Summary
Duane’s syndrome is a common form of the congenital cranial dysinnervation disorders. The ocular motility pattern presents in a wide clinical spectrum, and the choice of treatment needs to be individualized depending upon the severity of the clinical findings. There is no perfect method of treatment and no real “cure” in Duane’s syndrome. In this chapter, etiologic factors that may influence surgical results, goals of treatment, and surgical treatment methods with possible results will be reviewed with a decision-making approach.
15 Duane’s Syndrome
15.1 Introduction
Duane’s syndrome (DS) is a congenital ocular motility disorder characterized by abduction deficiency with variable limitation of adduction and globe retraction on adduction that may be in association with oblique elevation or depression. 1 Duane’s syndrome represents 1 to 4% of the strabismic population, with left eye and female predisposition. In recent years it has been accepted as a disorder within the congenital cranial dysinnervation disorders (CCDDs). 2 Duane’s syndrome may be bilateral and nearly 10% of the cases are familial. It may present in association with other systemic or ocular problems, but the majority of cases are sporadic and isolated.
15.2 Etiology
Duane’s syndrome includes the problems of both restrictive and innervational abnormalities. Electromyographic (EMG) studies have demonstrated the paradoxical contraction of lateral rectus (LR) muscle on adduction. 3 , 4 , 5 It is well understood that DS is primarily an innervational disorder with secondary restrictive problems. This was proven by histopathologic studies that clearly demonstrated the absence of abducens nucleus as well as partial innervation of the LR muscle by branches of the oculomotor nerve. 6 , 7 , 8 The number of cases documented histopathologically has been limited, and it is therefore not possible to obtain this information for all types of DS. Magnetic resonance imaging (MRI) studies have added an enormous amount of information in DS. Large numbers of DS patients with broad clinical spectra have been studied with MRI, leading us to understand the variable manifestations of abnormal ocular motor nerve development. 9 , 10 , 11 In our previous study with the early technological capacity of MRI, we could only demonstrate the abducens nerve on the normal side of 2 out of 10 patients, but we had been able to demonstrate that the extraocular muscles (EOMs) appeared the same as normal controls. 12 With the rapid improvement of MRI technology, it has recently become possible to obtain reliable and precise information about the absence or presence of cranial nerves and the nerve supply to the EOMs. Kim et al 13 demonstrated that the abducens nerve was absent in all cases with type 1 DRS DS, was present in all type 2 patients, and was either absent or present in type 3 DS. The affected LR muscle is not a paretic muscle but is actually a malinnervated muscle. This prevents the development of denervation atrophy and provides tonic contraction of the LR muscle in its resting position. The absence of denervation atrophy in the dysinnervated LR muscle has also been confirmed with other MRI studies—a valuable finding, which may serve as a clue to rule out sixth cranial nerve palsy from the differential diagnosis. 12 , 14 , 15
The genetic background of DS was studied with genetic mapping in familial, isolated DS. 16 DS has been accepted as a common form of the CCDDs. Associated abnormalities and the connection of DS with thalidomide embryopathy suggest a teratogenic effect during the second gestational month. No common maternal factor has been been demonstrated to date in isolated DS. 17 We have seen a case of isotretinoin teratogenicity associated with DS.
15.2.1 Classification
DS may present with a wide spectrum of clinical forms and severity. In Huber’s well-known classification, 2 DS is divided into three types. Although other classifications have been proposed, Huber’s classification (which is primarily based on the functional capacity of abduction and adduction) is still the most widely used, facilitating understanding of the disorder. The features of these three types are summarized as follows.
15.2.1.1 Type 1
In type 1 DS, there is marked limitation of abduction, and normal or slightly defective adduction with globe retraction on adduction. The LR muscle does not contract on abduction, and maximal contraction of the LR muscle is on adduction. This is the most common type of DS.
15.2.1.2 Type 2
In type 2 DS, there is marked limitation of adduction, and normal or slightly defective abduction with globe retraction on adduction. The LR muscle contracts in both abduction and adduction. Exodeviation is more common in this type of DS.
15.2.1.3 Type 3
In type 3 DS, there is marked limitation of abduction and adduction with globe retraction on adduction. Both the LR and medial rectus (MR) muscles contract in abduction and adduction.
All types of DS may present with orthophoria in primary position. There is a tendency toward esodeviations in type 1 and exodeviations in type 2, but this is not a rule.
In most DS cases the main EMG abnormality is paradoxical contraction of the LR muscle. The innervational pattern in DS is not as straightforward as described in Huber’s classification. Small variations, such as paradoxical co-innervation of the LR and vertical rectus muscles, result in variable ocular motility. Paradoxical cocontraction of the LR with one or both vertical rectus muscles presents with better abduction on upgaze and/or downgaze. Previous EMG studies showed paradoxical contraction of the MR, inferior oblique (IO), and vertical rectus muscles in typical forms of DS, but the contribution of abnormal contraction of these muscles has not received much attention in the ophthalmic literature. 3 , 4 , 5 , 18
15.2.2 Atypical Duane’s Syndrome
Huber’s classification does not include all of the clinical types of DS, and those cases that do not fit the typical forms are termed “atypical DS” in the literature. Atypical forms of DS may present in an isolated manner or in combination with typical clinical forms.
15.2.2.1 Synergistic Divergence (Simultaneous Abduction)
Synergistic divergence (simultaneous abduction) is an atypical form of DS, characterized by divergence on attempted adduction. EMG data demonstrated cocontraction and excessive LR firing on adduction unopposed by the weak MR muscle. 19 Synergistic divergence may also be associated with congenital fibrosis of extraocular muscles (CFEOM). 20 , 21 The fibrotic changes appear to be secondary to innervational abnormalities in both CFEOM and DS, so it may be suggested that these two ocular motility disorders are varieties of the same clinical CCDD spectrum.
Synergistic divergence may be considered as an exaggerated form of type 2 DS, and it may also develop iatrogenically following excessive MR weakening in type 1 DS.
15.2.2.2 Vertical Retraction Syndrome
Vertical retraction syndrome is another atypical form of DS. These patients may have the features of a horizontal DS plus globe retraction on vertical positions of gaze, with or without limitation of vertical eye movements. We performed EMG in a case with type 1 DS plus globe retraction on adduction, elevation, and depression, and demonstrated paradoxical contraction of vertical rectus muscles on elevation, depression, adduction, and attempted abduction. In a similar manner, Scott 4 demonstrated abnormal activity of the superior rectus (SR), inferior rectus (IR), and IO muscles on adduction.
15.2.2.3 Y-Pattern Deviation
Y-pattern deviation is another form of atypical DS. Kushner 22 demonstrated paradoxical contraction of the LR muscle in a Y-pattern deviation and suggested that it was a variant of DS. Those cases are characterized by elevation of the adducting eye and a sudden upshoot beyond a certain point. It is termed “pseudo–inferior oblique overaction” by Kushner. 22 We reported on a group of four patients with Y-pattern deviation, and our results also confirmed it as a variant of DS. 23 We also demonstrated that the IR muscle as well as the LR muscle may be cocontracting. 23 , 24 In our cases the paradoxical contraction of the IR muscle was demonstrated either by EMG or by kinematic MRI examination.
Upshoots and downshoots on adduction are considered secondary to the leash effect of paradoxically contracting fibrotic LR muscle. 25 We suggested that the mechanism of the Y pattern with a cocontracting IR muscle is similar to the mechanism of upshoot on adduction. 24 If a cocontracting LR muscle may cause an upshoot on adduction, then a cocontracting IR muscle may cause abduction on elevation—a similar condition just rotated 90 degrees clockwise.
15.2.2.4 Enlarging Huber’s Classification
In an attempt to demonstrate some common clues among atypical forms of DS, we reported on nine patients with atypical DS. 26 Four of these patients had no globe retraction, and three had paradoxical contraction of vertical rectus muscles. Our findings suggested that globe retraction is not a common abnormality in atypical DS. We also demonstrated that globe retraction may not be present in every case of typical DS. 27 We concluded that the term retraction syndrome does not include all types of DS and suggested the terminology of simply “Duane’s syndrome.” We recommended enlarging Huber’s classification to include the atypical forms as follows 26 :
Type 4: synergistic divergence.
Type 5: vertical retraction syndrome.
Type 6: Y-pattern deviation.
A seventh category, the “unclassified” type, is necessary, as even more atypical forms may be observed in DS. We previously reported a case with λ–pattern exodeviation and globe retraction on adduction. 28 In this case kinematic MRI examination demonstrated bilateral accessory EOMs below the optic nerve that produced paradoxical contraction on downgaze. Even more interesting was that this case also had bilateral IR hypoplasia. This was the first documented case of paradoxical contraction in an accessory EOM.
Problems with Huber’s classification include the lack of reference to primary position deviation, lack of descriptors of upshoots and downshoots, and overlap between type 1 and type 3 cases. Although Huber’s classification does not perfectly cover all of the cases and does not refer to the type of the deviation, it remains a useful tool to document DS cases (especially with our suggested additions).
15.3 Common Clinical Features
In DS the major clinical finding is limitation of abduction and/or adduction, associated with esotropia, exotropia, or orthophoria (Fig. 15‑1). Vertical deviation on adduction as an upshoot and/or downshoot is common in DS. The etiology is a tethering effect of the paradoxically contracting inelastic LR muscle, causing instability of the globe on adduction (Fig. 15‑2). During upshoots and downshoots there is also a small limitation of adduction related to the paradoxically contracting tight LR muscle. Although it is not common, vertical deviation in primary position may also be observed in DS, suggesting paradoxical contraction of the vertical rectus muscles. Coexistence of dissociated vertical deviation (DVD) may also be observed as another rare combination.
Globe retraction is the other major typical finding. Although it is highly diagnostic for DS, its absence does not rule out the diagnosis. Globe retraction presents in a wide clinical spectrum. It may be severe with a disfiguring enophthalmic appearance on adduction and may even be observed in primary position in a lesser degree, but it may also be very mild or absent. In those cases with minimal to no globe retraction, the differentiation from sixth cranial nerve palsy may prove complicated, especially in infants. Helpful clues to differentiating DS from sixth cranial nerve palsy include a smaller than expected deviation in primary position given the magnitude of the abduction deficiency. Even eyes with severe abduction deficiency due to DS may remain orthophoric. Due to paradoxical contraction of the LR muscle on adduction, there is usually a small exotropia on adduction despite limitation of abduction. Sixth nerve palsy would cause a large esodeviation in primary position and no limitation of adduction.
Abnormal head posture is another common clinical feature of DS. Upshoots and downshoots on adduction and alphabetical patterns are also frequent. Children with DS require regular follow-up to rule out and treat amblyopia, which is also common. Most DS patients have good binocular function, as many of them are orthophoric in a certain position of gaze (possibly with abnormal head posture).
Although motility in DS is usually stable, it may worsen over time in some patients. Due to increased muscle fibrosis, upshoots and downshoots may appear later in life. Abduction limitation may increase due to increased MR fibrosis, causing head posture to worsen.
15.4 Treatment
As with all other types of strabismus, refractive correction and amblyopia treatment is the first step of treatment. In some patients there may be a coexisting accommodative element contributing to esodeviation, and correction of refractive error may eliminate or decrease the primary position deviation, as well as occasionally a small abnormal head posture.
If any surgery is planned the surgeon must be ready for surprises, since DS combines dysinnervation with restriction, and the EOMs do not behave the same as in concomitant strabismus. The general principle is not to operate without clear-cut indications. The usual dose–response relations cannot be applied in DS. Abnormal features of the EOMs, such as paradoxical contraction and tightness, have great interindividual variability. As the predictability of surgical outcome is low compared to conventional strabismus surgery, adjustable sutures are preferred when possible. There is a downside to all normal EOM procedures in DS. Recessions usually cause a gaze limitation in the functional field of action, and resections are avoided due to the high risk of increasing restrictions. Transpositions carry the risk of increased globe retraction and secondary vertical deviations.
In both typical and atypical forms of DS, paradoxical contraction of EOMs other than the LR may be present, and this may also affect accessory EOMs. These complexities must be taken into account when planning surgery.
The goals of surgical correction are to eliminate the primary position deviation and abnormal head posture, to center the diplopia-free field, and to reduce upshoots and downshoots. Secondary surgical goals are to reduce globe retraction, to improve ductions, and to enlarge the binocular field of single vision.
Treatment options include recession of the appropriate horizontal rectus muscle of the affected eye and, when necessary, the sound eye; asymmetrical recession of both horizontal recti of the same eye; transposition of the vertical rectus muscles; and LR inactivation by periosteal fixation.
15.4.1 Recession of One Horizontal Rectus Muscle of the Affected Eye
Advantages.
Decrease in the deviation in primary position.
Decrease in abnormal head posture.
Disadvantages.
Possible limitation of adduction.
Possible decrease in binocular field of single vision.
No significant improvement on abduction.
No decrease in globe retraction.
No decrease in upshoot/downshoot.
Indications.
Horizontal deviation.
Minimal or no globe retraction.
No upshoot/downshoot.
This is the simplest approach to management of DS with favorable results, but it also has limitations. 29 , 30 , 31 , 32 Most patients with DS have some degree of adduction limitation, which is identified by a small exodeviation on adduction. As MR recession increases limitation of adduction, this may cause a troublesome narrowing of the binocular field of single vision. Recessed muscles in DS are usually tight muscles and do not exhibit the same surgical dose–effect relationship as in concomitant strabismus. Recession of tight muscles produces larger corrections of deviation per millimeter of recession. It is therefore difficult to plan the amount of recession. Too much recession may cause the paradoxical contraction of the LR to dominate over the MR contraction and lead to iatrogenic synergistic divergence. 32 The amount of recession is determined with the forced duction test during surgery, recessing just the amount that allows free passive movement of the eye. In some cases orbital fibrosis may develop, even with a moderate angle of deviation, resulting from the constant adducted position and the abnormal head posture. Those cases usually require conjunctival recession (Chapter 28 Managing Excessive Scar Tissue (Adhesive Syndrome)).
If the deviation is large, recession of the appropriate horizontal rectus muscle in the sound eye may be considered. 30 , 33 , 34 However, surgery of the yoke muscle of the sound eye must be approached with caution. Paradoxical contraction of the LR or vertical rectus muscles may cause unexpected motility results. 35 , 36
15.4.2 Asymmetrical Recession of Both Horizontal Rectus Muscles of the Affected Eye
Advantages.
Decreased primary position deviation.
Decrease in abnormal head posture.
Possible decrease in globe retraction.
Possible decrease in upshoot/downshoot.
Disadvantages.
No significant improvement of abduction.
Possible decreased adduction.
Possible decrease in binocular field of single vision.
Technical difficulty, as the operative site is posterior.
Indications.
Cases with horizontal deviation and moderate to severe globe retraction.
Upshoots/downshoots—combined with Y-splitting of the LR muscle.
In this type of recession both horizontal rectus muscles are recessed, usually about 5 mm, with additional recession of one of the muscles to account for the deviation, in combination with Y-splitting of LR muscle when necessary. 37 , 38 , 39 , 40 , 41 Recession of both horizontal rectus muscles is the most commonly used DS procedure in our clinical practice. Our results demonstrated that recession of both horizontal rectus muscles decreased globe retraction in 75% of patients, as well as decreasing upshoots/downshoots, primary position deviation, and abnormal head posture (Fig. 15‑3, Fig. 15‑4). 38 In our series, we concluded that transposition surgery should be reserved for those with minimal globe retraction due to the subclinical abnormal innervation of vertical rectus muscles and the risk of increased globe retraction. 38
In both single muscle recession and recession of both horizontal rectus muscles of the DS eye, forced duction testing must be repeated after disinsertion of the MR or LR muscle due to the possible accessory tissue bands that restrict ocular movement. These tissue bands may be thin and translucent and can be “felt” on forced duction test. According to Gobin 42 the incidence of such bands is 34.3% in DS cases. The excision of the tissue band allows free forced duction testing. Such bands may readhere to the globe, so it is preferable to excise them (Fig. 15‑5).
15.4.3 Resections of Horizontal Rectus Muscles
As previously mentioned, is best to avoid resections in DS, but in esotropic DS with minimal globe retraction, ipsilateral recess-resect surgery is reported to be successful if the resection is kept under 3.5 mm. 43 In our experience, resection of the MR muscle may work in selected cases of type 2 DS. The forced duction test must be negative for the muscle resection to be considered. Even a small resection in a paradoxically contracting fibrotic EOM may cause unexpected results, and adjustable sutures are advised.
15.4.4 Transposition of Vertical Rectus Muscles (Usually Combined with Medial Rectus Recession)
Advantages.
Possible increased abduction.
Possible increased binocular field of single vision. 28
Disadvantages.
Possible increased globe retraction.
Risk of anterior segment ischemia related to combined MR recession.
Possible decreased vertical muscle function.
No decrease in upshoot/downshoot.
Possible restriction on adduction that may be exacerbated by augmented transpositions.
Indications.
Cases with horizontal deviations and with minimal or no globe retraction.
Severe limitation of abduction.
No globe retraction on up and down gaze.
No upshoot/downshoot.
Transposition surgery is usually combined with MR recession, and it may be performed as full tendon or half tendon transposition. Rosenbaum 44 reported that temporal transposition of the vertical rectus muscles may induce vertical deviation. Addition of Foster augmentation sutures increases the tightening and abducting effect. 45 , 46 Vertical deviations and increased cocontraction was reported in 8.5 to 30% of cases, and consecutive exodeviation in 25.5%. 47
Transposition of the SR muscle alone may be performed with or without MR recession. 48 , 49 , 50 Augmentation sutures are also possible with this technique. SR muscle transposition is reported to have an effect similar to transposition of both vertical rectus muscles. Induced incyclotorsion is a potential complication of this technique. In our clinical practice, we use transposition surgery when we plan to perform LR periosteal fixation.
Editor’s Comment
Some of the problems seen with transposition of the vertical rectus muscles, namely inadequate improvement of gaze and induced vertical strabismus, may occur due to healing abnormalities. The vertical rectus muscles are strong and subject to scar migration and scar stretch (Chapter 5, Chapter 27). Small resections prior to transposition will enhance the transposition effect, and of course, the use of augmentation sutures, which displace the pulleys, is another aid. However, it needs to be considered that both of these aids carry the risks of increasing globe retraction and restrictions on adduction in an eye with DS. Half tendon transfers are prone to failure due to the powerful rejoining of the cut ends during wound healing with induced scar tissue formation, and are not totally safe from anterior segment ischemia.
Another useful approach, after having achieved centration and maximal abduction of the type 1 DS eye, is to restrict adduction of the fellow eye without impacting its primary position alignment. These concepts are discussed in Chapter 33.
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