Nuclear magnetic resonance study of free and bound water fractions in normal lenses

Proton NMR relaxation times T1 and T2 were determined for normal lenses excised from sexually mature animals from seven different species. Lenses were immersed in physiological buffer during measurements, and suppression methods were employed to null the buffer signal. This enabled selective analysis of lenticular water. Observed relaxation times were correlated with protein and water content. At 37 degrees C and 1.89 Tesla, single-exponential spin-lattice relaxation was observed, but spin-spin relaxation was found to be double-exponential. It was shown that the short-T2 fraction is proportional to protein concentration; this fraction was attributed to water bound to protein. The long-T2 fraction was attributed to free lenticular water. The amounts of free and bound water thus obtained were used in the spin-lattice relaxation rate equation for rapid exchange in a two-component system to calculate the magnitudes of the two corresponding T1 relaxation components.