Micro‐Raman spectroscopic study of organ cultured corneae

Raman spectroscopy of water was used to assess the metabolic state of fresh corneae and those which had been stored under long‐term organ culture conditions. Both human and porcine tissue were employed. The data showed a semi‐quantitative relationship between corneal hydration (determined using wet and dry weights of the tissue) and the integrated intensity of the water to collagen bands in the spectral region 2700—4000 cm −1 . Variables included duration of storage, composition of culture medium and, for the human specimens, the age of the cornea. Raman assessment of hydration may provide a better measure of the functional state of the stored cornea that the density of live endothelial cells, which is a commonly used criterion. The spectra showed that the healthy cornea of low water content contained more weakly hydrogen‐bonded water than either bulk water or a swollen cornea. This is to be expected as groups on proteins and proteoglycans in the cornea form weak bonds with water. These weakly bonded surface groups are diluted when water is imbibed, hence resulting in the spectrum becoming more like that of bulk water in swollen tissue. Addition to the culture medium of dextran, which osmotically thins the cornea, converted its water spectrum back towards that of a healthy cornea.