Evaluation of the relationship between disorganization of retinal inner layers and retinal function in patients with diabetic retinopathy

Purpose: In diabetic retinopathy patients without macular edema, it was aimed to investigate diabetes-related OCT biomarkers, to measure choroid, RNFL and GCC thicknesses, and to evaluate retinal neural functions with SAP, SWAP and FDT tests, to examine associations between DR severity, and compare with non-diabetic control patients, as well as investigating the effect of DRIL on visual function by comparing the OCT markers and visual field tests between patients with and without DRIL. Method: In this prospective study; patients who admitted to our clinic, 148 eyes of 100 patients with diabetic retinopathy without edema, and 40 eyes of 20 patients without diabetes were included. Complete ophthalmological examinations, colored fundus photographs taken according to the ETDRS protocol, and OCT scan were recorded by a single physician. SAP, SWAP, and FDT tests were performed by a single experienced technician. The fundus photographs, OCT findings, and visual field tests were evaluated blinded by the two physicians at the end of the study. Results: When DR and control groups were compared; DRIL and HRN percentages were significantly higher in the DR group (p = 0,000, p = 0,000, respectively), choroidal thickness was significantly reduced (P = 0,000), RNFL thickness, was significantly reduced in all quadrants except for the nasal quadrant (p = 0.013, p = 0,000, p = 0.021), GCC thicknesses were significantly reduced in each quadrant (p = 0.006, p = 0.023, p = 0.002, p = 0.003, p = 0.003, p = 0.038). When the FT, MD, PSD values of the SAP, SWAP and FDT tests were compared between the DR and the control group, there was a significant decrease sensitivity in the DR group except for the FT and MD values of the FDT (p = 0,000, p = 0,000, p = 0.001, p = 0,000, p = 0,000, p = 0,000, p = 0.011). Although FDT was not significant in FT and MD parameters, low sensitivity was detected. When mild DR, moderate DR and control patients were compared; as the severity of DR increased, age increased significantly (p = 0,000), whereas VA and choroidal thickness decreased significantly (p = 0,000, p = 0,000). DM duration was significantly higher in patients with moderate DR (p = 0.045). Between the same groups, significant differences were detected in the inferior and superior quadrants of RNFL (p = 0.046, p = 0.000), in all quadrants of the GCC except superotemporal (p = 0.007, p = 0.033, p = 0.003 p = 0.007, p = 0.011). DRIL and EZ damaged patients were significantly higher in the modarate DR group (p = 0.042, p = 0.015), no significant results were found between the two groups in terms of DRIL extent and the number of HRN. There was a significant difference between MD, PSD, FT values of SAP and SWAP, and PSD of FDT between mild and modarate groups (p = 0,000, p = 0,000, p = 0,002, p = 0,000, p = 0,000, p = 0,000, p = 0.009). When patients with and without DRIL were compared; the number of HRN was significantly higher in DRIL patients (p = 0.043), no significant difference was found in ELM damage, EZ damage, and PAMM, no significant results were found in visual field tests, but lower sensitivity was detected in patients with DRIL in SWAP parameters. PAMM was detected in 8 (5.4%) of 148 DR patients. Conclusion: In our study, the presence of diabetes-related OCT biomarkers, thinning in RNFL, GCC, choroid thicknesses, decreased sensitivity in SAP, SWAP and FDT tests prove that morphological and functional changes begin in DR patients without edema. Determining the findings of DR before macular edema can help both diagnose and prognosis. Key Words: Diabetic retinopathy, OCT, DRIL, SAP, SWAP, FDT