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S. R. Topgi, A. Joy, K. J. Al-Ghoul; Structural and Functional Assessment of the ‘Terminal Web’ in Mammalian Lens Fibers. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2630.
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Our prior studies have shown that a terminal web-like structure is present in fiber ends adjacent to lens sutures of rat, rabbit, pig, and guinea pig, but not chicken. The objective of this ongoing study is two-fold: first, to determine whether a terminal web-like apparatus is present at apical and/or basal ends of human lens fibers, and second, to assess the functional significance of the terminal web-like structure via laser scan analysis in the animal models.
Human donor lenses (17-40 years old) were fixed, Vibratome-sectioned and labeled with phalloidin-FITC. F-actin was visualized in both anterior and posterior polar sections by confocal microscopy. Functional parameters (focal length and focal variability) were evaluated by laser scan analysis after Cytochalasin-D treatment on rabbit, pig, and guinea pig lenses, all of which possessed the web-like structure. Contralateral lenses were utilized as untreated controls. Statistical comparisons (Wilcoxon rank sum test) were conducted to compare functional parameters in control versus experimental lenses.
In human donor lenses, no evidence of an F-actin web was noted at anterior ends of fully elongated fibers. Posterior fiber ends showed evidence of a web-like F-actin structure which was structurally underdeveloped in relation to ‘terminal web’ seen in rodent lenses. Cytochalasin-D treatment resulted in disruption of the actin web and consequent disorganization of fiber ends in all experimental animal lenses. Laser scan analysis revealed that Cytochalasin-D treated lenses had a greater average focal length and increased focal variability as compared to controls in both rabbits and pigs. However, preliminary laser scan data for guinea pigs did not show any significant difference between control and experimental lenses.
Interspecies analysis revealed that a terminal web-like actin structure is present adjacent to posterior sutures in rabbit, pig, guinea pig, and human lenses, but not in chicken lenses. The data indicates that the ‘terminal web’ functions to stabilize fiber end organization and its disruption leads to degradation of focal ability. A highly developed F-actin web-like apparatus is likely to restrict fiber end movement, thereby contributing to limited accommodative ability.
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