Blink-induced variations in visual performance with toric soft contact lenses.

BACKGROUND

Blink-induced lens movement causes a reduction in visual performance that is potentially greater with toric than with spherical soft contact lenses because of the combination of vertical lens movement and rotation. This study examined the effect of the two most common methods of toric lens stabilization (prism ballast and dynamic stabilization) on vision.

METHOD

Four toric soft contact lens wearers were the subjects (astigmatic range 1.25 to 2.25 D). Stimulus presentation (10.5 cpd sine wave grafting flashed for 16 ms) occurred at specified times up to 400 ms after the blink. Contrast thresholds were determined monocularly with spectacles and the two types of contact lenses.

RESULTS

For the grouped data, the prism balasted lens gave better overall visual performance than the dynamic stabilization at all times after the blink. Separate analysis of subject data suggested that this general pattern was not true for all individuals.

CONCLUSIONS

Clinical evaluation of different lens designs on individual patients is required for achieving the optimum visual performance with toric soft lenses.