Disorders of Supranuclear Eye Movements

Forward Head Posture Fix

Forward Head Posture Fix

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We focus here on a few disorders in which the normal physiology of supranuclear eye movements, such as saccade, smooth pursuit, vergence, and gaze holding, is disturbed.

Saccade Initiation Failure/Ocular Motor Apraxia The term saccade initiation failure or ocular motor apraxia is used to specify impaired voluntary saccades and variable deficit of fast-phase saccades during vestibular or optokinetic nystagmus.380,447 Congenital ocular motor apraxia, first described by Cogan,96 is a congenital disorder that is characterized by defective horizontal saccades, but it does not represent a true apraxia because reflex saccades may also be impaired. The incidence of this condition is dependent upon the underlying etiology.

Etiology Patients with congenital saccade initiation failure show abnormal initiation and decreased amplitude of voluntary saccades; saccadic velocities in these patients are normal, and fast phases of nystagmus of large amplitude can occasionally be generated, suggesting that the brainstem burst neurons that generate saccades are intact.288 Acquired saccade initiation failure may be caused by any number of conditions, as listed in Table 5-2. Some of these patients with the acquired type, such as those with Gaucher's disease (type 1 and some type 3 patients), do have abnormal saccadic velocities.83,194 Although the exact cause or localization of the defect in congenital saccade initiation failure has not been determined, there is strong evidence suggesting that most disorders that cause saccade initiation failure can be localized subtentorially, particularly to the cerebellar vermis 83,137,196,235,429,450

Clinical Features The clinical presentation varies with the age and motor development of the child. Infants and children with poor head control who are affected are commonly thought to be cortically blind because the expected visually driven eye movements are not observed.164,417 In such an infant, demonstration of vertical saccades, vertical pursuit, OKN response in any direction, or normal acuity on visual evoked response testing suggests the diagnosis of saccade initiation failure. However, lack of appropriate response to such testing does not exclude this diagnosis. Another suggestive clinical sign in young infants is an intermittent tonic deviation of the eyes in the direc-

TABLE 5-2. Congenital and Acquired Saccade Initiation Failure (SIF) (Ocular Motor Apraxia).

Classification by cause Specific etiologies

Idiopathic195 Perinatal problems

Cerebral palsy195; hypoxia195; hydrocephalus19

Congenital malformations

Neurodegenerative conditions with infantile onset of SIF

Neurodegenerative conditions with later onset of SIF

Acquired disease

Other associations

Agenesis of corpus callosum450; fourth ventricle dilation and vermis hypoplasia450; Joubert's syndrome282,332; macrocerebellum63; dysgenesis of cerebellar vermis and midbrain523; Dandy-Walker malformation195; immature development of putamen472; heterotropia of gray matter472; porencephalic cyst195,515; hamartoma near foramen of Munro515; macrocephaly195;

microcephaly147,195; posterior fossa cysts375;

chondrodystrophy dwarfism and hydrocephalus98; encephalocele375; occipital meningocele11; COACH syndrome162 (cerebellar vermis hypoplasia, oligophrenia, congenital ataxia, coloboma, hepatic fibrocirrhosis)

Infantile Gaucher's disease (type 2 , 3)85,100,507; Gaucher's disease type 256,497; Pelizaeus-Merbacher disease195; Krabbe's leukodystrophy195; proprionic academia195-

GMi gangliosidosis195; infantile Refsum's disease1

hydroxybutyric aciduria147,397 Ataxia telangectasia473,499,532; spinocerebellar degenerations7,21,36,228,270,369,512; juvenile Gaucher's disease (type 3)194; Huntington's disease31,471; Hallervorden-Spatz disease17; Wilson's disease265

Postimmunization encephalopathy195,335; herpes encephalitis195; posterior fossa tumors195,298,477,536,540

Alagille's syndrome12; Bardet-Biedl syndrome284; carotid fibromuscular hypoplasia195; Cockayne's syndrome147; Cornelia de Lange syndrome195; juvenile nephronophthisis129; Lowe's syndrome181; neurofibromatosis type 1168; orofacial digital syndrome305; X-linked muscle atrophy with congenital contractures524

Source: Adapted from Cassidy L, Taylor D, Harris C. Abnormal supranuclear eye movements in the child: a practical guide to examination and interpretation. Surv Ophthalmol 2000;44:479-506, with permission.83

tion of slow-phase vestibular or optokinetic nystagmus; in these infants, fast-phase saccades may be impaired, again confounding our definition of oculomotor apraxia.288

Natural History With time, often by 4 to 8 months of age, the child develops a striking stereotypical "head-thrusting" behavior to refixate. First, the eyelids blink ("synkinetic blink")

and the head begins to rotate toward the object of interest. Next, the head continues to rotate past the intended target, allowing the tonically deviated eyes, which are now in an extreme con-traversive position, to come into alignment with the target. Finally, as the eyes maintain fixation, the head rotates slowly back so that the eyes are in primary position. This apparent use of the VOR to refixate continues for several years, but with increasing age, patients demonstrate less prominent head thrusting and may even be able to generate some saccades although these are abnormal.97,542

In some infants, generalized hypotonia may be associated. This hypotonia seems to be more pronounced in boys and improves with increasing age. These babies later demonstrate the motor delay, incoordination, and clumsiness that have been noted in the literature.153,395

Clinical Assessment The parents of children are asked about any associated developmental abnormality. A complete ophthalmic examination is performed to rule out any strabismus or amblyopia, as strabismus has been reported in 22% of these patients in one series.195 Vision, electroretinogram (ERG), and visual evoked potential (VEP) are normal in the congenital saccade initiation failure patients.164,451 Any coexistent abnormal vision, nystagmus, or abnormal ERG or VEP suggests associated disease.451 Neurological abnormalities or dysmorphic features are further investigated by the appropriate subspecialists. A brain MRI is necessary for any suspected neurological disorder, to look for any midline malformation, particularly around the fourth ventricle and cerebellar vermis.83

Systemic Associations Significant structural abnormalities of the central nervous system (CNS) may be associated, such as lipoma477 or brainstem tumor.540 Joubert's syndrome is associated with cerebellar hypoplasia and agenesis of the corpus callosum.282 A neuroradiologic correlation has been made in children with saccade initiation failure, in which 61% of 62 children had abnormal scans, primarily the brainstem and cere-bellar vermis; however, significant abnormalities in the cerebral cortex and basal ganglia were also found.450

Gaucher's disease,185,197 ataxia telangiectasia7,473 and its variants, and Niemann-Pick variants100 may also present with the inability to generate saccades as well as blinking and head thrusting before refixation. Unlike congenital saccade initiation failure, these disorders generally involve vertical as well as horizontal saccades and, of course, eventually manifest systemic signs.

Early-onset vertical saccade initiation failure has been observed in children with lesions at the mesencephalic-diencephalic junction, presumably infarcts resulting from perinatal hypoxia.135,219

Inheritance Occasional familial occurrence,196,345,387,398,501 increased frequency in males, and occurrence in monozygotic twins67 suggest a genetic process in some cases. Association with nephronophthisis has been described in two patients, each of whom exhibited deletions on chromosome 2q13.55

Treatment No treatment is available for congenital saccade initiation failure, but associated strabismus is treated accordingly.

Prognosis The visual and clinical prognosis of those patients with the congenital type is good. Many can adapt over time to allow gaze shifts with less head thrusting and can even generate some saccades, albeit still abnormal.97,542

Induced Convergence Retraction/Parinaud or Dorsal Midbrain Syndrome Lesions of the posterior commissure in the dorsal rostral mid-brain (see Fig. 5-2) may result from many disease processes and can affect a variety of supranuclear mechanisms, including those that control vertical gaze, eyelids, vergence, fixation, and pupils. Other terms such as pretectal syndrome, Koerber-Salus-Elschnig syndrome, Sylvian aqueduct syndrome, posterior com-missural syndrome, and collicular plate syndrome all refer to this condition.

Incidence A report of 206 patients with pretectal syndrome in one neurologist's practice at a general hospital in southern California indicated the incidence to be 2.3% of all patients examined by this neurologist in an 18-year period.255 Of these 206 patients, 71 exhibited induced convergence retraction.

Etiology and Systemic Associations The pretectum was confirmed as the critical structure that is affected in this disorder, investigated clinicopathologically in humans91 and experimentally in monkeys.371,372 Also, isolated interruption of the

TABLE 5-3. Causes of Childhood Dorsal Midbrain Syndrome.

Classification by cause

Specific etiologies

Tumor

Pineal germinoma, teratoma and glioma; pineoblastoma; others386

Hydrocephalus

Aqueductal stenosis with secondary dilation of third ventricle and aqueduct, or with secondary suprapineal recess compressing posterior commissure,89,366 commonly caused by cysticercosis in endemic areas

Metabolic disease

Gaucher100'492; Tay-Sach; Niemann-Pick154; kernicterus214; Wilson's disease265; others

Midbrain/thalamic damage

Hemorrhage; infarction

Drugs

Barbiturates138; carbamazepine; neuroleptics

Miscellaneous

Benign transient vertical eye disturbance in infancy; trauma; neurosurgery445; hypoxia; encephalitis; tuberculoma; aneurysm102; multiple sclerosis

posterior commissure in humans produces the entire syndrome of upward gaze palsy, pupillary light-near dissociation, lid retraction, induced convergence retraction, skew deviation, and upbeat nystagmus.251 Among the many underlying causes of this condition are hydrocephalus, stroke, and pinealomas. Table 5-3 lists other reported etiologies and systemic associations.

Clinical Features and Assessment The constellation of deficits are (1) vertical gaze palsy, (2) light-near dissociation of the pupils, (3) eyelid retraction (Collier's sign), (4) disturbance of vergence, (5) fixation instability, and (6) skew deviation.

Limitation of upward saccades is the most reliable sign of the convergence retraction. Upward pursuit, Bell's phenomenon, and the fast phases of vestibular and optokinetic nystagmus may also be affected either at presentation or with progression of the underlying process. It is rare for upgaze to be unaffected. Pathological lid retraction and lid lag are also common (Collier's sign).

When the patient attempts upward saccades, a striking phenomenon, convergence and globe retraction, frequently occurs; this is not true nystagmus, despite the common description of this clinical finding as convergence-retraction nystagmus, because there is no true slow phase. This action is best elicited with down-moving OKN targets because each fast phase is replaced by a convergence-retraction movement. Cocontraction of the extraocular muscles has been documented during this convergence-retraction jerk.161

Unlike the pathways from upward saccades, the pathways for downward saccades do not appear to pass through the posterior commissure (Figs. 5-3, 5-6). Perhaps because of this, disturbances of downgaze are not as predictable or uniform. Usually down-going saccades and pursuit are present, but they may be slow. Sometimes, especially in infants and children, there is a tonic downward deviation of the eyes that has been designated the "setting sun" sign, and down-beating nystagmus may also be observed. The "setting sun" sign may also be seen in children with hydrocephalus.

Convergence spasm may occur during horizontal saccades and produce a "pseudoabducens palsy" because the abducting eye moves more slowly than the adducting eye.113 This phenomenon can cause reading difficulties early in the course of dorsal midbrain syndrome because it provides an obstacle to refixation toward the beginning of a new line of text. Indeed, older children may present with numerous pairs of corrective

Posterior Commissure Posterior Commissure

Posterior Commissure Posterior Commissure

Refixation Saccades

FIGURE 5-6A,B. Schematic of brainstem pathways coordinating downward (A) and upward (B) saccades. (A) Downward saccades. The PPRF activates neurons in the riMLF that send fibers caudally to synapse upon the inferior rectus subnucleus of the ipsilateral third nerve and the contralateral superior oblique nucleus. Not shown in this diagram, fibers from the contralateral PPRF carry corresponding signals simultaneously. (B) Upward saccades. The PPRF activates neurons in the riMLF that send fibers through the posterior commisure to the superior rectus subnucleus of the contralateral third nerve and fibers to the inferior oblique subnu-cleus of the ipsilateral third nerve. Not shown in this diagram, fibers from the contralateral PPRF carry corresponding signals simultaneously. riMLF, rostral interstitial nucleus of the medial longitudinal fasciculus; INC, interstitial nucleus of Cajal; III, third cranial nerve nucleus; IV, fourth cranial nerve nucleus; PPRF, paramedian pontine reticular formation.

FIGURE 5-6A,B. Schematic of brainstem pathways coordinating downward (A) and upward (B) saccades. (A) Downward saccades. The PPRF activates neurons in the riMLF that send fibers caudally to synapse upon the inferior rectus subnucleus of the ipsilateral third nerve and the contralateral superior oblique nucleus. Not shown in this diagram, fibers from the contralateral PPRF carry corresponding signals simultaneously. (B) Upward saccades. The PPRF activates neurons in the riMLF that send fibers through the posterior commisure to the superior rectus subnucleus of the contralateral third nerve and fibers to the inferior oblique subnu-cleus of the ipsilateral third nerve. Not shown in this diagram, fibers from the contralateral PPRF carry corresponding signals simultaneously. riMLF, rostral interstitial nucleus of the medial longitudinal fasciculus; INC, interstitial nucleus of Cajal; III, third cranial nerve nucleus; IV, fourth cranial nerve nucleus; PPRF, paramedian pontine reticular formation.

spectacles that have been prescribed due to their "vague" complaints about reading and other near work. In other patients complaining of difficulties with near vision, convergence may be paralyzed. "Tectal" pupils are usually large and react more poorly to light than to near, and anisocoria is not uncommon.

All children with convergence retraction deserve thorough, prompt neurological and neuroradiologic evaluation because timely intervention may be decisive. The natural history of this disorder is dependent on the underlying etiology.

Treatment The underlying medical cause requires investigation and primary treatment. Once the condition is stable for a period of time, from 3 to 12 months, surgery has been performed with some success. In addition to treating the coexistent diplopia from skew deviation or horizontal strabismus, which may be surgically corrected, the anomalous head posture from defective vertical gaze may also be treated by inferior rectus recession or vertical transposition of horizontal recti during simultaneous horizontal strabismus correction.74 Faden operation (posterior fixation suture, or retroequatorial myopexy) on both medial recti to control convergence spasms and bilateral superior rectus resection to alleviate the anomalous head posture have also been reported.465

Prognosis The medical prognosis is dependent upon the underlying etiology. In the aforementioned review of 206 patients, only 20 patients died: 11 of tumors, 7 after strokes, and 1 with transtentorial hernation with tuberculous abscess. The good prognosis in this series may have been skewed by the preponderance of patients with cysticercal hydrocephalus.255

The prognosis of strabismus surgery in all eviating anomalous head posture and diplopia was good in all three patients in one study after a minimum of 6 months follow-up.74 In another report, head posture and ocular motility improved beyond expectation and remained satisfactory after a minimum of 1 year follow-up.465

Transient Vertical Gaze Disturbances in Infancy Vertical gaze abnormalities may be benign and transient in infants. Four babies with episodic conjugate upgaze that became less frequent over time have been described.6,113 During these episodes, normal horizontal and vertical vestibulo-ocular responses could be observed.

Tonic downgaze has been observed in 5 of 242 consecutively examined healthy newborn infants215 as well as in other infants.113,285 Again, the eyes can easily be driven above the primary position with the vestibulo-ocular reflex. Also, the eyes show normal upward movements during sleep. In contrast, infants with hydrocephalus who manifest the "setting sun" sign do not elevate the eyes during sleep or with an oculocephalic maneuver.

Premature infants with intraventricular hemorrhage may also develop tonic downgaze, usually in association with a large-angle esotropia.480 These infants do not elevate the eyes with vestibular stimulation. Upgaze often returns during the first 2 years of life, but the esotropia does not resolve when upgaze returns.

Double Elevator Palsy/Monocular Elevation Deficiency Monocular deficiency of elevation, that is, an apparent weakness of both the superior rectus and inferior oblique muscles, has been termed double elevator palsy or monocular elevation deficiency. This deficit may be caused by mechanical restriction of the globe or neural dysfunction at the supranuclear, nuclear, or infranuclear level. Congenital double elevator palsy of supra-nuclear origin is confirmed on clinical examination if the affected eye elevates during Bell's phenomenon or doll's head maneuver.44,52

Spasm of the Near Reflex Spasm of the near reflex, also referred to as convergence spasm, is characterized by intermittent spasm of convergence, of miosis, and of accommodation.95 Symptoms include headache, photophobia, eyestrain, blurred vision, and diplopia. Patients may appear to have bilateral sixth nerve palsies, but careful observation will reveal miosis and high myopia (8-10 D) on dry retinoscopy, accompanying the failure of abduction.172 This key clinical clue prevents misdiagnosis and misdirected testing.172,182,252,430

Most commonly, spasm of the near reflex is psychogenic, and treatment may include simple reassurance, psychiatric counseling, or cycloplegia with bifocals. However, a number of cases of spasm of the near reflex associated with organic disease have been reported.487 In a series of seven patients, two had posterior fossa abnormalities (cerebellar tumor, Arnold-Chiari malformation), two had pituitary tumors, one had a vestibulopathy, and two had antecedent trauma.112 None of these patients appeared to have a personality disorder, and none complained of significant disability. Nevertheless, no clear causal relationship or unified neuroanatomic localization has been established. It is prudent to keep in mind that just as any patient with organic disease may also have a functional disorder, disturbances that are clearly functional do not exclude coexisting organic disease.

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