Background: This study was undertaken to determine whether the interval between visual field tests affects the ability to detect progressive glaucomatous field loss.
Methods: One hundred and nineteen retinal locations which were deteriorating significantly by > or = 1 dB/ year (untreated normal tension glaucoma patients: 6 eyes) were studied. Analysis was repeated using 'thinned' visual field tests: one test per year instead of the complete three per year over a period of 4 years.
Results: The 'thinned' tests identified only 45.4% of the deteriorating points over the 4-year period. Furthermore, there was a mean delay of 1.10 years in detection (P < 0.01).
Conclusions: Less frequent visual field testing detects fewer progressing locations and detects them later.