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Visual electrophysiology

What the service does
How to access the service
Location of service

What the service does

The visual electrophysiology service is a specialist regional service for adults and children across Northern Ireland.

At your appointment, small sensors attached to your skin measure signals from your eyes and brain while you watch some lights.

These tests help us:

  • understand how your vision is working
  • find out the cause of a visual problem
  • monitor changes to your vision or the effects of a treatment

The tests are painless. They can take up to one hour and may involve spending a short time in the dark.



Sometimes dilating eye drops are used. These can sting for a few seconds and may blur your vision for several hours after the tests.

Anyone who has had eye drops should NOT drive until the effects have fully worn off.

Shorter tests are used for young children and babies. Parents / guardians stay with the child at all times and are encouraged to help the child feel safe and secure.

The tests include the following:

  • visual-evoked potential (VEP) measures signals from the vision centres in the brain to find out how well the eyes and brain work together
  • electroretinogram (ERG) measures the electrical activity in the retina (the light sensitive lining inside the eye), which makes a picture of what we see

How to access the service

Patients are referred to the visual electrophysiology service by their eye doctor or another clinician.

You will then receive an appointment for visual electrophysiology testing.

If you need an interpreter for your appointment or you would like help with our communications (for example information in other languages or formats), this can be arranged with the booking office when you make your appointment.

When you come for the test:

  • it is VERY important to bring your current glasses with you
  • your hair should be clean and free from all oils, gels and sprays
  • do not wear eye make-up or skin creams as we need to have clean skin around your eyes and forehead

Following your tests, a report will be sent to the eye doctor who referred you.

Location of service

The visual electrophysiology service is located in the Eye Outpatient Diagnostic Unit (EODU).

Locations where this service is delivered

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