Growth of the eye lens: I. Weight accumulation in multiple species

PURPOSE To examine the accumulation of wet and/or dry weight in the ocular lens as a function of age in different species. METHODS Wet weights and/or fixed dry weights were obtained from measurements in the author's laboratory and from the literature for over 14,000 lenses of known-ages, representing 130 different species. Various algorithms were tested to determine the most suitable for describing the relationship between lens weight and age. RESULTS For 126 of the species examined, lens growth is continuous throughout life but asymptotic and can be reasonably described with a single logistic equation, W=Wm e(-(k/A)), where W is lens wet or dry weight; Wm is the maximum asymptotic weight, k is the logistic growth constant and A is the time from conception. For humans, elephants, hippopotami, minks, wild goats and woodchucks, lens growth appears to be biphasic. No gender differences could be detected in the lens weights for 70 species but male lenses are reportedly 10% larger than those of females in northern fur seals and pheasants. Dry weight accumulation is faster than that for wet weight in all species except birds and reptiles where the rates are the same. Low lens growth rates are associated with small animals with short gestation periods and short life spans. CONCLUSIONS Lens growth is continuous throughout life and, for most species, is independent of gender. For most, growth takes place through a monophasic asymptotic mode and is unaffected by events such as hibernation. This makes lens weight measurement a reliable tool for age determination of species culled in the wild. Compaction of the growing lens generates different properties, appropriate to an animal's lifestyle. How these events are controlled remains to be established.