Opticin, also known as OPTC or OPT, is a 332 amino acid protein that is secreted into the extracellular matrix and contains seven LRR repeats. Expressed in skin and fetal liver and also present in ocular tissues, such as the retina, cornea and iris, opticin functions to bind collagen fibrils and, via this interaction, is thought to regulate fibril spacing, morphology and organization. Opticin is subject to post-translational O-glycosylation and may be associated with the pathogenesis of primary open angle glaucoma.