Abstract
Abstract: :
Purpose: To determine the effect of topical anesthetic drops on central corneal thickness (CCT) measurement using contact ultrasound pachymetry and its influence on intraocular pressure (IOP) adjustment. Methods: A prospective study involved 92 eyes of 46 non–glaucomatous patients, on no topical ocular medications and with no history of laser treatment or ocular surgery. CCT was measured without the use of topical anesthetic drops. CCT was then measured following one drop of topical anesthetic (proparacaine hydrochloride ophthalmic solution .5%) at 1 and 5 minute intervals. Three consecutive ultrasonic pachymetry (Quantel Medical) measurements of CCT were obtained and an average value was computed for each interval. Paired t–tests were then used to compare the differences in CCT between baseline (no anesthetic drop) and 1 minute post–anesthetic drop administration, and between baseline (no anesthetic drop) and 5 minute post–anesthetic drop administration. IOP adjustment values based on CCT at baseline, 1 min. and 5 min. intervals were determined using algorithm based on Ehlers et al (1975) modified from Stodimeister(1998). Paired t–tests were also used to compare the differences in IOP adjustment values between baseline and 1 min., and between baseline and 5 min. Results: The mean CCT was 559.39 +/– 3.21 µm at baseline, 561.76 +/– 3.26 µm at 1 min. after anesthetic, and 562.36 +/– 3.49 µm at 5 min. after anesthetic. The difference between mean CCT at 1 min. and baseline was 2.37 +/– .981 µm, which was statistically significant (p=.018). The difference between mean CCT at 5 min. and baseline was 2.97 +/– 1.284 µm, which was significant (p=.023). The mean IOP adjustment value was –.978 +/– .228 mmHg at baseline, –1.196 +/– .226mmHg at 1 min., and –1.239 +/– .246 mmHg at 5 min. The difference between mean IOP adjustment at 1 min. and baseline was –.228 +/– .082 mmHg, which was significant (p=.009). The difference between mean IOP adjustment at 5 min. and baseline was –.272 +/– .103 mmHg, which was also significant (p=.013). Conclusions:While the use of topical anesthetic drops appears to increase CCT with statistical significance, and also appears to be related to a statistically significant decrease in corrected IOP, this variation is smaller than the variability observed in IOP measurement (+/– 2 mmHg) by Goldman tonometry (Sudesh et al, 1993). The use of topical anesthetic drops to facilitate CCT measurement using contact ultrasonic pachymetry probably does not induce clinically significant error.
Keywords: intraocular pressure • cornea: clinical science