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.