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R. Gerometta, A. Zamudio, O. Candia; Fluid Flow During Lens Accommodation in an in vitro Bovine Model . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4720.
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To develop an in vitro model of accommodation to further test our hypothesis that during this process the lens looses and gains fluid. When a spherical body becomes flatter it must increase its surface area at constant volume, or loose volume at constant surface. Previously, we have demonstrated that the lens looses fluid when it is compressed. Now we reproduce accommodation as it occurs in vivo, by pulling the zonulae around the equator with a stretching force.
The eye was cut around the sclera posterior to the limbus. The ciliary body–zonulae–lens was isolated as a unit. The base of the ciliary body was glued on a rubber washer with a central hole 2–mm larger than the lens equator. Eight concentric hooks with attached strings pierced the periphery of the rubber washer. A device pulled the strings with a symmetrical force stretching the washer. As it stretched, the glued ciliary body separated from the lens and exerted tension on the zonulae that in turn forced the lens to adopt a more flattened shape. The lens was photographed so that its equatorial diameter (EQ) and anterior–posterior length (APL) can be computed with appropriate software. These values were confirmed by direct measurement with a precision caliper.
In 8 experiments the mean control EQ was 17.7 ± 0.23 mm, and its APL 12.7 ± 0.29 mm. After stretching, those measurements were 18.5 ± 018 and 12.1 ± 017 mm respectively (P<0.05 as paired data) indicating that the lens was deformed as it occurs in natural accommodation.. Assuming the lens to be an ellipsoid, its volume was calculated with appropriate equations. The accuracy of the methods was validated by comparing the calculated volume with the weight of the isolated lens at the end of the experiment. It was found that the bovine lens weighting 2.275 mg loses and regain about 4 % of its weight.
We have shown that an in vitro model that simulates natural accommodation indicates a movement of fluid out and into the lens during the process. This fluid movement should also occur internally between lens fibers connected by aquaporin 0. Thus, any impediment to this movement should impair the accommodative process.
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