228 MONOFIXATION SYNDROME

228SyndromeCHAPTERMonofixation •

Muscles Extraocular • 20 SECTION

COURSE/PROGNOSIS

●Monofixation syndrome, once established, is permanent.

●Congenital absence of central binocular vision (primary monofixation syndrome) may predispose to strabismus just as strabismus may predispose to monofixation syndrome.

●Children with congenital esotropia most commonly develop monofixation syndrome (peripheral fusion without central fusion) when they are operated early in life. Newer studies suggest that post-operative stereopsis is better when the duration of esotropia is reduced. Bifixation (central binocular vision) may be achievable in some of these infants if the eyes are straightened within 60 days of the onset of constant esotropia.

●Monofixation syndrome promotes better stability of alignment (orthotropia or microtropia) compared with no binocular vision, but manifest strabismus of more than 8 prism diopters may recur with time.

●Central binocular vision, even when normal at birth, is tenous and easily lost if the two foveae are not stimulated simultaneously.

●Constant strabismus lasting a few months or longer may result in the permanent loss of bifixation, even in older children and adults. Peripheral fusion, in contrast, is more durable and usually returns postoperatively even after years of constant strabismus, resulting in monofixation syndrome as the postoperative sensory state of the eyes.

DIAGNOSIS

●Small angle tropia is usually present, measuring up to 8 to 10 prism diopters; however, as many as one third of patients with monofixation syndrome are orthotropic.

●Amblyopia often (but not always) coexists with monofixation syndrome.

●A history of prior surgery for infantile/congenital or child- hood-onset strabismus often is present.

●This syndrome can occur without any prior history of strabismus, often in relatives of patients with congenital esotropia.

●For a definitive diagnosis, both the presence of peripheral fusion and the absence of central fusion must be established.

●The presence of peripheral fusion is indicated by the following:

●There is subnormal (gross) stereopsis;

●A fusion response to the Worth-four-dot at 0.33 m occurs;

●There is tropia by simultaneous prism and cover test with overlying phoria by alternate-cover test;

●Fusional vergence amplitudes are measurable.

●The absence of central fusion is indicated by the following:

●Microtropia is a manifest tropia on the cover test or simultaneous prism and cover test of 1 to 10 prism diopters; larger tropias are not considered microtropias and are incompatible with monofixation syndrome -the examiner should not be misled by phorias that may overlie a microtropia;

●Facultative macular scotoma is shown on the Worth- four-dot (patient sees two or three dots at distance despite seeing four dots at near) or Bagolini glasses

(patient sees two oblique lines that form an X but with a central gap in the line from the lens over the nonfixating eye);

●Facultative macular scotoma is shown by the deletion of letters viewed by the nonfixating eye via vectographic projection of Snellen letters (BVAT II BVS, Mentor O and O or vectographic projector chart slide, American Optical Company);

●There is a positive 4-prism diopter base-out test (no vergence movement); this is the least reliable method and is not recommended.

Differential diagnosis

●Strabismus with pathologic cortical suppression and abnormal retinal correspondence (ARC) is characterized by the following:

●There is no stereopsis;

●Patients see two or three lights when viewing Worth- four-dot test at 0.33 m, rather than four as in monofixation syndrome, but may give a four-light response at 6 inches or closer (suppression scotoma in large angle esotropia is often about 6 degrees as opposed to 3 degrees with monofixation syndrome; therefore, lights must be much closer to the patient to project onto the peripheral retina outside of the larger scotoma);

●The deviation is more than 8 to 10 prism diopters;

●There is no phoria overlying the tropia;

●There are no measurable fusional vergence amplitudes.

●Intermittent strabismus with bifixation is characterized by the following:

●Patients with intermittent deviations may show suppression and ARC when deviated but retain central binocular vision when orthotropic. Perform sensory testing early in the examination, when alignment control is better;

●Some sensory tests require glasses or goggles, which may disrupt strabismus control and fail to show bifixation.

PROPHYLAXIS

●When normal binocular vision is present in infancy, the loss of central binocular vision, and thus the development of monofixation syndrome, can be prevented by promptly correcting any acquired constant eye misalignment (with the use of glasses, surgery, prisms).

●Surgical overcorrections in the treatment of intermittent exotropia are usually constant and can result in the loss of central binocular vision if not corrected within a few months. Use glasses or prisms to promote fusion temporarily if spontaneous resolution does not occur in the first few weeks after surgery and the decision for repeat operation will be delayed.

●Infants with classic congenital/infantile esotropia have been thought to have a congenital absence of central binocular vision. For this reason, monofixation syndrome has been the desired outcome. Monofixation syndrome can be achieved with surgery within 18–24 months. Some patients, however, may retain the potential for central binocular vision. For this reason, the duration of esotropia has taken on increased significance. Monofixation syndrome may be avoided if the duration of infantile esotropia does not exceed 60 days.

229 CHAPTER Nystagmus •

Muscles Extraocular • 20 SECTION

evaluation for a primary sensory cause. Conditions known to be associated with afferent infantile nystagmus include, among others, early (usually bilateral) visual deprivation (congenital cataracts, severe glaucoma, Peter’s anomaly), foveal hypoplasia (albinism, aniridia), retinal disease (Leber’s congenital amaurosis, achromatopsia, macular toxoplasmosis), retinal detachment (severe retinopathy of prematurity, persistent fetal vasculature, familial exudative vitreoretinopathy) and congenital optic nerve abnormalities (coloboma, atrophy, hypoplasia). It can also accompany cortical visual impairment from a perinatal insult.

The nystagmus is typically binocular and conjugate, dampened by convergence, increased with fixation effort, and abolished in sleep. Improved visual function with convergence often translates to better near acuity, and is the basis for treating with base-out prism glasses, which sometimes improve distance acuity. Patients with high refractive errors usually benefit from contact lens correction to minimize the aberration from constant ocular movement behind thick spectacles. Attempts to reduce the amplitude and/or frequency of the nystagmus and increase foveation time have involved medication (e.g. baclofen), recession of multiple rectus muscles simultaneously, and injection of botulinum toxin (Botox) into the muscle cone. All have had limited success.

Patients with efferent nystagmus (historically known as congenital motor nystagmus but recently termed idiopathic infantile nystagmus) often have a null point in an eccentric position of gaze and manifest an anomalous head position to maximize visual acuity. Strabismus surgery, specifically an Anderson or Kestenbaum procedure, may place this null zone in primary position, thereby reducing or eliminating the head position. Variations of this technique are employed if there is accompanying strabismus or if the head position has a vertical or torsional component.

Latent nystagmus is a benign condition that appears only when one eye is covered, or when light stimulus to one eye is diminished, but can coexist with manifest nystagmus (in which case the nystagmus amplitude increases with occlusion). This is a jerk nystagmus with the fast phase toward the side of the fixing eye; it is often seen following surgery for infantile esotropia and probably results from subnormal binocular interaction. Visual acuity measurement should be performed using the polarized vectograph or blurring one eye with a high plus lens to avoid iatrogenic reduction of acuity with occlusion. So-called manifest latent nystagmus can occur if monocular visual loss occurs in this setting.

Acquired nystagmus

Spasmus nutans classically presents as a triad of nystagmus, head nodding and torticollis between 4 months and 3 years of age, and usually resolves within a year. The nystagmus is usually very fine, rapid and pendular, but may be vertical or rotary. It is usually asymmetric, may appear monocular, and varies over time and with position of gaze. Head nodding is inconstant and irregular, and tilting or turning of the head occurs less frequently. Pathogenesis is unknown and no treatment exists, but the condition appears to be self-limited. It is associated with strabismus and refractive error. Chiasmal glioma can present in a manner identical to spasmus nutans, prior to visibly affecting the anterior visual pathways. Some authors recommend that all patients with this condition undergo neuro-imaging; this is particularly important in the setting of visual loss, afferent pupillary defect, papilledema or optic atrophy.

Vestibular nystagmus can be divided into peripheral and central types. The etiology of peripheral disease includes labyrinthitis, acoustic neuronitis, ischemia, trauma and toxicity; the nystagmus is frequently associated with vertigo, tinnitus or deafness. It is invariably a jerk nystagmus, usually with a horizontal and rotary component, and the fast phase is toward the normal side. Central vestibular nystagmus is due to bilateral brainstem dysfunction from tumor, stroke, trauma or demyelination. This nystagmus may be purely horizontal, vertical or rotary and may change with the direction of gaze. Treatment is primarily aimed at reducing the vertigo and may include anticholinergics, monoaminergics, antihistamines, phenothiazines, benzodiazepines and butyrophenones. The sheer number of drugs involved reflects the lack of effective treatment.

Seesaw nystagmus is a dissociated pendular nystagmus in which one eye elevates while the other depresses. In the acquired form, the rising eye intorts while the falling eye extorts. In the less common congenital form, these torsional movements are reversed. Etiologies include parasellar tumors, trauma, and vertebrobasilar insufficiency; it has been reported in septo-optic dysplasia and even with severe visual loss from progressive cone-rod retinal dystrophy. Visual field results are helpful in considering neoplastic or vascular etiologies. The use of baclofen, a GABA analog, may be beneficial.

In upbeat nystagmus, the upgoing fast phase may be of large or small amplitude but is always present in primary position. Most patients have intrinsic brainstem or cerebellar disease. Associated conditions include multiple sclerosis, cerebellar degeneration, tumors or infarction of the medulla or midbrain, and infection or toxicity of the brainstem, such as Wernicke’s encephalopathy. Treatment is directed at identification and resolution of the underlying cause.

Downbeat nystagmus is commonly seen with disease affecting the cerebellum or craniocervical junction such as cerebellar degeneration, Arnold–Chiari malformation, multiple sclerosis, trauma, tumor, infarction and many toxic-metabolic entities. The use of clonazepam, a GABA agonist, may decrease amplitude and oscillopsia. MRI may indicate a surgically correctable lesion.

Periodic alternating nystagmus (PAN) is a continuous, horizontal nystagmus in which the fast component spontaneously reverses direction approximately every two minutes. It may be congenital or indicate vestibulo-cerebellar dysfunction from stroke, tumor, multiple sclerosis, trauma, infection, drug intoxication or degenerative disease. It has also occurred with severe, acquired bilateral visual loss from cataract, vitreous hemorrhage, or optic atrophy. Correction of the visual loss may abolish the nystagmus. Other patients have responded to treatment with baclofen.

The hallmark of gaze-evoked nystagmus is its absence in primary position. The fast component is in the direction of gaze but its presence does not signify location or etiology. It is commonly drug-induced by anticonvulsants, sedatives, ethanol and other recreational drugs. It can also be seen with posterior fossa disease (tumor, trauma, infarct, demyelination) and is called Bruns’ nystagmus in the setting of cerebellopontine tumors; in this case, the nystagmus is slow and coarse when looking toward the side of the lesion and fast and fine in the opposite field of gaze. Gaze-evoked nystagmus can also be seen with cranial nerve palsies, myasthenia gravis, and restrictive muscle disease such as thyroid ophthalmopathy.

Gaze-paretic nystagmus is a type of gaze-evoked nystagmus seen in patients recovering from a gaze palsy and is character-

ized by slow frequency and large amplitude. As with all types of gaze-evoked nystagmus, it is due to dysfunction of the neural network that integrates pursuit, saccade and vestibular signals. When this mechanism fails, the eyes drift back toward midline from an eccentric position of gaze; displacement of the image from the fovea triggers a saccadic movement to regain fixation. Two other types of gaze-evoked nystagmus are rebound nystagmus and the dissociated nystagmus seen in internuclear ophthalmoplegia. Rebound nystagmus can occur after prolonged eccentric gaze, with reversal of the fast phase (toward primary position), or can be seen transiently when the eyes return to primary position following sustained eccentric gaze. Both types are associated with ataxia and cerebellar disease.

Related ocular oscillations

Superior oblique myokymia is caused by rapid, torsional, monocular movements due to isolated, intermittent contraction of the superior oblique muscle. Patients report brief episodes of vertical or torsional diplopia and oscillopsia. It is best appreciated at the slit lamp or during fundoscopy and may be exacerbated with gaze into the field of action of the affected muscle. It is generally benign but may follow trochlear palsy or head trauma, and has been reported in multiple sclerosis and occasionally with cerebellar tumor. Treatment with carbamazepine may be beneficial; surgical weakening of the affected muscle is sometimes required.

Convergence retraction ‘nystagmus’ is seen in Parinaud’s (dorsal midbrain) syndrome and is due to co-contraction of the extraocular muscles with attempted convergence or upgaze. It is a saccadic disorder, rather than a form of nystagmus, and is best seen with fixation on down-going OKN targets. Other findings in the dorsal midbrain syndrome are impaired vertical gaze, pupillary light-near dissociation, lid retraction, abnormal convergence and accommodation, and skew deviation. J. Lawton Smith has given the following age-differential: in infancy, congenital aqueductal stenosis; 10 years old, pinealoma; 20 years old, head trauma; 30 years old, brainstem vascular malformation; 40 years old, long-standing multiple sclerosis; and 50 years old, basilar artery stroke.

Several fixation instabilities are frequently seen in patients with cerebellar disease. Square-wave jerks are back-to-back macrosaccades that first interrupt fixation and then bring about refoveation. Ocular dysmetria is the ocular equivalent of ‘past-pointing’ seen with an intention tremor: as the eyes return to primary position, they overshoot the target and oscillate about the new fixation point before coming to rest. Ocular flutter is a spontaneous intermittent burst of several conjugate micro-oscillations while maintaining fixation in primary position.

Opsoclonus refers to rapid, involuntary, chaotic, conjugate eye movements known as ‘saccadomania’ that may signal an occult neuroblastoma in children. It has also been seen in infants with an autoimmune disorder that responds to ACTH, and as a paraneoplastic manifestation in adults with visceral carcinoma. Other causes include multiple sclerosis and head trauma; it may be a benign, self-limited finding after viral encephalopathy. It is believed due to impairment of function in the pontine pause cells that normally inhibit saccadic burst cells.

Ocular myoclonus is a vertical pendular oscillation that persists during sleep and is often associated with synchronous contraction of the face, palate, pharynx and diaphragm. This is due to a lesion in the ‘myoclonic triangle’ which connects the red nucleus with the ipsilateral inferior olive and the con-

tralateral dentate nucleus. GABA agonists such as valproate have been reported to decrease the movement.

Two final ocular oscillations are usually observed in comatose patients. Ocular bobbing is characterized by a fast, conjugate, downward movement followed by a slow drift back up to primary position, usually in the absence of any horizontal eye movement. Patients typically have a massive pontine lesion, or metabolic encephalopathy. Ping-pong gaze is periodic, horizontal deviation of the eyes with the direction alternating every few seconds. It is seen with bilateral infarction of the cerebral hemispheres, but the etiology is unknown.

DIAGNOSIS

●Thorough understanding of the normal mechanisms for gaze stability and the difference between physiologic and pathologic nystagmus is required.

●Meticulous history and careful clinical observation, along with a consistent method of recording the nystagmus, is essential. Clinical maneuvers – such as caloric, positional, and optokinetic stimulation – can be used to induce nystagmus for diagnostic purposes.

●If an eye movement recording laboratory is available, more accurate categorization of the abnormal eye movement can be obtained.

●Use of MRI search coil technique with a calibrated contact lens has moved from the research arena into clinical application.

Differential diagnosis

●Many forms of nystagmus indicate underlying neurologic disease. The role of the ophthalmologist is to identify the nystagmus and its localizing value so that appropriate diagnostic steps (neuro-imaging, etc.) may be undertaken. The concept of differential diagnosis is only meaningful following initial examination.

●The differential diagnosis of afferent infantile nystagmus is broad and often requires additional steps such as examination under anesthesia, ocular echography, electroretinography, visual evoked response and MRI.

●MRI should be considered in patients presenting with spasmus nutans in order to rule out glioma, especially if there is any evidence of anterior visual pathway or hypothalamic disease.

●Previously well children with opsoclonus should undergo measurement of urine vanillylmandelic acid and abdominal CT to rule out neuroblastoma.

TREATMENT

Our limited knowledge of the pathogenesis of nystagmus hinders optimal treatment. Except for the use of baclofen in PAN, few controlled clinical trials have been performed for any intervention. Careful evaluation before and during therapy, particularly noting distance and near visual acuity, is warranted. Eye movement recordings with video and/or magnetic search coils are of value.

Systemic

●Pharmacologic agents are primarily GABA agonists and potentiate the inhibitory effect of this neurotransmitter on ocular motor pathways. These drugs include baclofen,

229 CHAPTER Nystagmus •

Muscles Extraocular • 20 SECTION

gabapentin, clonazepam, valproate and carbamazepine, among others.

●Alternative measures such as biofeedback, acupuncture, or cutaneous head and neck stimulation have been reported to decrease nystagmus in select patients.

Ocular

●Refraction with full correction should be done, as seemingly mild refractive correction can significantly improve vision in these patients.

●Optical therapies utilize prisms to place the eyes in a position of least nystagmus and thereby maximize foveation time and visual acuity. Another approach has been retinal image stabilization, which consists of high-plus spectacle lenses worn in combination with high-minus contact lenses; this is useful for monocular viewing when the patient is stationary. Contact lens wear alone has been noted to diminish congenital nystagmus, presumably by a trigeminal efferent pathway.

Medical

●Retrobulbar or intramuscular injection of botulinum toxin (Botox) has been demonstrated to abolish nystagmus temporarily, but patient satisfaction has been poor due to side effects such as ptosis or diplopia, and the need for re-injection.

Surgical

●Strabismus surgery has been utilized in certain forms of nystagmus with varying degrees of success. Anderson or Kestenbaum procedures are used to move the eyes into the ‘null zone’ to diminish an anomalous head position. Recessions of all four horizontal recti have been performed with mixed preliminary results. Four-muscle tenotomy has been suggested, but some studies show clinical improvement, while others show no statistically significant effect. Surgery is occasionally needed in superior oblique myokymia. In secondary nystagmus, removal of the offending lesion can improve symptoms.

COMPLICATIONS

Medical treatment should be administered by persons familiar with potential adverse drug effects. Carbamazepine can cause bone marrow suppression, baclofen is not approved for children, and clonazepam may be teratogenic; these agents should probably not be given to children or pregnant females. Surgery carries the risk of anesthesia, as well as potential loss of vision; this consideration becomes more important when potential benefits are less certain. Alternative therapy is probably harmless at worst, but should not delay diagnosis or treatment of an underlying disorder.

REFERENCES

Arnoldi KA, Tychsen L: Prevalence of intracranial lesions in children initially diagnosed with disconjugate nystagmus (spasmus nutans). J Pediatr Ophthalmol Strabismus 32:296–301, 1995.

Averbuch-Heller L, Leigh RJ: Medical treatments for abnormal eye movements: pharmacological, optical and immunological strategies. Aust New Zealand J Ophthalmol 25:7–13, 1997.

Breen LA: Nystagmus and related ocular oscillations. In: Walsh TJ: Neuroophthalmology: Clinical signs and symptoms. 4th edn. Baltimore, Williams & Wilkins, 1997:504–520.

Burde RM, Savino PJ, Trobe JD: Clinical decisions in neuro-ophthalmology. 2nd edn. St Louis, Mosby — Year Book, 1992:289–320.

Helveston AM, Ellis FD, Plager DA: Large recession of the horizontal recti for treatment of nystagmus. Ophthalmology 98:1302–1305, 1991.

Hertel RW, Dell’osso LF, Fitzgibbon EJ, et al: Horizontal rectus muscle tenotomy in children with infantile nystagmus syndrome: a pilot study. J AAPOS 8:539–48, 2004.

Leigh RJ, Averbuch-Heller L: Nystagmus and related ocular motility disorders. In: Miller NR, Newman NJ, eds: Walsh & Hoyt’s clinical neuro-ophthalmology. 5th edn. Baltimore, Williams & Wilkins, 1998: 1461–1505.

Pratt-Johnson JA: Results of surgery to modify the null-zone position in congenital nystagmus. Can J Ophthalmol 26:219–223, 1991.

Reinecke RD: Idiopathic infantile nystagmus: Diagnosis and treatment. J AAPOS 1:67–82, 1997.

Tychsen L: Pediatric ocular motility disorders of neuro-ophthalmic significance. Ophthalmol Clin North America 4:615–643, 1991.

230 OCULOMOTOR (THIRD NERVE)

PARALYSIS 378.51

Ann U. Stout, MD

Portland, Oregon

ETIOLOGY/INCIDENCE

Paralysis of the oculomotor nerve may be congenital or acquired. An oculomotor palsy may occur in association with atrochlear nerve palsy. This is significant both diagnostically and in the choice of surgical procedure.

DIAGNOSIS

Clinical signs and symptoms

Patients with this disorder typically present with symptoms of crossed diplopia with or without blurred vision. The patient may assume a head position to enable fusion. The findings are primarily ipsilateral to the lesion.

A complete paralysis includes four of the six extraocular muscles (superior, medial, and inferior rectus, as well as inferior oblique) with exotropia, hypotropia, and incyclotropia of the involved eye; paralysis of the ciliary muscle and iris sphincter, resulting in absent accommodation and a dilated pupil; and paralysis of the levator, resulting in blepharoptosis. A partial form, or paresis, produces an intermediate degree of weakness of these muscles. The upper division can be involved alone, producing a double elevator paresis with true or pseudoptosis. The lower division may be selectively involved, sparing the superior rectus and levator.

A diabetic oculomotor paresis frequently involves partial pupillary function. A sufficiently discrete nuclear lesion may involve the contralateral instead of the ipsilateral superior rectus muscle and may produce bilateral partial ptosis, although these findings are exceedingly rare.

TREATMENT

Ocular

If there is a field of single vision, bifocal correction for near vision may be needed if accommodation is impaired. If the

patient is in the amblyopic age range, patching and refractive correction are required. Surgical realignment is best deferred until after amblyopia therapy is completed. Prism correction may help if the vertical deviation is small. Deformity resulting from anisocoria is particularly troubling to blue-eyed patients, and may be treated with a cosmetic contact lens painted with a pupil and an iris.

Surgical

The goal of surgery is to realign the eyes at or close to primary position. The choice of procedure depends on which muscles are involved and the completeness of the paralysis. Paresis of the vertical rectus muscles may cancel out, leaving a minimal vertical deviation, which is readily controlled with a mild head position or with prisms. In partial paralysis, there may be sufficient medial rectus function to respond well to a resection of the medial rectus muscle and recession of the ipsilateral lateral rectus muscle. Single vision across a maximum range of horizontal gaze directions is achieved by including recession of both horizontal rectus muscles on the other eye, with adjustable sutures being placed on selected or all four muscles. With very poor to no medial rectus function, if there is significant vertical rectus muscle function, the vertical rectus muscles can be transposed to the medial rectus muscle, combined with a resection and recession of these muscles for any vertical deviation. Adjustable sutures are useful here as well.

In complete paralysis of the third nerve, medial rectus function can be replaced to some extent by the transposition of a sound superior oblique muscle. The superior oblique must be weakened to alleviate the incyclotropia. The superior oblique does not respond to horizontal gaze innervation but will provide an adducting force that opposes the abducting action of the recessed lateral rectus and improves ocular alignment. The tendon can be released from the trochlea by cutting the trochlea with scissors (technically difficult). Care must be taken to avoid crushing the tendon. If the tendon is severed, then the surgeon proceeds as though the superior oblique were also paralyzed. The free tendon is resected until it is snug and sutured to the insertion of the medial rectus muscle. The new superior oblique insertion is optimally placed under the medial rectus muscle at the axis of vertical rotation (to avoid an inadvertent hypertropia).

An alternative approach to transposition of the superior oblique is to leave the trochlea intact and relocate the superior oblique tendon 2 to 3 mm anterior to the medial end of the superior rectus insertion, accompanied by the right amount of resection.

To optimize results, the lateral conjunctiva and Tenon’s capsule can be recessed all the way to the orbital margin and the lateral rectus muscle should be recessed as far as practically possible. The eye can also be anchored in an adducted position for 2 weeks with orbital fixation sutures. This is especially important if the superior oblique tendon has been lost and cannot provide an adducting force. There is no value in resecting the medial rectus muscle unless it has some residual function.

Surgical elevation of the lid may be required if the ptosis is sufficiently severe. This should be deferred until after the eye is aligned. A maximal levator resection with a transcutaneous approach can suspend the upper lid; however, a frontalis sling is preferable for setting the correct lid height. Since the protective Bell’s reflex is usually impaired, the ptosis should be corrected to cover only half of the cornea with the brow relaxed. Frequent blinking and moisturizing drops must be relied on to

prevent corneal drying. Children tolerate corneal exposure better than adults.

In double elevator paresis without resistance to passive elevation, a full tendon transposition of the medial and lateral rectus to the insertion of the superior rectus is the operation of choice (Knapp procedure). The ptosis may be a pseudoptosis caused by the hypotropia and should not be corrected until after the strabismus repair. If it is a real ptosis, elevation of the eye will aggravate the ptosis and the patient or family should be forewarned.

A paralysis of the lower division of the third nerve (affecting the medial rectus, inferior rectus, and inferior oblique muscles) is treated by transferring the functioning superior rectus to the medial rectus muscle, the lateral rectus to the inferior rectus muscle, and tenectomizing the superior oblique muscle.

Supportive

Accurate diagnosis and appropriate medical treatment are necessary. Prism therapy is generally of limited benefit because of marked incomitance. The involved eye is occluded, if necessary, for relief of diplopia. urgery should be deferred for as long as 6 to 9 months because spontaneous recovery may occur. If so, it must be followed to its end; surgery should be considered only for the remaining deviation.

COMPLICATIONS

Because of the severe loss of function of extraocular muscles in third nerve paralysis, the only attainable goal is realignment of the eye in primary position. In patients with incomplete paralysis, a small horizontal and vertical range of fusion may be obtained, but care must be taken that the lid is not elevated too far and corneal function is not compromised. Children learn to suppress the double image; however, adults frequently require an occlusive lens because of the absence of fusion anywhere except in one direction of gaze.

COMMENTS

Total third nerve paralysis is devastating to oculomotor function, and even the limited goal of repositioning the eye near primary position is a considerable achievement. Useful function of the eye in a binocular context can be obtained only in some cases of partial paralysis. Accurate diagnosis and the ruling out of other neurological involvement are essential before any consideration can be given to surgical repair.

REFERENCES

Buckley EG, Townshend LM: A simple transposition procedure for complicated strabismus. Am J Ophthalmol 111:302–306, 1991.

Glaser JS: Infranuclear disorders of eye movements. In: Duane TD, ed: Clinical ophthalmology. Hagerstown, Harper & Row, 1982:12:1–38.

Gottlob I, Catalano RA, Reinecke RD: Surgical management of oculomotor nerve palsy. Am J Ophthalmol 111:71–76, 1991.

Peter LC: The use of the superior oblique as an internal rotator in thirdnerve paralysis. Trans Am Ophthalmol Soc 31:232–237, 1933.

Scott AB: Transposition of the superior oblique. Am Orthoptics J 5:11–14, 1977.

Paralysis230Nerve)CHAPTER(Third Oculomotor •

Muscles Extraocular • 20 SECTION

231 SUPERIOR OBLIQUE MYOKYMIA

358.8

Andrea C. Tongue, MD

Lake Oswego, Oregon

ETIOLOGY

Superior oblique myokymia is a rare disorder reported almost exclusively in adults. Although Duane first described this condition in 1906, Hoyt and Keane, in 1970, were the first to refer to it as superior oblique myokymia, based on the clinical findings in five patients and EMG studies in one. The signs and symptoms include bouts of oscillopsia (microtremor, twitching), and vertical and/or torsional diplopia due to unilateral superior oblique muscle contractions. The disorder is often chronic and is rarely associated with any life-threatening intracranial mischief. It was considered a benign, although aggravating, disorder of unknown etiology until MRI showed that vascular compression of the fourth nerve at the root exit zone (REZ) may be one etiologic factor. Other extremely rare associated factors or potential etiologies cited are preceding superior oblique paralysis, tumors, AV fistula, demyelinating disease, adrenoleukodystrophy, lead poisoning, and stroke. All of these disorders can cause injury to the trochlear nerve and it has been postulated that the myokymia is caused by discharge of regenerating or regenerated motor neurons of the fourth cranial nerved.

COURSE/PROGNOSIS

The course appears to be chronic, with spontaneous remissions and recurrences which may be years apart. In recent years MRI studies in multiple cases have shown compression at the root exit zone of the fourth cranial nerve by a blood vessel. It appears that the right side is more frequently affected than the left in these cases

DIAGNOSIS

Clinical signs and symptoms

The clinical sign of oscillopsia is subtle and may be best detected by slit lamp examination or video photography. Symptoms include intermittent or episodic vertical jumping, shimmering, twitching, or blurring of images. Diplopia may also be present. The symptoms are usually unilateral but have been reported to be perceived as bilateral. Signs are unilateral in that no case of bilateral superior oblique myokymia has been described. Usually individual bursts of superior oblique contraction last seconds but may recur continuously for hours or days at a time. In some patients the symptoms may be provoked by down gaze and may be most easily recognized on slit lamp examination.

Laboratory findings

MRI is essential in identifying vascular compression. It should be noted that vascular contact with the trochlear nerve at the REZ was found in 14% of 30 normal volunteer subjects. Magnetic search coil technique can be used to measure the rotations of the eye during periods of superior oblique contraction. In the past, EMG studies have also shown superior oblique contraction.

TREATMENT

Systemic

Pharmacologic agents used in the treatment of this disorder include oral carbamazepine (tegretol), gabapentin, propanolol, phenytoin and baclofen. It is difficult to assess the effect of these medications because of the variable course of this disease in any individual and between individuals. The drugs may also be associated with serious and significant side effects and require ongoing and frequent laboratory and medical monitoring. Anyone prescribing these drugs should be familiar with the reported adverse effects, contraindications, and required monitoring of the patients.

Topical

Use of topical betoxalol has also been reported with varying success.

Surgical

Surgery is reserved for patients who are unable to tolerate their symptoms and do not respond or have adverse effects to medical therapy. Extra-ocular surgical procedures are directed at weakening the affected superior oblique and ipsilateral inferior oblique. Post-operative superior oblique paralysis may occur, leading to diplopia, which in some cases spontaneously resolves and in some requires further surgery. Recently the newest surgical intervention for SOM reported in the literature is intracranial micro-vascular decompression. This is a neurosurgical procedure involving a craniectomy. However, it is a procedure that attempts to correct the cause of the disease in cases where micro-vascular compression at the REZ is identified by special MRI studies. Temporary as well as lasting superior oblique paralysis (one year follow-up) has been reported in cases after micro-vascular decompression.

REFERENCES

Hashimoto M, Ohtsuka K, Suzuki Y, et al: Superior oblique myokymia caused by vascular compression. J Neuro-Ophthalmol 24:3327, 2004.

Katz SE, Anderson DP: Superior oblique myokymia as a bilateral subjective phenomenon. Can J Ophthalmol 32:256, 1997.

Palmer EA, Shults TW: Superior oblique myokymia: preliminary results of surgical treatment. J Pediatr Ophthalmol Strabismus 21:96, 1984.

Scharwey, K, Krzizok T, Sarnii M, et al: Remission of superior oblique myokymia after vascular decompression. Ophthalmologica 214:425, 2000.

Yousry I, Dieterich M, Naidich TP, et al: Superior oblique myokymia: magnetic resonance imaging support for the neurovascular compression hypothesis. Ann Neurol 51:361, 2002.

232 SUPERIOR OBLIQUE (FOURTH

NERVE) PALSY 378.53

Ann U. Stout, MD

Portland, Oregon

ETIOLOGY

Superior oblique palsy is the most commonly occurring cranial nerve palsy encountered by the strabismologist. The length and

Palsy Nerve)232(FourthCHAPTEROblique Superior •

Muscles Extraocular • 20 SECTION

233V-PATTERN STRABISMUS 378.03, 378.12

Jorge Alberto F. Caldeira, MD

São Paulo, Brazil

ETIOLOGY/INCIDENCE

Patients with a horizontal strabismus that becomes incomitant in vertical gaze, with more divergence of at least 15 prism diopters in the upward position as compared to the downward, are considered to have a significant V-pattern strabismus (Figure 233.1).

Horizontal, vertical and oblique muscle dysfunctions, orbital factors, and anomalies of muscle insertions (followed or preceded by cyclotorsion of the globes) can cause this incomitance. Loss of fusion may also predispose to cyclodeviations which, in turn, can produce a V-pattern. Heterotopia of extraocular muscle pulleys may be responsible for elevation or depression in adduction and a V- or A-pattern.

It is of paramount importance that a significant V-pattern is identified, properly characterized, and adequately corrected to obtain a good result, whether or not in conjunction with horizontal surgery. V-pattern is the most common anomaly among the alphabetical strabismus patterns. The relation of V- pattern : A-pattern is approximately 2 : 1.

COURSE/PROGNOSIS

Anomalous head posture is not rare in patients with a V- pattern. V esotropia with fusion in upward gaze can cause a chin depression; conversely, a patient with V exotropia and fusion in downward gaze may hold the chin in an elevated position. If the reward of fusion is not attained in any position of gaze the head posture is normal, unless there is a vertical imbalance in primary position.

A V-pattern is frequently found in association with Brown syndrome. The same holds true for bilateral paralysis of the trochlear nerve, although in some cases of unilateral paralysis the V-pattern can also be observed. In both instances, excyclotropia is a common sign, detected with the Maddox double-rod test and fundus examination.

FIGURE 233.1. V-pattern strabismus.

DIAGNOSIS

If fusion is present in one postion of gaze, the effort to maintain it for a long time may cause asthenopia and/or diplopia. The deviation should be measured in the nine diagnostic positions of gaze, with the patient wearing the full refractive correction. Accommodation should be controlled with appropriate targets during the measurements. The above requirements are mandatory to avoid the appearance of a pseudo V-pattern or the concealment of a true V-pattern.

Measurements should be made at distance (6 meters) in primary position and with the eyes in position of 25 degrees elevation and 35 degrees depression, while fixating an accommodative target. The head is tilted backward or forward to obtain depression or elevation of the eyes. In very young patients an accurate prism-and-cover test in the diagnostic positions of gaze may be impossible. In this situation the examiner can move the head passively up and down, while the patient fixates a distant accommodative target. The deviation for near is measured at 33 centimeters.

In examining the binocular rotations the patient is encouraged to make extreme effort in the secondary and tertiary positions. Possible elevation in adduction, overaction of each inferior oblique and underaction of each superior oblique should be carefully registered.

The triad of bilateral elevation in adduction, bilateral overaction of the inferior oblique, and bilateral underaction of the superior oblique is more consistent in V-esotropia than in V- exotropia. Overaction of the superior oblique, bilateral or unilateral, is very seldom seen in V-esotropia, but is not rare in V-exotropia.

The significance of a V-pattern depends not only on its amount but also on whether it is functionally significant, interfering or not in the important primary and downward positions.

TREATMENT

Surgical. In most patients, an oblique muscle dysfunction is apparent and horizontal surgery should be combined with procedures on the inferior oblique muscles. Weakening surgeries on the inferior obliques have no significant effect on the deviation in primary position.

Graded recession of the overacting inferior oblique muscles is the weakening procedure of choice. Underacting superior oblique muscles frequently return to normal function after recession of the inferior obliques. Disinsertion, myotomy, or myectomy offer less predictable results than recession. The recession can be enhanced by anteriorization of the new insertion, but keeping it parallel to the temporal border of the inferior rectus. Recession and transposition (with the new insertion parallel to the insertion of the inferior rectus) usually causes some limitation of elevation. A denervation of the inferior oblique or its extirpation is very seldom indicated.

If the inferior obliques are not overacting they should not be touched. In case of a V esotropia, if both medial rectus muscles are to be recessed a downward one-half width or full tendon width transposition is indicated. If an uniocular recessionresection is planned, downward transposition of the medial rectus and upward transposition of the lateral rectus are indicated.

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Strabismus pattern-V 233 CHAPTER

Muscles Extraocular • 20 SECTION

V exotropia without overacting inferior obliques is uncommon. Faced with a basic type of exodeviation requiring recession of the lateral rectus and resection of the medial rectus, the former is transposed upward and the latter, downward.

COMMENTS

V-pattern incomitance is a common finding in horizontal deviations. It requires a painstaking measurement of the deviation and investigation of overacting and underacting oblique muscles. A neglected significant V-pattern may transform a potentially good functional case into a disastrous one.

REFERENCES

Caldeira JAF: Some clinical characteristics of V-pattern exotropia and surgical outcome after bilateral recession of the inferior oblique muscle: A

retrospective study of 22 consecutive patients and a comparison with V-pattern esotropia. Binocul Vis Strabismus Q 19:139–149, 2004.

Caldeira JAF: V-pattern esotropia: A review; and a study of the outcome after bilateral recession of the inferior oblique muscle: A retrospective study of 78 consecutive patients. Binocul Vis Strabismus Q 18:35–48, 2003.

Elliot RL, Nankin SJ: Anterior transposition of the inferior oblique. J Pediatr Ophthalmol Strabismus 18:35–38, 1981.

Goldstein JH: Monocular vertical displacement of the horizontal rectus muscles in the A and V patterns. Am J Ophthalmol 64:265–267, 1967.

Parks MM: The weakening surgical procedures for eliminating overaction of the inferior oblique muscle. Am J Ophthalmol 73:107–122, 1972.