Abstract
BackgroundThe goal of this investigation was to correlate particular age-related structural changes (compaction) to the amount of scatter in rabbit lenses and to determine if significant fiber compaction occurred in the nuclear and inner cortical regions.MethodsNew Zealand White rabbits at 16–20 months old (adult; n = 10) and at 3.5–4 years old (aged; n = 10) were utilized for this study. Immediately after euthanising, scatter was assessed in fresh lenses by low power helium-neon laser scan analysis. Scatter data was analyzed both for whole lenses and regionally, to facilitate correlation with morphometric data. After functional analysis, lenses were fixed and processed for scanning electron microcopy (SEM; right eyes) and light microscopy (LM; left eyes). Morphometric analysis of SEM images was utilized to evaluate compaction of nuclear fibers. Similarly, measurements from LM images were used to assess compaction of inner cortical fibers.ResultsScatter was significantly greater in aged lenses as compared to adult lenses in all regions analyzed, however the difference in the mean was slightly more pronounced in the inner cortical region. The anterior and posterior elliptical angles at 1 mm (inner fetal nucleus) were significantly decreased in aged vs. adult lenses (anterior, p = 0.040; posterior, p = 0.036). However, the average elliptical angles at 2.5 mm (outer fetal nucleus) were not significantly different in adult and aged lenses since all lenses examined had comparable angles to inner fetal fibers of aged lenses, i.e. they were all compacted. In cortical fibers, measures of average cross-sectional fiber area were significantly different at diameters of both 6 and 7 mm as a function of age (p = 0.011 and p = 0.005, respectively). Accordingly, the estimated fiber volume was significantly decreased in aged as compared to adult lenses at both 6 mm diameter (p = 0.016) and 7 mm diameter (p = 0.010).ConclusionMorphometric data indicates that inner cortical fibers undergo a greater degree of age-related compaction than nuclear fibers. Increased scatter appears to be only tentatively correlated with regions of fiber compaction, suggesting that it is simply one of an array of factors that contribute to the overall decreased transparency in aged rabbit lenses.
Highlights
The goal of this investigation was to correlate particular age-related structural changes to the amount of scatter in rabbit lenses and to determine if significant fiber compaction occurred in the nuclear and inner cortical regions
The average scatter was significantly greater in aged lenses as compared to adult lenses for both overall scatter (p = 0.012) and for each of the regions evaluated separately
It is interesting that the most pronounced difference in the mean scatter was found in the intermediate region (7.5-5.5 mm equatorial diameter) which corresponds to the inner cortical region of the lens
Summary
The goal of this investigation was to correlate particular age-related structural changes (compaction) to the amount of scatter in rabbit lenses and to determine if significant fiber compaction occurred in the nuclear and inner cortical regions. Structural, biochemical and physiological studies of age-related cataract have all uncovered a multitude of senescent changes affecting lens fibers at both the molecular and cellular levels. But are not limited to, posttranslational protein modifications resulting from glycation, phosphorylation, deamidation, and especially oxidation [1,2,3]. These modifications affect protein conformation, and may initiate cross-linking and aggregation[4] and are likely to negatively impact function. Numerous structural modifications have been documented that are likely to contribute to light scattering. Compaction of lens fibers is of particular interest because it has been shown to begin before middle age[18], potentially contributing to presbyopia as well as agerelated cataracts
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