Calcium-binding protein critical for proper photoreceptor cell maintenance and function. Plays a role in intracellular calcium homeostasis by decreasing ATP-induced calcium release (PubMed:23023331). May be involved in the mechanotransduction process (By similarity). Homodimer (By similarity). Interacts with WHRN and MYO7A (By similarity). Interacts with ITGA2B (via C-terminus cytoplasmic tail region); this interaction is stabilized/increased in a calcium and magnesium-dependent manner (PubMed:18611855). Interacts with ITGA7 (via C-terminus cytoplasmic tail region); this interaction is stabilized/increased in a calcium and magnesium-dependent manner (PubMed:18989529). Colocalized with ITGA7 at the myotendinous junctions (MTJ) and at the neuromuscular junctions (NMJ) (PubMed:18611855). Localizes in the cuticular plate along and at the tip of the stereocilia of vestibular sensory hair cells (By similarity). Expressed in the supporting cells in both the organ of Corti and the vestibular sensory epithelia. Expressed in inner and outer segments of photoreceptor cells, as well as in the pigmented epithelium. Also observed in the inner and outer plexiform layers and in the ganglion cell layer (at protein level) (PubMed:23023331). Widely expressed (PubMed:23023331). Strongly expressed in skeletal muscles, brain, kidney and liver (PubMed:23023331). Also expressed in the skeletal muscle, retina and cochlea (PubMed:18611855, PubMed:23023331). Expressed in megakaryocytes and endothelial cells (PubMed:18989529). Expressed in the central nervous system and in muscle at 16 dpc, onward (PubMed:18611855). Expressed in the inner ear and retina at 15.5 and 17.5 dpc (PubMed:23023331). The binding of either calcium or magnesium significantly increases the structural stability of the protein in comparison to apo-CIB (calcium- and magnesium-free form).