Electroretinographic findings in the Standard Wire Haired Dachshund with inherited early onset cone-rod dystrophy.

PURPOSE

To describe electroretinographic (ERG) findings in a strain of Standard Wire Haired Dachshund (SWHD)-derived dogs at the ages of approximately 5, 8 and 52 weeks selected for inherited early onset cone-rod dystrophy.

METHODS

Nineteen affected and 13 age-matched control SWHDs were included in the study. All dogs were subjected to standardized bilateral Ganzfeld ERGs and ophthalmoscopic examinations at regular intervals.

RESULTS

Photopic cone-derived ERG amplitudes were significantly lower and never reached similar levels as those recorded in control dogs. In affected dogs there was no increase with age in amplitudes recorded using 30.1 and 50.1 Hz flicker stimuli. In contrast, in the control groups the photopic b-wave amplitude recorded at 50.1 Hz increased significantly from age 5 to 8 and from 5 to 52 weeks. In affected animals, scotopic rod-derived amplitudes were significantly lower for most recordings compared to those of control dogs, although they increased significantly from age 5 to 8 weeks in both affected and controls. Both a- and b-wave implicit times were significantly longer in the youngest affected group when compared to the age-matched control group at 0.6 log cd s/m(2) and 5.1 Hz single flash light stimuli. In the control dogs, however, there was a significant shortening in a-wave implicit times from age 5 to 8 weeks, and in a- and b-wave implicit times recorded at 5.1 Hz single flash stimuli from age 5 to 52 weeks.

CONCLUSIONS

The described retinal degeneration in the SWHD is an early onset cone-rod dystrophy, initially affecting the cone system most severely. Early functional changes are seen in the rod system as well. Inner retina also appears affected already at a young age with findings indicating postsynaptic functional changes already at the earliest time point studied, at age 5 weeks. The present study further indicates that the canine retina reaches maturity later than previously reported, or that there exist major breed differences.