Noninvasive metabolic analysis of eye bank corneas: a magnetic resonance spectroscopic study

Nondestructive, noninvasive metabolic analysis of corneal donor tissue preserved in modified McCarey-Kaufman medium was achieved using phosphorus-31 magnetic resonance spectroscopy (31 P MRS). Clear corneas (n = 10) with minimal Descemet's folds and an endothelial cell density of 2990 +/- 166 cells/mm2 from donors aged 26 to 89 years were used. Relative amounts of low- and high-energy phosphatic metabolites were quantitated during a 1-h period using the integral of the 31P spectrum. The following indicators of the tissue's energy status were determined: (1) 31P spectral energy modulus (ratio of high- to low-energy metabolites, average 0.95 +/- 0.14); (2) adenosine triphosphate/inorganic orthophosphate (ATP/Pi) ratio, 1.97 +/- 0.55; (3) sugar phosphate/inorganic orthophosphate (SP/Pi) ratio, average 1.07 +/- 0.12; and (4) intracorneal pH, calculated from the resonance shift position of inorganic orthophosphate, average 7.28 +/- 0.05. The 31P MRS technique measures key corneal metabolic processes (maintenance of the high-energy phosphate complement, interrelationship of inorganic orthophosphate and its bioesters, and pH). This study provides baseline data for eventually determining optimal parameters of eye bank corneal tissues and for evaluating the metabolic status, or health, of the cornea.