The Maturation of the Electroretinogram of the Dog

Abstract

Abstract: : Purpose: To investigate the maturation of the canine electroretinogram. Methods: The electroretinogram of eight normal crossbred puppies was recorded at 11 timepoints between 2 and 28 weeks of age. The puppies were anesthetized and pupils dilated with tropicamide. Burian-Allen bipolar corneal contact lenses were fitted. Following dark adaptation for 45 minutes a scotopic white light intensity series was recorded. Then following light adaptation to a background light of 30cd/m² a white light intensity series was recorded. An LKC Utas 3000 Electrophysiology unit (LKC) with a ganzfeld bowl was used to deliver the flash stimulus and record and average the ERG tracings. Results: The puppies initially had an a-wave dominated response with the b-wave not becoming prominent until 4 weeks of age. Intensity/response plots showed that the dark-adapted b-wave threshold (using a 10µV criterion response) decreased by approximately 2 log units between 3 and 4 weeks of age and that the intensity for dark-adapted 1/2Vbmax (a measure of photoreceptor sensitivity) had stabilized by 5 weeks of age. The value of dark-adapted Vbmax peaked at 7 weeks of age and then gradually declined until the puppies reached about 16 weeks of age and then remained at a similar level for the duration of the study period.Analysis of a-wave responses showed that photoreceptor sensitivity and maximal responses are mature by about 7 weeks of age for rod-mediated responses but that the cone–mediated responses mature at an earlier age. Conclusions: The canine electroretinogram matures over the first 6 or 7 weeks of age with cone mediated responses maturing at a slightly earlier age than rod responses.

Keywords: electrophysiology: clinical • animal model • photoreceptors