Massive increase in the stiffness of the human lens nucleus with age: the basis for presbyopia?
Massive increase in the stiffness of the human lens nucleus with age: the basis for presbyopia?
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DOI：
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发表时间：
2004-12
期刊：
影响因子：
2.2
通讯作者：
Karl R. Heys;S. Cram;R. Truscott
中科院分区：
文献类型：
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作者：
Karl R. Heys;S. Cram;R. Truscott
目的确定人晶状体不同区域的硬度随年龄的变化，并将透镜中心的生物物理测量值与核水含量相关联。方法：采用一种定制的探头，安装在动态力学分析仪上，以1 mm的增量测量单个人晶状体赤道部分的刚度值。热重分析用于确定人晶状体核中的含水量百分比。结果在14 ~ 78岁年龄段，透镜硬度显著增加。在核中，硬度值在这个年龄范围内变化近1,000倍，在20至60岁之间的晶状体中观察到的变化最大。核硬度值平均增加了450倍。相比之下，在皮质中，在同一时间段内刚度的平均增加约为20倍。在年龄小于30岁的晶状体中，发现核比皮质软。这对于检查的所有6个晶状体都是如此。相反，所有年龄超过30岁的晶状体的特征在于具有高于皮质的核值。在年龄超过50岁的晶状体中，透镜核的刚性通常比皮质的刚性大一个数量级。当皮质和核硬度值相似时，交叉年龄在30多岁。从13岁到82岁，人类透镜核的含水量没有显著变化。结论：随着年龄的增长，人透镜的硬度显著增加。这在细胞核中最为明显。由于体内数据表明核在调节过程中必须显著改变形状，因此这些测量的物理性质的变化很可能会显著降低透镜的调节能力，因此可能是老花眼的主要影响因素。由于晶状体核区域的含水量没有可测量的差异，因此硬度的显著增加不是由于透镜核的压实。
PURPOSE To determine the stiffness of different regions of human lenses as a function of age, and to correlate the biophysical measurements in the lens center with nuclear water content. METHODS A custom made probe fitted to a dynamic mechanical analyzer was employed to measure stiffness values at 1 mm increments across equatorial sections of individual human lenses. Thermogravimetric analysis was used to determine the percentage water content in the nuclei of human lenses. RESULTS There was a pronounced increase in lens stiffness over the age range from 14 to 78. In the nucleus, stiffness values varied almost 1,000 fold over this age range, with the largest change observed in lenses between the ages of 20 to 60. Nuclear stiffness values increased on average by a factor of 450. By contrast, in the cortex the average increase in stiffness was approximately 20 fold over this same time period. In lenses younger than age 30, the nucleus was found to be softer than the cortex. This was true for all six lenses examined. In contrast all lenses older than 30 were characterized by having nuclear values higher than those of the cortex. In lenses over the age of 50, the lens nucleus was typically an order of magnitude more rigid than that of the cortex. The crossover age, when the cortical and nuclear stiffness values were similar, was in the 30s. There was no significant change in the water content of the human lens nucleus from age 13 to age 82. CONCLUSIONS There is a marked increase in the stiffness of the human lens with age. This is most pronounced in the nucleus. Since in vivo data indicate that the nucleus must change shape significantly during accommodation, it is highly likely that these measured changes in physical properties will markedly diminish the ability of the lens to accommodate, and thus may be a major contributing factor to presbyopia. Since there was no measurable difference in the water contents of the nuclear regions of the lenses, this marked increase in stiffness is not due to compaction of the lens nucleus.