Monocular elevation deficit

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Disease Entity

Monocular elevation deficit ( Double elevator palsy)

Disease

Monocular Elevation Deficiency (MED) is the limitation of elevation of the affected eye from any position of gaze with normal ductions in all other gazes. MED is a frequent cause of hypotropia and can be associated with ptosis/pseudoptosis. Superior rectus palsy, inferior rectus restriction and supranuclear lesions have been found to be contributory to MED.


Etiology

MED can be congenital or acquired in onset. Congenital cases of MED occur sporadically .[1] The causes include -Supranuclear defects -Primary SR paresis

-Primary IR restriction  as in cases of congenital fibrosis of inferior rectus.[2] 

Acquired MED is usually caused by trauma, cerebrovascular diseases like hypertension, thromboembolism, sarcoidosis, syphilis, and midbrain tumors like pineocytomas, acoustic neuromas and metastatic tumors affecting supranuclear pathways.[3]


General Pathology

MED has been classified into three types by Ziffer et al. [4] Type 1 includes patients with primary IR restriction or fibrosis. Forced duction test (FDT) demonstrates a tight IR. The upward saccades are usually normal until stopped by tight IR preventing further upgaze. Bells phenomenon is usually poor.

In Type 2 MED cases of primary SR palsy are included. FDT is free and upward saccades are slow both below and above midline. Bell’s phenomenon is usually absent

Type 3 MED is supranuclear type and is usually congenital. It is characterized by intact or mildly reduced vertical saccadic velocity below midline but abnormal or absent velocity above midline and FDT is free.

Pathophysiology

There are different school of thoughts regarding the pathogenesis of MED. It has been established that superior rectus is the main muscle for elevation of the eye, be it in abduction, adduction or primary position. Thus, the defective elevation can be explained by presence of a superior rectus palsy alone, inferior rectus (IR) restriction can also be considered as a cause of MED in presence of a normal superior rectus.

Efferent tracts for upgaze leave the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), cross the midline in the posterior commissure, course through the pretectum and enter the superior rectus (SR) subnucleus of the oculomotor nucleus, leaving the subnucleus, upgaze fibres to the SR immediately cross the midline again. As a result of double decussation of upgaze fibers, the SR receives innervation from ipsilateral riMLF as well as contralateral pretectum and SR subnucleus. In cases of MED, it is presumed that supranuclear input from riMLF into third cranial nerve nucleus is interrupted. Supranuclear deficiency affects upgaze, therefore causes monocular elevation deficiency


Clinical features

Age: Average age of presentation is 14 years as reported in previous studies.[5]

Gender: No gender predisposition

Chief Complains: Patients usually present with the following complains -Vertical misalignment of the eyes -Diplopia -Abnormal head posture

-Inability to elevate the affected eye. 
-Drooping of eyelid
-Decrease vision 

Signs

Extraocular movements in nine gazes in a patient of monocualr elevation deficit

Ptosis/Pseudoptosis: Ptosis can be associated with hypotropia because of fascial attachments between levator palpebrae superioris and superior rectus muscle. Pseudoptosis can be present that disappears when hypotropic eye takes up fixation in primary position. Pseudoptosis disappears after the successful vertical alignment of the globe surgically. Pseudoptosis and true ptosis both the components can be present in the patient. In these cases when the patient is made to fix with the affected eye the ptosis recovers only partly. True ptosis when present is usually complex type and has associated Marcus Gunn phenomenon (MGP).


Deviation: There is hypotropia of the affected eye when the normal eye is fixing , but as the affected eye takes up fixation there is hypertropia of the normal eye.

 MED cases may also have co-existent horizontal deviations.


Bell’s phenomenon is usually absent in cases of IR restriction and SR palsy which limit the upward rotation of the globe, but will be present in cases of MED resulting from supranuclear defects.

Amblyopia may be present if there is a constant deviation of the affected eye or associated ptosis, or anisometropia.


Abnormal Head Posture : Most commonly patient has a chin elevation if binocular fusion is present. Abnormal head posture may not be present if the affected eye is amblyopic.

Upward Saccades: Upward saccades are slow/floating in cases of SR palsy, absent above the midline in supranuclear deficiency, and intact (coming to an abrupt halt) in cases associated with IR restriction.


Diagnostic procedures

Forced duction test

Forced duction test is a clinical test which should be done pre-operatively to reveal any restriction. The test is typically performed under topical anaesthesia, conjunctiva is held at limbus with Pierce Hoskin forceps or globe holding forceps, and patient is asked to look in opposite direction of testing muscle to relax the concerned muscle A positive Forced Duction Test (FDT) is seen in patients of IR restriction.

Active Force Generation Test

Active force generation test is done under topical anaestheia by asking the patient to look in the direction of muscle being tested, presence of a tug is suggestive of residual SR action.


Differential diagnosis

The main differential diagnosis of monocular eleavtion deficit includes -Brown’s Syndrome is characterised by limitation of elevation in adduction, with divergence in upgaze caused by slippage of globe resulting in characterstic Y pattern -Vertical Duane Syndrome can be diagnosed by the presence of globe retraction in downgaze along with limitation of elevation in upgaze. -Congenital fibrosis of extraocular muscles initially affecting inferior recti can be misdiagnosed as MED. Bilateral presentation and involvement of other extraocular muscles are features that help distinguish it -Partial third nerve palsy involving the superior division of oculomotor nerve may simulate the findings of MED. - Progressive external ophthalmoplegia involves multiple extraocular muscles. - Orbital inflammatory disease and orbital cellulitis present with a tender inflamed globe.


Management

Management of MED includes both non-surgical and surgical components. The correction of underlying refractive error is to be done and amblyopia therapy is given if needed, followed by surgery whenever indicated.


Surgery

Indications for surgery include -Significant vertical deviation in primary gaze -Significant abnormal head posture

-Deviation-induced amblyopia 

-Diplopia in primary gaze, and restricted binocular fields

The goal of surgery is to improve the position of the affected eye in primary gaze and to increase binocular field of vision.

The surgery of choice in the management of monocular elevation deficit depends on results of forced duction test. In patients with positive forced duction test, inferior rectus recession is the first choice of management. In patients with negative forced duction test but a positive active force generation test, superior rectus resection can be done. In patients with negative forced duction test and a negative active force generation test Knapp's procedure is preferred.

Knapp's procedure (6) Knapp’s procedure is commonly practiced and is now a well-established treatment for monocular elevation deficiency. In the Knapp’s procedure, the tendons of the medial and lateral rectus muscles are transposed to the insertion of the superior rectus muscle. Knapp’s in his work studied 15 patients over a period of eight years. The procedure showed marked variability correcting 21-55 PD (average 38 PD) hypotropia.(

Modifications of Knapp's procedure (7) For management of MED cases with associated horizontal deviation partial tendon Knapp’s (Modifed Knapp’s) procedure is described, in which the superior part of equally divided horizontal muscles is placed near the superior rectus muscle insertion, allowing the correction of horizontal deviation with the untouched inferior half.

Augmented Knapp's procedure Knapp's procedure can be combined with posterior fixation sutures on the horizontal recti, known as Augmented Knapp's.

Following the surgical correction of hypotropia, and improvement in Bell’s phenomenon, associated ptosis and/or Marcus Gunn phenomenon be addressed.

Management of Acquired MED As there are wide variety of causes of acquired MED, thorough investigations (general, ophthalmologic, neurologic, neuro-ophthalmologic and orthoptic (ocular motility work up) should be undertaken.




References

1) Bagheri A, Sahebghalam R and Abrishami M. Double Elevator Palsy, Subtypes and Outcomes of Surgery. Journal of Ophthalmic & Vision Research 3.2 (2008): 108.

2) Jampel RS, Fell P: Monocular elevation paresis caused by a central nervous system lesion. Arch Ophthalmol 1968: 80:4.

3) Rosenbaum AL. Clinical strabismus management. 1st ed. Philadelphia: WB Saunders; 1999.

4) Ziffer AJ, Rosenbaum AL, Demer JL, Yee RD. Congenital double elevator palsy: vertical saccadic velocity utilizing the scleral search coil technique. J Pediatr Ophthalmol Strabismus. 1992; 29:142–9.

5) Bandyopadhyay R, Shetty S, Vijayalakshmi P. Surgical outcome in monocular elevation deficit: A retrospective interventional study. Ind J Ophthalmol 2008; 56:127-33.

6) Knapp P. The surgical treatment of double elevator paralysis. Trans Am Ophthalmol Soc. 1969; 67:304–23

7) Kamlesh, Dadeya S. Surgical management of unilateral elevator deficiency associated with horizontal deviation using a modified Knapp’s procedure. Ophthalmic Surg Lasers Imaging. 2003; 34:230–5.