Purpose: To examine different definitions of incident visual field loss among patients with elevated intraocular pressure and varying numbers of abnormal glaucoma hemifield test results over an average of 6 years of follow-up. Methods: A cohort of patients with annual C-30-2 Humphrey visual fields were followed for a minimum of 5 years. Three different definitions of field loss were compared: 1, 2, or 3 consecutive annual abnormal glaucoma hemifield test results. Results: Of 253 subjects, 506 eyes were followed for 5 to 9 years. If incident field loss was defined as one or more normal fields followed by one abnormal glaucoma hemifield test result, the incidence of field loss was 63.6 per 1000 person-years of follow-up. For two or three consecutive abnormal glaucoma hemifield test results, the rates were 27.6 and 19.2 per 1000 person-years of follow-up, respectively. Among patients with field loss in one eye at the start of the study, the incidence of field loss in the fellow eye using 1, 2, or 3 consecutive abnormal fields as the definition of incident field loss was 60.9, 55.5, and 26.5 per 1000 person- years of follow-up, respectively. Three years after incident field loss, 31.9% (1 abnormal test result), 76.5% (2 abnormal test results), and 88.6% (3 abnormal test results) of eyes with incident field loss had an abnormal hemifield test result. For eyes with one, two, and three consecutive abnormal glaucoma hemifield test results at the start of the study, 59.2%, 83.6%, and 89.1%, respectively, had an abnormal field 3 years later. Conclusions: One abnormal glaucoma hemifield test result is not a consistent criterion for defining incident field loss. The use of two or three consecutive abnormal fields to define incident field loss makes it more likely that subsequent test results will be abnormal.
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