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Retinopathy associated with ivermectin toxicosis in two dogs

Patrick J. Kenny BVSc, DACVIM1, Karen M. Vernau DVM, MAS, DACVIM2, Birgit Puschner DVM PhD, DABVT3, and David J. Maggs BVSc, DACVO4
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  • 1 William R. Pritchard Veterinary Medical Teaching Hospital, University of California, Davis, CA 95616.
  • | 2 Department of Surgical and Radiological Sciences, University of California, Davis, CA 95616.
  • | 3 School of Veterinary Medicine, and the California Animal Health and Food Safety Laboratory, University of California, Davis, CA 95616.
  • | 4 Department of Surgical and Radiological Sciences, University of California, Davis, CA 95616.

Abstract

Case Description—2 dogs (dogs 1 and 2) were examined for sudden onset of blindness. Both dogs had mild obtundation and mydriasis in both eyes. It was thought that dog 1 may have ingested ivermectin; dog 2 had been treated with ivermectin for demodectic mange.

Clinical Findings—On initial examination, both dogs had mydriasis and decreased pupillary light reflexes in both eyes. Dog 1 had an absent menace response bilaterally. Fundic examination of both eyes in both dogs revealed regions of multifocal retinal edema and folds with low-lying retinal separation. The electroretinogram was extinguished in dog 1 and attenuated in dog 2. Ivermectin was detected in serum samples from both dogs.

Treatment and Outcome—Both dogs made a complete clinical recovery following cessation of exposure to ivermectin; electroretinographic findings improved, and retinal edema resolved with some residual chorioretinal scarring.

Clinical Relevance—To our knowledge, this is the first report of resolution of retinal edema and electroretinographic changes associated with ivermectin toxicosis in dogs. In dogs that develop blindness suddenly, fundic examination, electroretinography, and assessment of serum ivermectin concentration are diagnostically useful, even if exposure to ivermectin is unknown.

Abstract

Case Description—2 dogs (dogs 1 and 2) were examined for sudden onset of blindness. Both dogs had mild obtundation and mydriasis in both eyes. It was thought that dog 1 may have ingested ivermectin; dog 2 had been treated with ivermectin for demodectic mange.

Clinical Findings—On initial examination, both dogs had mydriasis and decreased pupillary light reflexes in both eyes. Dog 1 had an absent menace response bilaterally. Fundic examination of both eyes in both dogs revealed regions of multifocal retinal edema and folds with low-lying retinal separation. The electroretinogram was extinguished in dog 1 and attenuated in dog 2. Ivermectin was detected in serum samples from both dogs.

Treatment and Outcome—Both dogs made a complete clinical recovery following cessation of exposure to ivermectin; electroretinographic findings improved, and retinal edema resolved with some residual chorioretinal scarring.

Clinical Relevance—To our knowledge, this is the first report of resolution of retinal edema and electroretinographic changes associated with ivermectin toxicosis in dogs. In dogs that develop blindness suddenly, fundic examination, electroretinography, and assessment of serum ivermectin concentration are diagnostically useful, even if exposure to ivermectin is unknown.

Contributor Notes

Dr. Kenny's present address is The Queen Mother Hospital for Animals, The Royal Veterinary College, Hawkshead Ln, North Mymns, Hatfield, Herts, AL9 7TA, England.

The authors thank Dr. Angela M. Hughes and Katy Robertson for genetic testing for the multidrug sensitivity mutation and John Doval for assistance with figures.

Address correspondence to Dr. Vernau.