Knowledge Is Power
Knowing what happens during a visual field test can help you feel reassured, especially if you're nervous about this test or have health anxiety.
If your ophthalmologist ordered this test, most likely there's a good reason for it. Perhaps he/she noticed an unexplainable reduction in your visual acuity (how well you can see) or maybe there is a finding of elevated intraocular pressure.
Regardless of what prompted the test, you may be wondering what happens exactly and whether the procedure is painful.
What Is a Visual Field Test?
In order to understand what a visual field test is, you will first need to understand exactly what a visual field is.
The visual field is basically the portion of space that is visible when your eye is fixed on a specific area. In other words, it's all the surrounding space you see if you would stare at something specifically.
For example, if you were to focus on what you are reading at this very moment, the visual field would encompass all of the surroundings you see without moving your eyes around.
A visual field test, therefore, is a test that was purposely designed to test your ability to see these surroundings without moving your eyes.
What Happens During a Visual Field Test?
While there are several different types of visual field these, in this article the focus is on the Humphrey Visual Field Test, a form of static perimetry.
In this visual field test, you will be asked to sit down in front of a machine. You will have one eye covered with a patch.
The reason why one eye is covered is due to the fact that, when using both eyes, these help compensate for any visual field deficits since the visual fields of both eyes tend to overlap.
If you were to do this test without covering one eye, you would therefore not attain reliable results and would miss potential deficits impacting one eye.
Once one eye is covered, you will be told to rest your chin and forehead in a specific area. You'll need stare into a screen, more precisely a specific spot.
You will be also provided with a joystick-like tool that you will need to press when you notice flashes of lights.
When the test starts, the lights will be turned off and you'll be staring at the specific spot straight ahead. You will see lights dancing around the screen. You will have to press the button every time you see one.
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There may be times when you don't seem to see any lights and may feel concerned about it. This is normal. The machine deliberately does this so to find your "visual threshold." In other words, it will show dimmer and dimmer lights up to where you may struggle to notice them.
Tip: you will need to blink during the test which can cause you to miss seeing some lights. The best time to blink is right after you click.
Is the Field Vision Test Painful?
No, the field vision test is not painful at all. One main problem people struggle with is sometimes the length of the procedure which can cause eye fatigue. The length may vary between one test and another.
You are free though to take breaks if needed. Ask the technician prior to the beginning of the test for info on what you need to do to pause the test if they don't inform you of this option.
On top of struggling with a lengthy procedure,, in some people, visual field testing induces anxiety and this emotional state ultimately ends up negatively affecting the performance of the test.
Not surprisingly, research has revealed that glaucoma patients rank visual field testing among the least popular procedures used in the management of glaucoma.
Can You Make Mistakes During the Test?
It may happen that occasionally you may be distracted or feel fatigued and fail to press the button when you see a light or you may press the button even when you do not see any lights (some of us are prone to being "trigger happy!"). This will show as false positives and false negatives.
The machine tends to detect mistakes. For instance, it notices that you could not detect a light in the same spot you noticed it earlier, so it may repeat the same to give you a chance to correct this.
In order to be valid, the visual field test must be reliable. In other words, you'll have to have a score that helps determine if it was a reliable test.
If you are having a bad test day then, the reliability score will be on the lower end and the doctor may not trust these results and ask you to reschedule.
My Personal Experience
When I did my test, the test on my left eye took longer than the other. I was feeling fatigue at one point and felt a bit overwhelmed, but carried on.
The ophthalmologist told me I was blinking too often and not focusing on the spot at one point. This caused the machine to do several reps to gain a better insight on what was going on.
I must have detected some dim, small lights and then not detected them again when bigger or brighter, which must have confused the machine!
When the results were printed, I noticed how the test with my right eye lasted only 14 minutes while with the left eye it took 21 minutes!
Struggling With the White Background
Another issue that I greatly struggled with was the surrounding white background. With this white background and the flashing lights, I was really struggling.
I was barely able at some point to see the dimmer and smaller lights because I think that the white background sort of gave me some kind of "snow blindness" effect. In other words, I was struggling to see at times as if I was out in the bright sun with snow fields in front of me.
When I tried to do the test at home on my computer using a free program where the background was black, I scored perfectly, but of course, the reliability of this online test may questionable. My doctor said to not rely on these tests at all.
4 Common Types of Visual Field Tests
|Confrontation Visual Field Test||Automated Static Perimetry Test||Kinetic Visual Field Test||Frequency Doubling Perimetry|
The doctor holds up different numbers of fingers in your peripheral vision field
Stationary (static) dim lights appear in different places across the screen
Moving lights appear in different places on the screen
Vertical bars will flicker at varying rates on the screen
How Are the Vision Field Tests Interpreted?
The ophthalmologist of course is the person to interpret the results, but if you're just curious about the meaning behind those pictures, consider that the round circles represent your eyes.
You'll therefore likely end up with one eye being evaluated per paper. You should find some reference as to what eye the report belongs to. In ophthalmology, OS stands for left eye and OD stands for right eye.
The dark areas of the test indicate a loss of vision in that area. Therefore, the lighter the area, the more vision you have in the eye.
Usually a grey scale is used so the lighter the grey, the better, the darker the grey, the worse. Black indicates areas with vision loss. These areas are known as "scotomas.'
- Gardiner SK, Demirel S Assessment of patient opinions of different clinical tests used in the management of glaucoma Ophthalmology 2008 115 212731
- Kaliaperumal S, Janani VS, Menon V, Sarkar S, Behera G, Kattamani S Study of anxiety in patients with glaucoma undergoing standard automated perimetry and optical coherence tomography - A prospective comparative study Indian J Ophthalmol 2022
- American Academy of Ophthalmology, Visual Field Test
This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.
© 2022 Adrian Rolla