Massive increase in the stiffness of the human lens nucleus withage: the basis for presbyopia?

[摘要] Purpose: To determine the stiffness of different regions of humanlenses as a function of age, and to correlate the biophysicalmeasurements in the lens center with nuclear water content.Methods: A custom made probe fitted to a dynamic mechanical analyzerwas employed to measure stiffness values at 1 mm increments acrossequatorial sections of individual human lenses. Thermogravimetricanalysis was used to determine the percentage water content in thenuclei of human lenses.Results: There was a pronounced increase in lens stiffness over theage range from 14 to 78. In the nucleus, stiffness values varied almost1,000 fold over this age range, with the largest change observed inlenses between the ages of 20 to 60. Nuclear stiffness values increasedon average by a factor of 450. By contrast, in the cortex the averageincrease in stiffness was approximately 20 fold over this same timeperiod. In lenses younger than age 30, the nucleus was found to besofter than the cortex. This was true for all six lenses examined. Incontrast all lenses older than 30 were characterized by having nuclearvalues higher than those of the cortex. In lenses over the age of 50,the lens nucleus was typically an order of magnitude more rigid thanthat of the cortex. The crossover age, when the cortical and nuclearstiffness values were similar, was in the 30s. There was no significantchange in the water content of the human lens nucleus from age 13 to age82.Conclusions: There is a marked increase in the stiffness of thehuman lens with age. This is most pronounced in the nucleus. Since invivo data indicate that the nucleus must change shape significantlyduring accommodation, it is highly likely that these measured changes inphysical properties will markedly diminish the ability of the lens toaccommodate, and thus may be a major contributing factor to presbyopia.Since there was no measurable difference in the water contents of thenuclear regions of the lenses, this marked increase in stiffness is notdue to compaction of the lens nucleus.

[学科分类] 生物化学/生物物理