Gerometta R, Zamudio A C, Escobar D P, Candia O A
Dept of Ophthalmology, Mount Sinai School of Medicine, One Gustave L Levy Place, New York, NY 10029, USA.
Am J Physiol Cell Physiol. 2007 Aug;293(2):C797-804. doi: 10.1152/ajpcell.00094.2007. Epub 2007 May 30.
During accommodation, mammalian lenses change shape from a rounder configuration (near focusing) to a flatter one (distance focusing). Thus the lens must have the capacity to change its volume, capsular surface area, or both. Because lens topology is similar to a torus, we developed an approach that allows volume determination from the lens cross-sectional area (CSA). The CSA was obtained from photographs taken perpendicularly to the lenticular anterior-posterior (A-P) axis and computed with software. We calculated the volume of isolated bovine lenses in conditions simulating accommodation by forcing shape changes with a custom-built stretching device in which the ciliary body-zonulae-lens complex (CB-Z-L) was placed. Two measurements were taken (CSA and center of mass) to calculate volume. Mechanically stretching the CB-Z-L increased the equatorial length and decreased the A-P length, CSA, and lens volume. The control parameters were restored when the lenses were stretched and relaxed in an aqueous physiological solution, but not when submerged in oil, a condition with which fluid leaves the lens and does not reenter. This suggests that changes in lens CSA previously observed in humans could have resulted from fluid movement out of the lens. Thus accommodation may involve changes not only in capsular surface but also in volume. Furthermore, we calculated theoretical volume changes during accommodation in models of human lenses using published structural parameters. In conclusion, we suggest that impediments to fluid flow between the aquaporin-rich lens fibers and the lens surface could contribute to the aging-related loss of accommodative power.
在调节过程中，哺乳动物的晶状体形状从更圆的形态（近聚焦）变为更扁平的形态（远聚焦）。因此，晶状体必须具备改变其体积、囊表面积或两者的能力。由于晶状体的拓扑结构类似于圆环面，我们开发了一种方法，可根据晶状体横截面积（CSA）来确定体积。CSA是通过垂直于晶状体前后（A-P）轴拍摄的照片获得，并使用软件进行计算。我们通过一个定制的拉伸装置模拟调节过程中的形状变化，在该装置中放置睫状体-小带-晶状体复合体（CB-Z-L），计算了分离的牛晶状体的体积。通过两次测量（CSA和质心）来计算体积。机械拉伸CB-Z-L会增加赤道长度，并减小A-P长度、CSA和晶状体体积。当晶状体在生理水溶液中拉伸和放松时，控制参数会恢复，但浸没在油中时则不会恢复，在油中流体离开晶状体且不会再进入。这表明先前在人类中观察到的晶状体CSA变化可能是由于流体从晶状体中流出所致。因此，调节可能不仅涉及囊表面的变化，还涉及体积的变化。此外，我们使用已发表的结构参数，计算了人晶状体模型在调节过程中的理论体积变化。总之，我们认为富含水通道蛋白的晶状体纤维与晶状体表面之间的流体流动障碍可能导致与衰老相关的调节能力丧失。
