Contrast Sensitivity Impairment in Diabetic Retinopathy: Clinical and Structural Correlates

Diabetic retinopathy (DR) is one of the main causes of vision impairment globally, and it is increasingly recognized as a neurovascular disease characterized by both microvascular and neural dysfunction. Traditional assessment approaches primarily focus on structural retinal alterations and visual acuity, which may fail to identify early functional impairments. Contrast sensitivity (CS), which measures the capacity to distinguish subtle luminance differences, is increasingly recognized as an early manifestation of retinal dysfunction in diabetes mellitus. This narrative review seeks to describe current knowledge on the role of CS in DR, including its pathophysiological foundation, clinical importance, and link to structural retinal alterations. A systematic literature search of PubMed, Scopus, and Google Scholar (2000-2026) was performed to identify studies on CS in diabetes mellitus and diabetic retinopathy. Multiple investigations found that diabetic patients, including those with no clinically evident DR and normal visual acuity, had lower contrast sensitivity. CS impairment was associated with retinal neurodegeneration, ganglion cell dysfunction, microvascular alterations, and diabetic macular edema severity. OCT and OCT-A findings showed important structure-function correlations between reduced CS and retinal thinning, capillary dropout, and impaired perfusion. CS testing may provide additional functional information beyond standard visual acuity assessment and may improve early disease detection and monitoring. In conclusion, contrast sensitivity represents a promising functional biomarker for early diabetic retinal dysfunction and may complement structural imaging and visual acuity testing in DR evaluation. Although methodological variability currently limits widespread clinical implementation, advances in digital technologies and multimodal assessment strategies may facilitate its future integration into routine ophthalmologic practice.