Thickness of the retinal photoreceptor outer segment layer in healthy volunteers and in patients with diabetes mellitus without retinopathy, diabetic retinopathy, or diabetic macular edema

PURPOSE: The purpose of this study was to investigate whether the severity of diabetic disease in the retina is paralleled by changes in the photoreceptor layer. METHODS: This cross-sectional study included healthy volunteers (30 volunteers, 60 eyes) and patients with diabetes (48 patients, 96 eyes). Each patient underwent a single session of spectral domain optical coherence tomography (OCT) in which each retina was imaged twice. On each OCT image, the thickness of the PROS layer was measured at the foveal center and at points 750 μm temporal to and nasal to the center. For statistical analyses, OCT images were assigned to one of the following groups: healthy, diabetes without retinopathy (DM), diabetic retinopathy (DR), or diabetic retinopathy with macular edema (DME). RESULTS: The mean PROS thickness at the foveal center in the first and second-obtained OCT images was as follows: healthy, 38.5 μm and 38.6 μm; DM, 38.2 μm and 38.2 μm; DR, 35.6 μm and 36.1 μm; DME, 32.6 μm and 32.6 μm. In the first and second-obtained images, significant differences were found between the healthy group and DR and DME (p < 0.05 for all), between the DM group and the DME (p < 0.05 for all), and between the DR group and the DME group (p < 0.05 for all). No significant differences between groups were found at the nasal and temporal locations. CONCLUSION: The PROS layer at the foveal center was thinner in patients who had diabetic retinopathy or diabetic macular edema than both the healthy volunteers and diabetic patients without retinopathy.