Evaluation of the Comparative Effect of Tetracaine on Central Corneal Thickness Measured by a Contact and Noncontact Pachymeter

Abstract

To compare the effect of tetracaine 1% on central corneal thickness (CCT) measurements obtained by the ultrasound pachymetry (USP) and Topcon SP-3000P specular microscope. In the following sequence, SP-3000P before anesthesia, USP before anesthesia, SP-3000P 10 mins after anesthesia, USP 10 mins after anesthesia, CCT measurements were obtained from 100 randomly selected eyes of 50 oculo-visually young adults in 2 measurement sessions. The CCT before instilling anesthetic did not vary significantly in each technique within session (P>0.05) and between sessions (P>0.05). Baseline CCT measurements obtained by the USP were significantly (P<0.0001) higher than that of SP-3000P by about 28 μm and 29 μm in sessions 1 and 2, respectively. A small but statistically insignificant increase in CCT (P>0.05) was observed 10 mins after instilling one drop of 1% tetracaine in both sessions of SP-3000P, whereas a statistically significant increase (P<0.05) in CCT in both sessions of USP was observed. The precision of the effects of anesthesia in the USP for sessions 1 and 2 was±15 μm and±31 μm, and in SP-3000P sessions 1 and 2, respectively, was±16 μm and±13 μm. Topical anesthetic might have an effect on CCT measurements made with the ultrasound pachymeter. Such an effect could be due to instability of the tear film caused by the anesthetic, and this effect was not measurable with the SP-3000P suggesting that the difference in the principles of operation of both pachymetry devices might play a significant role in the detection of changes in CCT induced by topical anesthetic and the difference in CCT measurements observed between techniques.