Relaxographic studies of aging normal human lenses

Ten excised normal human lenses of various ages were studied. Seven sections of each lens, from anterior outer cortex to posterior outer cortex were imaged and the T₁ (spin-lattice) and T₂ (spin-spin) relaxation data on each section were collected. T₁ and T₂ relaxation were analysed by fitting pixel intensity to one term exponential expressions. Both T₁ and T₂ relaxation times showed minimal values in the nuclear region and maxima at the two outer cortexes. The pre-exponential terms of the fittings of both T₁ and T₂ relaxation, M₁ and M₂, were normalized in order to eliminate instrumental variations over a 2 year period. M₂ had a maximum in the nucleus and minima in the two cortexes. M₁ exhibited minimal value in the nucleus and maxima at the two cortexes. The positional dependence of T₂ relaxation times as well as that of M₂ indicated that they represent the behavior of the bound water in the lens. The positional dependence of M₁ suggests that this relaxation represents the total water that has a minimal value in the nucleus. The T₂ relaxation time decreases with increase in the age of the lens at each location. The slope of the change in T₂ relaxation time with age is greatest in the outer cortexes and diminishes as one proceeds to the nucleus. T₁ relaxation times and M₁ do not show significant change with age. This and the age dependence of the other relaxographic parameters imply that the aging of the lens involves major changes in its hydration properties that are more accentuated in the cortexes. The interpretation of these changes is in agreement with the syneretic theory of lens aging.