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					ELECTROPHYSIOLOGY DEPARTMENT                                            (b) children

                                                                        When testing young children and babies, special contacts and
What is visual electrophysiology?                                       simpler, shorter testing is used.

When you look at something, an image of the object is projected         What tests can I expect?
onto the retina at the back of the eye. The retina converts this
optical image into very small electrical signals, which pass a long     When you attend you will have a selection of the following tests
the optic nerve to the brain, where the sensation of ‘seeing’ occurs.   depending on the reason for your referral.
Visual electrophysiology measures these very small signals both in
the eye and the brain.                                                  Pattern electroretinogram (PERG)
                                                                        * measures the function of the central retina, the macula, which you
Why am I being referred?                                                use for detailed vision e.g. reading.
                                                                        * you will be asked to look at a moving checkerboard pattern on a
Your consultant has asked us to examine the function of your visual     TV whilst we record the small electrical signals generated in the
system in order to help diagnose the cause of your visual problem.      macula.
It can also monitor disease progression or the effects of any
treatment you may be receiving.                                         Electroretinogram (ERG)
                                                                        * records the electrical signals from the retina to flashes of light
What is involved?                                                       both in darkness and in light.c
                                                                        * the brightness, flash rate and colour of light are varied to allow the
Firstly, all the tests are non-invasive and do NOT need an              rods (night vision) and cones (daytime vision) to be examined
anaesthetic or injections.                                              separately.

(a) adults                                                              Visual-evoked potential (VEP)
                                                                        * investigates the pathways carrying signals from the eye to the
• small contacts are fastened to the skin around the eyes or scalp
    (depending on test), using tape or paste. Some tests also use       brain, the optic nerves, and how the brain interprets these signals.
                                                                        * you will be asked to observe a moving checkerboard pattern on a
    soft gold contacts that rest on the lower eyelid. These are not
    uncomfortable but may initially make your eyes water a little.      TV or flashes of light while we record the electrical signals.
• dilating drops are used in most cases for some of the tests and
                                                                        Electro-oculogram (EOG)
    a 20 minute period is required for them to take effect.
                                                                        * measures the function of the boundary between the retina a nd the
• you will have to spend 20 minutes in the dark before the ERG is
                                                                        layer under the retina (retinal pigment epithelium).
    carried out. This will allow us to measure how your eyes work in
                                                                        * you will be asked to make regular eye movements between 2
                                                                        small red lights for approximately 20 seconds every minute for 15
• the testing can take up to 3 hours depending on the number of         minutes in the dark and 12 minutes in the light.
What do I have to do?

* Please be punctual, otherwise it may not be possible to perform
all of the tests required.                                                                    ELECTROPHYSIOLOGY
* It is VERY important that you bring to your appointment all current
glasses and recent prescriptions. If you are a contact lens wearer                               DEPARTMENT
please also bring your lens case and necessary solutions, as we
may need you to remove them.
* Your hair should be freshly washed and free from all oils, gels,
sprays etc. No eye make up should be worn.
* A list of all medication you are taking should be brought.
* If you intend to bring young children, other than for testing, please                       Information for patients
ensure that there is another responsible adult to look after them as
there are no childcare facilities within the department.

Are there any side effects?
Dilating drops will cause blurred vision a nd increased sensitivity to
bright light/sunlight, but this will wear off after a few hours. Dark
glasses may help on a sunny day.
You should NOT drive for several hours after the testing has
finished and the effects of the eye drops have fully worn off.

What happens afterwards?

A report will be sent to the consultant who referred you for testing.

If you require any further information regarding the department or the tests carried out
within the department, please don’t hesitate to contact us on 020 7566 2120.
This leaflet is intended to provide general information for patients. Any patient who is
worried about his or her individual circumstances should seek specialist advice relating to
his or her circumstances.
MOORFIELDS DIRECT is a telephone helpline available between 9.00 am and 5.00 pm.
Telephone 020 7566 2345.

Issue 1 – February 2004 (review December 2004)                           Vikki A McBain
                                                                                              Moorfields Eye Hospital

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