Purpose: To evaluate the integrity of the photoreceptor inner segment/outer segment (IS/OS) junction using spectral-domain optical coherence tomography (SD OCT) in patients with diabetic macular edema and to correlate the relationship between the integrity of the IS/OS junction and visual acuity.Design: Observational, prospective study.Methods: 40 eyes of 22 diabetic patients having diabetic macular edema. The authors performed spectral-domain optical coherence tomography in all eyes before treatment,1month and 6 months after treatment. The authors defined central subfield thickness as the average retinal thickness of the1-mm central scanned area. The length of disruption of the inner and outer segments of the photoreceptors in the fovea were measured and graded according to their length as follows: grade 0 : intact IS/OS line (no disruption at all),grade 1: mild disruption (<400microns).grade 2: moderate disruption (>400 microns but <1400 microns), Grade 3: severe disruption ( >1400 microns )or completely lost.Results: At baseline, there was no correlation between the VA and grade of defect (r= 0.214, p-value= 0.190). After one month and six months of treatment , there was moderate correlation between the VA and the grade of the defect ( r = 0.538 , p-value < 0.001) (r =0.603, p value < 0.001) respectively .There was no significant association between the improvement in the IS/OS and final VA( p-value < 0.385). The mean change in VA from base line to 1 month in those who showed improvement in the defect was better than those in the non improved group (p value =0.001) , and the mean change in the VA values from base line to 6 months in the improved group was better than those in the non improved group (p value= 0.001).Conclusions: Spectral-domain optical coherence tomography showed that the integrity of the inner and outer segments of the photoreceptors was moderately correlated with best-corrected visual acuity.