PERG (Pattern Electro-retinography)

Pattern Electro-retinogrpahy

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Pattern Electro-retinogram (PERG)

What is an PERG examination?

This is a test which measures the electrical activity from the eye.  It is used to determine how healthy particular cells are in the retina.  The test takes upto 60 minutes to complete and your results will be sent to the referring GP/clinician and are usually available within seven days.


How is the test performed?

The test is painless.  A very fine thread is placed between the lower eyelid and the eyeball.  The thread is placed quickly and you may feel a little discomfort for a few seconds but this will not last.   Leads will also be placed on your face at the side of your eyes and one lead on your forehead.   You will then be asked to concentrate on a reversing chequerboard pattern for 2-3 minutes.  This test is then repeated.  

This test is usually performed along with an electro-retinogram (ERG).  If you have been booked for an ERG, a separate explanation leaflet is available. 


At the start of the test you MAY be given some eye drops (Tropicamide 0.5% and Proxymetacaine 0.5%) to anaesthetise and dilate your pupils (the black part of your eye). 


The eye drops will sting for a few moments but then will settle down.  The effect of the eye drops can last for between 4-6 hours.  This means that when you leave the department after the test, your pupils will still be dilated.  You may find it uncomfortable in daylight/bright light and your eyesight may be blurry.  You must not drive following the administration of eye drops until your eyes have returned to normal, which can take up to 6 hours.  If you attend in a vehicle please ensure there is someone you can contact who is able to drive you home. PLEASE BRING SUNGLASSES WITH YOU.


If you think you may be pregnant, please let the member of staff who is doing your test know.  Eye drops will not be used if you are pregnant, but the test can still be done.


How do I prepare for the test?

It is important that if you wear glasses please bring them with you.  We may not be able to perform this test if you are wearing contact lenses.


If you are taking any medication, please continue to take it and bring a list of your medication with you.  You may continue to eat meals as normal.


Please inform the physiologist at the START of your test if you have been diagnosed with epilepsy.