Interaction between mechanical and osmotic forces in the isolated rabbit lens.

Based on our previous work showing that cow and rabbit lenses isolated with their accommodation anatomical components intact change volume during simulated accommodation in vitro, and that hyposmolality and hyperosmolality also produce volume changes, we tested the idea that exerting these forces simultaneously may add or counteract each other. Further, we attempted to find a point at which osmotic and mechanical forces may cancel each other. Using previously described methodology, we found that combined stretching and anisotonic conditions applied to a lens always produced less of a volume change than that observed on its paired lens from the fellow eye that was only subjected to anisotonic conditions. Our results suggest that a stretching force that increases the equatorial diameter by 0.4% and reduces the lens volume by 1.8% could be canceled by a hyposmotic force of about -20 to -30 mOsM. Counter-intuitively, lenses that were subjected to stretching and hyperosmolality had less volume decrease than their paired lenses only exposed to hypertonicity. This latter observation is likely due to the prevention by the mechanical stretching forces of the shortening of the equatorial diameter, which normally occurs in hypertonic media.