VISUAL EVOKED POTENTIAL(VEP)
What is a Visual Evoked Potential?
VEP is a procedure where electrical activity of occipital area of brain is recorded by electrode after visual stimuli. It is a simple test taking approx 40 mints.
When is the VEP used?
A doctor may recommend that you go for a VEP test when you are experiencing changes in your vision that can be due to problems along the visual pathway. E.g.
- Loss of vision
- Blurred vision
- Alterations in colour vision
- Weakness of the eyes, arms or legs (suspicion of multiple sclerosis).
How it’s done and What does the VEP detect?
Stimuli used is either a checkerboard pattern or a LED goggle. Signals are recorded from posterior aspect of scalp. Abnormality in waveform detects even subtle abnormality in optic pathway.
How to prepare for a VEP test?
You will be given instructions on how to prepare for the test. This will depend on where you are going to get the test done. Some things that you may need to do include:
- Washing your hair the night before, but avoiding hair chemicals, oils and lotions.
- Making sure you get plenty of sleep the night before.
- If you wear glasses, make sure you bring these along with you to the test.
- You are usually able to eat a normal meal and take your usual medications prior to the test. However any medications that may make you drowsy should be avoided.
- Arrive on time and try to relax before the test.
- On the day of the test, you should also let the technician know if you have any eye conditions such as cataracts or glaucoma as this can affect the test and should be noted in your records by the doctor.
BRAINSTEM AUDITORY EVOKED POTENTIAL (BAEP)
What is BAEP?
A BAEP is an evoked potential caused by a sound, usually a series of ‘clicks’. Electrodes positioned on the scalp record responses to the sounds; these are then observed as a reading on an EEG.
When is the BAEP used and what does it detect?
A doctor may recommend you go for a BAEP test if you have been experiencing changes in your hearing ability that may be due to problems with a particular nerve pathway.
From the readings the neurologist can get an idea whether the auditory nerve is functioning properly or not. For example, an acoustic neuroma (a benign tumour of the ear canal) can stretch or compress the auditory nerve resulting in a long time for the processing of aural stimuli.
How to prepare for a BAEP test?
- Wash your hair the night before
- Eat a normal meal and taking your normal medication on the day of the test should be fine.
- You should let the person conducting the test know if you use a hearing aid or have any obvious hearing problems. The BAEP testing procedure is painless and without side-effects.
- BAEPs can be helpful in the diagnosis of: Hearing loss, Acoustic neuroma, Multiple sclerosis, Sub arachnoid inflammation, Friedreich’s ataxia, hereditary cerebellar ataxia and B2 deficiency.