By electrooculography, ophthalmologists mean a measurement procedure to determine the retinal resting potential, which is often used to diagnose diseases of the vestibular organ. The procedure works with the help of two electrodes and is entirely objective. There are no risks or side effects associated with the measurement.
What is electrooculography?
If the ophthalmologist diagnoses problems with the retina, electrooculography, which involves placing two electrodes on the right and left sides of the eye, can measure the resting potential of the retina. Electrooculography objectively measures the resting potential of the retina. The measurement procedure is also called electronystagmography. The resting potential of the retina is the permanently existing voltage difference between the back and the front. This voltage difference gives positive charge to the cornea and negative charge to the back of the eyeball. To measure this resting potential, the ophthalmologist uses two electrodes in electrooculography. These electrodes are either located on the right and left side of the eye or are placed above and below. The measurement allows the smallest eye movements to be detected, since every movement changes the resting potential. Therefore, electrooculography is often used in the context of neurological findings and, in this case, is intended to document barely visible tremors of the eyes.
Function, effect, and goals
Electrooculography may be required in the context of various disorders. For example, if a patient’s vestibular system is diseased, then this can produce symptoms such as nystagmus. Nystagmus is a pathological tremor of the eye that is not always visible to the naked eye. The tremor is involuntary and usually unconscious to the patient. A patient first has the two measuring electrodes placed on the skin around the eye as part of an electrooculography procedure. The resting potential is first measured at absolute rest when evaluating the vestibular organ. In the case of nystagmus, voltage changes can already be observed in this process, which can be traced back to minimal eye movements. In the course of the vestibular examination, the measurement at rest is followed by a measurement after a slow rotation of the patient. In most cases, the auditory canal is also rinsed with water at 27 degrees cold and later 44 degrees warm before the physician takes a third measurement. However, electrooculography does not necessarily have to take place as part of a balance examination; it is often used to diagnose retinal diseases. In this scenario, after the doctor attaches the electrodes, the patient must perform various eye movements. With an eye movement, the front of the eye gets closer to one of the electrodes. The back of the eye, on the other hand, moves closer to the opposite electrode. This process causes a voltage difference to occur between the two electrodes. This voltage difference is recorded during electrooculography and normally behaves in a certain proportion to the angle of vision. Typically, during ophthalmic electrooculography, the team asks the patient to look back and forth between two fixed points in space at regular intervals. If the resting potential of the retina is constant, then this allows the same voltage difference to be recorded each time the direction of gaze changes. As soon as the light conditions change, the resting potential of the retina also changes in a healthy person and thus the difference at a change of the direction of gaze changes at the same time. Normally, therefore, during ophthalmic electrooculography, the physician additionally evaluates how the voltage changes in the dark. This change is also known as dark adaptation. In a healthy patient, a slight drop in the resting potential occurs in the dark and lasts for several minutes. As soon as the patient is illuminated again, the resting potential usually rises sharply. If these typical patterns cannot be observed on electrooculography, there is probably a pathological change in the retinal pigment epithelium. Sometimes electrooculography is also used in sleep medicine. In polysomnography, for example, the REM phases of the sleeper are recorded. REM stands for rapid eye movement. In some cases, sleep medicine uses the measurement to determine how the sleeping patient reacts to certain sounds.
Risks, side effects and dangers
Electrooculography is usually performed on an outpatient basis and does not involve any pain for the patient. Neither risks, nor side effects are to be expected. However, if the procedure is used as part of an equilibrium examination, the patient may experience balance disturbances for the day, which usually resolve the following day. The flushing of the auditory canals may be perceived as unpleasant during the balance examination. However, the advantages of the measurement method outweigh the disadvantages in any case. The procedure is a completely objective measurement method, which therefore cannot be falsified by the patient. This distinguishes electrooculography, for example, from many other, subjectively perceived balance examinations. Basically, falsification of the results can only occur with electrooculography if the electrodes have not been attached professionally or if they are too loose. In this respect, the professionalism of the supervising team is crucial for a reliable diagnosis. Under certain circumstances, further ophthalmologic examinations may be required after an ophthalmic electroretinography to diagnose retinal diseases. For example, electroretinography could be used for further examination of retinal function. Different light stimuli are selectively applied to the retina and the potential formed by the retina is determined with the aid of several electrodes. Findings may also prompt follow-up examinations or targeted measures of therapy in the context of a balance test.
