Catalyzes the synthesis of cyclic GMP (cGMP) in rods and cones of photoreceptors. Plays an essential role in phototransduction, by mediating cGMP replenishment (  ). May also participate in the trafficking of membrane-asociated proteins to the photoreceptor outer segment membrane (By similarity).
Subcellular locations: Photoreceptor outer segment membrane, Endoplasmic reticulum membrane
Retina.