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H.C. Howland, S. Merola, J.R. Basarab; The allometry and scaling of of the size of vertebrate eyes. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2754.
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Purpose: We wished to examine the allometry and scaling of vertebrate eyes as a function of major taxonomic units, in order to provide standards by which an eye could be judged as relatively large or small. Methods: We compiled existing data on eye axial lengths and body weights of 297 species of vertebrates from the literature, and from our own measurements. For some animals axial length had to be estimated from weight of the eye, and for others the weight of the animal from length measurements. In all cases we recorded the method for obtaining the allometric data. Logarithmic and semi–logarithmic plots were made of axial length vs. body weight of all vertebrates and of birds, mammals, (rodents and primates also separately) reptiles and fishes. We lacked sufficient data for the amphibians. We used analysis of variance to determine if the regression slopes were significantly different from zero, and analysis of covariance to determine whether the slope and intercept of each taxon's regression line differed from the vertebrate line, and one sample t–tests to determine whether their residuals with respect to the vertebrate regression line differed from zero. Results: Data for all groups could be well fit by the equation of the form: log (axial length) = slope constant* log (body weight) + intercept constant. Birds, mammals and primates have large eyes compared to the regression for all vertebrates, and rodents and reptiles have small eyes. Fishes show a remarkable range of variation in eye size, but (and in part because of this) are not significantly different in size from those of all vertebrates when their individual axial lengths are compared to those predicted from the all vertebrate regression. Conclusions: The question of whether an eye is relatively large or small can be answered by comparing its axial length to the axial length vs. body weight regressions provided by this study.
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