Temperature Under Contact Lenses In The Open And Closed Eye.

The human cornea, which is usually 3-5·c cooler than body temperature, has a wider normal temperature range than other parts of the body. Although this range may be related to certain corneal metabolic characteristics, the transient tear film nature, and an exposed anterior location, the cornea relies heavily upon exogenous and/or environmental sources for its heat. Corneal surface temperature raises in the presence of contact lenses, due to both the insulating effect of the plastic lens and the subsequent decreased evaporative cooling of tears. This rise in corneal temperature stimulates a higher metabloic rate, thereby,
changing corneal demand for oxygen and other metabolites necessary for maintaining a healthy contact lens - cornea relationship. For each 10°C increase in tissue temperature, there is a doubling of metabolic rate, therefore, even a 1 to 2°C rise in corneal temperature could significantly alter metabolism. As different contact lens materials have different heat conductivities, the purpose of this study is to determine if a difference in corneal temperature exists under HEMA (poly hydroxyethylmetharcylate) lenses as compared to those made of silicon elastomer. We will use both high plus and standard thickness minus lenses to also investigate the effect of lens thickness differences. Temperature measurements will be made in both open and closed eye conditions.