Perimetry is a method of vision field examination with a special apparatus called perimeter. The examination consists in assessment of a field visible with motionless eye. The examination may reveal loss of parts of field of vision, which usually results from retinal disorders or abnormalities of a patchway leading to visual areas of the brain. Perimetry consists in assessment of retinal ability to distinguish brightness of a test mark from background luminance. This sensitivity is highest in the centre of vision field and decreases peripherally.
The examination requires maximal concentration as the field of vision is defined on the basis of patient’s answers. The examination is performed when the patient is sitting. The patient sits before semicircular, illuminated perimeter dome. Patient’s chin and forehead are supported to assure appropriate head position. The examination is performed for each eye separately (at first one eye is covered, then the other one). During the whole examination the patient should look into the point in the dome centre directly before examined eye – it is essential for proper performance of the examination. In the other dome area luminous mark of specific diameter and light intensity appears. This spot moves usually along the meridians, from the perimeter to the centre. The patient has to tell (while looking into central point) whether luminous mark is visible, is diminishing or disappears.
Preparation for the examination
The examination does not require any special preparation. Ophthalmological consultation is required before and correction of the sharpness of vision if necessary. You should take reading glasses with you for the examination. It is a complicated examination for the patient, requires concentration and strong cooperation with the person carrying out the examination. It is recommended to come to the examination after a good sleep and well rested.
The time of the examination
The examination is painless, requires cooperation between the patient and the doctor.
Indications for the examination
- Suspicion of glaucoma
- Neural system disorders
- Optic nerve disorders
- Retinal detachment
- Other retinal and choroid disorders
The examination is non-invasive and can be performed on people of all ages. However, due to necessity of cooperation with the examiner, examination of field of vision is not recommended in children, people with intellectual disabilities, and elders with orientation disorders.