Evaluation of the effect of tetracaine 1% on central corneal thickness obtained by ultrasound and SP-3000P

ABSTRACT

To study the effect of tetracaine 1% on central corneal thickness measurements obtained by the ultrasound pachymetry and Topcon SP-3000P specular microscope. In the following sequence, SP-3000P before anaesthesia, Ultrasound pachymetry before anaesthesia, SP-3000P 10 minutes after anaesthesia, Ultrasound pachymetry 10 minutes after anaesthesia, central corneal thickness measurements were obtained from 100 randomly selected eyes of 50 oculovisually young adults in two measurement sessions. The central corneal thickness before instilling anaesthesia did not vary significantly in each technique within-session [p>0.05] and between sessions [p>0.05]. Baseline central corneal thickness measurements obtained by Ultrasound pachymeter was significantly [P<0.0001] higher than that of SP-3000P by about 28 micro m and 29 micro m in sessions one and two respectively. A small but statistically insignificant decrease in CCT [P>0.05] was observed 10 minutes after instilling one drop of 1% tetracaine in sessions 1 whereas a statistically insignificant increase [P>0.05] in CCT in session two measurements of SP-3000P was observed. There was a statistically significant increase in CCT [p<0.05] obtained by ultrasound pachymeter 10 minutes after instilling one drop of 1% tetracaine in sessions I and an increase that was not quite significant [P>0.05] also observed in the second measurement session of ultrasound pachymetry. The precision of the effects of anaesthesia in ultrasound pachymeter for sessions 1 and 2 were+l5 micro m and+31 micro m, and in SP-3000P sessions 1 and 2 respectively were+16 micro m and +/- 13 micro m. Topical anaesthesia 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 anaesthetic, and this effect was not measurably with the SP-3000P suggesting that the difference in the principles of operation of both pachymeters might play a significant role in the detection of changes in CCT induced by topical anaesthesia