Author(s): Wise EN, Foster ML, Kremers J, Mowat FM. A modified silent substitution electroretinography protocol to separate photoreceptor subclass function in lightly sedated dogs. Vet Ophthalmol. 2020 Nov 24. doi: 10.1111/vop.12847. [Epub ahead of print] PMID 33232560
Journal: Veterinary Ophthalmology, Nov 2020
OBJECTIVE A previously published study successfully isolated photoreceptor responses from canine rods, long/medium-wavelength (L/M) cones, and short-wavelength (S) cones using silent substitution electroretinography (ERG) performed under general anesthesia. We hypothesized that responses would be similar in dogs under sedation and that a curtailed protocol suitable for use in clinical patients could effectively isolate responses from all three photoreceptor subtypes.
ANIMALS STUDIED Three normal adult purpose-bred beagles (2 females and 1 male).
METHODS Dogs were dark-adapted for 1 hour. Sine wave color stimuli were delivered using LEDs in a Ganzfeld dome. The ERG protocol under anesthesia was performed as previously published; sedated ERG protocols were performed after a 3-day washout period. Intravenous sedation (dexmedetomidine 1.25 mcg/kg, butorphanol 0.1 mg/kg) was administered for sedation. Statistical analysis was performed using two-way repeated-measures ANOVA and linear regression.
RESULTS In both anesthetized and sedated animals, rod-derived responses peaked at low frequency (4-12 Hz), L/M-cone responses peaked at high frequency (32-38 Hz), and S-cone responses peaked at low frequency (4-12 Hz). The frequencies eliciting maximal responses were similar in sedated and anesthetized protocols, although rod amplitudes were significantly higher in the sedated protocols compared with anesthetized (P < .001).
CONCLUSION We present a clinically applicable method to consistently isolate rod and cone subclass function in sedated dogs. This may allow detailed evaluation of photoreceptor function in clinical patients with rod or cone subclass deficits without the need for general anesthesia or protracted adaptation times.