AIM:To use in vivo spectral-domain optical coherence tomography (SD-OCT) to investigate ocular surface epithelial thickness changes in patients treated with oral isotretinoin.METHODS:A total of 64 eyes of 64 acne vulgaris patients were enrolled into two group:thirty-two patients received 0.5 mg/kg isotretinoin daily (Group A),and the other 32 patients received 0.8 mg/kg daily (Group B).The central corneal thickness (CCT),central corneal epithelium thickness (CCET),central corneal epithelium basal membrane thickness (CCEBMT),non-epithelial central corneal thickness (NECCT) and bulbar conjunctival epithelium thickness (BCET) were evaluated using SD-OCT at baseline,at the 45th day,at the fourth month of treatment and at the first month after the end of treatment.RESULTS:There were 44 females (68.75％) and 20 males (31.25 ％) with a mean age of 21.68±3.75y.In both groups,CCET,CCT and BCET were significantly thinner at the 45th day,at the fourth month of the treatment and at the first month after the end of treatment as compared with baseline.CCEBMT decreased significantly at the 45th day and at the fourth month of treatment,but there was no difference between the baseline and the last visit.There were no significant difference in NECCT during and after treatment as compared with the baseline.CONCLUSION:Ocular surface epithelial thickness decreased in patients treated with oral isotretinoin,whereas NECCT was not affected.The decreasing corneal thickness in patients treated with isotretinon is mainly due to epithelial thinning.After a one-month cessation of isotretinoin treatment,CCEBMT returned to the baseline value,and ocular surface epithelial thickness increased.