Corticosteroids are known to increase intraocular pressure in human patients and also experimentally in the cat and rabbit. They have also been shown to have a similar effect in beagles with inherited glaucoma, although this was not confirmed in normal dogs in a later report. In the present study intraocular pressure was measured in dogs on corticosteroid treatment and results compared with a population of normal dogs.

Intraocular pressure was measured in forty dogs, twenty receiving topical steroid and twenty treated with systemic steroid, each for a minimum of 14 days. Those treated with topical steroid were cases of conjunctivitis or keratitis and not uveitis, as the latter would have been likely to have an aberrantly low intraocular pressure because of their disease rather than the treatment given. For ten additional dogs intraocular pressure was determined before and during steroid treatment, allowing changes in iop on steroid treatment to be determined longitudinally. Intraocular pressure was measured with a Tonovet rebound tonometer which was also used to determine the intraocular pressure in one hundred normal dogs.

Mean±standard deviation of intraocular pressure in the eyes of control normal dogs was 14.8±4.3mmHg. Intraocular pressure in eyes of all dogs treated with steroid was 19.7±3.5mmHg, this being significantly different from intraocular pressure in normal dogs at p<0.00001. Intraocular pressure in eyes treated with topical steroids was 18.2±3.2mmHg while those of dogs treated with systemic steroids had a mean intraocular pressure of 21.6±3.6mmHg. In dogs for which intraocular pressure values were available before and during treatment the pre-treatment intraocular pressure was 15.2±1.5mmHg and the intraocular pressure after at least two weeks of treatment was 18.9±2.9mHg with a mean rise in intraocular pressure of 3.7mmHg.

No animals in this study developed overt glaucoma as a result of steroid therapy but it would be prudent to monitor the intraocular pressure of dogs before and during steroid therapy to identify any pre-existing ocular hypertension and monitor changes during treatment to ensure that glaucoma does not ensue. The mechanism by which steroid increases iop is as yet unclear but this study shows that in the dog as with other species including man, steroid both topically and per os can have this deleterious effect.