Evoked potentials and their applications to Neuro-Ophthalmology

Abstract

Sensory stimuli cause electrical signals to be generated in cerebral cortex and brainstem structures that, by means of computer techniques, can be recorded noninvasively and without risk from EEG electrodes placed on the scalp. This review discusses the role of these so-called evoked potentials in the research laboratory and in the clinic. Evoked potentials (EPs) can objectively confirm weak clinical evidence of visual, auditory or somatosensory dvsfunction, and may even detect subclinical abnormality. They are useful in demonstrating an organic cause for symptoms that might otherwise be supposed to be of psychogenic origin: conversely, unequivocally normal EPs may bediagnostically significant. A limitation of the technique is that EP abnormality is seldom, if ever. specific to a particular disease entity; its significance is in relation to the overall clinical picture. The procedure can be clinically overused.

By providing evidence of a second CNS lesion, EPs can be useful in the differential diagnosis of multiple sclerosis, though the significance of a negative finding is not clear because the false negative rate has not been shown to be negligible. Misrouting of optic nerve projections, a significant point in the diagnosis of albinism, can be detected by visual EP recording. Visual EPs can detect residual excitability of visual cortex neurons in cortically blind patients, and this can be relevant to the eventual recovery of vision. Auditory brainstem EPs are a sensitive screening test for acoustic neuroma, and have been used to monitor brainstem function during surgery. EPs can provide a useful objective index of sensory pathway function in neonates and infants, including measurements of visual acuity, contrast sensitivity and binocularity. These EP tests may be useful since available clinical tests of sensory function are less adequate with infants than with adult patients, though technical problems remain to be solved before the use of visual EPs is widespread outside the infant laboratory. The role of visual EPs in research into glaucoma, amblyopia, Parkinson's disease and early visual development is reviewed.

Key Words:

• evoked potentials
• multiple sclerosis
• spatial vision
• glaucoma
• albinism