Ethambutol scotomas

The onset of visual loss can be sudden and dramatic, with color vision defects in the red-green or blue-yellow spectra, as well as variable field defects. In acute cases, disc edema is accompanied by sphnter hemorrhages. Retrobulbar neuritis with ethambutol can be predominantly axial, presenting with reduced visual acuity and central scotoma, or periaxial, with peripheral field defects. In non-acute tjrpes the fundi and discs appear normal (13). Visual defects can be unilateral or bilateral. 

A 40-year-old patient underwent unsuccessful cadaver kidney transplantation and was treated with ethambutol and isoniazid (27). Bilateral retrobulbar neuropathy with an unusual central bitemporal hemianopic scotoma developed and ethambutol was withdrawn, but there was only a small improvement. When isoniazid was also withdrawn, there was dramatic improvement in visual acuity. 

Defects in vision after ethambutol are due to axial retrobulbar neuritis with a central scotoma and to periaxial retrobulbar neuritis with a partial concentric defect of the visual field (Mellin and Waubke 1978). This syndrome is caused by toxic, not allergic pathomechanisms. 

Reduced visual acuity and central or centro-cecal scotomas on visual field testing have been reported as the usual presentation of eth-ambutol-induced optic neuropathy. Bilateral temporal hemianopia has been reported in a case of ethambutol toxicity [64 ]. 

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