Toric contact lens designs in hyper-oxygen materials

A high proportion of eyes show significant astigmatism, and therefore toric silicone hydrogel lenses are required to satisfy the demand for continuous wear. Two concerns arise from the inevitable, increased thickness associated with toric designs: reduced oxygen transmissibility and increased rigidity leading to possible mechanical trauma. An improved understanding of the mechanisms governing toric soft-lens orientation and fit will enable the development of thinner designs. Gravity has little effect on prism-ballasted soft lenses within approximately 30 degrees of the base-down position. Some correlations have been noted between lid position and orientation. Measurements from video recordings of toric soft lenses during reorientation indicate that lid-induced rotation takes place during rather than between blinks. However, high-speed video recordings indicate that the influence of the lower lid can override that of the upper lid depending on its position, tightness, and amount of lateral movement. This knowledge gives some pointers toward optimizing toric soft lens designs in hyper-oxygen materials.