 week to 3 months. All patients had visual deficits characteristic of ethambutol-induced optic neuropathy at their initial visit, and the follow-up examination was performed within 12 months. Compared with the initial RNFLT, there was a statistically significant decrease in the mean RNFLT of the temporal, superior and nasal quadrants (p = 0.009, 0.019 and 0.025, respectively), with the greatest decrease in the temporal quadrant (mean decrease 26.5 mum).
A decrease in RNFLT is observed in all quadrants in patients with ethambutol-induced optic neuropathy who have recently discontinued the medication. This decrease is most pronounced in the temporal quadrant of the optic disc.

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    • "Depending on the dosage of EMB, the incidence of EON has been reported to be in the range of 1-5% (Sivakumaran et al., 1998). It has been suggested that the cause of EON might be linked to a disturbance in the optic nerve that is induced by EMB through an excitotoxicity pathway (Campbell and Elmes, 1975; Chai and Foroozan, 2007; Figueroa et al., 1971; Heng et al., 1999; Yoon et al., 2000; Zoumalan et al., 2005). The toxic effects of EMB in retinal cells have also been studied in recent works (Chung et al., 1989; Liu et al., 2008; Tsai et al., 2008a; Vistamehr et al., 2007). "
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    • "It is well known that there are regional variations in retina regarding the susceptibility to damage (Tanito et al. 2008). Interestingly, the effect of VGB is different from that encountered in individuals with ethambutolinduced optic neuropathy, where the greatest decrease of RNFLT was in the temporal quadrants (Chai & Foroozan 2007). "
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    • "Results from mfERGs have been found to be abnormal in ethambutol-induced macular toxicity, and should therefore be useful in diagnosis and serial assessment of ethambutol-related ocular toxicity [7]. Furthermore, where available and affordable, tests such as magnetic resonance imaging (MRI) and optical coherence tomography (OCT) [8] could be employed to investigate ethambutol ocular toxicity. MRI scans of the optic nerves and chiasm, with normal findings in toxic and/or nutritional optic neuropathy, could be useful to differentiate between bilateral cecocentral scotomas and compressive or infiltrative lesions of the optic chiasm. "
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