It is a test that checks a patient’s central and peripheral or side vision, and can diagnose or determine visual defects in the patient. This test measures the quality of a person’s entire field of vision, hence the name visual field test. It is usually done with the help of a special equipment, but is also done manually by an optometrist/ophthalmologist sometimes. The manual test is not very reliable, and is normally done as a preliminary measurebefore testing with computerised devices.
Visual field test is mostly done to diagnose and monitor glaucoma, which is a condition that damages the optic nerves and eventually leads to blindness. Most of the times, glaucoma doesn’t produce any symptoms, but it does gradually affect the peripheral vision. That is why visual field test can effectively determine glaucoma. It is also used to diagnose other conditions like hyperthyroidism, multiple sclerosis, and certain tumours that affect the optic nerves and vision.
There are different ways to conduct a visual field test, but the basic procedures are more or less same. The patient is asked to fix their eyesight on stationary object or point at all times. Then certain lights or objects are introduced in the area of their peripheral vision, and patients will need to respond to them. Based on the patient’s response, the doctor will examine if there are any spots in the patient’s visual field where vision is deteriorating.
Visual field tests can be done in different ways, but the most commonly used and sophisticated method is the Computerised automated perimeter test. The doctor or ophthalmologist will recommend a person to take a visual field test if they suspect any eye defects or other disorders that affect eyesight. First, a preliminary test will be conducted, which is known as confrontation visual field exam. Here, the optometrist will ask the patient to cover one eye with a patch and focus their vision on a fixed point with the open eye. They will move their hands or fingers around the patient’s field of vision and get their response accordingly. Then the same process will be repeated for the other eye. This will give the doctor a general idea of the patient’s visual field strength. Once this exam is over, the patient will have to take the computerised automated perimeter test. The procedures involved in this test are explained below:
The lights that appear in the screen of the perimeter will vary in size, intensity and the duration for which they are projected on the screen. Standard tests usually take 5 minutes for each eye, but this can differ in some cases. After the test is over, the doctor will prepare a report based on the patient’s responses. The report will include figures that represent the patient’s field of vision in four quadrants. Blind spots and areas with defective vision will appear as black patches in the report. Further diagnosis will be done as per doctor’s understanding.
Any person who is suffering from eye diseases, as well as those who are under suspicion of having vision problems are eligible for this test. Those being diagnosed for other diseases and conditions that affect eyesight might also need to go through visual field test. In most situations, it will be the ophthalmologist or doctor who decides if the patient is eligible and in need of this test.
There aren’t any conditions that can make someone ineligible for a visual field test. Needless to say, people with perfect eyesight do not need this test. But the test does require patients to focus their central vision on a fixed point for some time. So small children, people with mental problems and people who have difficulty focusing may not be able to sit for this test successfully, as they might fail to keep their central vision focused on one point. Thus, they cannot get accurate results from the test.
Visual field test is a simple procedure that takes 10 to 15 minutes to complete, and it does not have any side effects on patients. In rare circumstances, a patient may experience tired eyes or blurry vision but that is just due to staring continuously at the perimetry screen. Such effects will go away within a few minutes.In case any of these side effects persists or there any other health issues arising during or after treatment, it is advised to kindly consult the health specialist immediately.
There aren’t any strict instructions that need to be followed before a visual field test. But it is best to let the eyes rest well a day before the test to ensure you have a clear vision. That means you might need to cut off activities that strain your eye (like prolonged use of mobile/computers) and get a good night’s sleep before the test.
In the visual field test, different types of lights are flashed within the range of vision for both eyes, and the entire process takes an average of 10 minutes, i.e., 5 minutes for each eye.
The cost of visual field tests will vary significantly, depending on a lot of conditions. It may be cheaper in public hospital as opposed to private ones, and the city and location of the hospital orhealth centre will also make a difference. But it is not an expensive test and an average estimation of cost can be considered to start from INR 2000.
Results of visual field tests mostly show a four-quadrant mapping of the patient’s eyes and field of vision. Spots with low or no visibility are seen as black patches on the report, and this lets the doctor analyse the overall peripheral vision of the patient. For people who take this test first time, the black patches will represent deteriorating peripheral vision which may be caused by glaucoma and other conditions. For patients who keep taking the tests on regular interval, the doctor will monitor these black patches in each test to see if the vision is getting better or worse.
There are no known alternatives to examine a person’s peripheral vision other than visual field tests. However, visual field tests can be performed in different ways depending on the patient’s situation and equipment available.