We review the literature regarding changes in the structure and function of the cornea as an index of the physiological status of the tissue. Accurate measurement of corneal sensitivity may be the most reliable test of long-term corneal compromise inasmuch as the edema response, the most popular test of corneal physiological integrity, shows "adaptation". Although reduced sensitivity has been associated with corneal hypoxia, decreased corneal pH may also play a major role. Certainly, small departures of pH from normal levels in the body can lead to major depression of neural function. Traditionally, mechanical sensitivity of the cornea has been measured with procedures based on the von Frey hair. More recently, esthesiometry has been performed with the use of a puff of air, a chemical stimulant, and heat. Results from early trials with these procedures are encouraging in terms of the development of a viable clinical method for assessing metabolic effects on the cornea from contact lens wear.