Purpose To characterize a canine model of autosomal recessive RP due to a PDE6A gene mutation. Methods Affected and breed- and age-matched control puppies were studied by electroretinography (ERG), light and electron microscopy, immunohistochemistry and by assay for retinal PDE6 levels and enzymatic activity. Results The mutant puppies failed to develop normal rod-mediated ERG responses and had reduced light-adapted a-wave amplitudes from an early age. The residual ERG waveforms originated primarily from cone-driven responses. Development of photoreceptor outer segments was halted and rod cells were lost by apoptosis. Immunohistochemistry demonstrated a marked reduction in rod-opsin immunostaining outer segments and relative preservation of cones early in the disease process. With exception of rod bipolar cells that appeared to be reduced in number relatively early in the disease process other inner retinal cells were preserved in the early stages of the disease although there was marked and early activation of Müller glia. Western blotting showed that the PDE6A mutation not only resulted in a lack of PDE6A protein but the affected retinas also lacked the other PDE6 subunits, suggesting expression of PDE6A is required for normal expression of PDE6B and PDE6G. Affected retinas lacked PDE6 enzymatic activity. Conclusions This represents the first characterization of a PDE6A model of autosomal recessive retinitis pigmentosa and the PDE6A mutant dog shows promise as a large animal model for investigation of therapies to rescue mutant rod photoreceptors and to preserve cone photoreceptors in the face a rapid loss of rod cells.

Electroretinography is commonly used to assess the functional integrity of the retina. There are many external variables that can influence the electroretinographic waveforms recorded, and it is important to be aware of these so as not to misinterpret their effects as abnormalities in retinal function. In this study we examined the effect of three different recording electrodes on the ERGs recorded from normal dogs. A bipolar Burian-Allen lens, a monopolar Dawson Trick Litzkow (DTL) fiber electrode, and a monopolar ERG-Jet lens electrode were compared. The effect of altering the distance of the reference electrode from the eye was also examined; using the ERG-Jet lens electrode, the ERG was recorded with the reference electrode placed over the zygomatic arch at 1, 3 and 5 cm caudal to the lateral canthus. The ERGs recorded with the bipolar Burian-Allen lens had significantly lower amplitudes, higher a-wave thresholds and a shallower initial a-wave slope, than those recorded by the two monopolar electrodes. Positioning the reference electrode further from the eye resulted in significantly higher amplitudes. Naka-Rushton fitting and calculation of retinal sensitivity (K) gave significantly different results between the Burian-Allen lens and ERG-Jet lens electrode with the reference electrode 5 cm from the lateral canthus. These results demonstrate that recording electrode type and distance of the reference electrode from the eye significantly affect the ERG tracings of the dog, and may alter the assessment of retinal function that can therefore be derived. Results obtained using these three different types of electrodes cannot be directly compared.

A reverse transformation of the formula can be used to predict AGL in mesocephalic cross-bred dogs: AGL = 10.847 * age in weeks 0.1653.

Results suggest that at least 60 minutes of dark adaptation should be allowed before ERGs are performed in dogs after fundus photography or indirect ophthalmoscopy.

Seventy-eight dogs and ten cats with corneal lesions, including deep corneal stromal ulcers (n = 32), keratomalacia and recurrent erosions (n = 25), descemetocoeles (n = 18), staphylomas and perforating corneal defects (n = 5) and feline corneal sequestrations (n = 8) were treated with 3 types of conjunctival pedicle grafts. Breed, age, sex of the patients, size and depth of corneal lesions, suture material used, surgical technique and postoperative application of antibiotics were evaluated to determine their influence on the success rate of conjunctival pedicle graft. The success rate of the therapy was high (93.18%) and depended chiefly on the surgical technique employed.