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R.C. Augusteyn; Growth of the Human Eye Lens . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2536.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the accumulation of wet and dry weight and protein content in human lenses as a function of age and to compare these with lens growth rates in other species.
Wet weights and protein contents were obtained by the author from over 160 human lenses and > 200 fresh lenses of known ages from each of 15 species. Wet weight data for >600 more human lenses were obtained from the literature, as were wet or dry weights for another 40 species. Logistic plots were used to obtain growth rate constants and compression constants were obtained from allometric analyses.
The highly variability of many published human data sets precluded their use in the present analysis. Data were eliminated if the lenses were known to be fixed or had been frozen, or > 3day post–mortem, leaving ∼450. For most species examined, lens growth is asymptotic and can be accurately described with a logistic equation, W = a *exp(–b/A), where W is lens or protein weight; a is the maximum asymptotic weight, b is the growth rate constant and A is the time from embryonic lens vesicle formation. Human lens growth appears to be asymptotic from lens vesicle formation until early childhood and, thereafter, increases linearly with age. Best fit of the human data was obtained with the expression, Wt = [1.3A + 140exp(–0.35/A)]. Allometric analyses revealed that wet weight and protein content or dry weight increased at different rates in different species, with compression constants ranging from 1.00, in birds and reptiles, to 1.33 in mammals. Compression in the logistic phase in the human lens generates a maximum protein concentration of 35–40%. The linear growth mode adds tissue at a constant maximum concentration of 40%.
Unlike other body parameters, lens growth is independent of gender, environment or diet and depends only on age. Human lens growth differs from that in other species in that it occurs in two distinct modes. The first follows a logistic relationship and provides an initial burst of growth through prenatal development with an apparent termination in early childhood at a weight of 140 mg. The second is linear, adding 1.33 mg/yr to the wet weight, throughout life. The two processes both generate a maximum protein concentration around 40%. The variability observed in published human lens weights suggests that many lenses were adversely affected by storage and raises questions about the reliability of data obtained from studies with these tissues.
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