Abstract0.5% proparacaine HCl is commonly used for topical anaesthesia in ultrasound pachometry prior to refractive surgery. This drug is known to alter corneal epithelial adhesion. Does 0.5% proparacaine result in an alteration in corneal thickness due to changes in the corneal epithelium? Corneal thickness was measured by optical pachometry at 30 sec intervals for 15 min under 3 experimental conditions; 1) 2 drops of artificial tears, 2) 1 drop of 0.5% proparacaine, 3) 2 drops of 0.5% proparacaine. Baseline measurements were recorded before each trial. No significant differences were found between the mean corneal thicknesses measured in the baseline, 2 drops of artificial tears and 1 drop of 0.5% proparacaine conditions. The mean corneal thickness in the 2 drops of 0.5% proparacaine condition was significantly greater than those measured in the other conditions. In particular the measured corneal thickness was significantly different from the baseline measurements 1 to 2 min after instillation of the 2 drops of 0.5% proparacaine. Exponential modelling of the corneal edema recovery function demonstrated that recovery to baseline corneal thickness occurred 7 to 8 min following the instillation of 2 drops of 0.5% proparacaine. The data of this study suggest that only 1 drop of 0.5% proparacaine should be used for topical anaesthesia prior to ultrasound pachometry. This recommendation may minimize the possibility of measuring artifactually large corneal thickness estimates, and thus reduce the possibility of corneal microperforation during refractive surgery.