Stimulates retinal guanylyl cyclase when free calcium ions concentration is low and inhibits guanylyl cyclase when free calcium ions concentration is elevated (PubMed:18706439, PubMed:19459154, PubMed:30184081, PubMed:30622141). 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). {ECO:0000250|UniProtKB:P43081, ECO:0000250|UniProtKB:P46065, ECO:0000269|PubMed:18706439, ECO:0000269|PubMed:30184081, ECO:0000269|PubMed:30622141}. This is the function of GUCA1A (guanylate cyclase activator 1A, Ensembl gene identifier ENSG00000048545).