Pathophysiology
Strabismus can be caused when the cranial nerves III (oculomotor), IV (trochlear) or VI (abducens) have a lesion. A strabismus caused by a lesion in either of these nerves results in the lack of innervation to eye muscles and results in a change of eye position. A strabismus may be a sign of increased intracranial pressure, as CN VI is particularly vulnerable to damage from brain swelling, as it runs between the clivus and brain stem.
More commonly however, squints are termed concominant (i.e. non paralytic). This means the squint is not caused by a lesion reducing innervation. The squint in this example is caused by a refractive error in one or both eyes. This refractive error causes poor vision in one eye and so stops the brain from being able to use both eyes together.
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