NUCLEAR-RELAXATION TIMES IN-VIVO AND IN-VITRO OF HUMAN AND RABBIT LENSES

Nuclear relaxation times T1 and T2 of water in human eye lenses were m easured in vivo and in vitro in the temperature range 35-41-degrees-C. Measurements were also done for rabbit lenses in vitro in the tempera ture range from 20 to -45-degrees-C. Measurements in vitro for both ty pes of lens showed monoexponential spin-lattice (T1) and biexponential spin-spin (T2) relaxation behaviour. Such relaxation time behaviour c an be explained by a two-phase model of water in the lens. The monoexp onential behaviour of T1 is shown to be due to rapid exchange occurrin g in water molecules in the lens, termed free water. The biexponential character of T2 results from the absence of fast exchange processes b etween the above types of water. One can distinguish two T2 values: T2 A is ascribed to so-called free water, with an activation energy of 10 .5 +/- 1.5 kJ mol-1 for human lenses and 13.9 +/- 2.0 kJ mol-1 for rab bit lenses, while the shorter T2B time is ascribed to water strongly b ound to proteins, with an activation energy equal to 32.1 +/- 5.0 kJ m ol-1 for human lenses and 8.5 +/- 2.0 kJ mol-1 for rabbit lenses. More over, a distribution of correlation times has been assumed for both ph ases in order to explain significant differences between the T1 and T2 values. The results of in vivo measurements are discussed as well as the applicability of this technique for early diagnosis of pathologica l changes in a human lens.