Visual Field Test

What is the Visual Field Test?

Visual field testing is a diagnostic procedure used to assess a patient’s visual field. This test is used to detect any abnormalities or defects in the patient's peripheral or central vision. It is typically performed by an ophthalmologist, optometrist, or other eye care professionals.

What is a Visual Field?

Visual field refers to the total area in which objects can be seen while the eyes are focused on a central point. It is the entire extent of the observable world that can be seen by an individual without moving their eyes or head. The visual field is often measured in degrees of arc, both horizontally and vertically, and it is affected by various factors such as the structure and function of the eye and the visual processing pathways in the brain.

In general, the visual field is divided into two parts: the central visual field and the peripheral visual field. The central visual field is the area directly in front of the eyes, which includes the macula, the small, central portion of the retina responsible for sharp, detailed vision. The peripheral visual field, on the other hand, refers to the area outside of the central visual field and includes everything that can be seen to the side, above, and below the central point of fixation.

A loss of the visual field can occur due to various conditions such as glaucoma, optic neuritis, stroke, brain tumors, and other neurological disorders. A visual field test is often performed to evaluate and diagnose such conditions.

Types of Visual Field Tests

There are several types of visual field tests, each with its own advantages and disadvantages. The most commonly used tests are:

Confrontation Visual Field Test

This test is performed by having the patient sit directly in front of the examiner and covering one eye. The examiner then moves their hand or an object in from the side of the patient's visual field, asking them to indicate when they can first see it. This is repeated in all four quadrants of the visual field. This test is quick and easy to perform but has limitations in terms of sensitivity and specificity.

Amsler Grid Test

This test involves a grid with straight lines and a central dot. The patient is asked to stare at the central dot and report any distortion or missing areas in the lines. This test is used to detect any central vision defects.

Automated Perimetry

This test uses a computerized machine that presents stimuli at various locations in the visual field. The patient responds when they see the stimuli, and the results are recorded and analyzed. This test is more sensitive and specific than the confrontation visual field test but takes longer to perform.

Goldmann Visual Field Test

This test is similar to the confrontation visual field test but uses a special instrument called a Goldmann perimeter. The examiner presents stimuli at different locations in the visual field and records the patient's responses. This test is highly specific and sensitive, but it is time-consuming and requires specialized equipment.

Procedure for Visual Field Testing

Visual field testing is typically performed in a dark room to minimize distractions and maximize the patient's ability to see the stimuli. The patient is seated comfortably and asked to focus on a central point while the examiner presents stimuli at various locations in the visual field. The patient is asked to respond as soon as they see the stimulus, either by pressing a button, saying "yes," or raising their hand.

During the test, the examiner may adjust the brightness or size of the stimuli to determine the patient's threshold for detection. The test may take anywhere from a few minutes to an hour to complete, depending on the type of test and the patient's ability to concentrate.

Results of Visual Field Test

The results of visual field testing are typically presented in the form of a visual field map, which shows the areas of the visual field where the patient can or cannot see stimuli. Normal visual fields have a characteristic shape, with the central visual field having the highest sensitivity and the sensitivity decreasing towards the periphery. Abnormal visual fields may show missing areas, defects, or reduced sensitivity in specific regions of the visual field.

The results of visual field testing are used to diagnose and monitor a variety of eye and neurological conditions. In some cases, further testing or imaging may be necessary to confirm a diagnosis or determine the underlying cause of visual field defects.