What is a visual field test?
A visual field test is an important part of a routine eye exam.
A visual field test is a method of measuring an individual's entire scope of vision, that is their central and peripheral (side) vision. Visual field testing maps the visual fields of each eye individually and can detect blind spots (scotomas) as well as more subtle areas of dim vision. The visual field test is a subjective examination, so the patient must be able to understand the testing instructions, fully cooperate, and complete the entire visual test in order to provide useful information.
What is a visual field test used for?
Visual field testing is most frequently used to detect signs of glaucoma damage to the optic nerve. In addition, visual field tests are useful for detection of central or peripheral retinal diseases of the retina, eyelid conditions such as drooping (ptosis), optic nerve damage and disease, and conditions affecting the visual pathways from the optic nerve to the area of the brain (occipital cortex) where this information is processed into vision.
The following are uses of visual field testing:
- Screening for glaucoma: Peripheral vision loss is often an early and subtle sign of glaucoma. Visual field tests are helpful in detecting vision loss and making the diagnosis of glaucoma, and repeat testing is used to monitor treatment.
- Screening and testing for lid droop (ptosis)
- Testing for toxicity from certain medications (for example, screening for toxicity from hydroxychloroquine [Plaquenil], which can affect the central retina)
- Measuring the extent of retinal diseases, such as retinitis pigmentosa
- Detecting conditions affecting the optic nerve, such as tumors, injury, poor circulation or stroke, optic neuropathy, swelling of the optic nerve (optic neuritis), compression from swelling in the eye socket or orbit, and severe nutrient deficiencies
- Detecting conditions that affect the visual pathways from the optic nerves to the occipital lobe of the brain, including tumors, inflammatory disease, increased intracranial pressure, injury, poor circulation, or stroke
- Testing for malingering behavior or factitious disorders
Visual Field Testing
Visual field testing actually maps the visual fields to detect any early (or late) signs of glaucomatous damage to the optic nerve. In order to find and follow glaucoma, visual fields are measured by a computer one eye at a time. One eye is covered and the patient places his or her chin in a type of bowl. Lights of various intensity and size are randomly projected around inside of the bowl. When the patient sees a light, he or she pushes a button. This process produces a computerized map of the visual field, outlining the areas where each eye can or cannot see. In glaucoma, there are characteristic changes in the visual field examination.
How is a visual field testing procedure performed?
There are a variety of methods to measure the visual fields. During an eye exam, visual field testing is performed one eye at a time, with the opposite eye completely covered to avoid errors. In all testing, the patient must look straight ahead at all times in order accurately map the peripheral visual field. Most modern visual field testing devices also continuously monitor fixation, or the ability of the patient to maintain a consistent straight ahead gaze.
What types of specialists perform visual field tests?
Visual field tests are performed most often by eye doctors (optometrists and ophthalmologists) and neurologists. These specialists have training in visual field interpretation. The cost of visual field testing is usually covered by medical insurance.
What are the different types of visual field tests?
- Confrontation visual field testing: The doctor faces the patient and asks the patient look straight ahead. The doctor will present stationary or moving targets in the patient's peripheral (side) visual fields. While maintaining a straight-ahead gaze, the patient lets the doctor know when he/she can see the target in the peripheral vision. The target may be a small disc on a stick, but most commonly the target is the doctor's hand holding up one or two fingers.
- Amsler grid: This is a printed image of a grid with a dot in the center. The patient is asked to look at the dot, one eye at a time, and note whether the grid lines surrounding the dot appear distorted, faded, or partially missing. This test is most often used to detect central visual field defects.
- Static automated perimetry (such as Octopus or the Humphrey Field Analyzer): Pinpoint flashes of light of varying size and brightness are projected within a large white bowl. The patient is asked to look at the center of the bowl and press a button each time a light is seen in the peripheral vision. The machine collects the data and uses sophisticated software to analyze the results.
- Kinetic perimetry (such as Goldmann perimeter): Moving targets of various light sizes and intensities are shown and the patient indicates when they become visible in the peripheral vision. The resulting data is used to map the full visual field. The full, normal range of the visual field extends approximately 120° vertically and a nearly 160° horizontally.
- Frequency doubling perimetry: This test utilizes varying intensities of a flickering image to analyze the visual field. It is particularly useful in detecting early glaucoma field loss.
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How long does a visual field test take?
Visual field testing requires a minimal amount of time for most otherwise healthy patients, but it may be tiring or stressful for those who are ill or elderly. Visual field testing is also very difficult for younger children, patients with mental disabilities or developmental delay, or anyone with slowed reflexes or poor attention span.
If the first visual field test is read as abnormal or inconclusive because it was inaccurate, it may need to be repeated. It is not uncommon for patients to forget to keep their gazed fixed straight ahead. With repeat visual field testing, most patients find their ability to maintain a steady straight-ahead gaze improves, thus improving the reliability of the results.
The following are common testing times for visual fields in both eyes:
- Amsler grid: a few minutes
- Confrontation visual field: a few minutes
- Static field for lid droop or ptosis screening: approximately eight minutes
- Static field for complete glaucoma evaluation: approximately 15 minutes
- Frequency Doubling Perimetry Testing (FDT) for glaucoma screening or evaluation: approximately 10 minutes
- Kinetic Goldmann Perimetry for complete glaucoma evaluation: approximately 20 minutes
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