Electroperimetry

Perimetry is a method of clinical investigation of wide application in the fields of Ophthalmology, Neurology, Neurosurgery, and Internal Medicine. For more than half a century, alterations in the visual field have provided diagnostic clues concerning the site, stability, and nature of various ocular and intracranial lesions. Although the value of Perimetry has long been recognized, its application has often been limited for a number of reasons. Conventional perimetry is basically a time-consuming subjective test, which demands a verbal response from the patient and, hence, cannot be administered to young children, the seriously ill, or comatose patients where the information would often be of the most immediate significance; as, for example, in locating the side of an intracranial hemorrhage. To circumvent these limitations of conventional perimetry, a test has been devised for mapping visual field defects on an objective and automatic basis. Electroperimetry is based on the principle of photically evoking very small focal responses from selected parts of the retina by means of flickering a set of spatially distributed Xenon light sources encompassing a normal visual field. Conduction or nonconduction of each of the evoked focal retinal signals, which are ``buried in brain noise,´´ to the visual cortex is determind by real-time digital computer analysis of data recorded at the occiput via scalp electrodes. The computer instructs a recorder unit to display the visual field patterns.