All-trans-retinal is a crucial intermediate in the visual cycle, formed by the photoisomerization of 11-cis-retinal (the chromophore in rhodopsin and cone opsins) upon light absorption in the retina. This isomerization initiates the phototransduction cascade, activating G-proteins and leading to nerve signals that enable visual perception in the brain. It is then reduced to all-trans-retinol for recycling in the retinoid cycle. Additionally, all-trans-retinal can be converted to retinoic acid, which supports skin health by promoting cell differentiation, proliferation, and turnover, as well as immune function. Widely used in research on retinal diseases, vision disorders, retinoid signaling, and potential therapeutic interventions.