Visual field test: how it works

A visual field test is a diagnostic tool that assesses the full range of vision for each eye, including both central and peripheral vision. It identifies areas where vision is weak or missing, often before the individual notices these changes in daily life. This test helps doctors understand how various diseases affect visual ability and to monitor their progression or response to treatment.

This test is primarily used for diagnosing and monitoring conditions that affect the optic nerve or the visual pathways in the brain. It is particularly crucial in conditions like glaucoma, where optic nerve damage can lead to gradual visual field loss. Additionally, it aids in diagnosing optic neuritis or edema, orbital or brain tumors, stroke, and degenerative retinal diseases such as retinitis pigmentosa. The test can also detect visual field changes caused by certain medications.

The test is conducted in a darkened room. The patient sits in front of a machine, resting their chin and forehead on a support. One eye is covered, while the other eye focuses on a fixed central point on the screen. During the test, small lights flash at varying intensities and locations on the screen. The patient is instructed to press a button each time they see a light, without shifting their gaze from the central point. The test typically lasts about five to ten minutes per eye, depending on the specific program used.

To ensure reliable results, it is important to arrive for the test feeling alert and relaxed, as it requires significant concentration and full cooperation. It is advisable to bring your regular eyeglasses, whether for reading or distance, as instructed by the medical staff. No other special preparations, such as fasting or stopping medications, are usually necessary.

The machine generates a computerized map showing the visual sensitivity in different areas of the visual field. This map is compared to statistical data for the patient's age group. The ophthalmologist interprets the printout, which includes a grayscale map and statistical calculations, to determine if the visual field is normal or if there are any defects. It is important to remember that the reliability of the test heavily depends on patient cooperation, and therefore, repeat tests may sometimes be necessary to confirm findings.

The visual field test is a non invasive, painless procedure with no known risks. It does not require pupil dilation and does not cause any side effects. Patients can resume their normal activities immediately after the test, without any restrictions.

The test printout will be provided to the patient and discussed with the referring physician. Based on the test findings, the doctor will determine the need for further examinations, treatment, or ongoing monitoring. If you experience sudden or significant changes in vision, such as an abrupt loss of part of your visual field, you should seek an eye examination promptly, regardless of your next scheduled appointment.