RCVRN (recoverin) is a calcium-sensing photoreceptor protein localized to chromosome 17 that serves as a critical regulator of phototransduction in rod and cone cells 1. The protein functions primarily as a negative regulator of rhodopsin kinase in a calcium-dependent manner, forming a feedback loop that modulates light sensitivity and photoreceptor recovery 1. In response to elevated intracellular calcium levels during low-light conditions, recoverin binds to and inhibits GRK1-mediated phosphorylation of rhodopsin, thereby enhancing signal transfer between rod photoreceptors and bipolar cells 2. This mechanism is essential for scotopic vision and enables photoreceptor sensitivity adjustment across varying light intensities. Clinically, RCVRN serves as a pan-photoreceptor marker used to monitor photoreceptor development and specification in retinal organoids 34. The protein is downregulated in photoreceptor developmental delays associated with X-linked retinoschisis, though expression recovers following RS1 gene augmentation therapy 5. Additionally, RCVRN expression is modulated in retinoblastoma through legumain signaling 6. These characteristics make RCVRN a valuable biomarker for photoreceptor cell enrichment in stem cell-based retinal therapies and for understanding phototransduction mechanisms in health and disease.