Bilateral third nerve palsy. Posttraumatic, left more severe. Third nerve deficits produce more severe ptosis with mydriasis, not miosis, as well as weakened extraocular movements (EOMs) of adduction and elevation (“down and out” position; Fig. 65–22). Ptosis is seen not only with Horner's syndrome and third nerve pathology but also with some muscle pathologies including facioscapulohumeral muscular dystrophy (FSHD), myotonic dystrophy, and myasthenias and may also be an isolated congenital or posttraumatic finding. Note that EOM will be unaffected in FSHD and myotonic dystrophy. Thyroid myopathies, oculopharyngeal dystrophies, and mitochondrial disorders may cause both. Fourth nerve palsy produces slight loss of depression and rotation of the eye that is difficult to discern, especially in the presence of a third nerve problem, unless a patient can reliably report directions of diplopia or one can observe rotation of markings on the sclera or iris. Sixth nerve palsy causes a lack of abduction. All three nerves can be affected by increased intracranial pressure (ICP). Duane's syndrome is a contraction of adduction and abduction that limits movement and retracts the globe slightly on attempts to track horizontally; it is usually congenital and can be isolated or part of another syndrome.