Duane’s retraction syndrome (DRS) is a congenital complex strabismus. This condition was first described by Stilling in 1887. However, it was later made popular by Alexander Duane who published a series of 54 patients having this condition. The frequency of this syndrome in the general population of strabismus patients is 1–4%.[1] DRS is included in a group of disorders called Congenital Cranial Dysinnervation Disorders (CCDDs).[2] These are secondary to some neurologic pathology of congenital origin and have a wide spectrum of phenotypic presentation. This wide spectrum results due to either primary or secondary dysinnervation.
Etiopathogenesis: A maldevelopment or any insult to the development of the sixth nerve nucleus at 4 to 8 week of gestation has been shown to be the causative factor in the development of this disease process.[3] The branches of the third nerve, in turn, are redirected to the lateral rectus. This abnormal or paradoxical innervational impulses to the horizontal recti are the basis pathology of this disease.The lateral rectus(LR) may exhibit may exhibit a spectrum of abnormal innervational pattern ranging from paradoxical to the subnormal innervation. In a few cases, even the medial rectus(MR) may have subnormal innervations owing to the redirection of developing nerve fibres to the sixth nerve. Secondary muscle changes may occur in form of contracture of medial rectus and superior rectus as a result of constant esotropia and upshoots respectively.
Clinical features and diagnosis: The diagnosis of DRS is usually clinical. Molecular genetic testing is being investigated for this disease, however, it remains in infancy. It involves single gene testing using sequential and deletion/duplication analysis of the CHN1 gene.[4] This disease has been differentiated into three subtypes on the basis of myography by Huber.[5] Apart from these it can also be classified on the basis of the primary position deviation into eso DRS, exo DRS and ortho DRS. MRI imaging has shown the absence of abducens in many studies.[6],[7] DRS is characterised by the limitation of abduction and /or adduction along with a narrowing of palpebral aperture and retraction of the globe and variable upshoot and downshoot of the globe on attempted adduction. The patients may also have a face turn to achieve binocularity.
Other ocular findings may include nystagmus, anisocoria, ptosis, epibulbar, dermoidcongenital cataract, heterochromia and optic nerve hypoplasia. DRS has also been shown to be associated with gustatory lacrimal reflex or crocodile tears. The clinical features may vary case to case and one may see a myriad of presentations. Several syndromic associations of DRS have been noted out of which the most common ones include Goldenhar syndrome, Klippel – Fiel anomaly and Wildervanck syndrome. Major differentials of this condition include sixth nerve palsy, Moebius syndrome, infantile esotropia and congenital oculomotor apraxia. However, these conditions can be ruled out on the basis of the absence of characteristics like globe retraction, narrowing of the palpebral aperture on attempted adduction and upshoots or downshoots. A simple patch test can rule out the presence of infantile esotropia.
Sugical management:
The primary indication for surgery in DRS is the correction of primary position deviation and face turn. Apart from this surgery can also be done to ward off cosmetically unacceptable globe Retraction and upshoots or downshoots which are present as a result of severe co-contraction of LR and MR on attempted adduction. While planning surgery, it is important to look for any contracture in medial and lateral rectus by doing force duction tests. The presence of anomalous lateral rectus activity can be detected by the help of force degeneration test of Romero-Apis. This test is extremely useful in confirming co-contraction in adduction and the missing LR innervation on abduction and thus helps in deciding the plan of surgery. If binocular vision is present with cosmetically acceptable ocular appearance, surgery must not be undertaken just for improving the abduction limitation.
Eso DRS
Classic eso DRS cases do not have normal LR function, but anomalous action occurs during adduction. These patients have an esodeviation in the primary position and as a result, they assume a corrective face turn. A single medial rectus recession (Figure 1) can be done in the affected eye in case of deviations less the 20PD.[8] Other treatment options include asymmetric MR recessions or transposition surgeries in form of vertical rectus transpositions. Asymmetric MR recession can be done in the good fellow eye to produce a fixation duress without fearing adduction deficiency in the good eye. This not only corrects the primary position esotropia but it also decreases the likelihood of contracture of the medial rectus in the affected eye through the fixation duress in the right eye which leads to a continuous inhibition on affected eye’s MR. However, before planning any surgery in DRS, it is imperative to check force duction test to rule out MR contracture in the affected eye as a tight MR should always be recessed. One must take care to never resect lateral rectus or medial rectus in the involved eye.
Superior rectus transposition (SRT) or a vertical recti transposition (VRT) to lateral rectus to achieve an abduction force can be done if there is no anomalous LR recruitment. The combination of SRT and MR recession has been found to be more effective than MR recession or bilateral MR recession at improving abduction while allowing for a smaller recession to align the eyes and eliminate a compensatory head posture.[9] However, in cases with uncorrected severe anomalous LR recruitment, any transposition procedures are not indicated. And in case the MR and LR are both to be operated adding the SRT is fraught with the danger of anterior segment ischemia. In cases where the affected eye is the fixing eye, surgery should be performed in the affected fixing eye to ward off the large secondary deviations that occur in non- fixing eye.
In cases with minimal anomalous LR activity and normal LR abducting force, a MR recession in the affected eye may suffice. Those with anomalous LR activity should be tackled by LR weakening procedures. The abduction deficit can be tackled by transposition procedures like SRT[10] (Figure 2) and VRT, however we prefer a balanced partial VRT to SRT as the latter has risk of vertical incomitance and inducing torsion . In cases with significant upshoot or downshoot, the co-contraction can be countered by the recession of both LR and MR of the affected eye. Another strategy is lateral rectus recession with Y split.[11] In this procedure the LR is split from its insertion to 18-20 mm posteriorly and the two halves are placed at a distance of 20 mm apart. This procedure has been shown to be effective in tackling severe upshoot and downshoot.
Exo- DRS:
These patients present with a primary position exotropia and may have upshoots or downshoots along with deviation. Such patients can be tackled by a LR weakening in form of supramaximal LR recession or a periosteal fixation of lateral rectus to the medial rectus. In cases where supramaximal recession fails to redress the exodeviation, lateral rectus of the normal eye can be recessed to achieve successful outcome. (Figure 3) A LR recession with Y split is also an option is cases with normal LR activity where the upshoots and downshoots are a problem (Figure 4). It may be noted that the LR recession should be substantial to correct the retraction in adduction, as the Y split per se does not affect the retraction. The PF wards off the anomalous LR activity most substantially. Some authors have even suggested extirpation of the lateral rectus[12],[13]! The resultant lack of abduction can be taken care of by transposition procedures to LR. A standalone PF may lead to consecutive esodeviation in a few cases which can be corrected by the help of transposition procedure like VRT(Figure 5). A study done at our centre has shown LR periosteal fixation to be effective surgery to correct the exodeviation, anomalous head posture and improving adduction in Exo DRS and partial VRT in addition to be effective in improving abduction and binocular single visual field.[14]
Ortho DRS: These patients are orthophoric in position deviation. These patients may still have symptoms like palpebral aperture narrowing and upshoots which may be cosmetically disfiguring. The treatment in such cases may lead to a consecutive heterotopia as such should be tackled only by the experienced surgeons. The author manages such patients by the symmetrical recession of both lateral and medial rectus in the affected eye in presence of co-contractions with the use of adjustable surgery on one muscle to control the risk of undesirable under or over corrections.(Figure 6)
Bilateral DRS: Bilateral DRS is seen in 15% cases and most of them are either eso or ortho DRS.[15] This disease may present as an asymmetric entity as well. In patients with bilateral DRS with fusion (binocularity) the eyes may be aligned in primary position with straight head or there may be presence of deviation along with head posture. In these cases all four horizontal recti need to be recessed depending upon the deviation in primary position. These can be managed on the basis of similar principles as the unilateral cases. These cases are treated as unilateral DRS and balancing of MR and LR forces is done depending on the deviation governed by the dominant eye. Bilateral eso DRS can be managed by bilateral MR recessions.(Figure 7) Bilateral exo DRS are quite rare and bilateral LR recessions have been recommended for its management. LR Y split can be added in cases with marked upshoots.
CONCLUSION: As a result of its varied clinical presentation, the treatment of DRS should be individualised for the patients.With the advent of newer transposition techniques the surgical outcomes have improved. These newer techniques not only help in achieving deviation free primary position but also ensure the improvement in the binocular field of vision. One must remember to follow the simple prescription for strabismus management that is, observation, confirmation, inference, planning, and finally excecution.[16]