A familial abnormal negative photopic ERG in Papillon dogs

Abstract

 

Purpose

 

To report a familial unusual negative photopic electroretinographic waveform in the Papillon breed of dog. We hypothesized that this was an inherited trait in the breed.

 

Methods

 

Electroretinographic studies were performed on Papillon dogs from within an extended pedigree. They consisted of a dark-adapted intensity response series recorded from below threshold up to a bright flash. Then following light adaptation (10 mins; 30 cd/m²) a light-adapted intensity response series was recorded. Vision testing was also performed using a previously described four-choice exit device. Tunnel choice and time to exit the device were recorded. Ability to exit the device was tested under a series of lighting conditions ranging from bright to very dim.

 

Results

 

The dark-adapted ERGs appeared of normal shape. However, the amplitude of the STR of the dogs with the abnormal photopic ERG was significantly greater than that of unaffected breed matched control dogs. The dark-adapted b- to a-wave ratio was significantly lower in affected dogs compared to controls. The light-adapted waveforms of affected dogs had a negative component that led to a large post b-wave negativity. In the more severely affected dogs the b-wave was reduced to a small elevation on a negative slope. The ratio between the amplitudes of post b-wave negativity and the b-wave was significantly greater in affected dogs compared to controls and increased with age. Vision testing did not suggest a major effect on vision. However, affected dogs took longer to exit the device at the brightest lighting intensity compared to the second brightest light intensity. Whereas the normal control dogs took the same time to exit the device at the brightest and second brightest light intensities. Crossbreeding an affected Papillon to a normal beagle produced a litter with 2 of 8 puppies developing the negative photopic ERG.

 

Conclusions

 

We report an unusual familial negative photopic ERG in Papillon dogs with evidence of increased negative components in the scotopic ERG. Similar ERG changes have been reported to develop in RCS rats as a result of aberrant amacrine cell signaling (Machida et al IOVS 2008). Although the affected Papillons appeared to have a slight reduction in visual performance in bright light there was no evidence of a retinal degenerative process. Further studies are required to show the origin of this negative component of the ERG waveform.

 

Keywords: 510 electroretinography: non-clinical • 688 retina • 691 retina: proximal (bipolar, amacrine, and ganglion cells)