RTBDN (retbindin) is a retina-specific riboflavin-binding protein with a primary function in flavin homeostasis and transport. The protein is secreted by rod photoreceptors into the inter-photoreceptor matrix, where it localizes at the photoreceptor/retinal pigment epithelium interface 1. RTBDN binds riboflavin and its derivatives (FAD and FMN) 2, facilitating flavin delivery to photoreceptors and protecting them from flavin-sensitized light damage 2. Mechanistically, RTBDN maintains retinal flavin levels critical for energy production and enzymatic cofactor functions 3. Its absence blocks glycolytic flux and disrupts metabolic homeostasis; RTBDN-deficient retinas show reduced pyruvate kinase M2 activity, accumulation of glycolytic intermediates, and elevated toxic metabolites including acylcarnitines and ceramides 4. This metabolic reprogramming forces the retina to prioritize glucose for free-radical mitigation over ATP production, eventually causing metabolic collapse and neurodegeneration 4. Clinically, RTBDN ablation leads to retinal degeneration in mice associated with reduced flavin levels 3. This parallels human riboflavin transporter deficiency, which causes neurologic abnormalities 3. RTBDN represents a therapeutic target for flavin-related retinal diseases and metabolic disorders affecting photoreceptor function.