PALSIES OF THE TROCHLEAR NERVE - DIAGNOSIS AND LOCALIZATION - RECENT CONCEPTS

In this review, the anatomy of the trochlear nerve, the diagnosis of p alsies of the trochlear nerve, and the localization of lesions of the trochlear nerve are discussed. Paresis of the superior oblique muscle is often not evident on duction testing; therefore, subjective diplopi a testing with use of a Maddox rod is often necessary. The torsional c omponent of the deviation may be evaluated by double Maddox rod testin g. Palsies of the trochlear nerve must be distinguished from other cau ses of vertical diplopia, such as oculomotor palsy, skew deviation, my asthenia gravis, and Graves' ophthalmopathy. Trauma is the most common cause of isolated, unilateral or bilateral, acquired palsies of the t rochlear nerve when a cause can be determined. The localization of les ions of the trochlear nerve to the nucleus or fascicles (or both), sub arachnoid space, cavernous sinus and superior orbital fissure, or orbi t depends on the associated damage to neighboring neurologic structure s. Myokymia of the superior oblique muscle is usually idiopathic and b enign but may rarely be an isolated manifestation of tectal disease.