Visual field testing is one of the vital diagnostic tests for glaucoma. During this test, the patient looks straight ahead into a lighted bowl and then responds every time a light is flashed and perceived at different points of your peripheral (or side) vision. This helps draw a map of your field of vision.
When you test vision on an eye chart, only the central vision is tested. But in glaucoma, even in cases when the IOP appears stable, in most cases the field of vision is the first to be affected. By the time central vision is impacted, glaucoma may already be far advanced with almost all peripheral vision lost.
Visual field testing devices all incorporate an internal computer with the ability to store, print, and transmit important patient data. There are many variables involved in obtaining reliable results and it often takes several tests before a reliable initial baseline is established. This is a recognized phenomenon. Further field tests are then performed periodically, their frequency depending on other factors but at least once a year, to detect any new field defects, to visually compare a sequence of reliable field tests, and to look for changes in the field defect pattern that are indications of how the disease is progressing.