Electrodiagnostic tests

What are electrodiagnostic tests?

Electrodiagnostic tests involve using special sensors called ‘electrodes’ to record the tiny electrical responses that are produced by the eyes and the brain when your child looks at flashing lights or moving patterns.

These electrical responses can be abnormal in many conditions that affect the eyes, the nerve pathways that connect the eyes to the brain, or the parts of the brain concerned with vision.

Electrodiagnostic tests can be useful in determining whether a child has a particular condition, the location of any problem and its extent. They can also be used to estimate the level of vision.

EDTY6 (paediatric screening tests)

If your appointment letter is for the EDTY6 clinic your child will most likely be having paediatric screening tests.

This clinic is aimed at young children, or children who might otherwise have difficulty complying with the procedures for standard testing. These tests do not need any eye drops.

Your child will be asked to sit on a comfortable chair (babies and toddlers sit on your lap).

Your child will then have electrodes (sensors which look like stickers or small buttons) attached to the skin on the head and the face. The electrodes pick up and record electrical responses produced by the eyes and the brain. The skin will be rubbed gently with a gritty cream first. Some electrodes attach with paste which will be washed off with water after the test. Sometimes we hold these in place with a headband.

Your child will then be shown coloured flashing lights and moving patterns on a television screen.

EDTSC (standard tests)

If your appointment letter is for the EDTSC clinic your child will most likely be having standard electrodiagnostic tests.

This clinic is for standard testing (as carried out in our adult clinics) and is aimed at older children. It provides more diagnostic information but requires some concentration and co-operation. Eye drops may also be needed.

There are several different types of electrodiagnostic test that may be done during the appointment. We will choose the most appropriate tests based on the information we receive from your child’s consultant. The 3 most common tests are explained below:

Visual evoked potential (VEP)

The visual evoked potential (VEP) takes around 45 minutes.

The VEP is used to assess the function of the optic nerves which carry signals from the eyes to the brain.

Signals are recorded from the visual cortex (the part of the brain where vision is processed) by placing small sensors, called electrodes, onto the scalp at the back of the head. The electrodes are attached using a special water-based paste that we will clean out after the test. Each eye is tested separately so a patch will be used to cover one eye. The test then involves watching chequerboard patterns on a screen or looking at flashes of light.

Pattern electroretinogram (PERG)

Pattern electroretinogram (PERG) takes around 20 minutes.

The PERG measures the function of the macula (the part of the retina responsible for detailed central vision). It also gives information about the front-end of the optic nerves.

Signals are recorded from the retina using special sensors placed along the lower eyelids and sticky-pad electrodes on the forehead and temples. The test then involves looking at a chequerboard pattern on a screen.

Flash electroretinogram (ERG)

Flash electroretinogram (ERG) takes around 1 hour.

The ERG measures responses from the retina (the layer at the back of the eye that converts light into an electrical signal) to assess how well the different cells within the retina are working.

We will need to give some eye drops to enlarge the pupils, and we record the signals using the same sensors as for the PERG. Your child’s eyes need to adjust to darkness to start with, so there will be a 20-minute resting period with the room dimly lit by red light before the test begins. The test then involves looking at flashes of light of different brightness, rate, and colour.

How long do these tests take?

If your appointment letter is for a paediatric appointment (clinic code EDTY6), we should be able to complete your child’s tests in under 1 hour (45 minutes is typical).

If your appointment letter is for a standard appointment (clinic code EDTSC), we should be able to complete your child’s tests in around 1 to 2 hours, depending upon which tests are needed.

Preparing for the test and after effects

You should bring any prescription glasses with you because they may be needed for the test, even if your child finds them of little or no use.

The skin needs to be prepared before attaching the sensors by rubbing it gently with a gritty cream. This can cause mild irritation, but does not usually.

The flashing lights cannot harm your child’s eyes.

If we need to give your child eye drops these will sting for a short time.

You should bring any prescription glasses with you because they may be needed for the test, even if your child finds them of little or no use.

The eye drops can cause blurred vision and sensitivity to light for a few hours afterwards, so you may prefer for your child to stay out of school and other activities until the effect of the drops has worn off. We also recommend bringing sunglasses or a peaked cap to wear after the tests.

For younger children successful testing often depends on having plenty of favourite toys, food and drink. (Privacy is available for breastfeeding if you would like.)

For older children please avoid using hair products, make-up, and false lashes on the day of the appointment.

Where will the test take place?

Testing takes place in Zone 2 of the Eye Department at the Sheffield Children’s Hospital. Enter the hospital by the main entrance on Clarkson Street. From the main entrance hall turn right and then follow the signs to the Eye Department, near the Pink Lift.

When you arrive, please go to the Eye Department reception desk. Once checked in, you will be directed to the waiting area. A member of staff from the electrodiagnostics team will come and collect you when it is time for your appointment.

Can we bring someone else with us?

You are welcome to bring someone else with you, but we ask that you are not accompanied by more than one other person in the test room because space is limited.

Some tests are done under darkened conditions, so please consider that other children might become bored and could distract the one being tested. If you do need to bring other children, there are play areas located around the hospital they can use if accompanied by another adult.

When will we get the results?

You will not get the results on the same day. The recordings need to be analysed first. A report will then be sent to the consultant who requested the test. They will discuss the results with you at your child’s next clinic appointment.

Are there any alternatives to this test?

Much of the information we get from these tests cannot be obtained in any other way, although it is possible to do some parts of this test in theatre under general anaesthetic as part of a more general examination, but we prefer to avoid this if possible.

Who should I contact if I have any questions?

If you cannot attend, please telephone the clerical team on 0114 305 3691 as soon as possible so that the appointment can be offered to someone else and your child’s appointment can be rearranged without further delay.

Please visit Visual electrodiagnostics for more information.

If you have any questions or concerns, or need any further information about these tests before your appointment, please contact Dr Brown (Lead Clinical Scientist) on 0114 27 11746. You can also talk to us on the day.

Can I give feedback after the appointment?

We are always looking for ways to improve our service and we welcome feedback from patients and their family. If you have any comments about your appointment, positive or negative, please let us know via email (include “Feedback” as the subject): sth.electrodiagnostic@nhs.net