Required to maintain the integrity of photoreceptor cells (PubMed:27737822, PubMed:28378834, PubMed:30052645). Specifically required for normal morphology of the photoreceptor ciliary pocket, and might thus facilitate protein trafficking between the photoreceptor inner and outer segments via the transition zone (PubMed:27737822). Localizes to discrete puncta at, or adjacent to, the photoreceptor connecting cilium (PubMed:27737822, PubMed:30052645). May localize to the cilium axoneme (By similarity). May also be expressed in the interphotoreceptor extracellular matrix (By similarity). Unlike the primate ortholog, does not appear to be expressed in the photoreceptor outer segment (PubMed:27737822). Expressed in retina where it localizes between the retinal pigment epithelium and the outer nuclear layer (at protein level). Progressive loss of cone photoreceptors in the retina from two months post-fertilization (mpf) onwards, with almost complete loss by 9 mpf. Rod photoreceptors also show signs of degeneration in older animals of 14 mpf. Photoreceptor degeneration is accompanied by increased apoptosis and mislocalization of outer segment proteins. At the ultrastructural level, morphology of the photoreceptor ciliary pocket is frequently abnormal with either complete collapse of the pocket, or presence of multiple membranous vesicles. Belongs to the EYS family.