Glaucoma is a common eye disease that initially affects the peripheral vision but slowly progresses to late and advanced stages where the central vision is also hampered. Usually, it is quite difficult to realize that the peripheral vision has been affected since the deficits are subtle and the other eye compensates. To detect any such disorder, the visual field test is one of the key tests that a doctor would perform as a part of the diagnosis.
How can the visual field test help?
This particular test can detect any changes in one’s vision that is usually not noticed by the patient until the disease has progressed. It measures the area of a person’s vision and how wide the eyes can see. It is advised to take the test once annually but repeated periodically to determine the progression. Intruding the center can impair vision. Also, diseases like cataracts, stroke, diabetes, and macular degeneration can cause vision loss. All these factors taken into account make, formal visual testing so important.
This repetitive testing might seem unnecessary to many, but it helps in maintaining a baseline visual field and monitoring glaucoma over a period of time. Repeating the test not only helps the doctors in evaluating the changes occurring but also whether they are real or not, thus, improving the quality of the test. The visual field test is a measure of the vision that helps the doctor to guide him to the right treatment and see how it will benefit the patient in the future.
What happens during the test?
The test is a bit challenging and might put one under stress as it usually takes 5-10 minutes for each eye and one needs to remain alert for that duration. However, there is nothing to rush as the machines would be adjusting their timing with the patient’s reaction time and pace. The technician or the perimeters adjusts the seat in front of the machine. One needs to look straight ahead at the fixation light while keeping the upper eyelids high enough so as not to block the vision. The test is so designed that the light dims out gradually until one sees them no longer. Many flashes of light are focused but the patient may not necessarily see all of them. One can also hold the response button and pause for a while before resuming.
▶Types of visual field tests
Since the purpose of the visual field test is to detect changes in the peripheral vision, it is sometimes referred to as the perimetry examination. There are several types of which the Humphrey visual field test is the most common in the US. This consists of a center fixation light with blinking test lights at the side vision. While taking the test, one needs to concentrate on the center light and be alert when the blinking sidelight is seen. In the test result, the areas that appear gray or black reflect the areas in the vision that are missing or have got blurred. In the case of uncontrolled glaucoma, these areas appear darker and larger.
The other is the Goldmann visual field test which is performed with a mobile target that is controlled by the technician.
▶ The ongoing monitoring process
To detect the changes in the visual field due to glaucoma, a doctor can see the shape and location of the defect. Moreover, if the vision impairment is more central or the patient has a weaker vision in one eye, then different algorithms are required. For instance, a more zoomed-in visual field or a brighter light stimulus can be used. Depending on the condition of the patient’s visual field, the doctor would select the treatment against the best possible monitoring. If the pressure on the eye is too high and the condition is deteriorating, then further treatments are required. Once the test has been done, the patient is familiar with the proceedings, and monitoring the condition of glaucoma can be made sure in the follow-up visits. Sometimes, other tests are also necessary to get more information.
Glaucoma is often called “the sneak thief of sight” as it is painless, mostly affecting the side or peripheral vision. It is recommended by the doctors that a visual field test should be performed in order to monitor the situation. Most people hesitate to take this test but with a proper understanding of the purpose of the test and reviewing the results with a doctor, optimal eye health can be ensured.
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