Effect of corneal drying on central corneal thickness

PURPOSE: To determine the amount of corneal thinning induced by corneal drying, and to discuss its possible consequences on applanation pressure. PATIENTS AND METHODS: Two sets of central corneal thickness measurement from 100 eyes of 100 patients were taken by ultrasonic pachymeter at time settings of 0, 15, 30, 45, and 60 seconds. During the first set (group 1), patients were asked to blink voluntarily between the measurements. During the second set (group 2), the same patients were prevented from blinking during the measurements. RESULTS: Mean central corneal thickness at 0 second in groups 1 and 2 were 547.0 +/- 37.4 microm, and 546.7 +/- 37.6 microm, respectively. Corneal thickness did not change significantly in group 1, but did significantly decrease in group 2. Rate of thinning increased linearly during the first 30 seconds, and then leveled around 0.3 microm/s up to 60 seconds. Mean corneal thickness decreased 3.0% during the 60 second drying. The decrease in thickness was significant when each time point in group 2 was compared with the preceding one (P < 0.01). Neither age nor 0 second corneal thickness in group 2 showed a significant correlation with the amount of corneal thinning at 60 seconds. CONCLUSION: Corneal thickness may significantly decrease during 1 minute of drying. Decreased thickness may result in underestimation of applanated pressure as well as central corneal thickness.