Friday, 7 December 2012

Questions from A dyslexia specialist

Questions from A dyslexia specialist

What are the symptoms of

A. Imbalance in the field of vision overlap…

1.   The person experiences steady ‘double vision’ when looking at something with both eyes, then it is referred to as diplopia.
2.   The two images move across each other or the whole visual scene appears to be moving rhythmically it is referred to as oscillopsia

  It sounds like this could be described as an orthoptic issue. (eye muscle problem) but on its own that is a bit of a cop out...

If it does not occur when viewing pictures/diagrams but only when reading then it is likely be a task caused issue.  The two images are both having attention given to them but the brain cannot compute them into a single image. Essentially the centre of attention of each eye is too far apart for the system to combine the data. 

 If only when reading then it suggests that prisms (an orthoptic response) might be the answer.

Quite a lot of people find that the double images stop and start, if that happens then it is probably because the brain ‘decides to ignore the data from one eye. It suppresses it.  This can be considered to be associated with the idea of a lazy eye, or Amblyopia. This suppression may be a consequence of an uncorrected focussing problem in one eye.  You need to find out if both eyes are the same in terms of focussing?  If they are not then this will need correcting,

This suppression sometimes appears to be intermittent, dependent on visual task.
If the suppression alternates, then I think this is associated with the rhythmical head movements common in some people experiencing reading difficulties. They get the feeling that they have to ‘fight the words’! That in turn can lead to inner ear effects, nausea, a sense of disorientation, referred to by such as the Davis; I do not consider it to be much of a ‘Gift’ though. A certain Harold Levinson used to supply anti-sea sickness tablets to stop this happening!


 Although you may find that with a suitable computer setting the system is able to combine the images.  Are both eyes the same in terms of focussing?

B) Astigmatisms, please?

These are hard to see in terms of symptoms.  Many people have slight astigmatisms. What they do is to make it take longer for the visual system to create/compute a sharp image compared with a non astigmatic eye... An eye may need to refocus during the fixation and collect more data. If both eyes are the same then this just slows thing down. If one eye is worse then, it can lead the visual system suppressing the data from one eye and that eye then turning away from the object of attention. This can impact on separating the field of vision. Likely to happen when reading more than when looking at graphics targets. (This is associated with the iterative horizontal eye movements involved in reading.

Astigmatism is easily checked for.

1.     Find the nearest point that the student can focus on.
2.      Draw a cross (+) about 5cms both ways on a piece of white paper.
3.     Hold it in front of each eye in turn at the near point.
4.     Tell the person to look at where the lines cross.
5.     If either the horizontal or the vertical line appears fuzzy then there is an astigmatism in that eye.

I often find that candidates omit the middle of words when reading and sometimes also when writing. Should I recommend they are checked for the above two?
I think that what is happening is that their field of view is limited to around 2 or 3 letters. And they need to take several pictures to get through each word.  The correct colour and font size should solve that.  I do not think the points above would cause that.

What happens is they subconsciously guess what the rest of the word is based on the visual cues with the guess usually being in the context of the sentence rather than the paragraph!
Writing is associated with Hand eye coordination. If you put a binocular eye tracker on someone, put a cover on the front so that they cannot see what they are writing and then ask them to write down a sentence.  Then the eye tracker will show you that their eyes are moving as if they were reading the words...the visual memory guides the hands! 
If their eye movements are asymmetrical when they read this appears to lead to asymmetrical (messy) writing

Also: is scotopic sensitivity and eye strain the same thing? 

Sort of... SS was termed by Helen Irlen, and is actually incorrect wording really. 

If someone gets a high score on the Visual stress test (online use it freely!) 

They are likely to be identified by Irlen as having SS.  But they could have other optometric issues. I am also unsure (very) of the protocols employed by Irlen

Eye strain is a term with no actual definition. You could call it reading discomfort. Aetiology, origin of the discomfort, is mixed.

sometimes students who benefit from coloured overlays also mention sensitivity to bright light (artificial and/or sunlight) - is that due to eye strain on top of scotopic sensitivity or is it all the same thing and all comes under the heading of scotopic sensitivity?

Sensitivity to bright light can have several origins.

1.   Corneal problems such as Keratoconus.

2.   Delamination of the cornea/waterlogged cornea associated with undiagnosed/untreated glaucoma

3.     Lack of or limited pigmentation in the back of the eye (the sclerotic)   tends to go with easily sunburnt/ginger/blond hair/ freckles

3.   Poor pupil reflex management. The pupil is too large in bright light, it is not closing enough.

5.     Poor rebuild rate of the pigmentation to capture more light after bleaching.

I am becoming increasingly aware of visual weaknesses when assessing candidates and am trying to make the right recommendations for follow ups with opticians and optometrist. It seems incredibly common for someone to say they and their eyes checked recently and all is fine, but then I find it actually isn't.
This is an issue. Not many opticians really look for these problems. They are not always part of their professional qualifications… they need CPD!

No comments:

Post a Comment