Restrictive factors in strabismus.

Either muscle weakness (paresis) or mechanical restrictions can account for diminished ocular rotation. In practice, restrictions are more commonly seen. The forced duction test, differential intraocular pressure measurement and saccadic velocity studies can all assist in documenting the presence of restriction. Restrictions frequently occur with orbital floor fracture, endocrine ophthalmopathy and Brown's syndrome, and following multiple stabismus procedures, orbital or retinal detachment surgery, or muscle transposition surgery. They also occur as a result of antagonist muscle contracture after rectus muscle palsy or they may be due to orbital tumor or inflammation.