Visual Evoked Potentials (VEP)
It is a method used in the examination of the part of the visual pathway from the retina to the visual cortex of the brain using a visual stimulus. A flashing light or a black-and-white checkerboard pattern (pattern stimulants) sliding on a display are used as visual stimulation sources.
The patient is placed against a screen at a distance of up to 1 meter and asked to look at a flash stimulant or a fixed point in the center of the screen with one eye while the other eye is covered in turn. The records are usually done through the electrodes in the form of a cable placed on the special spots on the scalp. If the patient is using eyeglasses or lenses, he or she should wear them during the test. It can also be applied to pregnant women, people with pacemakers, and small children.
The waves are recorded in accordance with the anatomical areas where visual stimulus passes through to reach the visual cortex in the brain. The results are evaluated by a neurology specialist, and if there is a problem, its anatomical source is determined.
It is a diagnostic method that can be used in optic nerve inflammations called Optic neuritis, as well as in many cases such as circulatory disorder of the optic nerve (ischemic optic neuropathy), nutritional disorders (such as B12 deficiency), and optic nerve damage due to drugs. It is very valuable in terms of revealing the loss of function that cannot be shown by brain MRI or not noticed by the patient. It is applied in the field of neurology in demyelinating diseases, especially in patients with multiple sclerosis.
While pattern VEP application requires patient compliance, flash VEP is applied in small children who cannot adapt to the procedure, unconscious patients, and adults who cannot communicate properly due to causes such as dementia.
As in every test, it should be performed and interpreted by experienced neurologists.
What is the VEP Test?
The method that examines the functioning of the visual pathways and the parts between the retina and the neural networks in the visual cortex of the brain is called the VEP test. It can also be considered as checking the degree of visual acuity and evaluating possible visual disturbances internally.
During the test, a flash is turned on and off intermittently as a visual stimulus to the patient, or the patient is asked to watch a visual of checkerboard-like black and white squares on a monitor.
The VEP test is a method that can be used to detect all anatomical damage in the anterior visual pathway.
In Which Diseases Is VEP Test Required?
There is no harm in applying the VEP test in pregnant women, patients with pacemakers, patients with platinum, and pediatric patients.
The only technique used to diagnose an inflammatory disease in the optic nerve called Optic neuritis is the VEP test.
It is an essential examination to diagnose conduction disorders in the optic nerves, such as isthmic optic neuropathy.
Diseases for which a VEP test is required can be listed as nutritional disorders, B12 deficiency, and visual disturbances caused by drugs.
How is the VEP test performed?
Different procedures are applied for the VEP test depending on whether it will be performed over a monitor or with intermittent light. However, since the same results are obtained in both, the method is determined by the hospital.
If the VEP test is to be performed with the monitor, the patient is seated in front of the monitor at a distance of 1 meter and is asked to keep using glasses or lenses.
Each eye is examined separately by closing and opening the right or left eyes one by one, and the patient is asked to follow the specified commands.
In the meantime, functions of the eye are recorded through electrodes placed on the patient’s scalp.
In the test using intermittent light, the patient should close his or her eyes and be in a dark environment. Here again, electrodes are placed over the scalp. Then, a flash is sent to the eye at certain intervals by the healthcare professional who performs the application. In this way, the behavior of the eye is recorded.
Here, in both methods, it is possible to examine in detail where and how the image is transferred while the eye is processing the visual event. If there is any conduction problem, it can be detected.
There is no hurt or pain from the electrodes placed on the scalp before and during the procedure. The procedure can also be easily applied in children and can be used to detect conditions such as the lazy eye early in childhood.
In the VEP test, sometimes needles are placed on the scalp instead of electrodes, depending on the machine used. However, these needles are not like normal needles you know. These needles, which are made of metal parts, do not hurt the patient in any way.
Throughout the application, a healthcare professional is always next to the patient. Hence, you should know that in case of any fear or tension, a health professional will be with you, and all stages will be recorded by her.
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