What is the electrooculography?If the ophthalmologist diagnoses problems with the retina, electrooculography, with two electrodes attached to the right and left of the eye, can measure the resting potential of the retina.
Electro-culography objectively measures the resting potential of the retina. The measurement method 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 the cornea positive charge and the back of the eyeball negative charge.
To measure this resting potential, the ophthalmologist works with two electrodes in electrooculography. These electrodes are located either to the right and left of the eye or are placed above and below. By measuring the smallest eye movements can be identified, since each movement changes the resting potential. Therefore, the electrooculography is often used in the context of neurological findings and should in this case hardly visible trembling of the eyes document.
Function, effect & goals
The electrooculography may be required in the context of various diseases. For example, if a patient's balance system is affected, it can produce symptoms such as nystagmus. In nystagmus, a morbid tremor of the eye sets in, which is not always visible to the naked eye. The tremor is involuntary and usually unconscious to the patient.
A patient is first placed on the skin around the eye as part of an electrooculography, the two measuring electrodes. The resting potential is initially measured in the absolute state of rest in the assessment of the organ of equilibrium. In the case of nystagmus, tension changes can already be observed, which are due to minimal eye movements. As part of the balance examination, the measurement at rest is followed by a measurement after a slow rotation of the patient. Mostly, the ear canal is additionally flushed with 27 degrees cold and later 44 degrees warm water before the doctor makes a third measurement.
However, electrooculography does not necessarily have to be part of an equilibrium study, but is often used to diagnose retinal diseases. After the doctor has attached the electrodes, the patient must perform various eye movements in this scenario. With one eye movement, the front of the eye comes closer to one of the electrodes. The back of the eye, on the other hand, approaches the opposite electrode. Through this process, a voltage difference between the two electrodes occurs. This voltage difference is detected in the electrooculography and behaves normally in a certain proportion to the viewing angle.
As a rule, the team asks patients during ophthalmic electrooculography to look back and forth at regular intervals between two fixed points in space. If the resting potential of the retina is constant, then the same voltage difference can be detected each time the viewing direction changes. As soon as the lighting conditions change, the resting potential of the retina and, at the same time, the difference in a change in the direction of vision changes in healthy people. Therefore, in the case of ophthalmological electrooculography, the doctor usually assesses how the tension changes in the dark. This change is also known as dark adaptation. In the case of a healthy patient, a slight decrease in the resting potential occurs in the dark lasting several minutes.
As soon as the patient is illuminated again, the resting potential usually rises sharply. If these typical schemes can not be observed in 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 sleeping person are recorded. REM stands for rapid eye movement, ie fast movements of the eyes. In some cases, sleep medicine uses the measurement to determine how the sleeping patient reacts to certain sounds.
Risks, side effects & dangers
The electrooculography is usually performed on an outpatient basis and is associated with no pain for the patient. Neither risks nor side effects are to be expected. If the procedure is used as part of an equilibrium examination, however, balance problems may occur for the day, which usually recede on the following day.
The flushing of the auditory canals can be perceived as unpleasant in the context of the balance test. However, the advantages of the measuring method always exceed the downsides. The procedure is a completely objective measuring method which can not be falsified by the patient. This distinguishes electrooculography, for example, from many other, subjectively perceived balance tests. Basically, falsification of the results in electrooculography can only be present if the electrodes have not been expertly attached or are too loose.
The professionalism of the supervising team is therefore crucial for reliable diagnostics. Under certain circumstances, further ophthalmological examinations may be required following an ophthalmological electrooculography to diagnose retinal diseases. For example, an electroretinography could be used for further investigation of retinal function. Different light stimuli are specifically delivered to the retina and thereby the potential formed by the retina is determined by means of several electrodes. Even in the context of an equilibrium test, a finding may, under certain circumstances, lead to follow-up examinations or targeted measures of therapy.