Tuesday, 14 April 2015

April 2015 - Electroretinography

So today, off I went to Southampton General Hospital, Orthoptics department for a specialist eye test.

The very first thing to note, is don't entirely trust what Dr Google tells you! Inevitably when you have a procedure coming up it is human nature to want to know what to expect. Years ago this meant trying to track down someone else who has had the procedure, but nowadays just fire up your computer and all the information is at your fingertips. But as it happens I had viewed Electroretinography video's and information for the American market, and things aren't done quite the same over here in the UK.

In America the electrodes placed on your eye are contained in a kind of contact lens and an eye speculum. In order to do this the surface of your eye is anaesthetised. But over here, all that happens is a very thin wire is placed on the eye and fastened at either side, you hardly even know it is there, it just feels slightly itchy/scratchy and I forgot about it after a while.

So what happens is that you have a couple of wires stuck onto the back of your head and onto the forehead. The lights are turned off and you then look at a TV with various flashing chequerboard images shown, but you have to look at a red dot in the middle of the screen. Alternate versions are shown and initially to both eyes then a patch over each eye. Then the electrodes are placed on the eyes and the tests repeated. Then at the end, a bright strobing light is shone into each eye, first a white light, then a blue light, then a very bright white light. I wasn't asked if I was an epileptic! All in all it is a straight forward set of tests.

What I do find odd, is having had the test in its UK form, being very non-invasive, why the Americans do things differently....different technology but the same outcome? I would assume so, is one approach better than the other?

All this data is fed through the receivers stuck to my head into a computer which interprets what my eyes have seen. I assume there is an expected level of information being received through the optic nerve and I will be measured against that, as well as each eye being measured against the other. I didn't see the computer screen the clinician was working on, but my wife tells me the wavy lines were pretty unintelligible to her. So once the data has been unscrambled a report will go to my eye consultant, who I am seeing next month. Let's wait and see what that tells me.

Overall the tests were easy to sit through and barely uncomfortable. The flashing images were a bit mesmerising and sent the eyes a bit wobbly after a while, but no lasting effect. Another test to add to the few I've had over the last couple of years.

A techie side note, I noticed the TV used was an old cathode ray tube (CRT) version, very old looking technology. This at the moment is necessary apparently because the response times of old CRT telly's is very quick, and it is necessary to sync up the response times of the brain & optic nerve with the image being displayed. Using modern flat screen LCD/LED monitors isn't currently possible because their response times aren't quick enough right now. The scientist who did my test said she doesn't know what they'll do when their screens break as they are really hard to get hold of now, because no-one makes them any more! So if you have any old telly's lying around in the garage, don't take them down the tip, donate them to your local NHS Electroretinography unit (only joking!)

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