Tangent screen perimetry evaluates the central 30 degrees field at 1 m. The test is done on each eye separately, with the opposite eye patched. Testing at 2 m expands the field defects to twice their 1-meter size so that only 12 degrees to 15 degrees of central field is evaluated. 2. Maintain constant monitoring of the patient's fixation throughout the entire testing procedure. Move the target from nonseeing to seeing areas. Move along the stitched meridians at a constant speed of 5 degrees per second. Do not test directly on the vertical or horizontal meridians. 3. Test the fields using the appropriate screening protocols. Consider the Armaly/Drance protocol for glaucoma and vertical meridian mapping for neurologic problems. To maintain consistency in visual field interpretation, use standard color coding to document the size of the targets.
