Corneal crystallins and the development of cellular transparency

Past studies have established that the cornea like the lens abundantly expresses a few water-soluble enzyme/proteins in a taxon specific fashion. Based on these similarities it has been proposed that the lens and the cornea form a structural unit, the ‘refracton’, that has co-evolved through gene sharing to maximize light transmission and refraction to the retina. Thus far, the analogy between corneal crystallins and lens crystallins has been limited to similarities in the abundant expression, with few reports concerning their structural function. This review covers recent studies that establish a clear relationship between expression of corneal crystallins and light scattering from corneal stromal cells, i.e. keratocytes, that support a structural role for corneal crystallins in the development of transparency similar to that of lens crystallins that would be consistent with the ‘refracton’ hypothesis.