November 28, 2016

Variation in intraocular pressure following application of Tropicamide in three different dog breeds

 

          This study wanted to examine the effects of a medicine called Tropicamide, used to induce pupil dilation, on the intraocular pressure (IOP) of dogs. Researchers tested this drug on 76 dogs of three breeds: Golden Retrievers, Cocker Spaniels, and Siberian Huskies. Tropicamide is a fast-acting drug used in humans as well as dogs, but in some cases it has been known to increase IOP because of an increase of outflow resistance. This increase is more likely to develop in humans with glaucoma. Due to the large range in the likelihood of different breeds to develop glaucoma, researchers were interested in whether there would be interbreed variability in the effects of the drug on IOP.  

            Before the administration of the drug, each dog’s original IOP was measured and a routine ophthalmic examination was conducted. Once the original IOPs were recorded, the researchers put one drop of Tropicamide in the right eye of each subject. Once maximum dilation had been achieved, after 30 minutes, they took a second reading of each dog’s IOP.

            After compiling all of their data, the researchers first determined that age and sex did not seem to influence IOP of dogs in a significant way. They analyzed the original results before the administration of the Tropicamide and discovered that Siberian Huskies had significantly higher IOPs than both the Cocker Spaniels and Golden Retrievers. Then researchers compared the initial results with the IOPs recorded after pupil dilation, and found that overall, there was no significant change in IOP. However, there was an exception – four of the Siberian Huskies had abnormally high IOP levels. The scientists proposed that this may have occurred because those Huskies initially had unusually low IOP values.

            Overall, the researchers found that the IOP values of this group of dogs was consistent with previous records of average dog IOP. They were able to say that there is interbreed variability in IOP, evident from the initially higher IOP values in the Huskies. The Huskies also had larger changes in IOP after the administration of Tropicamide, which also suggests differences in breed responses to the drug. However, the researchers concluded that overall, differences in breed responses to the drug. Researchers the speculated that the four Huskies with abnormally high changes may have goniodysgenesis, a disease that results in abnormal and incomplete development of the intraocular fluid egress channels inside the eye. They also thought it would be interesting to follow those four dogs and see if they had a greater disposition to glaucoma. However, previous studies contradict each other, some saying that Cocker Spaniels and Huskies are more likely to develop glaucoma than Golden Retrievers, but others show that Cocker Spaniels and Golden Retrievers are more susceptible than Huskies. Therefore, changes in IOP values may not be connecting to glaucoma development in dogs. 

Reviewed by Sarah Slayton 

Taylor, Nicole R.Zele, Andrew J.Vingrys, Algis J.Stanley, Robin G. (2007) Variation in intraocular pressure following application of tropicamide in three different dog breeds. Veterinary Ophthalmology10(1(Supp.)), pp. 8-11.

Nicole R. Taylor,* Andrew J. Zele,* Algis J. Vingrys* and Robin G. Stanley†
 
*
 
Department of Optometry & Vision Sciences, University of Melbourne, Parkville, Australia, 3010;
 
 
Animal Eye Care, 181 Darling Road, Malvern, Australia
Nicole R. Taylor,* Andrew J. Zele,* Algis J. Vingrys* and Robin G. Stanley†
 
*
 
Department of Optometry & Vision Sciences, University of Melbourne, Parkville, Australia, 3010;
 
 
Animal Eye Care, 181 Darling Road, Malvern, Australia