Timothy C. Hain, MD
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An interesting situation arises when one eye is weaker than the other. This occurs in cranial nerve palsies such as 3rd and 6th nerve palsies, as well as in situation where the eye muscles are restricted, such as in Duane's syndrome.
If one is viewing from the good eye, then the weaker eye does not go all the way to the target, or takes longer to get there. This is fairly easy to follow. On the other hand, if one is viewing from the weaker eye, and the stronger eye is covered, the stronger eye may exhibit interesting behavior where it goes far beyond the target, as the person attempts to put more "effort" into moving the weaker eye, and this additional effort is transmitted to the covered normal eye.
If the audiologist or ENG technician does not check for ocular palsies, and furthermore does not indicate the eye that is viewing, this can result in some very confusing situation, which may be the subsequent topic for a course on ENG blunders (don't do this folks).
Here are some examples of someone who is viewing from their paretic right eye (a person with Duane's syndrome), and being recorded from the good eye.
|Here the normal eye (covered by the camera) goes far beyond the target.|
|The normal eye goes far beyond the target to the right, but is perfect to the left.|
|Vertical eye movements are pretty much on target.|