An unusual inherited electroretinogram feature with an exaggerated negative component in dogs

Objectives: To assess an inherited abnormal negative response electroretinogram (NRE) that originated in a family of Papillon dogs.

Animals studied: Thirty-eight dogs (Papillons, or Papillon cross Beagles or Beagles).

Procedures: Dogs underwent routine ophthalmic examination and a detailed dark-adapted, light-adapted and On-Off electroretinographic study. Vision was assessed using a four-choice exit device. Spectral-domain optical coherence tomography (SD-OCT) was performed on a subset of dogs. Two affected males were outcrossed to investigate the mode of inheritance of the phenotype.

Results: The affected dogs had an increased underlying negative component to the ERG. This was most pronounced in the light-adapted ERG, resulting in a reduced b-wave and an exaggerated photopic negative response (PhNR). Changes were more pronounced with stronger flashes. Similarly, the On-response of the On-Off ERG had a reduced b-wave and a large post-b-wave negative component. The dark-adapted ERG had a significant increase in the scotopic threshold response (STR) and a significant reduction in the b:a-wave ratio. Significant changes could be detected at 2 months of age but became more pronounced with age. Vision testing using a four-choice device showed affected dogs had reduced visual performance under the brightest light condition. There was no evidence of a degenerative process in the affected dogs up to 8.5 years of age. Test breeding results suggested the NRE phenotype had an autosomal dominant mode of inheritance.

Conclusions: We describe an inherited ERG phenotype in Papillon dogs characterized by an underlying negative component affecting both dark- and light-adapted ERG responses.