Influence of fentanyl, ketamine or lidocaine infusion on the intraocular pressure and pupil size in conscious dogs

Fifty-five healthy conscious dogs were included in a prospective randomised double-blinded clinical study. The dogs allocated to one of four groups received intravenous bolus followed by infusion of fentanyl (FEN-group), or ketamine (KET-group), or lidocaine (LID-group), or saline (SAL-group). The intraocular pressure (IOP), pupil size (PS), heart rate (HR) and mean arterial pressure (MAP) were measured prior to and at 2, 5, 10, 20 and 30 min after initiation of the drug administration. The data were analysed using an analysis of variance and the Steel-Dwass test. No significant difference in the IOP within or between the groups was detected. In the FEN-group, the PS decreased significantly at all the measured times. In the KET-group, the PS increased significantly at 2, 5 and 10 minutes. The PS was significantly smaller in the FEN-group compared to the KET-group at 2, 5, 10 and 20 min, compared to the SAL-group at 5, 10, 20 and 30 minutes. In the FEN-group the HR significantly decreased compared to the baseline and was significantly lower compared to the KET-group and LID-group. Fentanyl, ketamine or lidocaine administered at the doses studied as a bolus followed by a 30-min infusion seem to cause no effect on the IOP in healthy conscious non-painful dogs without ocular abnormalities. Fentanyl decreased and ketamine transiently increased the PS.