Involved in both the normal retinal photoreceptor ribbon synapse formation and physiological functions of visual perception. Necessary for proper bipolar dendritic tip apposition to the photoreceptor ribbon synapse. Promotes matrix assembly and cell adhesiveness (By similarity). Interacts with DAG1 alpha-dystroglycan. Detected in the synaptic cleft of the ribbon synapse around the postsynaptic terminals of bipolar cells. Colocalizes with BSN, CTBP2 and DAG1 in photoreceptor synaptic terminals. O-glycosylated; contains chondroitin sulfate and heparan sulfate.