Major water-soluble structural proteins found in fiber cells of vertebrate eye lenses; account for the transparency of the lens. Heterogeneous family composed of four groups α, β, γ, δ which have been separated on the basis of size, charge, immunological properties and source. α, β, δ crystallins occur in avian and reptilian lenses while α, β, γ crystallins occur in all other lenses. Several other minor forms have also been identified. Identification and isolation of α, β, γ: C. T. M"orner, Z. Physiol. Chem. 18, 61 (1894); of δ: M. Rabaey, Exp. Eye Res. 1, 310 (1962). Review of early isolation procedures: A. Spector, Invest. Ophthalmol. 3, 182-193 (1964). Structural studies of α: A. F. Van Dam, G. Ten Cates, Biochim. Biophys. Acta 121, 183 (1966); H. A. Kramps et al., Eur. J. Biochem. 50, 503 (1975); of β: H. P. C. Driessen et al., ibid. 121, 83 (1981); G. Wistow et al., FEBS Lett. 133, 9 (1981); of γ: T. Blundell et al., Nature 289, 771 (1981); L. Summers et al., Pept. Protein Rev. 3, 147 (1984); of δ: J. Horwitz, J. Piatigorsky, Biochim. Biophys. Acta 624, 21 (1980); L. A. Williams et al., ibid. 708, 49 (1982). Short-range spatial ordering is essential for lens transparency: M. Delaye, A. Tardieu, Nature 302, 415 (1983). Photoinduced aggregation; implications for cataract formation: U. P. Andley et al., Photochem. Photobiol. 40, 343 (1984); K. Mandal et al., ibid. 47, 583 (1988); M. Kono et al., ibid. 593. Role of crystallin aging in cataract formation: R. J. Siezen et al., Proc. Natl. Acad. Sci. USA 82, 1701 (1985); H. J. Hoenders, G. J. H. Bessems, Lens Res. 3, 281 (1986). Evolution and expression of crystallin genes: J. Piatigorsky, Cell 38, 620 (1984); W. W. de Jong, W. Hendriks, J. Mol. Evol. 24, 121 (1986). Reviews: A. Spector, Invest. Ophthalmol. 4, 579-591 (1965); W. W. de Jong, Co-ord. Regul. Gene Expression - Proc. 2nd Int. Workshop, R. M. Clayton, Ed. (Plenum Press, New York, 1986) pp 281-291; G. J. Wistow, J. Piatigorsky, Annu. Rev. Biochem. 57, 479-504 (1988). Review of δ-crystallin: J. Piatigorsky, Mol. Cell. Biochem. 59, 33-56 (1984). Book: Molecular and Cellular Biology of the Eye Lens, H. Bloemendal, Ed. (John Wiley & Sons, New York, 1981).