What is a Visual Field Test?

Questions such as what a visual field test is and why it is carried out are the ones most widely asked on this subject. Visual field tests are carried out to measure how effective peripheral vision is. They measure how far you can see to the sides, below and above the object you are looking at. The visual field test is also known as perimetry. It is important in conditions such as glaucoma. It generally takes ten minutes, and no surgical procedure or medication is involved. The visual field test matters because it allows the ophthalmologist to identify eye conditions in many different ways, or to follow them. The procedure is painless and entirely straightforward. It focuses on two things:

• How sensitive the eye is to the different parts of the visual field
• How far the eye sees to the right, the left, below and above while looking straight ahead without moving

Under normal conditions the eyes see a wide area in front of them. Without moving the eyes, we see not only the object directly ahead of us but also part of what lies below, above, to the right and to the left. The area that is not directly in front of us but can still be seen is called peripheral vision. Vision perceives the surroundings at the very centre of the area seen extremely well, which is why the eyes focus more comfortably on the area they want to see. The further the object or surroundings are from the main centre of vision, the less clearly they are seen. When an object moves far enough to one side, it leaves our field of vision altogether.

Why is a Visual Field Test Carried Out?

The question asked most on this subject is why a visual field test is carried out. When an ophthalmologist or optometrist is consulted, the visual field test is a natural part of the process. It also allows conditions such as glaucoma to be identified and followed earlier. Conditions that damage vision layer by layer are identified more easily this way, and it serves to reveal other eye conditions too. People with glaucoma may believe they have no difficulty with their vision, but the visual field test reveals the gaps and losses in their peripheral vision. Alongside this, the test gives a clearer understanding of what is happening in the part of the nervous system that carries out the function of sight. Those visual parts of the nervous system are:

• The retina converts the light reflected into our eye into electrical signals and passes them to the optic nerve.
• The optic nerves carry those signals to the visual part of our brain.
• The brain, one of our main centres, processes the signals arriving from the optic nerves and turns them into an image.

A problem in any part of this visual system causes changes in our field of vision. Depending on the result of the test, there are certain patterns used to identify the condition and its degree. The test is repeated at regular intervals so that the condition can be followed. The procedure is also used frequently in following conditions of vision. Your doctor follows developments in your condition according to the test results. The conditions for which the visual field test is applied, both to identify and to follow them, are:

• Scotoma (blind spot)
• Glaucoma
• Macular degeneration
• Graves' disease
• Pituitary gland disorders
• Multiple sclerosis (MS)

How is a Visual Field Test Done?

Questions such as how a visual field test is done, or whether it is painful, are widely asked. No additional preparation is needed for the test. There are no side effects during or after it. It is not painful and no anaesthesia is involved. The visual field test can be carried out in several different ways, but the basic aim of all of them concerns how clearly you can see your field of vision. In this test a point is focused on, and the test proceeds from there. There are two basic methods, the simplest of them all:

• Confrontation visual field: in this test the person carrying it out sits about a metre away from the person being tested. They open their arms straight out to both sides and move their arms or hand, and the person being tested says when they notice those movements.
• Amsler grid: this uses patterns made of straight lines forming a grid of squares. A point at the centre of the grid is looked at, and the areas where the lines appear blurred, broken or distorted are identified. The Amsler grid measures only the central part of the visual field.

Types of Visual Field Test

Visual field tests are not limited to confrontation and the Amsler grid. Kinetic and static perimetry tests exist as well. They are:

• Static visual field (perimetry) test: this is carried out by looking into a bowl-shaped device. When an object is seen in the machine, a button is pressed in response. Among the most widely applied static tests are the Octopus and the Humphrey.
• Kinetic visual field (perimetry) test: in kinetic perimetry the person carrying out the test moves an object and you say when you see it. The Goldmann test is generally used for this.

To analyse the results of these tests as accurately as possible, the results are taken through the devices used, which provide more accurate information. During these tests your head stays in the same place throughout, and there is always a central target for you to look at. Points of light are used for the device test so that the sensitivity of vision can be assessed more clearly. The most accurate result is reached this way and definite conclusions can be drawn about the person's condition. What Should Eye Pressure Be?