The lens of the eye as a focusing device and its response to stress

https://doi.org/10.1016/j.preteyeres.2005.10.001Get rights and content

Abstract

The continued peripheral growth of the lens, resulting in the concentration of older tissue toward the center, has the important optical consequence of producing a lens of variable refractive index. An approach consisting of the projection of fine laser beams through excised lenses in physiological solution has been used for in vitro study of lens optical quality. By varying the separation of the incident beams and/or the wavelength characteristics of the laser used, lens refractive properties and relative transparency may be examined. In the review provided, these optical properties are correlated to lens suture anatomy, lens mitochondrial morphology and function and the function of lens heat shock proteins. In addition, lens spherical aberration is evaluated as a function of accommodation. This work can be highlighted as follows: Mammalian lens suture morphology has a direct impact on lens optical function and, while suture structure of mammalian and avian lenses are very different, they both show an age-related deterioration in morphology and focusing ability. The distribution and appearance of mitochondria of the lens epithelium and superficial fiber cells are similar in all vertebrates. Lens mitochondrial integrity is correlated to lens focusing ability, suggesting a correlation between lens optical properties and lens metabolic function. The induction of cold cataract measured optically in cultured mammalian lenses is enhanced by thermal (heat) shock and this effect is prevented by inhibiting heat shock protein production. Finally, lens accommodative function can be studied by measuring lens refractive change using a physiological model involving an intact accommodative apparatus.

Section snippets

Introduction—vertebrate eye development and optical function

In a typical terrestrial eye both the cornea and lens are responsible for focusing an image on to the retina. Both structures have the same basic problem: how to maintain adequate physiological conditions for living tissue, while at the same time providing the image quality of a good optical device? Thus, the cellular physiology of the lens and the cornea include metabolic processes adequate for non-vascular tissue, while anatomically, both the lens and the cornea exhibit adaptations designed

Lens focal properties and lens stress

The review which follows describes recent research involving the in vitro study of the lens in relation to several different areas of lens research. Lens optical changes measured are compared and correlated to change in lens suture anatomy, lens mitochondrial function and morphology and the function of lens heat shock proteins. In addition, lens spherical aberration is evaluated as a function of accommodation. The common feature to this body of work is in the use of an in vitro approach that

Lens focus during mechanical stress (accommodation)

Previous attempts to directly measure the optical properties of the lens during accommodation have been thwarted by its location in the eye; measurements have been made indirectly, usually through the cornea (Glasser et al., 1995), or direct measurements have been made at the cost of the altering the natural physiology of accommodation or the apparatus of the eye itself (Glasser et al., 1995; Glasser and Campbell, 1998). The closest technique to approximating the in vivo condition has been to

Lens mitochondria

A novel recent study, using confocal microscopy, was undertaken to image the movement of the mitochondria-specific dye tetramethylrhodamine ethyl ester (TMRE) in the epithelium and superficial cortex of whole live bovine lenses (Bantseev and Sivak, 2005). The movement of TMRE fluorescence was acquired with a Zeiss 510 (configuration META 18) confocal laser scanning microscope for 10–15 min using 488 nm argon laser excitation and 505 nm Long Pass emission filter settings. The uncoupler of the

Acknowledgements

The authors’ research, described in the review, was supported by the Natural Sciences and Research Council of Canada, the Canadian Foundation for Innovation and Bausch & Lomb, Rochester, New York.

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