Third Nerve Palsy
In children, third nerve palsy can be congenital (more appropriately termed dysinnervation) or can be caused by conditions such as trauma, inflammation, or viral infection. It can also occur as a manifestation of ophthalmoplegic migraine, after vaccination, or (infrequently) as a result of a neoplastic lesion. In adults, the usual causes are intracranial aneurysm, microvascular infarction, inflammation, trauma, infection, or tumor. See BCSC Section 5, Neuro-Ophthalmology, for detailed discussion of the causes and manifestations of third nerve palsy. This section is concerned primarily with the principles of treatment of the strabismus.
Complete paralysis results in limited adduction, elevation, and depression of the eye, causing exotropia and often hypotropia. These findings are expected because the remaining unopposed muscles are the lateral rectus (abductor) and the superior oblique (abductor and depressor), except when the cause of the paralysis involves the nerves supplying these muscles as well. Upper eyelid ptosis is usually present, often with pseudoptosis due to the depressed position of the involved eye (Fig 12-6).
The clinical findings and treatment may be complicated by misdirection (aberrant regeneration) of the damaged nerve, presenting as anomalous eyelid elevation, pupil constriction, or vertical excursion of the globe—any or all of which can occur upon attempted rotation into the field of action of the EOMs supplied by the injured nerve. A miotic pupil is sometimes noted in congenital cases, irrespective of whether there is aberrant regeneration. Affected adults report incapacitating diplopia unless the involved eye is occluded by ptosis or other means.
Except in congenital cases, it is advisable to wait at least 6 months, possibly even up to 12 months, for spontaneous recovery before proceeding with surgical correction. Patients with at least partial recovery are much better candidates for good functional and cosmetic results. Because the visual system is still developing in pediatric patients, amblyopia is a common finding that must be treated aggressively.
Figure 12-6 Third nerve palsy, right eye, with ptosis (bottom photo) and limited adduction, elevation, and depression (upper eyelid elevated manually in top 9 photos).
(Courtesy of Edward L. Raab, MD.)
In adults with previously good binocular vision, occlusion from associated ptosis may actually be beneficial by preventing incapacitating diplopia associated with a limited or absent field of single binocular vision; ptosis repair should not be done without prism adaptation testing to demonstrate that the patient can achieve satisfactory binocular vision with prism. The incidence of diplopia in patients younger than 8 years is low because of suppression (see Chapter 5).
Third nerve palsy presents difficult surgical challenges because multiple EOMs, including the levator muscle, are involved. Replacing all the lost rotational forces on the globe is impossible; therefore, the goal of surgery is adequate alignment for binocular function in primary position and in slight downgaze for reading.
Selection of the surgical procedure is dictated by the number of involved muscles and their condition, as well as by the presence or absence of noticeable paradoxical rotations. In a case of incomplete paralysis, a large recession-resection of the horizontal rectus muscles to correct the exodeviation, with supraplacement of both to correct the hypotropia, is effective. Some surgeons perform a concurrent superior oblique tenotomy to reduce the hypotropia. For complete paralysis, one suggested approach is a large recession of the lateral rectus muscle, combined with either a large medial rectus resection or fixation of the globe to the nasal orbital periosteum. Disinsertion of the lateral rectus muscle and reattachment to the lateral orbital periosteum can maximize inactivation of the muscle. Splitting and transposition of the lateral rectus muscle to the nasal side of the globe has also been described. Transfer of the superior oblique tendon to the upper nasal quadrant of the globe has been used as well; however, anomalous eye movements can result from this procedure. Most surgeons reserve correction of ptosis for a subsequent procedure, which allows for more accurate positioning of the upper eyelid.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.