Table 5.

Results of negative binomial regression evaluating the association of demographic and health variables with the number of visual field tests that enrollees with open angle glaucoma (OAG) received per year.

Cofactor	Incident rate ratioa	Low 95% CI	High 95% CI	P value
Age (per each year older)	0.994	0.994	0.995	<0.001
Sex
Male	Reference
Female	0.989	0.985	0.993	<0.001
Macular degenerationb	1.038	1.033	1.044	<0.001
Diabetic retinopathyc	0.929	0.920	0.937	<0.001
Number of glaucoma medication classes received
None	Reference
1	1.103	1.096	1.110	<0.001
2	1.218	1.210	1.226	<0.001
≥3	1.397	1.388	1.406	<0.001
Location of residence
Rural	Reference
Urban	1.089	1.083	1.096	<0.001
Year of care
Each additional year	0.961	0.960	0.962	<0.001
Undergoing incisional glaucoma surgery
No	Reference
Yes	1.194	1.188	1.201	<0.001

^aIncident rate ratio = The adjusted ratio of the number of visual field tests for each of the cofactors listed above compared to the reference group for that cofactor. A higher incidence rate ratio indicates that patients with that cofactor received more visual field tests than those in the reference group.

^bReference group is those without macular degeneration.

^cReference group is those without diabetic retinopathy.