Have you ever had an eye exam? When we go, we usually think about whether our eyesight is getting worse and whether we need glasses. But did you know that an ophthalmologist checks a lot more about your eyes? One such important test is the Visual Field Test. This may sound like a difficult thing to do, but it is a very simple, painless test. Today, we will talk about everything in a very simple way.
Simply put, what is this Visual Field Test?
Imagine you are looking straight ahead. The entire range you can see when you look straight ahead, without moving your head or eyes, that is, the entire range you can see in all directions, up, down, right, and left, is what we call the visual field.
Simply put, even when you're looking straight ahead, you can barely see anyone coming from either side, right? That's what we call peripheral vision . What you're looking at directly is called central vision .
So, what this Visual Field Test does is "map" your entire field of vision, that is, the entire range of what you can see. It's like a map of Sri Lanka, and it looks at what your visual map looks like.
This test measures two main things:
1. How wide is your field of vision? - This means how far you can see up, down, left, and right when you look straight ahead without moving your head.
2. How is your visual acuity? - Within the entire range of your vision, some areas are clear, some areas are blurry, and some areas are completely invisible. So this also shows you how sensitive your vision is in each of these areas.
Normally, our eyes see best straight ahead. That's why when we want to see something clearly, we turn our heads in that direction and look straight ahead. As we move away from the center, our vision becomes a little blurry. When we move too far away, the object disappears from our view completely.
Why is this test so important?
When you visit an eye doctor, this can be done as part of a routine checkup. This test is very important because it can detect some conditions that can secretly damage the eyes early, before any symptoms appear.
The best example is a condition called glaucoma . When glaucoma develops, the pressure in the eye increases, gradually damaging the optic nerve that connects the eye to the brain. The first thing that is lost is peripheral vision. But because this happens so slowly, many people do not notice the difference. However, when a visual field test is performed, this loss of vision, these "blind spots", can be clearly identified.
This test also gives the doctor a lot of information about the functioning of our visual system. Our visual system has three main parts:
- Retina: This is located inside the eye. It's like the film in a camera. It converts light entering the eye into electrical signals.
- Optic Nerve: This is the "cable" that carries signals generated in the retina to the brain.
- Brain: The brain receives these signals, analyzes them, and converts them into the image we see.
If there is a problem in any of these three areas, it will be visible in the results of your Visual Field Test. There are specific patterns of changes in this visual map related to various diseases. By studying these patterns, your doctor can guess what kind of condition you have.
What are the main medical conditions for which this test is performed?
If you have any symptoms or suspect a disease, your doctor may order this test. The results of this test are used to diagnose the disease and to monitor whether a disease is under control or worsening.
| Medical condition | A brief introduction |
|---|---|
| Glaucoma | Damage to the optic nerve due to increased pressure in the eye. Peripheral vision is lost first. |
| Stroke | Impaired blood supply to the brain can cause damage to parts of the brain related to vision. |
| Macular Degeneration | Damage to the central part of the retina (macula). This impairs central vision. |
| Multiple Sclerosis (MS) | A disease that damages the nerves in the brain and spinal cord. It can also affect the optic nerve. |
| Graves' Disease | A condition caused by an overactive thyroid gland. The eyes may swell and the optic nerve may become compressed. |
| Pituitary Gland Disease | Tumors in the pituitary gland in the brain can cause compression of the optic nerve. |
| Blind spot (Scotoma) | The appearance of spots in the field of vision, complete or partial loss of vision. |
Why do some people have to keep taking this test?
This is also a question that many people ask. Sometimes the doctor may do this test and ask you to do it again in a few days. Or he may ask you to do it again in a few months, a year. There are several reasons for that.
1. Verify the results: Suppose you were tired on the day of the test, or your concentration was not good. Then there may be small errors in the results. So, you can ask to take the test again to make sure that the results are 100% accurate.
2. Monitor your condition: This is the main reason. Especially for people with long-term conditions like glaucoma, your doctor will do this test at regular intervals. Then he can see if the medication you are taking is working properly, if the disease is getting worse, or if it is under control. This is just like checking the sugar level of a person with diabetes or checking the blood pressure of a person with high blood pressure.
This test is essential for someone with glaucoma. It's the best way to know if you're losing your vision without realizing it. That's why it's important to go to the doctor every day and get tested.
What happens during the test?
There is no need to prepare much the day before this test. This is not a test that causes any harm or pain to the body.
There are several ways to do a Visual Field Test. But the common thing in all of these methods is that you have to look straight at one place. While doing so, you have to give a signal as soon as you see a light or an object coming from either side. You have to give that signal by pressing a small button on your hand.
To perform the test correctly, it is very important to look straight ahead as the doctor or technician tells you to.
The simplest test methods
These are not very complicated methods that are usually done as a basic check.
- Amsler Grid: This is like a square ruler. It has a large dot in the middle. All you have to do is close one eye and look at the dot in the middle with the other eye. As you look, you should tell the doctor if the lines in the squares are stretched, broken, wrinkled, or blurry in some places. This mainly tests your central vision.
- Confrontation Visual Field Test: In this test, the doctor sits in front of you, about 3 to 4 feet away. You close one eye and look straight at the doctor's nose. The doctor holds out his hands to the sides and brings them in. You have to tell him when you see his hand. This gives you a rough idea of the extent of your peripheral vision.
More accurate, modern tests (Perimetry Tests)
These are computer-aided tests that provide more accurate and detailed results. These are commonly called perimetry tests.
| Test type | How to do it? | Famous examples |
|---|---|---|
| Kinetic Perimetry | Here a point of light moves from outside the line of sight to inside. You must signal as soon as you see it. | Goldmann Perimetry Test |
| Static Perimetry | You put your head inside a bowl-shaped machine and stare at a point in the middle. At different points in the machine, dots of light of varying brightness flash on and off. As soon as you see the light, you have to press a button in your hand. | Humphrey Field Analyzer, Octopus Perimetry |
These computer-based tests are more accurate because they keep your head in the same place, your gaze fixed, and measure your visual sensitivity very precisely by changing the brightness of the light. They can also compare the results with the average results of a healthy person.
How long does this test take?
It usually takes between 5 and 10 minutes to test one eye, so this is not a long, tedious test.
What do the results say?
The doctor will explain to you the results of the test, which is your "vision map."
- A "Normal" result: This means that there are no problems with your field of vision, no blind spots.
- An "Abnormal" result: This means that you have decreased vision in some areas of your visual field. This loss of vision can be in a small spot or spread over a larger area.
The most important thing is the pattern of this vision loss. Specifically, where on the map are these dark spots? By studying that pattern, your doctor can get a good idea of what underlying medical condition you have. For example, there is a clear difference in the pattern of vision loss caused by a pituitary tumor and the pattern of vision loss caused by glaucoma.
If your results are abnormal, don't worry. Your doctor will clearly explain the reason, what to do next, and any necessary treatments.
What time should I see a doctor?
If you notice any new changes or discomfort in your vision, don't ignore it. Be sure to see your doctor .
If you suddenly lose your vision or experience severe eye pain, it is an emergency. Go to the nearest hospital's Emergency Treatment Unit (ETU) immediately.
Even if you think you're healthy, it's still important to get regular eye exams because that's when you can detect and treat eye conditions that you may not be aware of.
Take-Home Message
- A Visual Field Test is a simple, painless test that measures your entire field of vision (vision range).
- This can provide information about your central vision, as well as your peripheral vision, which is the area of vision that you can see on both sides.
- This test is very important to detect diseases like glaucoma at an early stage, before they show any symptoms.
- If you are already receiving treatment for an eye condition, this test helps monitor whether that treatment is successful.
- If you notice any changes in your vision, don't ignore it. See your doctor immediately.
- Even if there is no problem, getting regular eye exams is very beneficial for the health of your eyes.
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