Information for Patients « QEDIC

Information for Patients

Visual tests performed at the Centre (such as: VEP, ERG, EOG, PERG, AVEP, MFERG & COLOUR VISION) are elective tests that look at the way your visual system is working in order to help with the diagnosis of any visual problem and provide a guide towards appropriate management and prognosis.  Your ophthalmologist will discuss the test results with you.

What to expect:

The tests will take between one and four hours. You may have drops put into your eyes to dilate the pupils. Electrodes will then be placed on your head and face to monitor the working of different types of visual signals, usually checkerboard patterns or flashes of light and to record these responses. For part of the time you may be sitting in a very dark room. For some tests performed on older children and adults, a very fine silver thread electrode may be gently placed onto the surface of the eye, however most patients can barely feel the presence of these tiny electrodes.
Complications with these tests are very rare, but it is possible to have a reaction to the eye drops, causing some redness, or sore eyes. Very rarely patients have been known to faint. Micropore (adhesive medical tape) can cause irritation to sensitive skin and very rarely, people react to the placement of the very light electrodes onto the eye. You should alert the clinic if you have known allergies or have had a reaction to electrodes before.

Before coming to the Centre:

  • If your eyes will be dilated, you will have temporary sensitivity to light after the tests and your vision may be “blurry” it is necessary to organise a driver to pick you up as your vision will remain blurry for several hours after testing
  • Please ensure your face and hair are clean but do not wear face creams or makeup (especially eye makeup) on the day as these interfere with the electrodes’ ability to detect the visual signals
  • All current glasses should be brought with you
  • Contact lenses should not be worn
  • After testing, it is advised that you use sunglasses as your eyes will be sensitive to glare sensitive as a result of the dilation
  • For infants: it is suggested that you bring along a bottle,some favourite toys and, if possible, some calming music (on your phone) to help distract the child during testing.

Please note, your eyes may feel irritated for up to an hour after testing. If persistent problems occur, please phone the Centre on 07 3239 5010 or email: