Evidence for genetic linkage between the ure and trh genes in Vibrio parahaemolyticus

BACKGROUND: Many factors have been demonstrated to influence flexure of rigid contact lenses, but the contributions of surface tension and eyelid forces to flexure are not well understood. METHODS: We placed lenses on a model eye consisting of a polymethyl methacrylate (PMMA) base which could be flexed, and measured resultant flexure with a videokeratoscope. We varied the base toricity, sequence of measurement, and lens base curve. The effects of evaporation of the postlens fluid were also observed. RESULTS: Clinically significant flexure (> 0.50 D) occurred when two conditions were met: (1) the volume of the postlens space would increase if the lens unflexed, and (2) there was a paucity of fluid available to fill that space. Flexure was minimal (< or = 0.50 D) when ample fluid was present. CONCLUSION: Surface tension forces serve more to maintain rather than create rigid lens flexure. Our model helps to explain why steep-fitting lenses flex more and leads to several predictions for flexure, which appear generally to be obeyed.