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Robert C. Augusteyn, Jean-Marie Parel; Are Animals Good Models for Human Lens Growth and Presbyopia?. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1541.
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© ARVO (1962-2015); The Authors (2016-present)
For obvious reasons, animals are commonly used as models for exploring human cataract and presbyopia formation. Accessibility and convenience are generally the prime reasons for selection, rather than similarities in properties. In this presentation, the validity of using animal models will be examined by comparing the growth and properties of human, other primate and non-primate animal lenses.
Data on changes in isolated lens weights and dimensions, as a function of age, were collected for human and other primates, as well as several non-primates. These were compared using logistic and allometric analyses. In addition, lens dimensions, protein distribution patterns and metabolic features were obtained for a limited number of species.
Human lens growth, as judged from weight increases, is biphasic, asymptotic before birth and linear thereafter. This generates two distinct tissues, with different crystallin contents and properties, separated by a diffusion barrier. The metabolically inactive nucleus is of fixed size whereas the cortex grows continuously. By contrast, lens growth in all other species examined, appears to be asymptotic only with no clear demarcation between nucleus and cortex. Isolated human lens shape changes prior to adulthood, with central thickness decreasing while diameter increases. From early adulthood on, both diameter and thickness increase and the aspect ratio decreases. This does not appear to be the case with any other species. In other primates, lens thickness decreases throughout life while diameter increases, resulting in a continuous increase in the aspect ratio.
There are substantial differences in the growth mechanism and ultimate properties of human, other primate and non-primate lenses. Human lenses undergo complex changes in shape because of a decrease in central thickness up till adolescence and an increase thereafter. By contrast thickness decreases continuously in other primates. These observations raise questions about using animals as models for human presbyopia. Although the monkey's accommodation apparatus was shown to be the closest to man's, it may not be the ideal model for presbyopia.
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