Allometry of the Eye Lens

Abstract

Purpose:: To examine the relationship between lens weight and body size in various species.

Methods:: Wet and/or dry lens weights, as a function of age, were obtained for 90 species in the author’s laboratory and from the literature. Logistic plots [log (Lens weight)/1/Age] were used to obtain the maximum asymptotic lens weights while maximum body weights were obtained from a variety of sources. Where there were gender differences in body weights, female body weights were used. Scaling of lens size to body size was carried out using the allometric equation, Lens wt = P*Body wt^BME where P is the Proportionality constant, and BME is the Body Mass Exponent. When lens and body weights were available for individual animals, allometric plots were also used to examine the relationships.

Results:: The ratio, Maximum Lens weight/Maximum Body weight, ranged from 2 to >1000, increasing with decreasing body size for all species. An allometric plot (log Max Lens wet wt/log Max Body wt) for 31 species, excluding primates, yielded a single straight line with BME= 0.55 and P = 130 (R² = 0.95). For primates, BME = 0.26 and P = 85 (R² = 0.94).The allometric plot for Maximum Lens dry weights for all data from 90 species, excluding primates, gave a reasonable linear fit (R² = 0.85) with P = 60 and BME = 0.56. Some taxons fell above and others below this line, but all had the same BME. Lagomorphs and carnivores had P values of 148 and 83, respectively, indicating that, for animals of the same body size, lagomorph dry lens weight, is almost double that of the carnivores. Voles, with P = 17, have lens dry weights about one tenth of that in the lagomorphs for the same body size. Similar constants were obtained from analysis of data from different sized individuals of the same species. Primates also yielded a straight line for dry weights with BME = 0.24 and P = 37 (R² = 0 .85).

Conclusions:: Like other body parameters, lens size appears to be related to body size. For all species, except primates, lens wet weight scales at a BME of around 0.56, suggesting that the parameters regulating growth are the same. The lens BME is more than double that observed for other organs, including eye axial length. Dry weights scale similarly but different taxons have different Proportionality constants. These differences reflect the differences in compression.Primates lenses scaled with the same BME for wet and dry weight, indicating that there is little change in the rate of compression.

Keywords: aging • development