Valuable clues to the cause of visual changes can be found in the visual field also called perimetry. The visual field is an important tool do diagnose various eye conditions in ophthalmic practices. There are various methods for measuring the visual field. The department has two Octopus visual field testing devices. All methods present light stimuli at different locations in the visual field and the patient must indicate whether or not he or she sees each. The examinations are usually performed separately (in the same session) for both eyes. A visual field examination takes between 30 and 60 minutes.