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University Hospitals Dorset NHS Foundation Trust

ERG (Electroretinogram)

An ERG is a series of tests to evaluate the function of the light sensitive layer at the back of the eye – the retina.  This test is performed by one of our Healthcare Scientists. 

You must bring any glasses you wear with you.  Contact lenses cannot be worn for this test, and you must not wear eye make-up.

Firstly your vision will be assessed using an eye chart and your colour vision will also be checked.

Small electrodes will be applied to your head using paste, and fine thread electrodes will be placed along the bottom of each eye lid.  These may feel a little irritating at first but will not hurt.  You will then be asked to concentrate on a chessboard pattern on a monitor.

Next, we will need to dilate the pupils of your eyes with eye drops.  You will then sit in the dark for 20 minutes.  Again we will place fine thread electrodes along the bottom of each eyelid.  A light will then be flashed in front of you, varying in brightness.  We will remove any paste from your head before you leave.

The whole test will usually last between 2-3 hours.

You will need to make transport arrangements as your vision can be blurred for typically 4 hours following the administration of eye drops and you must not drive (in some cases effects can last for up to 24 hours).  It can be helpful to bring sunglasses to wear after the test.

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