Effects of base curvature on squeeze pressures in contact lenses

Calculations are made of the effects of base curvature on squeeze pressures in hard contact lenses during blinking. An axisymmetrical model with parabolic profile is used of a cylindrical body (the lens) moving along its axis toward a rigid surface (the eye), from which it is separated by a tear film. The results are compared with those obtained from a two-dimensional model having the same parabolic profile. It is found that the maximum pressures in the axisymmetric case are precisely one-half of those in the corresponding two-dimensional one, irrespective of the base curvature. Thus, estimated pressures using the latter model are likely to be too large. A simple formula is also obtained which shows the effect of base curvature on the force. The calculated pressures (and hence forces) will be further reduced if lens deformation occurs as is the case in soft contact lenses.