The use of colour Doppler imaging to determine the effects of administration of butorphanol, medetomidine and ketamine on indices of feline ocular impedance

Doppler impedance indices, such as the resistive index (RI) and pulsatility index (PI), are commonly used to characterise resistance to the flow in the vascular system. Chemical restraint can potentially affect these indices, although in some patients such restraint is necessary before ultrasonographic examination. The objective of this study was to compare ocular vascular velocity parameters, measured using Doppler imaging, in healthy conscious cats and in cats after administration of a combination of anaesthetics (butorphanol, medetomidine and ketamine). Twelve healthy cats of different breeds and both sexes were studied using Doppler imaging. The long posterior ciliary arteries in both eyes were examined. Mean comparison tests (paired and unpaired t-test) were used to determine whether any significant differences existed between right and left ocular indices and between sexes. A correlation study was applied between RI, PI and body weight. There were no significant differences in RI and PI between left and right eyes. Values also did not significantly differ among males and females. The RI and PI in long posterior ciliary arteries of cats anaesthetised with butorphanol, medetomidine and ketamine were significantly lower than those of healthy conscious cats. There was no correlation between impedance indices and body weight.