Comparative Aspects of the Eye and Relationship With Temporal Niche

Corresponding author e-mail: belmira@gmail.com Evolutionary attempts in modify the ocular structure may appear relatively quickly in the geologic time span, suggesting that eyes are able to modify face to environmental pressures. Adaptive mechanisms to the temporal niche are present in the visual system of most of vertebrates, which involve modifications in ocular dimensions and design, in the retinal cells distribution as well as in the organization of neurochemical circuits related to the retinal resolution or detection of changes in the luminance levels. The symmetry of the perceived environment is reflected in the arrangement of retinal cells. Nonoverlapping topographies of different classes of photoreceptor and retinal ganglion cells have indicated that there is parallel processing, where different components of the visual scene may be sampled by distinct subsets of cells. On the other hand, the quality of the optical system may limit the amount of information that can be made available to the brain since the retina can only encode information that is present in the image. Therefore, adjustment of focus is particularly important if an animal has eyes adapted for use under lowor high-light conditions. Together with knowledge of the position of the eyes in the head, the shape and size of the lenses, pupil and distribution of photosensitive retinal cells can identify adaptations of each species to the temporal niche. Animal eyes that are primarily used under low-light conditions, for example, usually have optical systems of short depth of focus, such that chromatic defocus may lead to considerable blurring of the images. In some vertebrates, this problem is solved by multifocal lenses having concentric zones of different focal lengths, each of which focuses a different relevant spectral range onto the retina. In combination with these multifocal lenses the presence of a slit pupil avoids the loss of wellfocused images at relevant wavelengths even in bright light. For maximum light-gathering ability, the eyes of nocturnal and crepuscular vertebrates have pupils that are large relative to the focal lengths of the optical systems. Moreover an increase in the eye size and in the retinal magnification factor improve the retina sensitivity without reduce its resolution when compared with eyes of diurnal animals. Thus, although the main characteristics of the eye can be preserved in the phylogeny, the history of each family or genus add specific features that can be more involved with the lifestyle within a temporal niche than with the relationship among the species. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil