Please read this information carefully before coming in for your Visually Evoked Potential (VEP).
What is a VEP?
VEP is a test that assesses the functioning of the visual system, from the eye to the brain along the optic nerve. A VEP is a non-invasive, painless procedure, that records the electrical activity of the brain in response to an alternating checkerboard screen.
Why do a VEP?
If you are experiencing changes to your vision in 1 or both eyes, a VEP may be requested to determine whether there is a problem with how the visual pathways are functioning.
What happens during a VEP?
Your VEP will take around 60-90 minutes. First your head will be measured and several small electrodes will be attached with sticky paste to your head. 2 other discs will be placed to the side of your eyes and 2 further sticky pad electrodes will also be attached below the lower eyelid of each eye.
You will be asked to sit comfortably in a chair and look at a black and white checkerboard screen which will be moving from side to side.
Full-field VEP
At first you will have both eyes open and look at the alternating screen whilst focusing on a red dot. As the test continues 1 eye and then the other will be covered with an eye patch. You will be asked to watch the screen for several minutes so that plenty of responses can be collected and averaged, which will give us a good understanding about how the optic nerve pathway is working. The brain will respond to the moving checkerboard stimulus and these waveforms will be recorded.
Half-field VEP
This is an extension of the first test. Again your eyes will be covered 1 at a time by an eye patch but at the same time half of the checkerboard screen will also be covered.
Flash VEP
Sometimes you may be asked to complete a third part to the test. A strobe lamp will be placed a short distance away and you will be asked to watch this lamp as it flashes. Once the recording has finished all electrodes will be removed and your head wiped with warm water.
Preparing for the test
- You should arrive with clean, dry hair with no grease, gel, wax, or other hair products.
- Continue taking all regular medication and eat as normal before the test.
- You will be asked if you understand this information and whether you consent to the test before we start. At your appointment you are welcome to ask the physiologist doing the test to give you further information or to explain more about the procedure.
How long until I get my results?
The results will be sent to your GP/consultant. You will not receive any results during the test. Your consultant may send you a letter with the results or see you again for a follow-up appointment. Please note, results are not sent directly to you.
Contact details
This information is intended as a guideline only. If you have any further questions about your test (excluding about results) please contact the department on the numbers below and a member of staff will be happy to help.
Your responsibility as a patient
Outpatient services at North Bristol NHS Trust are in great demand. Even so, every week an average of 600 patients fail to attend, which wastes appointments. Please tell us with as much notice as possible if you no longer need your appointment and we can allocate this to another patient.
What if I am unwell or need to change my appointment?
If you have an infectious condition, such as COVID-19, measles, mumps, chickenpox, flu, stomach upset, have head lice, or are unable to attend your appointment for any other reason, please let us know with as much notice as possible so that your appointment can be rescheduled and offered to someone else.
If you want to change the appointment for a second time, we cannot offer you another date unless there are exceptional circumstances.
What if I don’t attend?
We will assume that you no longer require your appointment, and we will not offer you another one. We will write to the consultant/doctor who referred you and inform them that you did not attend.
© North Bristol NHS Trust. This edition published December 2024. Review due December 2027. NBT003747
