The 31P spectral modulus and corneal metabolism.

Metabolic health can be measured by phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy in both intact living and extracted corneas. 31P Spectroscopic analysis measures organophosphates principally involved in intermediary metabolism. This allows for calculation of the phosphorus spectral modulus (PSM), an index of tissue metabolic health and the ratio of the high-energy-phosphate to the low-energy-phosphate spectral bands of the 31P NMR spectrum. Such measurements are important for studies of corneal metabolic health and maintenance and in corneas subjected to metabolic stress. The PSM of normal healthy tissues, generally are significantly greater than stressed tissues. Using the integral function of 31P NMR spectroscopy, the PSM can be employed to make spectral measurements where only barely detectable resonance signals are present. The phosphorus concentration can be so low as not to even permit detection of individual or groups of metabolites. This allows the study of minimal tissue volume and size, a necessity for measurements of individual corneas. Determination of the PSM only requires spectra of low signal-to-noise resolution that includes a clear spectral integral inflection point at ca. -0.13 δ. The PSM among normal corneas averaged 1.16 ± 0.06, PSM among stressed corneas 0.80 ± 0.12. This study concludes (1) the higher the metabolic activity in the cornea, the higher the corneal spectral modulus; (2) as is necessary in the case of measuring an individual cornea, the PSM does not require a highly resolved 31P spectrum. The PSM provides a numeric assay for determining health status statically or over a time-course in normal and stressed corneas.