History
Patients with Duane syndrome (DS) can present with a history of the following:
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Strabismus
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Head tilt
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Loss of binocular vision
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Reduced abduction
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Picture of paralytic squint
Physical
Duane syndrome can be isolated, or it can be associated with other congenital anomalies. Duane syndrome is an isolated finding in approximately 70% of patients, but it may be associated with other malformations. Major anomalies associated with Duane syndrome can be grouped into 4 categories: skeletal, auricular, ocular, or neural. Duane syndrome also can be associated with other well-defined syndromes, including Okihiro syndrome, Wildervanck syndrome, Holt-Oram syndrome, morning-glory syndrome, and Goldenhar syndrome.
Duane syndrome can be associated with both ocular anomalies and systemic anomalies. Ocular anomalies commonly associated with Duane syndrome include dysplasia of the iris stroma, pupillary anomalies, cataracts, heterochromia, Marcus Gunn jaw-winking, coloboma, crocodile tears, and microphthalmos. Systemic anomalies include Goldenhar syndrome, Klippel-Feil anomalad, and congenital labyrinthine deafness.
Most cases are sporadic. The congenital anomaly consists of absence of the abducens nerve nucleus in the brainstem and simultaneous innervation of the affected lateral rectus muscle by the inferior branch of the oculomotor nerve. The left eye is involved in 60% of cases. Duane syndrome often is bilateral but asymmetrical.
Clinical types
Duane syndrome often is clinically divided into 3 types (see the Table below). Different clinical types may be present within the same family; this occurrence suggests that the same genetic defect may produce a range of clinical presentations. The clinical spectrum of different types of Duane syndrome result from the variability of the 3 innervational portions of the lateral rectus muscle, namely, the normal abducens innervated portion, the abnormal oculomotor innervated portion, and the noninnervated fibrotic portion.
In Duane syndrome type 1, the ability to move the affected eye outward toward the ear (abduction) is limited, but the ability to move the affected eye inward toward the nose (adduction) is normal or nearly so. The palpebral fissure narrows, and the eyeball retracts into the orbit when the patient looks inward toward the nose (adduction). When he or she looks outward toward the ear (abduction), the reverse occurs.
In Duane syndrome type 2, adduction of the affected eye is limited, whereas abduction of the eye is normal or only slightly limited. The palpebral fissure narrows, and the eyeball retracts into the globe when the affected eye attempts to adduct.
In Duane syndrome type 3, adduction and abduction of the affected eye are limited. The palpebral fissure narrows, and the eyeball retracts when the affected eye attempts to adduct.
These 3 types can be further classified into 3 subgroups designated A, B, and C to describe the eyes when looking straight (in primary gaze). In subgroup A, the affected eye is turned inward toward the nose (esotropia). In subgroup B, the affected eye is turned outward toward the ear (exotropia). In subgroup C, the eyes are in a straight primary position.
Table 1. Types of Duane Syndrome. (Open Table in a new window)
Category |
Description |
Type |
|
1 (70-80%) |
Inability to abduct Normal or minimal defect in adduction Esotropia with head straight A or V pattern Usually updrift or a downdrift of affected eye on adduction or attempted abduction Globe retraction and palpebral-fissure narrowing on adduction Usual face turn to affected side Normal stereo possible |
2 (about 7%) |
Inability to adduct Normal or minimal defect in abduction Exotropia of the affected eye Marked upshoot Globe retraction and palpebral-fissure narrowing on adduction Stereo normal or suppressed Face turn to normal side |
3 (about 15%) |
Inability ability to abduct and adduct Globe retraction and palpebral-fissure narrowing on attempted adduction Possible upshoot and downshoot on adduction Straight or nearly straight head position Usually, normal stereo |
4 |
Not usual Duane syndrome or Duane syndrome-type appearance Large-angle exotropia Face turn to uninvolved side Limited adduction Simultaneous abduction when looking toward uninvolved side Usually suppresses 1 eye |
Subtype |
|
A |
Affected eye turned inward toward the nose (esotropia) |
B |
Affected eye turned outward toward the ear (exotropia) |
C |
Eyes in a straight primary position |
Clinical manifestations
The aberrant innervation produces several manifestations. These manifestations include a face turn with strabismus in primary position, an upshoot or downshoot during adduction, a vertical deviation in primary position, retraction during adduction, and enophthalmos.
An individual diagnosed with Duane syndrome in the left eye. In this image, the affected person is attempting to look far right. Notice the afflicted left eye faces straight and up (an "upshoot"), rather than following the right eye to the right.
On occasion, fusion is impossible in a patient with Duane syndrome, usually because bilateral involvement or a vertical deviation precludes fusion with any head posture.
Duane syndrome is characterized in its typical and most frequently observed form by abduction deficiency, globe retraction, and palpebral fissure narrowing on attempted adduction; widening of the palpebral fissure on attempted abduction; and normal or only slightly defective adduction.
Sensory adaptation
Most patients with sensory adaptation demonstrate a peculiar sensory adaptation with excellent binocular functions in directions of gaze where visual axes are aligned and usually suppression without diplopia in the field of the paretic muscles.
Some suggest that the second image is ignored, rather than suppressed, in view of the difficulties encountered in plotting the suppression scotoma.
Signs
Signs of Duane syndrome include the following:
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Head turn to maintain fusion (about 66% of cases, 76% of unilateral cases)
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Strabismus (about 77% of cases)
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Globe retraction
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Palpebral fissure narrowing
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Anisometropia and/or amblyopia (though not more prevalent than in the general population)
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Heterochromia
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Iris dysplasia
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Ptosis
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Nystagmus
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Choroidal coloboma
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Hypoplasia of the optic nerve
Clinical evaluation
A thorough family history and an ocular examination are conducted, with special attention to other ocular or systemic malformations. Measurements of visual acuity, ocular misalignment, ocular range of motion, head turn, globe retraction, size of the palpebral fissure size, and upshoots and downshoots are indicated. In addition, an examination of the cervical and thoracic spine, palate, vertebrae, hands, and hearing is recommended to rule out disorders associated with Duane syndrome.
Differential diagnosis and other problems to be considered
One type of inherited Duane syndrome that is associated with other birth defects is Duane syndrome with radial-ray anomalies. The association of Duane syndrome with radial-ray anomalies is referred as Duane/radial dysplasia syndrome, DR syndrome (acronym for Duane anomaly, deafness, radial dysplasia, renal dysplasia), and Okihiro syndrome.
The familial association of Duane syndrome with radial-ray anomalies appears to be autosomal dominant with incomplete penetrance and variable expressivity. Duane syndrome can be unilateral or bilateral. Radial dysplasia can range from hypoplasia of the thenar eminence (base of the thumb) with or without thumb abduction and apposition weakness, hypoplasia or absence of the thumb, and hypoplasia or absence of the radial and ulnar bones to an absent forearm. Hearing loss, dysmorphic facies and cardiac, renal, and vertebral anomalies are variably expressed in some families. The chromosomal location of the gene for this syndrome is unknown, but families are being enrolled to identify the gene or genes involved in this condition.
Other diagnostic considerations include medial-wall fracture with incarceration of orbit contents; retraction of the globe with attempted abduction is seen on examination. Retraction of convergent nonfixating eye with associated loss of conjugate lateral gaze and occurrence of the near reflex on attempted lateral gaze also might be considered. Because Duane syndrome mimics sixth nerve paresis, the differential diagnoses can be similar to those described for sixth nerve paresis.
In 1977, Duane and coauthors described entirely unrelated pseudo-Duane syndrome in which abduction is restricted and narrowing of the palpebral fissure and retraction of the globe occur after fracture of the medial orbital wall with entrapment of the medial rectus muscle. [17]
Causes
Duane syndrome is thought to be a miswiring of the medial and the lateral rectus muscles, or the muscles that move the eyes. Also, patients with Duane syndrome lack the abducens nerve, or the sixth cranial nerve, which is involved in eye movement. However, the etiology or origin of these malfunctions remains a mystery. Many researchers believe that Duane syndrome results from a disturbance due to either genetic factors or environmental factors during embryonic development. Because the cranial nerves and ocular muscles are developing between the third and eighth weeks of pregnancy, this most likely is when the disturbance happens. It appears that several factors may be involved in Duane syndrome, and a single mechanism is unlikely to be responsible for this condition.
Although Duane syndrome has been well described clinically, the etiology remains unclear. Various theories have been put forward on the basis of data collected from surgical, autopsy, and EMG studies. A high prevalence of ocular and systemic disorders associated with Duane syndrome suggests that a common teratogenic stimulus at 8 weeks of gestation may cause this problem. The most noted and believed theory is based on an absence of cranial nerve VI, an absence of the abducens nucleus in the pons, and a marked abnormality of the lateral rectus muscle.
Most likely, both genetic factors and environmental factors play a role in the development of Duane syndrome. In patients with evidence of a genetic cause, both dominant forms and recessive forms of Duane syndrome have been found. The chromosomal location of the proposed gene is currently unknown. Research shows that more than 1 gene may be involved. Evidence suggests that the gene involved in the development of Duane syndrome is located on chromosome 2. Also, deletions of chromosomal material from chromosomes 4 and 8, as well as an extra marker chromosome thought to be derived from chromosome 22, have been linked to Duane syndrome. See also Genetic and environmental factors in the Pathophysiology section.
Structural anomalies
In the early literature, most authors believed that structural anomalies were the cause of the retraction phenomenon. People found posterior insertion of the medial rectus muscle, which acts as a retractor bulbi.
von Noorden found a broad, flat, tendinous band containing a few visible fibers inserted into the sclera at a point 6 mm behind the medial rectus insertion. [16]
Turk believed that fixation of the globe by a nonelastic lateral rectus muscle was the cause of retraction on adduction. [4]
The abnormal vertical eye movement that frequently occurs with adduction has been blamed on oblique overaction. Narrowing of the palpebral fissure usually is explained as passive adjustment of the lid to retraction of the globe, rather than active innervation of the orbicularis muscles.
Innervational anomalies
Evidence accumulated from EMG studies has indicated an innervational mechanism rather than anatomic abnormalities as the cause of this syndrome.
The currently favored theory is that Duane syndrome is a neurogenic disorder involving either a supranuclear lesion or a cranial nerve anomaly in which branches of the oculomotor nerve innervate the lateral rectus.
Hoyt and Nachtigaller have proposed that ocular retraction during adduction, as well as the EMG findings of synergistic innervation of medial and lateral rectus muscle, can be explained on the basis of substitute innervation of the paretic lateral rectus muscle by an extra branch of the oculomotor nerve. [18]
Primary brainstem anomaly
On autopsy, authors at the Wilmer institute found the absence of abducens nuclei and nerves from the brainstem. Matteucci has described absence of abducens nerve and hypoplasia of its nucleus. [19]
Given the clinical evidence, anomalies of the vestibulo-ocular reflex, auditory evoked responses, optokinetic nystagmus, and frequent association of gustatolacrimal reflex (crocodile tears) with Duane syndrome suggests that a primary brainstem abnormality is a likely cause in at least some cases.
Iatrogenic factors
Duane syndrome may occur on an iatrogenic basis unrelated to congenital, mechanical, or innervational anomalies. von Noorden reports a patient who had normal ocular motility and developed retraction syndrome after massive scarring following removal of a dermolipoma from the temporal aspect of the bulbar conjunctiva of the left eye. [16]
At this time, several etiology factors may be involved, and it is doubtful that a single mechanism is responsible for this disturbance.
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Duane syndrome.
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Duane syndrome.
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An individual diagnosed with Duane syndrome in the left eye. In this image, the affected person is attempting to look far right. Notice the afflicted left eye faces straight and up (an "upshoot"), rather than following the right eye to the right.
Tables
Category |
Description |
Type |
|
1 (70-80%) |
Inability to abduct Normal or minimal defect in adduction Esotropia with head straight A or V pattern Usually updrift or a downdrift of affected eye on adduction or attempted abduction Globe retraction and palpebral-fissure narrowing on adduction Usual face turn to affected side Normal stereo possible |
2 (about 7%) |
Inability to adduct Normal or minimal defect in abduction Exotropia of the affected eye Marked upshoot Globe retraction and palpebral-fissure narrowing on adduction Stereo normal or suppressed Face turn to normal side |
3 (about 15%) |
Inability ability to abduct and adduct Globe retraction and palpebral-fissure narrowing on attempted adduction Possible upshoot and downshoot on adduction Straight or nearly straight head position Usually, normal stereo |
4 |
Not usual Duane syndrome or Duane syndrome-type appearance Large-angle exotropia Face turn to uninvolved side Limited adduction Simultaneous abduction when looking toward uninvolved side Usually suppresses 1 eye |
Subtype |
|
A |
Affected eye turned inward toward the nose (esotropia) |
B |
Affected eye turned outward toward the ear (exotropia) |
C |
Eyes in a straight primary position |
