Effects of chemical restraint on electroretinograms recorded sequentially in awake, sedated, and anesthetized dogs.

OBJECTIVE: To quantitatively and qualitatively compare electroretinography (ERG) recordings in awake, sedated, and anesthetized dogs. ANIMALS: Six 6-month-old Beagles. PROCEDURES: A brief ERG protocol for dogs was used. Following 1-minute and subsequent 5-minute dark adaptation, mixed rod-cone responses were recorded bilaterally with a handheld multispecies ERG device with dogs in each of 3 states of consciousness: awake, sedated (dexmedetomidine and butorphanol), and anesthetized (atropine and hydromorphone, followed by propofol and midazolam and anesthetic maintenance with isoflurane). Low- and high-frequency noise levels were quantified via Fourier analysis, and the effect of consciousness state on signal amplitude, implicit time, and noise was analyzed via repeated-measures ANOVA. In addition, 13 veterinary ophthalmologists who were unaware of the dogs' consciousness states subjectively graded the ERG recording quality, and scores for each tracing were compared. RESULTS: ERG amplitudes were highest in awake dogs and lowest in anesthetized dogs. Implicit times were shortest in awake dogs and longest in anesthetized dogs. Differences in b-wave amplitudes and a-wave implicit times were significant. Neither low- nor high-frequency noise levels differed significantly among consciousness states. Furthermore, no significant differences were identified among observers' scores assigned to ERG tracings. CONCLUSIONS AND CLINICAL RELEVANCE: Anesthesia and sedation resulted in significant attenuation and delay of ERG responses in dogs. Chemical restraint of dogs had no consistently significant effect on low- or high-frequency noise levels or on observer perception of signal quality.

Funduscopic abnormalities and electroretinography in cases of retinopathy in German Shepherd dogs.

OBJECTIVE: To perform a clinical, ophthalmological, and electroretinographic assessment of retinopathic lesions in German Shepherd dogs. ANIMALS: The study was conducted on 14 German Shepherds diagnosed with retinopathy during the course of an ophthalmological checkup. The animals were systemically healthy police dogs used for patrolling and tracking duties and which were, at times, exposed to considerable physical strain and stress. PROCEDURE: Periodic ophthalmological examinations using slit-lamp biomicroscopy, direct and indirect ophthalmoscopy, and photography, as well as maze testing, were performed on all dogs. Electroretinography (ERG) was performed on 10 affected German Shepherds and eight control dogs. RESULTS: Ophthalmological examination revealed areas of tapetal hyper-reflectivity with pigmented centers, which were characteristic of inactive chorioretinitis. Most of the lesions were in proximity to blood vessels, and in a number of eyes, progression was observed during repeated examinations. Transition from active to inactive lesions, as well as onset in previously unaffected eyes, was also recorded. The ERG recordings showed impaired cone function, with significantly lower b-wave amplitudes and prolonged implicit times, in the mixed rod-cone, photopic, and flicker tests of affected dogs (P < 0.05). CONCLUSIONS: Retinopathy observed in German Shepherd dogs is characterized by areas of tapetal hyper-reflectivity with pigmented centers. The underlying causes of retinopathy in German Shepherd dogs remain unknown, although husbandry conditions and proximity of the lesions to blood vessels may suggest an association with physical exertion or circulatory disorders, respectively.