Electroretinography in Labrador retrievers given ketamine-xylazine anesthesia

Abstract

Electrophysiologic examination of scotopic and photopic retinal function was done in 31 young healthy Labrador Retrievers and 6 Labrador Retrievers with ophthalmoscopic signs of generalized progressive retinal atrophy (PRA). Scotopic responses to 4 stimulus intensities (b-wave threshold and 0.65-, 1.60-, and 2.59-log relative units above b-wave threshold, tests 1, 2, 3, and 6, respectively) were determined, using single-flash stimulation. Alternating current recorded single-flash c waves (stimulus intensity 3.18-log relative units above b-wave threshold, test 4) and 30-Hz photopic flicker (stimulus intensity 1.92-log relative units above b-wave threshold, test 7) responses were recorded. Results of the single-flash recordings from 31 healthy dogs were analyzed statistically. The method used allowed for a separation of rod and cone function. Tests 3, 6, and 7 were most useful in determination of retinal disease, when results of the healthy young dogs were compared with results obtained from generalized PRA-affected dogs. Various doses of ketamine and xylazine in dogs with ophthalmoscopically normal fundi had no significant effects on a- and b-wave amplitudes when dogs were given single-flash stimuli 1.60-log relative units above b-wave threshold (test 3). Three 3-year-old dogs, with ophthalmoscopic signs of generalized PRA, had greatly reduced a- and b-wave amplitudes and unaltered or slightly shortened a- and b-wave latencies. One 3-year-old dog with normal-appearing fundi had responses similar to those of dogs with generalized PRA of the same age. On repeated examination 6 months later, this dog had ophthalmoscopic and angiographic signs of generalized PRA.(ABSTRACT TRUNCATED AT 250 WORDS)