The relationship of cataract maturity to intraocular pressure in dogs

To determine the distribution of intraocular pressure, as measured by applanation tonometry, in dogs with cataracts, and compare these tonometric results to the different stages of cataract formation (incipient, immature, mature, and hypermature). Animals studied Retrospection study of canine clinical patients (86 dogs).

All records of dogs presented from 1991 to 1996 to the university veterinary medical teaching hospital for diagnosis of cataracts and evaluation for cataract surgery were reviewed. The tonometric measurements from the initial ophthalmic examination were selected in cataractous and nonglaucomatous eyes either receiving no topical or no systemic medications. The stage of cataracts was based on the degree of opacification, tapetal reflection, clinical vision, and visibility of the ocular fundus by indirect ophthalmoscopy. The distribution of tonometric results were grouped by the cataract maturity, and compared by anova and Tukey's general linear tests.

Intraocular pressure with incipient cataracts ranged from 9 to 17 mmHg (mean 12.7 +/- 1.2 mmHg). Intraocular pressure with immature cataracts ranged from 3 to 27 mmHg (mean 13.6 +/- 0.6 mmHg). For the mature cataracts, IOP ranged from 5 to 22 mmHg (mean 11.9 +/- 0.7 mmHg). For the hypermature cataract group, IOP ranged from 4 to 23 mmHg (mean 10.8 +/- 0.6 mmHg). Comparison of the tonometric results among the different stages of cataract formation indicated a significant difference (P = 0.0086) between only the immature and hypermature groups.

Intraocular pressure in lens-induced uveitis (LIU) is lowered but the relationship to the stage of cataract maturity is less clear. Significant tonometric differences were present between the immature and hypermature cataract groups, but these differences are too small to be clinically useful. Decreased intraocular pressure of dogs with all stages of cataract formation suggests concurrent LIU during all stages of cataract formation, especially with the mature and hypermature stages. The average tonometric measurements in dogs with these cataracts were about two standard deviations below the mean IOP reported in normal dogs.