The value of intraocular pressure asymmetry in diagnosing glaucoma.

PURPOSE To investigate the amount of intraocular pressure (IOP) asymmetry in a large group of ethnically diverse patients with and without glaucoma, and to delineate the risk for glaucoma which increasing amounts of IOP asymmetry confer upon the patient. PATIENTS AND METHODS Collaborative retrospective study of 326 glaucoma patients and 326 controls. Former Wills Eye Institute fellows collected single pre-treatment measurements of IOP on patients diagnosed as having definite glaucoma based on characteristic optic nerve damage and confirmatory visual field damage. Patients with a normal eye examination who had normal-appearing optic discs and no apparent glaucoma, or who had a normal eye examination in association with refractive error or cataract, were used as controls. RESULTS Intraocular pressure asymmetry is a significant risk factor for having glaucoma (odds ratio, 2.14; 95% confidence interval, 1.86-2.47; P<0.001). Absence of IOP asymmetry between the fellow eyes is associated with a 1% probability of having glaucoma. A difference of 3 mm Hg is associated with a 6% probability of having glaucoma, and a difference of >6 mm Hg with a 57% probability of having glaucoma. The association between IOP asymmetry and glaucoma status is significant for subjects with both elevated IOP (P=0.014) and statistically normal IOP (maximum IOP ≤ 21 mm Hg; P<0.001). CONCLUSIONS Inter-eye asymmetry of IOP is a common finding in patients with glaucoma. There is a direct relationship between the amount of IOP asymmetry between the fellow eyes and the likelihood of having glaucoma.