8/9/2019 eddleaflet

1/2

ELECTROPHYSIOLOGY DEPARTMENT

What is visual electrophysiology?

When you look at something, an image of the object is projectedonto the retina at the back of the eye. The retina converts this

optical image into very small electrical signals, which pass alongthe optic nerve to the brain, where the sensation of seeing occurs.Visual electrophysiology measures these very small signals both inthe eye and the brain.

Why am I being referred?

Your consultant has asked us to examine the function of your visualsystem in order to help diagnose the cause of your visual problem.It can also monitor disease progression or the effects of anytreatment you may be receiving.

What is involved?

Firstly, all the tests are non-invasive and do NOT need ananaesthetic or injections.

(a) adults

small contacts are fastened to the skin around the eyes or scalp(depending on test), using tape or paste. Some tests also usesoft gold contacts that rest on the lower eyelid. These are not

uncomfortable but may initially make your eyes water a little. dilating drops are used in most cases for some of the tests and

a 20 minute period is required for them to take effect. you will have to spend 20 minutes in the dark before the ERGis

carried out. This will allow us to measure how your eyes work indarkness.

the testing can take up to 3 hours depending on the number oftests.

(b) children

When testing young children and babies, special contacts andsimpler, shorter testing is used.

What tests can I expect?

When you attend you will have a selection of the following testsdepending on the reason for your referral.

Pattern electroretinogram(PERG)* measures the function of the central retina, the macula, which youuse for detailed vision e.g. reading.* you will be asked to look at a moving checkerboard pattern on aTV whilst we record the small electrical signals generated in themacula.

Electroretinogram (ERG)

* records the electrical signals from the retina to flashes of lightboth in darkness and in light.c* the brightness, flash rate and colour of light are varied to allow therods (night vision) and cones (daytime vision) to be examinedseparately.

Visual-evoked potential (VEP)* investigates the pathways carrying signals from the eye to thebrain, the optic nerves, and how the brain interprets these signals.* you will be asked to observe a moving checkerboard pattern on a

TV or flashes of light while we record the electrical signals.

Electro-oculogram (EOG)

* measures the function of the boundary between the retina and thelayer under the retina (retinal pigment epithelium).* you will be asked to make regular eye movements between 2small red lights for approximately 20 seconds every minute for 15minutes in the dark and 12 minutes in the light.

8/9/2019 eddleaflet

2/2

What do I have to do?

* Please be punctual, otherwise it may not be possible to performall of the tests required.* It is VERY important that you bring to your appointment all currentglasses and recent prescriptions. If you are a contact lens wearerplease 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, pleaseensure that there is another responsible adult to look after them asthere are no childcare facilities within the department.

Are there any side effects?

Dilating drops will cause blurred vision and increased sensitivity tobright light/sunlight, but this will wear off after a few hours. Darkglasses may help on a sunny day.You should NOT drive for several hours after the testing hasfinished 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 outwithin the department, please dont hesitate to contact us on 020 7566 2120.This leaflet is intended to provide general information for patients. Any patient who isworried about his or her individual circumstances should seek specialist advice relating tohis or her circumstances.MOORFIELDS DIRECT is a telephone he lpline available between 9.00 am and 5.00 pm.Telephone 020 7566 2345.

Issue 1 February 2004 (review December 2004) Vikki A McBain

ELECTROPHYSIOLOGYDEPARTMENT

Information for patients

Moorfields Eye Hospital