Background: Diabetic kidney disease (DKD) and diabetic retinopathy (DR) share common microvascular pathophysiology, yet the relationship between retinal neuronal alterations and kidney dysfunction remains unclear. This cross-sectional study examines the association between individual retinal layer thickness and kidney indicators to identify novel optical coherence tomography (OCT) biomarkers for DKD. Methods: A total of 410 type 2 diabetes (T2D) patients (815 eyes) were recruited from the outpatient clinics of a tertiary eye centre in Singapore. Retinal layer thickness was measured using OCT with automated segmentation software (Orion). The association between the thickness of individual retinal layers and estimated glomerular filtration rate (eGFR) as well as urine albumin-to-creatinine ratio (UACR) categories was analysed using a Generalised Estimating Equation (GEE) approach. Results: GEE analysis identified a significant association between outer plexiform layer (OPL) thickness and both eGFR and UACR category, with perifoveal OPL thickness showing the strongest inverse association with eGFR (adjusted p = 0.0007) and positive association with the category of UACR (adjusted p = 0.005). After stratifying by retinal thickness, this association remained robust in eyes without macular oedema (foveal total retinal thickness < 320 mu m). No significant associations were found for other retinal layers. Conclusions: OPL thickening serves as a potential indicator for DKD, and OCT imaging offers a noninvasive tool for investigating retinal-renal interactions. Further longitudinal studies are needed to evaluate its utility in monitoring DKD progression.