Visual field measurement
The visual field test, or otherwise perimetry, is an eye examination that verifies the range of vision, which is the area that we are able to see with a fixed eye. There are two complementary methods of vision testing – retinal projection to a spherical surface (perimetry) and a flat surface. The visual field test is carried out by perimeters. They are used in a dark or in a bright room. More often automated perimetry is used, which allows for precise determination of the sensitivity of the retina at one point.
Indications for a visual field measurement
Correct field of view shows the behavior of retinal function, which receives visual impressions throughout its surface, the proper conduction of visual sensations by nerve fibers, as well as the normal function of the occipital lobes of the cerebral cortex.
Existing defects in the visual field of both eyes of the patient are recorded during perimetry. In the diagram, you can see what is their size and location.
Visual field defects can occur for various reasons, for example:
Defects noticed most often occur on the retina where light stimuli are not received by the appearance of lesions in the retina itself or as a result of neuronal damage efferent stimuli visual centers in the brain.
Visual field measurement is carried out on the order of a physician. It’s preceded by a visual acuity test – it is necessary to determine the field of view. Perimetry test is completely safe, but cannot be performed on little children, people with mental disabilities and the elderly with poor orientation. The visual field test involves no risks or complications, so it can be done repeatedly. It is recommended that once in a while the measurements are done in order to diagnose possible changes in the eye, or to correct existing defects.
The most common technique to perform this test is the Donder’s test. During the test, one eye is covered ( with a hand, a piece of paper). The doctor will be sitting in front of the patient and will be moving his/her hand out of the patient’s visual field then bring it back in. The patient will be asked to look ahead (it is best to choose a single point at which you will be staring at throughout the entire examination). The doctor will ask you to signal when the hand comes back to view.
Another common method is called the Goldmann test. The exam is to assess the ability of the retina to distinguish the brightness of a symbol on a given background. It uses the sensitivity of the retina to light, which is the highest in the center of the field, decreasing toward the periphery. The test requires the patient to focus and pay attention because on the basis of his/her statements the field of view will be determined. The patient sits in front of the perimeter dome, with the head and chin leaning against it. One eye is covered, and the patient must look at one set point. There will be a second point that will be moving and changing its placement in the field. Respondents are to inform the doctor, when he sees the second point, and when it fades and disappears completely from view. The field of view is marked by a doctor on a special diagram. There will also be a so-called Mariotte blind spot as a place where you can not see the point at all. The test can be repeated by changing the diameter, light intensity and / or color of the moving mark. During the test, the patient is not allowed to move.