Purpose: To investigate the functional and morphologic changes that occur in ethambutol（EMB）-induced ocular toxicity in rabbit models and concomitantly evaluate the role of zinc（Zn）in EMB toxicity. Method: Eight eyes of four pigmented rabbits were used. EMB was orally administered to all rabbits at 110-180 mg/kg/day for 20 weeks. Two of these rabbits were also given Zn supplementation at a dose of 8 mg/kg/day. As functional evaluations, infrared pupillography and electroretinography were examined. All the EMB-treated rabbits were euthanized and the globes including the optic nerves were harvested. Histopathologic examination of harvested tissues was subsequently done by both electron and light microscope. Results: In none of the rabbits, any significant change was observed in functional evaluations of outer retina. Histopathologically, an observable decrease in the small type of retinal ganglion cells, vacuolar degeneration of many axons in the inner retina, and also demyelination in the optic nerve were noted. On the other hand, in rabbits given EMB with Zn supplementation, only the outer retina was affected with patches of choroidal depigmentation and damage to the retinal pigment epithelium. Conclusion: These results suggest that the inner retina and optic nerve were markedly damaged in rabbits with EMB-induced toxic neuroretinopathy. However, those given Zn supplementation were minimally affected by the toxic doses of EMB. Zn may be used as a prophylactic medication to avoid the occurrence of ocular toxicity.
Purpose: To report a case in which a woman developed an optic disc abnormality that was related to breast malignancy. Case Presentation: A 35-year-old woman presented with a complaint of sudden blurred vision in her right eye（RE）. She had a history of Sjögren syndrome and recurrent dyspnea. Visual acuity in her RE was only slightly reduced, but the visual field defect was prominent. Funduscopy was significant for a blunted optic nerve head margin with surrounding whitish lesion. Autoimmune optic neuropathy was initially suspected due to her history of Sjögren syndrome; therefore, an oral steroid was administered. During subsequent follow-up, the fundus abnormality became more visible and expanded to the retinal background, accompanied by a worsening visual field. Systemic evaluation revealed a breast malignancy, and the patient was diagnosed with malignancy-related optic neuropathy. Conclusion: Optic nerve abnormality due to malignancy remains among the most challenging diseases in diagnosis. In this case, the patient presented with a history of autoimmune disease and no known oncologic history. Evaluation of such patients should include a comprehensive systemic survey in order to find clues for the etiology, including the possibility of malignancy and metastatic disease.