COlour vision assessment for the Detection of Early diabetic Retinopathy (CODER): A study protocol

Introduction Diabetic retinopathy (DR) remains one of the leading causes of preventable vision loss. However, high-contrast visual acuity, which is routinely used in the clinic, is often preserved during the early stages of the disease, limiting its usefulness in detecting early functional deficits. Colour vision is a sensitive marker for detecting these early retinal changes. This study aims to investigate whether the Colour Assessment and Diagnosis (CAD) test, a quantitative measure of chromatic sensitivity, can serve as a functional biomarker for the early detection of DR and can reflect the severity of the disease. Methods and analysis This prospective observational study will be conducted at the L V Prasad Eye Institute, Hyderabad, India. Adults aged 18 years and above will be recruited into three groups: healthy controls, individuals with diabetes without diabetic retinopathy, and individuals with diabetic retinopathy. All participants will undergo a comprehensive ophthalmic examination, colour vision testing, fundus photography, optical coherence tomography (OCT), optical coherence tomography angiography (OCTA), and systemic metabolic investigations, including glycaemic, renal, and lipid profiles. The primary outcome measures are the Red–Green (RG) and Yellow–Blue (YB) Colour thresholds. Secondary outcome measures include retinal structural parameters and vascular parameters, such as retinal thickness, vessel density, and perfusion density. Systemic metabolic parameters, including HbA1c, random blood glucose, renal function, and lipid profile, will be evaluated as independent variables. Statistical analyses will include correlation, multiple regression, and receiver operating characteristic (ROC) curve analyses to evaluate the diagnostic accuracy of the CAD test in the detection of early DR. Conclusion The current study is expected to provide evidence whether quantitative colour vision assessment can act as a functional marker of early retinal changes in diabetes and diabetic retinopathy.