Further investigation of hydrogel lens power changes due to flexure.

Measured values for ametropia-correcting powers and front surface radii of lenses on the eye are compared to values which would be expected, using the Equal Change Hypothesis and the Invariant Normals-Constant Arc Hypothesis. Photographs of various lenses on the eye, with large molecule fluorescein instilled, are presented and show no noticeable tear lens of a finite power. These photographs and our data indicate that the Equal Change Hypothesis is not valid for predicting lens power changes due to flexure. In contrast, the Invariant Normals-Constant Arc Hypothesis appears to closely predict lens flexure effects. A clinical application of this study would be to note that thin minus hydrogels correct slightly more ametropia in their flexed state than in their unflexed state. Thin plus hydrogels correct slightly less ametropia in the flexed state than in the unflexed state.