thickness shows greater diagnostic power than other OCT parameters. We suggest several potential explanations: First, in the peripapillary area, the thickness of the nerve fiber layer is greatest, and the retinal inner layer is responsible for the largest proportion of retinal thickness. The break- down of the inner BRB provides the most apparent cause for the thickening of the retina in this area. Secondly, the thickening of the peripapillary retina is less variable than macular thickening, which results principally from edema of the outer plexiform layer. The erratic changes in macular thickness may exert a considerable degree of influence on the significance of statistical analyses. The smaller standard deviation of retinal thickness in the peripapillary area, when compared with that in the macular area, reinforces this assumption. This study has several limitations. We determined the retinal thicknesses using two-dimensional cross-sectional images with the Line mode. This procedure ignores possible information from the Radial Lines Mode of the acquisition software that utilizes a color-coded retinal thickness map with sectored topographic images [22]. Unfortunately, the topographic scanning on the Stratus OCT was unavailable in the peripapillary region. Again, because we could not obtain the average thickness directly in the Line mode of acquisition, we re-processed the original scan images, using an image analysis program, representing a potential source of error. Moreover, there is no normative database regarding the peripapillary retinal thickness in the general population. We used an arbitrarily selected cut-off value to evaluate predictive accuracy, and this is also a potential shortcoming of our study. Furthermore, the significant inter-individual variability of retinal thickness might limit the clinical ap- plication of our findings. As age is one of the possible fac- tors that influences inter-individual variability, we conducted age-matching between the diabetic and normal subjects, but matching was not fully accomplished in all sub-groups of DR. To the best of our knowledge, there have been no previous studies that analyzed OCT encompassing peripapillary retinal thickness in cases of DR. Prior studies have generally been limited to retinal thickness at the macula [23-25]. In this study, we have confirmed that the measurement of peripapillary retinal thickening determines the severity of DR more effectively than evaluations of macular thickness. Although AUC appears to have modest diagnostic accuracy, the measurement of peripapillary retinal thickness utilizing OCT is very simple and noninvasive. When combined with other factors in a predictive model, the measurement of peripapillary retinal thickness is expected to be useful for DR screening. 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