Multiple mechanisms of extraocular muscle "overaction".

OBJECTIVE

To assign more specific pathophysiologic processes to the protean patterns of extraocular muscle "overaction" that we see in clinical practice.

METHODS

By extrapolating from known principles of striated muscle physiology, a cohesive theory about extraocular muscle behavior is derived.

RESULTS

The key to understanding apparent extraocular muscle overaction is to differentiate between a muscle that has decreased elasticity and one that is strengthened. Primary inferior oblique muscle overaction has the characteristics of a muscle that primarily has decreased elasticity, the superior rectus overaction/contraction syndrome appears to represent a muscle that is strengthened, and inferior oblique overaction secondary to ipsilateral superior oblique palsy has elements of both decreased elasticity and strengthening. Many motility patterns that appear to be due to an overacting muscle may in fact be caused by other muscles than the suspected one.

CONCLUSION

Apparent extraocular muscle overaction can be caused by many different factors.