Progress has been made in elucidating causative factors for some cataracts but little is yet known about those factors involved in development of aging-related nuclear cataracts. The predominant theory of nuclear cataractogenesis is that the lens crystallins accumulate covalent modifications which ultimately lead to increased light scattering. This theory is based on several lines of evidence. Crystallins, the predominant components of the lens, are present at very high concentration and determine the refractive properties of the lens. A relationship between crystallin alterations and cataract formation comes from studies on animal cataract models where mutations in crystallin genes have been identified. Numerous studies have also demonstrated that covalent modification of crystallins occurs in the human lens. These modifications are reported to be developmentally related, age related and/or the result of toxic environmental influences. Data from this lab demonstrated that the human lens crystallins undergo extensive covalent modification as part of normal lens fiber cell maturation. Crystallin modifications that cause cataracts would have to be superimposed on these normally occurring modifications.

We have begun a study under the protocol entitled "Use of Human Lens Material for Possible Causes of Cataract" to compare crystallins in nuclear cataracts with those in normal lenses. The goal was to identify uniquely altered crystallins, isolate the modified species and determine the covalent modifications that could possibly be involved in cataract formation. Surprisingly, our preliminary findings indicated that the pattern of protein spots on a 2-dimensional display of the total lens proteins (soluble, water insoluble and membrane) in the nuclear region of nuclear cataracts is essentially the same as found in the nucleus of normal lenses. Only the relative concentrations of these protein species varied. The number of pure nuclear cataracts available was too few 1) to determine the relationship between nuclear cataracts and crystallin covalent modification and 2) to establish the significance of concentration differences in crystallin species between normal lenses and nuclear cataracts. Therefore, the purpose of this protocol is to recruit enough subjects with pure nuclear cataracts to complete this study which should provide significant insights into the mechanisms underlying nuclear cataract.