Background: The Advanced Glaucoma Intervention Study (AGIS) is a multicenter, randomized clinical trial designed (1) to determine the better of two surgical management strategies for glaucoma when medical treatment alone no longer adequately controls the disease and (2) to clarify the clinical course and prognosis of open-angle glaucoma after surgical interventions have begun. The investigators of this study have developed quantitative methods to assess the test reliability and measure the severity of glaucomatous visual field defects with the 24-2 threshold program of the Humphrey Visual Field Analyzer. This report details these methods and presents information about long-term fluctuation during a time interval short enough to render change due to disease unlikely.
Methods: In AGIS, reliability assessment of automated visual field tests is based on the number of questions asked; percent of fixation losses, false-positive responses, and false-negative responses; and amount of short-term fluctuation. The AGIS visual field defect score is based on the number and depth of clusters of adjacent depressed test sites in the upper and lower hemifields and in the nasal area of the total deviation printout of the threshold program single-field test STATPAC-2 analysis. The score ranges from 0 (no defect) to 20 (all test sites deeply depressed). The fluctuation in score between two tests obtained during an interval preceding AGIS surgical interventions, ranging from 1 day to 6 weeks on 756 eyes of 562 patients, is analyzed.
Results: The scores of the first visual field tests, which determined eligibility for the study, range from 1 to 17. Large positive or negative interest fluctuations (absolute changes of 4 or more) occurred in the second tests for 16% of eyes; more scores improved (11%) than worsened (5%). The frequency of large fluctuations tended to increase as the time interval between tests increased. Absolute interest fluctuations were independent of age.
Conclusion: For visual field tests obtained with the automated perimeter, AGIS investigators have developed objective, quantitative methods of scoring test reliability and severity of glaucomatous field loss. For 16% of eyes, long-term fluctuations were large enough (> or = 4 points) to suggest improvement or worsening of the glaucomatous defect even though the interval in which the fluctuations occurred was short enough (median time, approximately 1 week) to render changes in disease status unlikely.