Mechanisms and Functions of Chromophore Regeneration in the Classical Visual Cycle: Implications for Retinal Disease Pathogenesis and Therapy

11-cis-retinal, the indispensable chromophore of photoreceptor opsins, is fundamental for light detection and the initiation of visual signal transduction. Its synthesis and regeneration through the visual cycle are critical not only for phototransduction but also for maintaining retinal homeostasis. Disruption of key enzymes, such as retinal pigment epithelium (RPE)65 and retinol dehydrogenases, results in toxic retinoid accumulation, oxidative stress, and progressive photoreceptor degeneration. These pathological mechanisms contribute to inherited and acquired retinal diseases, including Stargardt disease type 1, age-related macular degeneration, Leber congenital amaurosis, retinitis pigmentosa, and fundus albipunctatus. Recent therapeutic advances, ranging from gene replacement therapy with RPE65 (voretigene neparvovec, Luxturna^®) to small-molecule modulators and antioxidant strategies, underscore the translational potential of targeting chromophore metabolism. This review outlines molecular processes underlying chromophore synthesis and regeneration, elucidates how disruptions in these processes contribute to inherited and acquired retinal pathologies, and evaluates existing and emerging therapeutic strategies that target chromophore metabolism. We highlight ongoing challenges and critical knowledge gaps to guide future investigations on basic science, translational research, and clinical practice. This review provides a comprehensive overview of the molecular mechanisms, current therapeutic approaches, and outstanding challenges, with a focus on future intervention directions.