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S.M. Petersen-Jones, N.W. Khan, N. Tuntivanich; Electroretinographic Features of the PDE6A Mutant Dog . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4537.
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Purpose: To characterize the electroretinogram of the PDE6A mutant dog model. Methods: ERGs were recorded from PDE6A mutant puppies and breed and age matched controls weekly from eyelid opening until 9 weeks of age and then less frequently. Following dark adaptation for 45 minutes a scotopic white light intensity series was recorded. Following light adaptation to a background light of 30cd/m2 a white light intensity series was recorded. Results: The dark-adapted b-wave amplitude increased with age in both control and affected dogs. In control dogs b-wave amplitude stabilized by 6 weeks, whereas in affected dogs, the amplitude decreased progressively beyond 4 weeks. In the control dogs a-wave amplitude increased with age, but in the affected dogs, amplitude decreased with age. Vamax was highly reduced in affected dogs at all intensities and for all ages. The dark-adapted ERG was characterized by three parameters: a threshold for criterion amplitude, rod-mediated maximum amplitude (Vbmax), and the intensity at which one-half the maximum amplitude is elicited (i.e intensity at V1/2Vbmax). The maximum b-wave amplitude for the controls occurred on the plateau of the intensity response function just before the second limb for higher intensities. In the affected animals, the second limb of the intensity-response function was not easily seen presumable because of their reduced a-wave amplitude. In both control and affected dogs, the intensity for 1/2Vbmax decreased with increasing age. At 4 weeks of age, Vbmax was reduced in affected dogs by more than 50% and sensitivity elevated by almost 2 log units. The b-wave threshold (using a 10 µV criterion response) was elevated by approximately 2.75 log units and coincided with the intensity for 1/2Vbmax. The photopic intensity series showed similar cone responses from normal and mutant puppies at 4 weeks of age, but by 7 weeks of age the photopic responses from affected puppies were lower than in control animals. These responses decreased with age but were recordable until the affected dogs were about 9 months of age. Conclusions: PDE6A mutant dogs never develop normal rod function. Although there is an initial decrease in dark-adapted b-wave threshold from 3 to 4 weeks of age and an increase in b-wave amplitudes, after this age amplitudes start to decrease and threshold increases again. Loss of rod function is followed by a progressive but slower loss of cone function.
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