Perimetry is the key diagnostic tool for monitoring glaucoma patients with an established visual field defect. As perimetry is demanding for both the patient and the organization, it is important to perform it as efficient as possible, that is, perform the right number of tests, schedule the tests at the right moments, and interpret the test results correctly. Practical guidelines will be given on optimal data acquisition and interpretation in clinical practice. The importance of an adequate monitoring depends on the risk of life-time blindness – and thus on age, glaucoma stage, and treatment. An easily applicable tool that can be used to estimate this risk will be presented.