NTRODUCTION

Brown’s syndrome and Duane’s syndrome are mechanical eye disorders and common forms of noncomitant strabismus in children. They have been classified by Brown in 1950 as the congenital fibrosis syndromes based on findings of both active and passive restriction of ocular motility and the congenital non-progressive nature of the condition. Brown’s syndrome is characterized by an inability to elevate the eye in adduction, Duane’s syndrome by horizontal duction deficits, with narrowing of the palpebral fissure and globe retraction in adduction. (Kekunnaya R. Negalur M., 2017) In both conditions binocular vision is present and they are not associated with amblyopia. Duane’s retraction syndrome (DRS) is also known as Stiling-Turk-Duane syndrome. Unlike Brown syndrome, DRS can be caused by genetic factors and can be associated with other disorders.

There are a few different types of Duane’s syndrome. Management of both varies widely. This report gives brief clinical features and characteristics of Brown’s syndrome and Duane’s retraction syndrome.

BROWN SYNDROME

Brown’s syndrome (or Superior Oblique Tendon Sheath Syndrome) is characterized by a limited active and passive elevation in adduction but normal depression in adduction.[Figure 1] ,,Most cases of Brown’s syndrome develop in infancy, but the syndrome can be acquired through inflammation or trauma affecting the trochlear region, which can trap the superior oblique tendon’’ (Ansons A.M, Davis H., 2014) The patients usually maintain BSV, although the anomaly can be associated with a large exotropia in upgaze or esotropia.[Figure 2]This is a rare disease and can be present with or without hypermetropia in primary position and a secondary turn away from the affected side without a chin-up position. There does not appear to be any genetic basis for this disorder. Brown’s syndrome is usually unilateral with less than 10% of bilateral cases. (Ansons A.M, Davis H., 2014)

CLASSIFICATION

Brown’s syndrome can be congenital or acquired.

AETIOLOGY

The exact cause of most cases of Congenital Brown’s syndrome is not known and its aetiology may vary from one patient to another. However, the possible causes that have been reported are:

• An abnormality of the superior oblique insertion.
• Fibrous attachments between the superior rectus and the underlying superior oblique tendon.[Figure 3]
• Paradoxical innervation of the inferior oblique and the superior oblique, similar to that found in Duane’s retraction syndrome but without supporting anatomical evidence. (Ansons A.M, Davis H., 2014)

Sevel (1981) noted that during embryological development the superior oblique tendon and the trochlea are connected by thick trabeculae, which gradually remodeled and the failure of the trabeculae to remodel could also cause Brown’s syndrome.

The acquired Brown’s syndrome may be a result of trauma, surgery or due to other underlying disorders such as Lupus.

CLINICAL FEATURES

The characteristics of Brown’s syndrome include:

• Limitation of elevation in adduction.
• Overaction of the contralateral superior rectus muscle.
• An A- or V-pattern.
• Down-drift of the affected eye on contralateral version together with the widening of the palpebral fissure.
• Absence of cyclotropia in primary and down-gaze.
• Abnormal head posture (head tilt to the affected side and a head turn to the contralateral side).

The A-pattern occurs in patients with esotropia, however an exotropia in up-gaze is dominant.

The majority of patients with Brown’s syndrome maintain comfortable BSV and remain compensated, usually with comparatively slight head-up AHP. Features that suggest that deviation is poorly compensated include loss of AHP, slow recovery to BSV after dissociation, loss of BSV, a manifest deviation. (Ansons A.M, Davis H., 2O14)

DIAGNOSIS

To diagnose Brown’s syndrome a full eye examination is performed. It should differentiate this disorder from other anomalies like isolated inferior oblique palsy, double elevator palsy, orbital blow-out fracture, congenital fibrosis of the extraocular.

MANAGEMENT

The majority of people with Brown’s syndrome require no treatment, as most of the patient maintain symptom-free BSV and are well compensated. If the person has straight eyes, good vision and no symptoms there is no need to intervene. Sometimes glasses are needed to improve their vision, but Brown’s syndrome does not increase the chance of needing glasses. When Brown’s syndrome is found in children, they are monitored in the Orthoptic Department. This is to ensure their vision develops normally and that they do not suffer from any symptoms from their condition. If there is a squint/turn in the eyes when looking straight ahead or if the person has an uncomfortable head position to keep their eyes straight, surgery may be appropriate. Surgery is only usually recommended for severe symptoms as the results can be unpredictable. Some cases of Brown’s Syndrome improve spontaneously with time. In children, it is preferable to wait and see if their condition changes as they grow. (NHS, 2018)

DUANE’S SYNDROME

Duane’s retraction syndrome is an unusual congenital form of strabismus rarely recognized until later in the childhood when defective eye movement or an obvious abnormal head posture brings it to attention. The main characteristic is the limitation of horizontal eye movement.It can be isolated or it can occur as part of syndromes that affect other areas of the body. Major anomalies that may be associated with DS may affect the skeletal system, ears, eyes, nervous system, and/or the kidneys and urinary tract. The syndrome is thought to be unilateral in approximately 80% of cases and it is the left eye that is most often affected. (Ansons A.M, Davis H., 2014) Females show a slightly higher incidence than males and a hereditary basis has been reported. (Mohan et al. 2008)

CLASSIFICATION

There are two classifications of Duane’s retraction syndrome. One presented in 1950 by Brown and another one presented in 1974 by Huber. Both describe three types of Duane’s syndrome and they are classified depending on the amount of aberrant innervation present.

Huber’s classification

• Type I with limitation of abduction only.
• Type II with limitation of adduction. There is exotropia of the affected eye and normal or minimally defective abduction.
• Type III with both adduction and abduction being defective.

Brown’s classification

• Type A with limited abduction and less-marked limitation of adduction.
• Type B with limited abduction but normal adduction.
• Type C with the limitation of adduction exceeding the limitation of abduction. There is an exotropic deviation and a head turn to. (Ansons A.M, Davis H., 2014)

Type I is most commonly encountered, as well as type III, however, the assignment can be difficult, as the boundary between those two types depends upon a subjective interpretation of the degree of limitation. ,,Electromyographic studies in type I Duane’s syndrome show peak discharges of the lateral rectus on adduction with reduced discharges on attempted adduction, in type II there are peak lateral rectus discharges on abduction with paradoxical discharges on adduction, and in type III there are intense discharges of both lateral and medial recti in the primary position, on abduction and adduction. ‘’ (Gutowski N.J., 2003)

All three types of Duane’s syndrome are associated with other vertical movement anomalies, which are characterized by changes in the ocular axes. ‘’The strabismus of Duane’s syndrome must be differentiated from abducens nerve palsy, Mobius syndrome, congenital oculomotor apraxia, congenital or familial esotropia, and acquired orbital lesions that cause a mechanical restriction.” (Gutowski N.J., 2003)

CLINICAL FEATURES

It may take several years for Duane’s syndrome to become noticeable, especially that some children may have learned to compensate for their visual difficulties. However, the symptoms of this disorder are subtle and include holding the head in an abnormal posturę, closing one eye to see better and misalignment of the eyes. Older children may experience double vision, headaches and neck pain.

The features of Duane’s syndrome include:

• Deficient horizontal eye movement.[Figure 4]
• Globe retraction.
• Palpebral fissure narrowing.[Figure 5]
• Abnormal vertical eye movements.[Figure 6]
• Deviation in PP is small, often BSV with or without AHP.
• Poor convergence.
• Absence of diplopia.
• Associated ocular abnormalities – coloboma, heterochromia irides, microphthalmus, lens opacities, persistent pupillary membrane, anisometropia. (Ansons A.M, Davis H., 2014)

Figure 4: Limited abduction in the right eye.

(Kekunnaya R. Negalur M., 2017)

Figure 5: Restricted abduction and upshoot  with narrowing of the palpebral fissure on attemted adduction in left eye.

(Basil T. D., Joseph J. V., 2018)

Figure 6: Abnormal vertical movements.

(Ramos de Souza-Dias C., 2009)

AETIOLOGY

Duane’s syndrome is a cranial dysinnervation disorder. It results from an absence of the abducens nerve and aberrant innervation. It is also thought to result from a disturbance of normal embryonic development by either a genetic or an environmental factor at the time when the cranial nerves and ocular muscles are developing. Blodi (1964) describes the pathogenetic principle accounting for Duane’s syndrome as a paradoxical anomalous lateral rectus innervation of the affected eye by axons destined for the medial rectus and this is based on electromyographic evidence showing increased electrical activity in a ‘paretic’ lateral rectus muscle. ,,Pathology in isolated cases has shown a hypoplastic or absent abducens nucleus and/or nerve with lateral rectus innervation from the inferior division of the third nerve and fibrosis in the areas that are not innervated, confirming the electromyographic evidence.’’ (Gutowski N.J., 2003)

Genetic studies established that mutations in the CHN1 gene were found to be the cause of Duane’s Syndrome too. (GARD, 2012) The CHN1 gene is responsible for making a protein that is involved in the early development of the nervous system and it appears to be critical for the formation of extraocular muscles.

DIAGNOSIS

The diagnosis of Duane syndrome is based on clinical findings. The examinations include the visual exam, testing the range of movement of both eyes, determining whether an abnormal head posture is used and obtaining a complete medical and family history. Most of the patients with Duane’s syndrome do not have any other detected congenital anomalies. ,,Approximately 30% of individuals with Duane syndrome have other congenital anomalies, particularly of the ear, kidney, heart, upper limbs, and skeleton.’’ (Andrews C.V, Hunter D.G, et al. 2007.)

MANAGEMENT

The treatment of Duane’s Syndrome often involves surgery by a horizontal muscle recession procedure – medial rectus recession for an esodeviation or lateral rectus recession for an exodeviation.

CONCLUSION

Brown’s syndrome and Duane’s syndrome are both rare disorders. Duane’s syndrome accounts for 1%-5% of all cases of strabismus and the frequency of Brown’s syndrome is 1 in 400-450 strabismus cases. (Andrews C.V., Hunter D.G., et al. 2007.), (Roque, B.L.,2018) Isolated Duane’s syndrome in familial and simplex cases has been identified worldwide. The prevalence of Duane syndrome is estimated at 1:1,000 in the general population. There is a higher incidence of Brown’s syndrome in females (59%) than in males (41%). (Roque, B.L.,2018)

REFERENCES

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