A visual field analyser measures your peripheral vision. With your head in a static position lights are flashed on and off and you are required to react by pressing a button whenever you see a light. The lights vary in brightness during different stages of the test. Each eye is screened independently and you should allow about 15 minutes to have the whole test. The test is not routinely advised, our Optometrist will determine its necessity. In the past it was one of the important tests for glaucoma as it determines whether you have lost any of your peripheral vision. However with the invention of the OCT scanner that can help diagnose Glaucoma before you loose any vision is has become less important.
The central part of the retina has definition and detailed vision, whereas the peripheral areas of the retina see less clearly and are less sensitive to light. These central and peripheral areas of our vision together are known as our visual field. The ganglion cells which make up the connections between our photo-receptors and the optic nerve are receptive to a particular part of the visual field and responsible for transmitting information to the brain. Damage to any of these ganglion cells will result in that part of the visual field being less sensitive to light.
Glaucoma is a process by which the optic nerve cells can become damaged and can die, which cause loss of our visual field areas in a very specific fashion, it partially due to the pressure within the eye. There are millions of these cells, we can lose up to 40% of them before being aware of any visual loss. Thus bring use back to the importance of the OCT in the modern world of technology.
The visual field is now only part of a glaucoma evaluation and detection. If only the visual field were used to diagnose glaucoma, Optometrists would miss most early stage glaucoma. The visual field is used to help diagnose and categorise the level glaucoma, to help plan treatment, we use it to establish a baseline for future comparison. If one of our Optometrist suspects a person may have glaucoma, a visual field test may help confirm or rule out glaucoma as the cause. In the later stages of glaucoma changes in the optic nerve become hard to detect, the visual field provides key information about whether the glaucoma is stable or progressing.
Another important use of the visual field analyser is for our clients attending with symptoms of headaches. As your visual pathways pass through specific areas of your brain it helps rule out brains conditions such as tumours as a cause. The areas missed on the visual field plot and accurately determine the location of tumours. Thankfully this is very rare.