Stimulates retinal guanylyl cyclase when free calcium ions concentration is low and inhibits guanylyl cyclase when free calcium ions concentration is elevated (PubMed:19459154, PubMed:30622141, PubMed:18706439, PubMed:30184081). This Ca(2+)-sensitive regulation of retinal guanylyl cyclase is a key event in recovery of the dark state of rod photoreceptors following light exposure (By similarity). May be involved in cone photoreceptor light response and recovery of response in bright light (By similarity). Homodimer. Present at higher levels in cone than in rod outer segments (PubMed:9620085). Subcellular location is not affected by light or dark conditions. In the retina, it is expressed in rod and cone photoreceptors. Binds three calcium ions (via EF-hands 2, 3 and 4) when calcium levels are high. Binds Mg(2+) when calcium levels are low. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Retina International's Scientific Newsletter