Effects of hydrogel lens transmissibility profiles on local corneal swelling during eye closure.

PURPOSE

To develop a unified model for describing the relations among local and regional contact lens transmissibility, topographical corneal location, and lens-induced corneal swelling under the closed eye.

METHODS

Thirteen adult male subjects, all adapted to daily wear of hydrogel lenses, wore a series of hydrogel lenses under patched eyes for 4 h. Corneal swelling was determined using an optical pachometer for five sites along the vertical meridian of test corneas. Four of the test conditions involved approximately uniform (no lens or parallel lenses) oxygen barriers over the central 8 mm of the cornea. Four additional sessions involved test lenses of -6, -3, +3, and +6 D, all having a center thickness of 0.2 mm.

RESULTS

For the uniform barrier conditions, corneal swelling followed a similar pattern at all sites. Swelling was greatest centrally and least at the most peripheral, 7 mm, chord. The swelling vs. lens thickness response could be closely described by a third-order polynomial. Swelling with nonuniform thickness lenses at all sites showed evidence of small thickness averaging effects. Average central corneal swelling under the nonuniform lenses could be estimated from the polynomial function by averaging lens thickness over 5.5 to 6.75 mm for minus lenses and approximately 7.75 mm for plus lenses.

CONCLUSIONS

The corneal swelling response to closed eye wear of hydrogel lenses follows a well ordered course over the central 7 mm. Over the same topographical area, the degree of swelling is influenced by both local and regional lens thickness profiles.