Comparison of two sedation protocols for long electroretinography in horses using the Koijman electrode

Background: Nowadays in addition to work and transport, horses are also used for competition and pleasure riding purposes. For all these activities vision has a critical role. Electroretinography is the most used test to diagnose diseases of the retinal outer segment. There is a wide variety of devices to perform the electroretinography being the main differences in the corneal electrode and the light stimulation. The Koijman electrode has been tested in dogs but not in horses. The main purpose of this study was to compare electroretinography parameters from horses sedated with detomidine alone or in combination with butorphanol, during a standardized protocol using the Koijman electrode and RETI-port® system. Seven mares, were allocated to the detomidine (D) and detomidine-butorphanol (DB) group in a randomised, controlled, crossover study. Friedman's and Willcoxon-signed ranked tests were used to compare the electroretinogram (ERG) parameters. A Student t-test was used to compare differences in the number of artefacts and valid values obtained under both sedation protocols. Results Dark adaptation peaked at 16 minutes in both groups. No significant differences in ERG parameters between both groups were observed. During the mixed rod and cone response evaluation under scotopic conditions, most mares made a movement of the head resulting in a high number of artefacts. The DB group showed a non-significant tendency to have fewer artefacts and a longer duration of sedation compared to the D group. Conclusions The Koijman electrode and the RETI-port® can be used to perform a standardized long protocol in horses with some adaptations.