A sub-Tenon’s capsule injection of lidocaine induces extraocular muscle akinesia and mydriasis in dogs

Abstract

The effect of local anaesthetic on the extraocular muscles was investigated in dogs by injecting lidocaine into the space between Tenon’s capsule and the sclera. A cross-over design was used with both eyes from five Beagle dogs randomly injected, under general anaesthesia, with 1mL of 2% lidocaine (1mL-lidocaine group), 2mL of 2% lidocaine (2mL-lidocaine group) or 2mL of normal saline (control group). Each eye was assigned to all treatments with a minimum 14day interval between injections. Changes in eye position, pupil diameter, and intraocular pressure (IOP) were evaluated during the procedure.All eyes in the 2mL-lidocaine group exhibited akinesia and mydriasis (pupil diameter >10mm) with an onset time of 6.5±4.9 and 4.2±4.3min, respectively. In the 1mL-lidocaine group, akinesia was induced in nine eyes and mydriasis occurred in seven eyes at 10.7±5.8 and 5.4±2.4min after the injection, respectively. No changes in eye position or pupil diameter were observed in the control group. Akinesia was maintained for 44.3±26.7min in the 1mL-lidocaine group and for 88.5±17.2min in the 2mL-lidocaine group. Duration of mydriasis was 51.7±28.9min in the 1mL-lidocaine group and 82.9±15.6min in the 2mL-lidocaine group. Marked chemosis and sub-conjunctival haemorrhage occurred in 16/30 and 15/30 eyes, respectively. No significant change in IOP was observed between the mean pre- and post-injection values in all groups. These results suggest that a sub-Tenon’s injection of 2mL of 2% lidocaine provided effective extraocular muscle akinesia and mydriasis in dogs.