The effect of lifting the lids on corneal astigmatism.

Corneal toricity was measured using a keratometer with the lids in the normal position, and with the lids retracted. Lid retraction usually changed the measured toricity. In corneas with more than 1.00 D of with-the-rule astigmatism, the change was in the direction of less with-the-rule astigmatism. In corneas with astigmatism between 1 D with-the-rule and 1 D against-the-rule, the change was not systematic. The results compare with the original experiment of Masci (1965), who also found that corneas with more with-the-rule toricity show a greater reduction in toricity when the lids are retracted. Clearly the pressure the lids exert on the eyeball is a major factor influencing astigmatism.