Measures of tear exchange under rigid contact lenses: Part II. Individual systems and a population model

Abstract Part I of this series discussed a model for using freezing-point osmometry techniques and the Cuklanz-Hill mathematical model to determine tear-exchange efficiencies of rigid contact lenses. In Part II, the model was applied, the tear-exchange percentages per blink being determined for six best-fit cornea-contact lens systems. The lenses were fitted “on-K” to the flattest corneal meridian (to the nearest 0.05 mm), all other design features (overall diameter, posterior optic zone, peripheral curve width, vertex power, center thickness, and edge lift) being identical across all of the system. The tear-exchange percentages per blink for this population ranged from 5.39% to 6.06%, with a mean value of 5.69%. The amount of exchange was not well correlated with the amount of corneal toricity present.