Impaired photoreceptor inner segment ellipsoid layer reflectivity in mild diabetic retinopathy

Objective: To determine alterations in retinal pigment epithelium (RPE), photoreceptor inner segment ellipsoid layer (ISel), and external limiting membrane (ELM) reflectivities using optical coherence tomography (OCT) image analysis in patients with mild nonproliferative diabetic retinopathy (NPDR). Design: Retrospective, single-centre, controlled clinical study. Participants: The study cohort included 42 eyes of 42 patients with mild NPDR (NPDR group) and 40 eyes of 40 healthy subjects (control group). Eyes with moderate and severe NPDR, proliferative DR, macular edema, and other macular pathologies were excluded. Methods: The reflectivities of RPE, ISel, and ELM were calculated using a medical image-processing software based on greyscale OCT images. The differences in the reflectivity values between the NPDR and control groups were analyzed. Results: The NPDR group comprised 22 males and 20 females (with a mean age of 61.3 6.5 years), and the control group consisted of 14 males and 26 females (with a mean age of 63.0 4.1 years) (p > 0.05). The ISel had significantly lower reflectivity (both absolute and relative) in eyes with mild NPDR compared with that of the control eyes (p < 0.001), whereas the reflectivities of RPE and ELM did not differ between the 2 groups (p = 0.126, p = 0.053 respectively). Conclusions: Although previous ex vivo studies reported photoreceptor degeneration in diabetic retinopathy, this is the first clinical study to investigate retinal layer reflectivities in NPDR using OCT. In eyes with mild NPDR, ISel seems to have lower reflectivity, and this finding might indicate early photoreceptor degeneration in diabetic retinopathy pathogenesis.