Suppression #2

SUPPRESSION'S GOT A HOLD O'ME! SUPPRESSION! GOTTA BREAK FREE!

There are a series of tests that can be done to measure the extent of a suppression scotoma. You have to investigate it under binocular conditions. There are two possible scenarios: one - you have two suppression scotoma - one at the fovea and one at the point receiving the image OR you have one big one because they've joined together. That happens if the strabismus is large angle or longstanding.

Here's another one of those things that you read about but never actually have to do in your life ever. It is Suppression Scotometry and it involves the Bjerrum screen. So y'all know it is old hat. The px sits in front of the Bjerrum screen in the corner of the room and a small mirror is mounted at 45 degrees in front of the fixing eye. This stops the eye seeing the screen but the eye can see a small marker to one side of the px at the same distance away as the screen. This allows the scotoma to be plotted with both eyes open throughout. You use the usual bjerrum targets and pins and crap.

You gonna see suppression of the nasal retina in esotropia and suppression of the temporal retina in exotropia. As you may have noticed the test is difficult to set up and takes ages so is not often done.

Something that is often done is the Prism Bar Method. The px fixates a spotlight with the dominant fixing eye and the prism bar is put in front of the suppressing eye. When the image of the spot has moved off the suppression scotoma the patient sees two spots. Simple yet effective. You can get a quantitative estimate of the angular extent of the scotoma by calculating the difference between the angle of strabismus (you've already got that from a prism cover test right) and the amount of prism which moves the spot out of the scotoma. You could do vertical deviations with that method anarl.

Sort Of Conclusion

The deeper the suppression and greater the extent across the retina the more difficult it is to treat. Take into account the age of the patient, the duration of the strabismus and how co-operative the patient is likely to be before even trying man. You must only treat suppression if the deviation can also be eliminated and if there's a strong chance of BSV occuring. Basically this boils down to only young kids where the strab can/has been corrected and binocularly driven cells can still develop. Otherwise you may end up with intractable diplopia which is very rubbish indeed. Suppression is an adaptation to prevent diplopia and confusion so if you try and treat it and the patient ends up with diplopia and confusion then he/she will be angry.

If it's suppression in conjunction with anisometropic amblyopia it can also be treated in a similar way in combination with Rx and amblyopia treatment. I will do the whole treatment shebang tomorrow.