COL15A1 and open-angle glaucoma: Mutations in collagen genes have been associated with glaucoma (recently reviewed).[59] Of particular relevance to this study is the observation that genetic variations in COL15A1 can modify the age of onset of early and late onset primary open angle glaucoma.[60–62] Type XV collagen is a fibril-associated collagen that is a component of the basement membrane and may be involved in outflow resistance.