The comparative chemical morphology of the mammalian cornea.

A simple model of mammalian corneal stroma has been tested against biochemical and ultrastructural measurements performed on a number of species. Contents of water, collagen and total sulphated polyanion were constant, as predicted from the model. Alcian blue CEC results showed great variability between species, with a rise in CEC as corneal size and thickness increased. These variations were due to changes in keratan sulphate content, and particularly to its oversulphated terminal domain, which is absent from mouse cornea. The increase in keratan sulphate content with corneal thickness was balanced by an increase in dermatan sulphate in thin corneas, thus maintaining total sulphated GAG levels at a constant "average", in all the mammals investigated. This balance is probably decided by oxygen tension, which will vary with corneal thickness.