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Duane retraction syndrome
Duane retraction syndrome (DRS) is a congenital form of strabismus characterized by horizontal eye movement limitation, globe retraction and palpebral fissure narrowing in attempted adduction. It is caused by a failure of development of the abducens nerve and can lead to amblyopia.
The prevalence of DRS is about 1/10, 000, representing about 1-5% of all strabismus cases. Females are more affected than males.
DRS is a congenital disorder, characterized by non-progressive horizontal ophthalmoplegia without ptosis. DRS is usually unilateral and the left eye is predominantly affected. At birth, affected infants have restricted abduction and/or adduction. Most individuals with DRS have strabismus in primary gaze but can use a compensatory head position to align the eyes, avoiding diplopia. DRS can be classified into type I: limited or absent abduction, normal or slightly limited adduction and globe retraction and narrowing of palpebral fissure on adduction; type II: limited or absent adduction, normal or limited abduction, globe retraction and narrowing of palpebral fissure on adduction; and type III: limited abduction and adduction, globe retraction, narrowing of palpebral fissure on adduction and eyes are straight in primary position with no head turn. The majority of DRS cases (70%) are not associated with other anomalies. Vertical eye movement abnormalities may be observed as well.
DRS results from failure of normal development of the pontine abducens nucleus or nerve resulting in failure of the normal innervation of the lateral rectus muscle on the affected side. At the same time, an aberrant branch of the oculomotor nerve innervates the lateral rectus muscle. Thus, globe retraction results from co-contraction of the medial and lateral rectus muscles on attempted adduction. Autosomal dominant DRS is found to result from mutations in CHN1 leading in most cases to bilateral DRS.
Diagnosis of DRS is based on clinical features. Magnetic resonance imaging of the brainstem reveal small or absent abducens nerves; optic, oculomotor and trochlear nerves can be hypoplastic. Moreover, eye movement recording may test the presence of some residual innervation in the affected abducens. Electromyography findings may reveal action potentials of the lateral rectus muscles ranging from no activity during abduction to essentially equal activity in adduction versus abduction.
Differential diagnosis includes Duane-radial ray syndrome, acro-renal-ocular syndrome, Bosley-Salih-Alorainy syndrome, Townes-Brocks syndrome, Athabaskan brainstem dysgenesis-related disorders, Wildervanck syndrome, Goldenhar syndrome, horizontal gaze palsy with progressive scoliosis, Moebius syndrome and congenital fibrosis of extraocular muscles (see these terms). Syndromic forms of DRS have been described resulting from mutations in SALL4 as seen in Okihiro syndrome (see this term), or from chromosomal anomalies primarily on chromosome 8.
Most cases are sporadic but up to 10% of patients show a familiar pattern with both recessive and dominant inheritance (incomplete penetrance with variable expressivity).
Management and treatment
Management of DRS is mainly supportive and involves wearing spectacles or contact lenses to correct refractive errors; occlusion or penalization of the better-seeing eye for treatment of amblyopia or prisms to correct for abnormal head posture. Muscle surgery may be indicated to correct abnormal head position, to align the eyes in primary gaze, or to correct for upshoot or downshoot on adduction. However, surgery does not restore full normal eye movements. Surveillance is necessary to prevent or detect amblyopia. Vision therapy is advised for secondary convergence insufficiency.
Isolated DRS is a benign disorder which, if managed appropriately, results in excellent long term prognosis for vision. In some cases, amblyopia or loss of binocular single vision might develop.