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A. C. Zamudio, R. Gerometta, D. P. Escobar, O. A. Candia; Surface Changes of Bovine and Human Lenses During Accommodation. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5861.
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Classical theories of accommodation suggest that the lens volume remains constant while the surface must change. We recently reported that the lens volume during un-accommodation decreases as the lens flattens. We now report that the surface of in vitro bovine lenses and human lens models changes between accommodation and un-accommodation, in addition to the volume change.
For bovine lenses, the isolated ciliary body-zonulae-lens was glued to a rubber washer from the stromal side of the ciliary body. This, in turn, was relaxed or stretched, with a custom-built apparatus, described elsewhere (Gerometta et al, Am J Physiol293, 2007), to simulate accommodation or un-accommodation. Experiments were carried out with lenses in Ringer’s, or in oil. Lateral photographs were taken with the lenses in the two accommodative states. For the humans lens models, geometrical figures were created in Photoshop® using data obtained from the literature. The lens models were 1) 20 year-old (y-o) lenses at 0 D and 10 D of accommodation; and 2) 45 y-o lenses at 0 D and 4 D. For the bovine and human lenses, ImageJ software was used to obtain a) the centroid of the curve that forms the perimeter of one of the two symmetrical halves of the profile, separated by the anterior-posterior axis; b) the perimeter of the figure. The first theorem of Pappus was applied to calculate the surfaces, in cm2.
In bovine lens, the stretching yielded (in most cases) a decrease in surface, with respect to its relaxed condition, in both: Ringer’s (n=6), and oil experiments (n=6). In Ringer’s, the values were 8.54±0.29 (mean±S.E.M.) for relaxed, and 8.43±0.34 cm2, for the stretched lenses (p>0.40). In oil, the surface was 8.01±0.16 for the relaxed lens, and 7.56±0.10 cm2 after the stretching (p<0.05). Human lens surfaces were as follow: for the 25 y-o, 1.72 cm2 at both 0 and 10 D; while for the 45 y-o, an increase from 1.89 to 1.92 cm2 was obtained when changing from the accommodated (4 D) to the unaccommodated (0 D) state.
The small mean reduction seen during the stretching of bovine lenses was a result of the surface increasing in some cases, but decreasing in most; implying that depending how the lens flattens, the surface can decrease (around the anterior pole) or increase (around the equator), or both. With human lens models, that were given a constant perimeter, the surface increased only in the older and larger lens, during un-accommodation. These results complement our previous findings, by indicating a change in surface as the lens accommodates, that occurs simultaneously with changes in volume.
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