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The Official Scientific Journal of Delhi Ophthalmological Society
Monocular Elevation Deficit-Simplified
Apurva Goray, Kamlesh, Shweta Dhiman, Prolima Thacker, Yashpal Goel, Babita, Anju Rastogi, Manisha Mishra
Guru Nana Eye Centre, Maulana Azad Medical College,
Maharaja Ranjit SIngh Marg, New Delhi, India
Corresponding Author:
Prolima Thacker
Guru Nanak Eye Centre,
Maulana Azad Medical College,
Maharaja Ranjit Singh Marg, New Delhi
Email: dr.prolima@gmail.com
Received: 18-MAY-2015 Accepted: 28-MAY-2015 Published Online: 23-JUN-2015
DOI: http://dx.doi.org/10.7869/djo.127
Abstract
Managing hypotropia is a challenge for strabismologists. Monocular Elevation Deficit (MED) is one of the causes of hypotropia seen frequently by a stabismologist. Co-existence of horizontal deviations, ptosis, amblyopia, Dissociated Vertical Deviation(DVD) make the management of MED difficult. Even for the correction of hypotropia, there are different surgical techniques, which reflect the variety of causative mechanisms. After reviewing available literature, we have attempted to simplify this complex entity in terms of its pathogenesis, presentation, differential diagnosis and finally, appropriate management. 
Keywords : hypotropia, elevation deficit, knapp’s surgery, inferior rectus recession
Monocular Elevation Deficiency (MED) is defined as limitation of elevation of the affected eye from any position of gaze with normal ductions in all other gazes. Hypotropia may occur due to a variety of local, peripheral and central nervous system etiologies. A specific entity characterized by an apparent paralysis of both the elevator muscles of the eye (superior rectus and inferior oblique) was first described by Dunlap, who coined the term “Double Elevator Palsy”.[1] However, now other causes, including isolated superior rectus palsy, inferior rectus restriction and supranuclear lesions have been found to be contributory to the above disorder. Therefore, the term “Monocular Elevation Deficiency” (MED) is more accurately used to describe the syndrome and has replaced the term Double Elevator Palsy to encompass all the causes.[2,3]

Anatomy

The efferent tracts for upgaze leave the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), decussate across the midline in the posterior commissure, course through the pretectum and enter the superior rectus (SR) subnucleus of the oculomotor nucleus. After leaving the subnucleus, upgaze fibres to the SR immediately cross the midline again. Because 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 there is an interruption of supranuclear input from riMLF into third cranial nerve nucleus. Supranuclear deficiency affects upgaze and hence causes monocular elevation deficiency.[4]

Pathogenesis

There are different opinions 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.[1] In some of the cases, the defective elevation can therefore be explained by the presence of a superior rectus palsy alone.[5] In the presence of a normal superior rectus, inferior rectus (IR) restriction can also cause MED. Secondary contracture of the IR due to a primary SR palsy can also lead to MED.[6] This is supported by studies which found thickened IR in a few patients of MED with normal third nerve on MRI examination.[7] Jampel and Fells suggested a unilateral supranuclear lesion in the pretectal area near or inside the third cranial nerve nucleus in some cases.[8]

Demographics

The exact incidence or prevalence of congenital MED is not known.[9] However, a study by Kocak et al shows an incidence of 0.5% among strabismic patients.[10] The age at presentation ranges from 7 months to 21 years as per Kamlesh et al.[11] Zafar et al[12], Kamlesh et al[11] and Bandopadhyay et al[13] noted a mean age of 11±6.74 years, 9.5 years, and 14.03 years respectively. No specific gender predilection is seen.[11,12] A preference towards right sided involvement has been reported by Zafar et al.[12] However, Kucak and co-workers and Bagheri et al have reported a predilection for left eye.[14-15] Calderia believed that right side involvement is somewhat more common in congenital cases and left side involvement is slightly more common in acquired cases.[16] There is however, insufficient evidence at this point to form such a conclusion.

Etiology

MED can be congenital or acquired in onset. Congenital cases of MED occur sporadically but cases occurring in twins have been reported.[14,17] The causes include supranuclear defects, primary SR paresis and primary IR restriction (congenital fibrosis of inferior rectus).[18] Acquired MED is usually caused by cerebrovascular diseases like hypertension, thromboembolism, arteritis. Other causes include sarcoidosis, syphilis, and midbrain tumors like pineocytomas, acoustic neuromas and metastatic tumors.[9]

Clinical Features

The presenting complaints of patients with MED can be a vertical misalignment of the eyes, diplopia, abnormal head posture, or inability to elevate the affected eye. Patients may also present with the complaint of ptosis or amblyopia, which are commonly seen.

Deviation: There is hypotropia of the affected eye when the normal eye is fixing and hypertropia of the normal eye when the affected eye is fixing. Usually the normal eye is preferred for fixation and the affected eye is hypotropic. Rarely the normal eye is amblyopic, or the hypotropic eye is preferred for fixation leading to a constant hypertropia of the normal eye. Cases of MED may also have co-existent horizontal deviations.[21,25] (Figure 1 & 2)





Elevation deficit: Monocular limitation of up gaze above midline (horizontal plane) is present in all the three horizontal positions, i.e., abduction, primary position and adduction.[9]

Ptosis/Pseudoptosis: A hypotropic eye is associated with ptosis because of the fascial attachments between the levator palpebrae superioris and the superior rectus muscle. Ptosis is most noticeable when the normal eye fixates. Patients may have associated pseudoptosis that disappears when the hypotropic eye takes up fixation in primary position.[22,23] Pseudoptosis disappears after the successful vertical alignment of the globe surgically.[24,25] (Figure 3) The patient can have a component of both pseudoptosis and true ptosis.(Figure 4) In these cases when the patient is made to fix with the affected eye the ptosis recovers only partly. True ptosis may be present in about 25% cases.[24] Marcus Gunn phenomenon (MGP) may be present with variable amount of severity.(Figure 5) It has been seen that up to 25% cases of MED have associated MGP.[26]







Bell’s phenomenon is usually absent in cases of IR restriction and SR palsy which limit the upward rotation of the globe, but present in cases of MED caused by supranuclear defects.[25]

Amblyopia may be present if there is a constant deviation of the affected eye or associated ptosis, or anisometropia.[9,13]

Diplopia: MED with congenital onset usually has no complaints of diplopia as the affected eye is usually amblyopic. In acquired MED however, bothersome vertical diplopia is present.[19,20]

Abnormal Head Posture (AHP): If binocular fusion is present, a chin elevation is usually seen.[12]Taking fixation with the affected eye is very rare, but has been reported.[21] Patient may not have an AHP if there is orthotropia in primary position or 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.

A positive Forced Duction Test (FDT) is seen in patients of IR restriction. A Force Generation Test can be performed to look for residual SR action. It has been seen that in MED cases where the underlying etiology is inferior rectus restriction, the affected eye shows tethering and buckling of mid lower lid in up gaze.[27] Olsen et al have shown that upto 29% children with MED develop dissociated vertical deviation.[28]

Classification

Using scleral research coil for evaluating saccadic velocities, Ziffer et al classified MED into three types:[29]

Type 1

It includes patients with primary IR restriction or fibrosis. They are often orthotropic in primary gaze. FDT demonstrates restriction of upward rotation because of a tight IR. The upward saccades are usually normal until stopped by tight IR preventing further upgaze. Bells phenomenon is usually poor.

Type 2:

This group includes cases of primary SR palsy and is characterized by a forced duction test demonstrating no restriction to full upward rotation of the eyeball. The upward saccades are slow both below and above midline. Bell’s phenomenon is usually absent in this type of MED.

Type 3:

It is the supranuclear type of MED, which is usually congenital and is characterized by intact or mildly reduced vertical saccadic velocity below midline but abnormal or absent velocity above midline. There is no resistance to upward rotation of the eyeball on FDT.

Differential Diagnosis

The diagnosis of congenital MED is mainly a clinical one and it needs to be differentiated from the following entities:
  1. In Brown’s Syndrome,the limitation of elevation is worse on adduction and improves on abduction. A V pattern strabismus and superior oblique restriction on FDT is characteristic.
  2. Vertical Duane Syndrome is identified by the presence of globe retraction in downgaze.
  3. Congenital absence of superior rectus and or inferior oblique often mimic MED but are usually associated with craniofacial abnormalities.
  4. Congenital fibrosis of extraocular muscles affects inferior recti initially and can be confused with MED. Bilateral presentation and involvement of other extraocular muscles are features that help distinguish it.A third nerve palsy may simulate the findings of MED. Abnormal pupillary reactions and esotropia of the affected eye are seen. A palsy of the superior division of the third nerve affecting the SR and levator muscle is very difficult to distinguish from MED.
Many disorders can present similar to acquired MED and these must be borne in mind while making a diagnosis of acquired MED. Thyroid orbitopathy shows characteristic bilateral involvement with proptosis, lid retraction and laboratory and clinical features of thyroid disease. Orbital floor fractures leading to IR palsy or entrapment can cause an elevation deficit. A history of trauma, and CT imaging would confirm the diagnosis. Myasthenia Gravis is suspected when the signs and symptoms worsen in the evening, and can be confirmed by the edrophonium test, Anti cholinesterase antibody tests and electromyography findings. Progressive external ophthalmoplegia is always seen to involve multiple extraocular muscles. Orbital inflammatory disease and orbital cellulitis present with a tender inflamed globe. Other disorders that can be confused with acquired MED are labyrinthine disorders (which will have tinnitus, vertigo, nystagmus and nausea) and cerebellar tumours (usually patients will have ataxia and papilledema).[9]

Management

Management of MED includes both non-surgical and surgical components. The correction of underlying refractive error is done, amblyopia therapy is given if needed, followed by surgery whenever indicated. Indications for surgery are significant vertical deviation in primary gaze, significant abnormal head posture, deviation-induced amblyopia, diplopia in primary gaze, and restricted binocular fields.[9] The goal of surgery is to improve the position of the affected eye in primary gaze and to increase binocular field of vision.[30]


The types of surgeries used to correct the vertical deviation in MED are:

Knapp’s Surgery

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. (Figure 6) 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. Postoperatively rotations were full in eight cases and mildly restricted in seven.[31]




Burke et al performed Knapp’s procedure in 19 patients. Out of those, 6 had had a prior IR recession. The average vertical correction was 37.5PD in patients who underwent a prior IR recession compared with 21.1 PD in patients who underwent Knapp’s procedure alone (p=0.0017). They concluded that the magnitude of vertical correction obtained by Knapp’s procedure did not correlate with the preoperative magnitude of deviation regardless of prior performance of IR recession.[32] Bandyopadhyay et al studied twenty eight patients with MED over three years. The mean correction they obtained with Knapp’s procedure was 29.4 PD. They also found that in 10 patients the elevation improved.[13] Cooper et al did Knapp’s procedure in 6 patients of MED with simultaneous horizontal resection and recession in one patient for horizontal deviation. The mean preoperative vertical deviation was 34.2 PD. The mean postoperative vertical deviation was 9 PD with mean correction of 25.2 PD. The patient in whom horizontal resection and recession was done did not show good results in horizontal correction.[33] Calderia et al noted a mean correction of 36.4PD for distance and 29.5 PD for near. They found that the effect of transposition surgery increases with time which probably was the cause of over corrections they noted on follow-ups.[16]

Though Knapp’s procedure is a well established surgery for MED, it is not free of shortcomings. There is no grading in the correction with Knapp’s and there is a large variability in the amount of correction obtained with this procedure, with a tendency to drift towards over correction with time.[11] The correction of horizontal deviation becomes difficult after Knapp’s procedure. The transposed muscle is already maximally stretched which makes resection impossible and doing recession will negate the benefit of surgery. Snir et al compared Knapp’s procedure with Augmented Knapp’s procedure (conventional Knapp’s with posterior fixation sutures on the horizontal recti) in 14 patients of MED. (Figure 7) Mean distance and near deviations decreased by 84% and 83%, respectively (P = 0.012), in the augmented-surgery group versus 48% and 47%, respectively (P = 0.03), in the standard-surgery group. Mean elevation deficiency in abduction and adduction improved by 64% and 65%, respectively (P = 0.01), in the augmented surgery group versus 42% and 55% (P = 0.02) in the standard group. They concluded that augmented Knapp’s is the surgery of choice in MED as it gives superior results to conventional Knapp’s and also avoids the need for re-surgeries.[38] 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.(Figure 8) Cooper et al did Knapp’s procedure with simultaneous resection and recession of horizontal muscles. But the postoperative horizontal corrections were not good. They concluded that the correction of horizontal deviation should be done with the surgery on horizontal recti of normal fellow eye when doing Knapp’s in the affected eye.[33]





IR recession

Recession of a tight IR allows the upward rotation of the globe and orthotropia in primary gaze. It also helps improve a previously poor Bell’s phenomenon.[6] 1 millimeter of IR recession corrects around 3 Prism Diopters (PD) of deviation.[9]

Vertical muscle recession and resection

Early surgical attempts to correct vertical misalignment from MED employed conventional vertical rectus muscle surgery. Beard approached the correction of hypotropia by superior rectus resection and inferior rectus recession with release of the lower lid retractors. The exact amount of resection and recession is not described for correction of hypotropia per se.[34] This procedure spares horizontal muscle for future correction of horizontal deviation.

Contralateral superior rectus recession with a Faden procedure is also described in MED cases by Ficker et al. This is done to increase the drive to the paretic superior rectus which helps in elevation of globe.[35]

Resection of inferior oblique of the affected eye was also done in one patient of MED by Ora Harold Wagman in cases of paralysis or paresis of this muscle but the results were not good.[36]

Resection or tuck of the contralateral inferior rectus has been described in a study done by Samir and Hakim et al where satisfactory result was not seen with Knapp’s procedure.[37] Thirteen patients who were managed by Knapp’s procedure showed worsening of ptosis and poor outcome in terms of correction of hypotropia for which the inferior rectus resection or tuck was done in the contralateral eye 2 months after the Knapp’s surgery.

A good lid height and an improvement in hypotropia were achieved after the procedure.

Planning the appropriate surgery:

Management on the basis of FDT for IR: (Figure 9)

The first step in surgical correction of MED is to confirm the type of MED- restrictive or paralytic. It is done by doing FDT (forced duction test) for inferior rectus.[9] If FDT is positive for IR (Type 1 MED), an IR recession (IRR) with conjunctival recession is done. The eye should now elevate freely if all the adhesions and tight inferior rectus fibres have been severed. FDT is repeated after the inferior rectus is reattached. Elevation of the eye by at least 20-25 degrees should be possible. In cases of secondary IR restriction, the hypotropia will persist after IRR because of primary superior rectus muscle (SR) palsy. In such cases, a Knapp procedure is described with IRR along with conjuctival recession. If vertical deviation is small, and eye is able to elevate above the midline, IR recession combined with SR resection can also be done.[9]







For hypotropia of 25-35 PD, IR recession followed by full tendon vertical transposition of horizontal rectus muscles near the SR tendon is recommended, the two procedures should be performed in two sittings to avoid anterior segment ischaemia. However, if the two procedures are planned at same sitting, ciliary circulation sparing procedure can be done.[9] In cases of hypotropia of more than 35 PD, classic Knapp’s operation with vertical transposition of the full horizontal rectus muscles to the SR insertion + posterior fixation suture on the transposed muscles has been described (augmented Knapp’s procedure).[9] Following the surgical correction of primary gaze hypotropia, 45-55% patients are seen to have an improvement in their Bell’s phenomenon(Figure 10). Associated ptosis and/or Marcus Gunn phenomenon can then be addressed. Figure 11 shows complete management of a patient with MED who underwent IR recession first followed by modified Knapp’s procedure followed by bilateral sling surgery. Treatment 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. In a case of recent palsy one has to wait for at least 6 months to allow for spontaneous recovery.[39] The planning and the surgeries for acquired MED are the same as for congenital MED. Cite

This Article as: Goray A, Kamlesh, Dhiman S, Thacker P, Goel Y, Babita, Rastogi A, Mishra M. Monocular Elevation Deficit-Simplified. Delhi J Ophthalmol 2015;26:7-13.

Acknowledgements: None

Conflict of interest: None


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