Objective To measure the changes in retinal nerve fiber layer （RNFL） thickness using OCT in patients treated with ethambutol， to detect the axonal loss caused by ethambutol， and to assess the value of OCT in the early diagnosis of toxic optic neuropathy. Methods This was a retrospective observation of 185 eyes of 93 patients collected in ophthalmology department， being treated with ethambutol. They were separated into short-time treatment group （2 months） and long-time treatment group （≥6 months）， and 92 eyes of 46 age-matched TB infected patients who haven′t started the treatment were chosen as the control group. The differences in RNFL thickness from the three groups were compared using ANOVA. All patients underwent a neuro-ophthalmologic examination including visual acuity， color vision， visual fields and fundus examination. Results RNFL thickness of short-time treatment group： temporal （90.35±12.58）μm， inferior （145.91±17.18）μm， nasal （93.18±16.9）μm， superior （139.07±18.65）μm， average thickness （117.01±10.14）μm. RNFL thickness of long-time treatment group： temporal （79.75±17.14）μm， inferior （135.47±19.14）μm， nasal （91.17±20.23）μm， superior （130.44±21.50）μm， average thickness （109.24±14.36）μm. The control group： temporal （95.43±15.61）μm， inferior （139.92±15.35）μm， nasal （90.06±15.61）μm， superior （140.71±19.02）μm， average thickness （116.49±11.49）μm. Compared with the control group， no significant changes of RNFL thickness were found in the short-term group （P>0.05）. There were statistically significant decrease in the mean RNFL thickness of the temporal and superior quadrants between the long-term medication group from the control group （P<0.05）. A prominent decrease in RNFL thickness was observed in all quadrants in 6 eyes diagnosed with ethambutol induced optic neuropathy. Conclusion The short-term administration of ethambutol （0.75 g·d-1） in most of the patients did not cause obvious axonal loss and visual damage， but in the long-term group the RNFL thinning could be found apparently in the temporal quadrant， which maybe of great importance for early diagnosis of ethambutol toxic optic neuropathy.
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