Visual Field Test
A visual field test is classified as an eye examination that diagnoses dysfunction in both (central and peripheral) vision which can be caused by many medical conditions (glaucoma, stroke, tumors, etc). This test can be done with the subject’s sight being fixated while certain objects are displayed in varying lengths. A tangent screen test or the Amsler grid can be used to undergo this test.
Visual Field test can be completed by a technician or by using a machine with a technician or by giving full control to the machine. This test is also known as the Tangent screen exam, automated perimetry exam, Goldmann visual field exam or the Humphrey field exam.
Methods of examination
Confrontation visual field examination, also known as Donders’ test is used to perform Visual Field Test. First, the subject will be asked to place one eye under cover and to stare at the technician with the other one. When the patient covers their left eye, the examiner covers their right eye, vice versa. Then, the examiner will sway his hand from the patient’s visual field only to bring it back in. The examiner can use a wagging finger or a hat pin for this. Then the patient notifies that the examiner’s hand has come into view again and this is done repeatedly as a simple test.
Also known as campimetry, is a way to check the visual field. This is a measurement to test the sensitivity of light in the visual field by detecting the presence of test targets on a set background. Perimetry helps to measure the visual field, at a detailed depth of the periphery of the visual field.
Automated perimeters are popular and it can be applied to diagnose diseases, complete visual assessments, school/community screenings, selection in military/jobs and to clarify disabilities.
Types of perimetry
The most basic form of perimetry, it uses a white tangent screen where vision is checked by showing differing sized pins that are attached to a black wand (it is moved too). The pins can be either white or different colored.
A hollow white spherical bowl is fixated at a certain distance from the patient (in front). The examiner displays a light of variable size and intensity. The light moves from the center (kinetic perimetry) or it remains in one position (static perimetry). This method tests the depths of the peripheral vision and is used for a long time. However, modern automated perimetry is more popular these days.
In this method, a mobile stimulus is moved by a perimetry machine. The patient pushes a button if he sees the light. A white background is used (white-on-white) and this is the most commonly used practice in clinics and in research. However, the white-to-white reduces the perimetry and sets the variability high. Automated perimetry is used to record blind spots. The patient is seated in a made-up small concave dome inside a machine with a target in the center. The chin sits on the machine and the non-testing eye is covered. The patient is told to press the button when he sees the light. Then, the computer automatically generates the patient’s visual field.
It uses the fundus image and an eye tracker to complete the macular function.
Methods of stimulus presentation
The test uses differing locations throughout the field at one time. Firstly, a dim light is shown at a certain location then the patient is shown the light (with increasing intensity) and told to notify when he can see the light. The least brightness required to detect the stimulus is known as the “threshold” sensitivity level of that location. This is repeated again and again in different locations until the whole visual field is checked.
This method is usually done with automated equipment. Used for rapid screening and follow up of diseases such as scotomas, loss of vision (peripheral) and low vision loss.
The test uses a mobile stimulus that the examiner moves (Goldmann kinetic perimetry). First, one light is used with constant size and brightness. Then, the light is moved towards the center of vision until the patient notifies of its presence. This is then repeated in different directions. Repeating will allow the vision to be tested from different directions. Different types of lights are used to have accurate results.
It helps in mapping the visual field and its boundaries. Kinetic perimetry helps the patient who cannot undergo automated perimetry due to several reasons.