Binds negatively charged membrane lipids, such as phosphatidylserine and phosphoinositides (PubMed:17325137, PubMed:20677810). May play a role in cell-cell adhesion processes in the retina, via homomeric interaction between octamers present on the surface of two neighboring cells (By similarity). Required for normal structure and function of the retina (PubMed:11983912, PubMed:17325137). Homooctamer of 4 homodimers; disulfide-linked. The homooctamer has a flat, cogwheel structure with a diameter of about 14 nm. Two stacked octamers can assemble to form a hexadecamer. Binds to phosphatidylserine-containing lipid membranes and embeds itself partially into the lipid bilayer. Lipid-binding requires the presence of Ca(2+) ions. Detected in the eye cup (PubMed:11983912). Detected in retina, in the inner segment of the photoreceptors, the inner nuclear layer, the inner plexiform layer and the ganglion cell layer (at protein level) (PubMed:10915776, PubMed:11983912, PubMed:17325137). Restricted to the retina (PubMed:10023077, PubMed:10915776). At the mRNA level, detected only within the photoreceptor cell layer, most prominently within the inner segments of the photoreceptors (PubMed:10023077, PubMed:10915776). Undetectable in the inner plexiform layers and the inner nuclear layer (PubMed:10915776). No visible phenotype at birth (PubMed:11983912). After two months, mutant males display a profound disorganization of the inner and outer nuclear layer of the retina, with increased extracellular spaces in the region of photoreceptor ribbon synapses and the appearance of gaps, and a decrease in the number of photoreceptor cell outer segments (PubMed:11983912, PubMed:17325137). The number of cone photoreceptors is reduced threefold (PubMed:11983912). After three months, mutant males display a layer of small, cyst-like structures in the inner retina (PubMed:11983912). They have profoundly altered electroretinograms, indicating a decreased light sensitivity due to a decrease in the number of functional photoreceptors (PubMed:11983912).