Cathepsins are proteases that were originally identified in the lysosome, where they participate in house keeping tasks such as degradation of phagocytosed photoreceptors. More recently, cathepsins have been detected outside of the lysosome, and associated with numerous diseases (keratoconus, retinal detachment, age related macular degeneration, and glaucoma). The most likely mechanism by which cathepsins contribute to ocular pathologies is via degradation of the extracellular matrix, and/or regulation of angiogenesis.