Visual Evoked Potentials (VEP)

Introduction

This leaflet is designed to give you some information about the investigation for which you have been referred. We hope it reassures you – We have a team experienced in these investigations and you will have the chance to discuss further questions or concerns before the start of the investigation.

Consent

We must obtain your consent for any procedure or treatment beforehand. Staff will explain all the risks and benefits before they ask for your verbal consent. If you are unsure about any aspect of the procedure or treatment proposed, please do not hesitate to ask them for more information.

What is a Visual Evoked Potential (VEP)?

Visual evoked potentials are signals produced by the brain in response to a visual stimulus. This test specifically assesses the function of your optic nerve, which is part of your visual pathway.

What is the reason for the test?

You have likely been referred for this test because you are having some problems with your vision. This test can be used to investigate if there is a problem along your visual pathway, that cannot be detected by other eye tests.

What do I need to do on the day of the test?

There is no restriction on eating or drinking before, or after, the investigation.

Please continue taking any medication you are prescribed. It would be helpful to bring a list of your current medications with you.

Please bring your glasses or contact lenses with you.

It is important that your hair is clean; please do not use mousse, gel, oil or other hair products as this can affect the recording. Please try to avoid wearing lots of eye make-up, particularly mascara. Please do not wear fake eyelashes if possible.

Where will the VEP be performed?

Neurophysiology have two departments. VEPs are performed in Clinic 33, in the Addenbrooke’s treatment centre, please use the map provided in this leaflet to guide you. Additional information on getting to Addenbrooke’s and different modes of transport can be found at Finding-us.

Please note, if you arrive more than 30 minutes late for your appointment, you may not be seen.

Please contact us if you are travelling via hospital transport as this may determine the time of your appointment. Unfortunately, we are unable to see patients on beds or on stretchers in our outpatient department; please call us if this affects you.

Who will be present?

There will be one or two clinical healthcare scientists present performing the test, if you would feel more comfortable with a healthcare scientist of a particular gender or would like a chaperone please let us know. It is possible to bring someone with you if you wish.

Addenbrooke’s is a teaching hospital and you may be asked if you would consent to trainee staff performing the test under supervision or if you would mind other healthcare professionals/students observing the test. Refusing consent for this will not affect your test.

We have no provision for accompanying children to be supervised whilst you are having this investigation.

What happens during the test?

A healthcare scientist will collect you from the waiting room and take you to the clinical room. They will explain the procedure and give you the opportunity to ask any questions you might have. You should expect be in the department for between one to one and a half hours.

Prior to the test, the healthcare scientist will briefly test how well you can see. The healthcare scientist will measure your head with a tape measure and crayon then use a cotton bud and gritty paste to clean small areas of the scalp. A special sticky paste, similar to Vaseline, is then used to apply small silver discs called electrodes to the surface of the scalp. This is not painful, but does involve some rubbing.

Once all the discs are on, you will be asked to look at a black and white pattern, like a checkerboard, one eye at a time. It is important that you remain alert during this as tiredness can affect the result.

Following this, it may be necessary to test the area at the back of your eye, called the retina. This test is known as a Pattern Electroretinogram (PERG). This is done by placing a very fine thread across your lower eyelid, which is held in place with stickers either side of your eye. You will then be asked to look at the black and white pattern again with both eyes at the same time. The healthcare scientist will use saline to make the electrode as comfortable as possible but some mild irritation may occur. This should resolve on its own.

What happens afterwards?

The healthcare scientist will remove the electrodes. This is not painful as the special paste stays soft. They will clean your hair, but it will feel a little sticky until it is washed with shampoo. Once the electrodes are removed you will be free to go home and you can return to your normal activities.

When do I get the results?

The results will not be available on the day of the recording. The healthcare scientist and doctor will review the test and will prepare a detailed report for the consultant that referred you. The results will be sent to your referring consultant within 2 weeks, sooner if urgent. It is best to discuss these results with the consultant that referred you as they will need to be explained alongside any other tests that have been performed.

Risks

There is a very small risk of mild skin abrasion due to preparation of the skin before applying the recording electrodes. Please inform the clinical healthcare scientist if you have any skin conditions, sensitive skin or any allergies. There is a very small risk of eye irritation from the PERG electrode. Any irritation should resolve on its own.

Contacts / further information

If you need any further information or have any other queries please contact the neurophysiology administrator by phone on 01223 217136 Monday to Friday 09:00-16:00 or by email

If your appointment is in Clinic 33 of the Addenbrooke’s Treatment Centre

We are on level 3 in the Addenbrooke’s Treatment Centre (ATC). We are at the end of the corridor, just before the double doors to Papworth Hospital. You will find us next to the Endoscopy department.

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My Chart:

We would encourage you to sign up for MyChart. This is the electronic patient portal at Cambridge University Hospitals that enables patients to securely access parts of their health record held within the hospital’s electronic patient record system (Epic). It is available via your home computer or mobile device

More information is available on our website: My Chart