Visual Field Testing Periprocedural Care

No equipment is necessary for visual fielding. A white, green, or red disc mounted on a stick is optional, as well as a perimetry device (listed below).

Goldmann perimeter

This perimeter uses static or kinetic perimetry and tests the entire visual field. The device is a white bowl that is positioned in front of the patient. This type of device uses a light that the examiner presents from behind the bowl as the stimulus.

Tangent screen

This perimeter uses static or kinetic perimetry to test the central 30º of the visual field. The tangent screen consists of a black screen that is placed in front of the patient. The examiner presents pins as the stimuli, in front of the screen while the patient focuses on a central target.

Amsler grid

This device tests the central 20º of the visual field. The Amsler grid is a grid of transecting lines with a central target marked on the grid. This device is used more for testing macular function. The patient focuses their gaze on the central target and notes whether or not the lines on the grid appear wavy or if any spots on the grid appear to be missing.

Computerized automated perimeter

This perimeter tests the entire visual field by using only static perimetry. Computerized automated perimeters (CAPs) are improved technologies that use a bowl placed in front of the patient. Computer generated light stimuli are created throughout the visual field, and when the patient signals visualization of each stimulus, the computer generates a numerical score related to that specific stimulus and the area of the field in which it was displayed and visualized. An overall numeric score is created at the conclusion of testing that corresponds to the degree of visual field deficit. A person's individual score may be compared to their own past scores or to the scores of patients with normal visual fields. These perimeters have a limitation in testing patients with macular (central) field deficits. Patients with central field deficits typically have difficulty focusing vision on a specific spot, a requirement of this technology.

Microperimeters

Also known as fundus-driven perimetry, microperimetry is the next iteration of visual field testing. These perimeters solve a substantial limitation of CAPs. Microperimetry is performed with simultaneous fundus viewing via an infrared camera, allowing accurate quantification of visual acuity at specific points on the retina. Significant deviations of fixation of the fundus cause testing to be interrupted until fixation is re-established. They can also be used to evaluate stability and location of fixation, important in evaluation of the progression of certain diseases. Many models of microperimeters allow automated static perimetry to be performed in addition to kinetic perimetry, fixation tasks, and reading tasks. Limitations include increased examination time and susceptibility to fatigue, although newer models are resolving many of these issues.

Positioning

The patient should be seated in a chair or on the examination table in an adequately lit room. The examiner should assume a position directly across from the patient at an arm's length, so that their eyes align on the same horizontal and vertical plane.

First, the patient has to understand the purpose and the nature of the examination by the trained staff to perform the perimetry. Second, new patients must be given specific instructions how to actually take the test. It has to be explained that it is a boring exam that needs time, so the pateint has to be relaxed and not in hurry.

In some indications, such as glaucoma and some neurological diseases, the visual field tests are performed on a regular basis (usually every 6-12 months) to detect any progression.