Electroretinogram responses of the normal thoroughbred horse sedated with detomidine hydrochloride

Fonte: Melanie L. Church and Joanna C. Norman

Recording ERG using the HMsERG and a contact lens electrode.
   Recording ERG using the HMsERG and a contact lens electrode.

Purpose: The main objective was to record electroretinogram (ERG) parameters of normal thoroughbred mares using the HMsERG, a mini-Ganzfeld electroretinographic unit, and a contact lens electrode. The second objective was to determine whether IV detomidine hydrochloride at 0.015 mg/kg is consistently an effective choice for sedation of horses undergoing this ERG protocol. Methods: The study population consisted of 30 normal thoroughbred mares. ERG data were harvested using a protocol that included three different light intensities (10, 3000, and 10 000 mcd s/m2) and a 30-Hz flicker at 3000 mcd s/m2. Results: Mean, median, standard deviation, and estimated normal ranges using the 5–95% of the data for a- and b-wave implicit times (IT), amplitudes (AMP), and b/a ratios were reported. Scotopic results at low intensity (10 mcd s/m2) had estimated ranges for b-wave IT of 41.8–72.9 ms and AMP of 19.8–173.3 lV. Middle intensity (3000 mcd s/m2) a-wave IT was 13.2–14.7 ms with a-wave AMP of 68.4–144 lV; the b-wave IT was 28.7–41.5 ms with b-wave AMP of 105.7–271.5 lV; and the b/a ratio was 0.95–2.71. The high-intensity (10 000 mcd s/m2) average recordings showed an a-wave IT of 13–14.9 ms, a-wave AMP of 85.7–186.8 lV; b-wave IT of 26.6–45.4 ms, b-wave AMP of 104.7–250.6 lV; and a b/a wave ratio of 0.7–2.0. The 30-Hz cone flicker showed an IT of 22.8–28.9 ms and AMP of 44.1–117.1 lV. Conclusions: Results of normal thoroughbred ERG responses are reported. The protocol proved to be simple and safe and provided consistent results.


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