The definition of the visual field is a variety of visual sensations that are seen within observations by introspectionist psychological experiments. However, an easier understanding is that the visual field is the area within space that can be seen by the eye. This is an important part of your vision and being able to know what your visual field is going to be vital for most disorders especially ones that have to deal with the brain, retina or optic nerves. This includes disorders like brain tumors, retinal dystrophy, and glaucoma.
In order to determine what your vision field is, an optometrist or even a neurologist will perform a certain test that will determine if your vision is affected that could cause scotoma or even severe vision loss or even sensitivity reduction.
Just because you are able to see your hand in your peripheral vision, does not always mean that your vision is fine. However, that type of testing is only used for those who have severe loss of vision which can sometimes happen when a person has a stroke. More subtle and common issues can only be found by using computerized analyzers like the Octopus 900 perimeter.
If you have a blind spot or scotoma within your normal field on a single eye or both of your eyes. In many cases these blind spots are going to be persistent, but there could be some points where it could only temporary and it could shift such as loss during a migraine headache. Your visual fields of your eyes will overlap, and any defects may not be seen without there being any type of test on each eye. The causes of these blind spots can include a lot of different things like vascular diseases, tumors, hereditary diseases, inflammatory issues, and even nutritional deficiencies as well as certain drugs or toxins.
When it comes to your visual field, the normal area or monocular field will extend to being 60 degrees towards your nose from the vertical meridian of your eye and 107 degrees from your nose and outwards and 80 degrees below the meridian and 70 degrees above the meridian.
However, the binocular field will be a mixture of both fields from the eyes. In binocular, the part that is to the left-hand side of the meridian is called the left field and for the right side it will be called the right field. The areas that are normally referred to areas are called upper and lower quadrants and left and right quadrants. Your nose is actually situated directly in your field of view for both eyes, but because of the processing that is done within your brain, it will never be noticed during any visual tasks.
In order to measure this area a perimeter is used. This machine is ran by a perimetrist and they use various machines and techniques to do various forms of testing. However, in each form of testing, it will include confrontation testing. This is where you have to maintain looking right ahead while different objects that are different in color, shape and size, even lighting are placed in different parts of your vision. Using kinetic perimetry, certain objects are moved from outside of your perception and towards fixation points. Whenever you are able to perceive the object, then threshold points are plotted. These lines are then connected and called isopter.
Static testing will systematically plot out your vision field using flashing light presentations of different intensities. This test will allow your doctor to see retinal sensitivity at any given location. It is very useful in being able to pick up defects and it is able to monitor changes as your eye develops from year to year. It is during this test that you are sitting at a machine that you are asked to look right ahead and told to focus on a certain object, and you are to click a button every time you see a light. Whenever the test is over, a map is printed that will provide results of your field of vision.
Kinetic testing will use moving targets in different light size and intensity to help map out all of your vision field, as well as any blind spots or decreased areas of vision. This testing type is very useful for mapping out sensitivity boundaries. It is during this test that you are seated at a machine and you are asked to look straight ahead at a certain focal point and then you are to click a button whenever you notice any moving targets enter into your field of vision. Whenever the test is over, a map will be printed out that will provide the results of your field of vision.
This testing is able to tell if there is maybe a underlying cause. For instance, if you have constriction in your vision field, then you may have chronic high intracranial pressure, hysteria, glaucoma or even tetinitis pigmentosa. If there is any type of increase in the pressure on your brain, it can cause your blind spots to become much larger because of the abnormal swelling of your optic disks that are located in both eyes. This condition is called papilledema.
Whenever there is a defect in a single eye, the cause is able to be found to be just in that eye or in between the optic nerves that meet at the optic chiasm. However, if the issue is in both eyes then it could show a disease processes in the optic nerves or even farther back into your brain. There are certain conditions that are in both eyes which is called homonymous hemianopia when the defects are part of both vision areas which is considered to be bitemporal or binasal.
The location and extent of your blind spots could even point to more clue about a condition as well as the location of what could be causing it. The testing done to help narrow down whatever could be causing the field of vision to be lowered.