The RPE65 gene encodes a protein of 533 amino acids that is essential for normal vision. It is produced in the retinal pigment epithelium (RPE), a cell layer that supports and nourishes the retina (the light-sensitive tissue that lines the back of the eye). RPE65 plays an important role in the visual cycle. In the cycle, when the light enters the eye, it is converted into electrical signals that are transmitted to the brain. When the light hits photosensitive pigments in the retina, it changes a molecule called 11-cis retinal (a form of vitamin A) to all-trans retinal, which triggers a series of chemical reactions that create electrical signals. RPE65 protein helps in converting all-trans retinal back to 11-cis retinal to start the cycle again.

The RPE65 has two forms; a soluble form called sRPE65, and a palmitoylated, membrane-bound form known as mRPE65. The soluble form binds vitamin A (all-trans-retinol), making it available for LRAT processing to all-trans-retinyl ester. The membrane form, palmitoylated by LRAT, binds all-trans-retinyl esters, making them available for IMH (isomerohydrolase) processing to all-cis-retinol.

Defects in the RPE65 protein are the cause of retinitis pigmentosa 20 (RP) and Leber congenital amaurosis type 2 (LCA 2). These are autosomal recessive disorders characterized by severe childhood blindness.