Abstract
<title>Abstract</title> <p> <bold>Purpose:</bold> To investigate early structural and functional alterations in diabetic retinopathy (DR) before the development of macular edema, with a focus on optical coherence tomography (OCT)-derived biomarkers, choroidal thickness, and selective retinal sensitivity changes. The clinical relevance of disorganization of the retinal inner layers (DRIL) was also evaluated. <bold>Methods:</bold> This prospective single-center study included 148 eyes of 100 patients with DR without macular edema. All patients underwent Early Treatment Diabetic Retinopathy Study-based fundus photography, spectral-domain OCT imaging with choroidal thickness measurement, and functional assessment using standard automated perimetry (SAP), short-wavelength automated perimetry (SWAP), and frequency-doubling technology (FDT). Eyes were stratified according to DR severity and the presence of DRIL. Imaging and functional outcomes were independently evaluated by two masked graders. Categorical variables were analyzed using the chi-square test, and continuous variables were compared using parametric or non-parametric tests according to data distribution. <bold>Results:</bold> Eyes with moderate-or-worse DR showed a significantly higher prevalence of DRIL (p=0.042) and reduced choroidal thickness (p=0.011) compared with eyes with mild DR. Paracentral acute middle maculopathy was identified in 5.4% of eyes. Eyes with DRIL had significantly more hyperreflective retinal foci (p=0.043). SWAP revealed selective functional impairment, with reduced foveal threshold (p=0.025) and increased pattern standard deviation (p=0.010) across DR severity groups, whereas SAP and FDT parameters did not differ significantly. Visual field parameters were not significantly different between eyes with and without DRIL. <bold>Conclusion:</bold> OCT-derived structural biomarkers, choroidal thinning, and selective short-wavelength sensitivity loss may be detected in DR before macular edema develops. These findings support early neurovascular involvement in DR and suggest that SWAP may reveal functional impairment not captured by conventional perimetry. </p>