As part of a proper Schoolvision assessment, there are 8 tests necessary to complete the child’s eye examination. With thanks to Geraint Griffiths, the founder of the schoolvision technique, in this series of blogs we will describe each test separately through series of questions and answers.
Here is a list of the eight tests:
- Brock string
- Dynamic fixation
- Accommodation facility
- Measuring Muscle Balance
- Trial Frame Challenges
- Follow – up
Measuring Muscle Balance
Here are the questions and answers on the Measuring Muscle Balance test
Q: When measuring muscle balance, what test do you usually prescribe from? I currently detect/measure phorias and take information from a number of tests eg:
- Cover test, distance and near,
- Brock (near),
- Near Mallet,
- Distance fixation disparity (polarised projector)
- Howell phoria, distance and near.
These tests can all give different, and sometimes conflicting and confusing, results, and I am wondering is this normal? If so, what should I base my prescribing prism decision on?
All of the above tests inform my decision, and at times they all agree, and a decision is straightforward, but if the results aren’t consistent, is there one test would you rely on from a prescribing point of view?
A: The answer to this multichoice question would indeed be all of the above.
When results conflict with each other there’s usually a reason and it is in fact another clue to the diagnosis. For instance Muscle balance measured by the Howell Phoria or the cover test can be contradict Fixation Disparity. When the eyes are dissociated and habituated to over accommodating by accommodation insufficiency or divergence excess they may appear to be esophoric. If at a later stage when latent hyperopia is corrected, the eso phoria may turn into a decompensated exo.
All these tests go together to paint the final picture, but I am appreciating more and more the sensitivity of the Brock after all the stages of careful refraction, as being the final arbiter
Q: The Von Graefe method of measuring a dissociated phoria was never something that I heard you talk about, is this a test that you use or recommend?
A: Von Graefe is the principle on which the Howell Phoria test is based and also our home grown Objective Muscle Balance (OMB) test, which does the same thing. This is a development since you did your diploma
Q: Am I right in saying that studies have shown that people with Type 2 dominance are more likely to have binocular vision problems and reading difficulties (was this a finding in the Moreton study)?
A: Type I Type II are two different physiological entities. You could say Type II has a less refined visual system but on the other hand is more robust. Type I on the other hand is finely tuned and deficiencies are more likely to have a devastating effect.
The Moreton study didn’t really go into the direct comparison of these two types and it would be simplistic to say that one is more prone than the other to binocular vision problems. For the time being it is safer to say neither is exempt.