The relation between eyelid tension, corneal toricity, and age.

It has been demonstrated that corneal toricity can be altered by lifting the lids from the surface of the eye. Thus, corneal curvature is modified by the position or tension of the lids. Does it follow that differences in lid tension between individuals are related to variations in corneal toricity? A lid tensiometer was designed that measured the force exerted by a lid as it was pulled away from its resting place on the eye. When this force was plotted as a function of the displacement of the lid, an elastic coefficient of the lid was obtained. This elastic coefficient was used to denote lid tension. In a sample of 195 eyes, the elastic coefficient of the lid had a mean of 3.22 g/mm (SD +/- 1.12), with a range from 1.16 to 6.78 g/mm. The results showed no correlation between the elastic coefficient and corneal toricity. Both the elastic coefficient and with-the-rule corneal toricity showed a statistically significant decrease with age. However, there was no significant relation between the elastic coefficient and corneal toricity when the effect of age was ruled out. From this experiment, and a reading of the literature, we conclude that there is no experimental evidence to show that lid tension determines corneal toricity.