Evaluation of corneal anaesthesia after the application of topical 0.5% bupivacaine, 2% lidocaine and 0.4% oxybuprocaine in normal horses.

The research article aims to compare the effectiveness of three different topical anaesthetics – 0.5% bupivacaine, 2% lidocaine, and 0.4% oxybuprocaine – on the corneas of healthy horses by measuring corneal touch threshold (CTT).

Research Method

• The article describes a prospective, blinded crossover study conducted on a group of 10 healthy horses to evaluate the effects of three types of topical anaesthetics on their eyes.
• The sensitivity of the cornea was measured through the corneal touch threshold (CTT). This measure indicates the level of pressure required for the horse to blink when the cornea is touched.
• The study was split into three phases, with each horse randomly assigned one of the three anaesthetics. There was a 72-hour washout period in between to allow the effects of the first treatment to wear off.
• Baseline CTT was recorded before application of the anaesthetic (T0), and then at intervals of 5 minutes (T1), 10 minutes (T2), and 20 to 90 minutes (T3 to T10).
• The CTT data were compared among treatments at each time point using statistical methods (Friedman test).

Results

• All treatments led to a significant decrease in CTT at T1, indicating that the anaesthetics had taken effect.
• The most significant anaesthetic effect was observed at T3 with Bupivacaine and Oxybuprocaine treatments. For lidocaine, the greatest anaesthetic effect was observed at T6 (50 minutes).
• On comparison, CTT was significantly lower with Bupivacaine treatment compared to the other two at T3, indicating a more profound anaesthetic effect.
• No significant difference in CTT values was observed between T1 and T6 for Bupivacaine, between T1 and T7 for Lidocaine, and between T1 and T8 for Oxybuprocaine indicating persistent anaesthetic effects throughout these time points.
• Regarding the duration of maximum effect, bupivacaine lasted for 45 minutes, lidocaine for 55 minutes, and oxybuprocaine for 65 minutes.

Conclusion

• The study concludes that 0.5% bupivacaine and 2% lidocaine have a similar anaesthetic effect as the commonly used 0.4% oxybuprocaine for corneal anaesthesia.
• Given the comparable effectiveness, the researchers propose that bupivacaine and lidocaine might serve as potential alternative anaesthetics for horse corneal procedures.