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K. O. Gilliland, S. Metlapally, M. J. Costello; Morphological Analysis of Extensive Fiber Cell Compaction in the Adult Nucleus of Aged Human Transparent Lenses. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4388.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the continuous change in fiber cell shape from the lens capsule through the adult nucleus of human transparent lenses over a wide age range. Previous microscopic studies of transparent and cataractous lenses suggested that adult nuclear fiber cells had reduced cross-sectional area and very irregular flattened shapes in contrast to the typical regular hexagonal shapes of cortical fiber cells and outer nuclear fiber cells in young animals. Recent evidence suggests that lens growth rate in aged humans is nearly zero and that presbyopic hardening of the nucleus occurs without significant changes in cell shape or number. Precise measurements of cell shape and density are required to evaluate these suggestions.
Whole human donor lenses, ages 23 to 71 yrs, were preserved by immersion fixation or fixation of Vibratome thick sections and processed for histological, transmission electron and confocal microscopy.
Elongating fiber cells are regular flattened hexagons with an average width of about 3 µm measured along very regular radial cell columns in the equatorial plane. Within the cortex about 0.2 mm from the capsule, cells are reduced in width and are more irregular in shape. At 1 mm from the capsule, clearly within the adult nucleus, the average width is about 0.6-0.8 µm in aged lenses. There is a corresponding reduction in average cross-sectional area of about a factor of 3X between the outer cortex and the adult nucleus. Comparisons of the adult nuclear fibers in aged (60 y.o.) and young (23 y.o.) show that compaction can be detected even in the young lens, but not to the same extent, where the band of compaction is smaller and the average fiber width is larger.
These new structural data clearly demonstrate that compaction is a prominent feature of the fiber cells in the adult nucleus. The adult nucleus, which shows the greatest compaction, is about 1 mm thick beginning about 1 mm from the capsule in aged human lenses. This position corresponds roughly to the proposed age-related diffusion barrier that precedes the formation of nuclear cataracts.
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