What is the visual field?
The field of view is the region or environment in which the eye can perceive objects. For example, how far can the patient perceive something in the upper field of vision without looking up? The same applies to the field of vision below, right, left and of course everything in between (top right etc.). The values determined during a visual field examination are given in degrees. The cooperation of the patient is of great importance in order to achieve representative and usable results.
For orientation even the non-medical practitioner can get an impression of the visual field and its possible failures with very simple means. All that is needed is a narrow object (a pen would be conceivable) and a cover for one eye (usually the patient simply covers the eye with the palm of his hand). Here too – as in the visual acuity test – each eye is tested individually.
This is because each eye can have a failure that can possibly be compensated by the other eye. To ensure that such important details are not overlooked, both eyes are tested individually. The examiner faces the patient.
Both hold the opposite eye to each other. (If the patient covers his left eye, the examiner must cover his right eye and vice versa). The fact that the examiner also covers one eye serves for comparison.
The examiner’s field of vision thus acts as a reference value in the layman’s test in order to be able to detect gross deviations. Now an object – the pen – is inserted into the visual field from all sides from outside. The patient indicates when he or she first sees the object.
It is important that the eyes are fixed on each other and do not move, but always look straight ahead. The head must also be kept absolutely still. If the field of vision is normal, the doctor and patient see the object at the same time.
This process is repeated for the other eye. With this approximate method, failures can be quickly detected. Here, for example, there is the possibility that a quarter or even a half (right or left) of the visual field has failed. Isolated failures also occur. In the case of glaucoma, for example, only the central part of the field of vision can be lost.