The effect of fit and parameter changes on soft lens rotation.

An evaluation of the effect of changing the base curve, overall diameter and amount of prism incorporated in the lens, on the extent of blink-initiated rotation of prism-ballasted and truncated soft contact lenses was undertaken. Increasing the prism power and the base curve (while increasing lens diameter to maintain a constant fitting relationship to the cornea) are both ineffective in changing the amount of rotation. Only steepening the base curve reduces rotation, and this change should be made cautiously because steep lenses tend to rotate to off-axis positions.