Catalyzes the synthesis of cyclic GMP (cGMP) in rods and cones of photoreceptors. Plays an essential role in phototransduction, by mediating cGMP replenishment (PubMed:15123990, PubMed:21928830, PubMed:26100624, PubMed:30319355, PubMed:9600905). May also participate in the trafficking of membrane-asociated proteins to the photoreceptor outer segment membrane (By similarity).
