Reduced plasma cortisol binding to albumin in ocular hypertension and primary open-angle glaucoma

Purpose. To compare plasma cortisol binding as well as total plasma cortisol, free cortisol and percent free cortisol in normals, ocular hypertensives and primary high pressure open-angle glaucomas. Methods. Blood samples were obtained on outpatient visits of 18 normals, 19 ocular hypertensives and 18 primary open-angle glaucomas. Plasma cortisol binding was determined after the endogenous steroids were removed by charcoal absorption. Scatchard analysis was used to determine both the affinity of binding and the cortisol binding capacity of corticosteroid binding globulin and albumin. Plasma total and free cortisol were measured by radioimmunoassay. Results. Both the ocular hypertensive and the open-angle glaucomas in comparison to normals were found to have a highly significant reduced cortisol binding capacity to albumin (p = 0.006) with a borderline significantly increased binding affinity to plasma corticosteroid binding globulin (p = 0.0495) and no significant difference in binding affinity to albumin or cortisol binding capacity to plasma globulin. Both the ocular hypertensives and the open-angle glaucomas in comparison to normals were found to have significantly elevated levels of free cortisol (p = 0.012) and percent free cortisol (p = 0.003). Multivariate analyses showed that the reduced cortisol binding capacity to albumin was significantly associated with an increased percent free cortisol, with ocular hypertension and open-angle glaucoma and with male gender. Conclusion. Both ocular hypertension and primary open-angle glaucoma are associated with elevated levels of plasma free cortisol which are related to a reduced cortisol binding capacity to albumin.