VISUAL FIELD TEST – VFA
A visual field test is a method of measuring an individual’s entire scope of vision, that is their central and peripheral (side) vision. But first things first. What is the persons visual field.
What is my visual field ?
Lets say you are looking at the television. While looking at this television can you see the lamp shade next to the television. Or something else lying next to the television. Can you see the wall around the television. Mind you, you are seeing these things inspite of looking directly at the television. That is your visual field.
What happens to my visual field in glaucoma ?
So as mentioned in other parts of this website, glaucoma is when the eye pressure increases. This increased pressure over a prolonged period of time damages the optic nerve. The optic nerve has fibres from all over the retina. Which means fibres responsible for your entire vision are present in the optic nerve. In glaucoma, certain fibres are damaged earlier than some others. The fibres responsible for peripheral vision are damaged before the fibres responsible for your central vision. If the fibres responsible for peripheral vision are damanged your visual field is affected. In other words, if you are watching the television, you would be able to see the wall around the television everywhere except the part above the television. Which means that the upper part of the visual field is damaged.
Since your visual field is damaged in glaucoma the Visual field test helps in detecting the amount of damage and thus helps in determining treatment.
When is the field test done ?
Visual field test is done for two broad conditions
Glaucoma and certain neurological or brain or optic nerve issues. Glaucoma you have already been explained. You may understand that the optic nerve enters the brain and transfers information from our eyes to our brain. If there is any damage to these fibres in the brain the person will have vision problems. When a visual field test is done in a such a person your treating doctor will be able to locate the area in the brain where there is a problem by looking at the visual field test result.
For glaucoma, the visual field test is done at the first visit when your doctor wants to confirm that you have glaucoma and also as a followup investigation to know how much the disease as advanced. It would help your doctor to decide if the treatment should be continued or changed.
How is the field test done ?
The visual field test is a subjective examination. This mean that we require the patient to understand the testing instructions, fully cooperate, and complete the entire test in order to provide useful information. It is not like taking a picture of the eye but more like you performing a test.
Some points to note
- The field test is done in a dark room.
- You will notice in the picture bellow that you will be placing your chin in the chin holder and then looking on the bowl. You will be instructed to look straight ahead at a dot.
- You will then be handed a button in your hand.
- You will have to look at the dot in front of all at all times.
- While this is happening the machine will show you lights from different parts of the bowl.
- If you have seen that flash of light you are expected to press the button.
- Your response is recorded by the machine for different areas and for different intensities of light.
- The complete analysis will result in the report of the test.
- Each eye is tested separately, and the eye not being tested is covered with a patch.
- It usually takes about 8 minutes per eye for the test. The test can sometimes take longer if the patient is feeling tired while doing the test. The test also takes longer if the patient is not following the instruction properly.
- After the test one can resume normal activity.
- Depending on results of the field test, further follow-ups, evaluation, or treatment may be recommended.
Frequently Asked Questions
If done correctly and quickly the field test would take about 8-10 minutes per eye.
However, this is a subjective test and patients cooperation and understanding is essential. Thus sometimes the test may take longer if the patients requires breaks while he is performing the test.
A visual field test costs Rs 1600 for both eyes or Rs 800 for one eye.
There are various formats of performing the test. Sometimes we may need to perform the test of the same eye in different formats depending on the eye condition and that would be considered as another test.
Sometimes glaucoma patients need to repeat this field test frequently along with other tests like OCT and Pachymetry. We have combined packages for all three tests for such patients. Please contact the hospital to know more.