Crystallins are water soluble structural proteins found in the vertebrate eye. Mammalian crystallins are classified in three forms, designated α, β and γ. Crystallins, as the principal components of the lens, function to increase the refractive index of the eye during accommodation by forming high-molecular weight aggregates which maintain transparency. γS-crystallin (Gamma-crystallin S), also known as Beta-crystallin S, is a 178 amino acid protein that exists as a monomer which does not aggregate. γS-crystallin contains a two-domain beta structure and belongs to the beta/gamma-crystallin gene family mapping to human chromosome 3. γS-crystallin has been linked to congenital cataract development, a disorder signified by increasing levels of lens opacity.