ABSTRACT

Symptomatic excyclotorsion is an important clinical problem, especially in acquired superior oblique muscle palsy. Excyclotorsion can disrupt the fusion and cause torsional diplopia. Harada-Ito surgery (HI) is a widely used method for treating excyclotorsions. This method relieves the torsional diplopia by increasing the effect of the incyclotorsion. In this study, we aimed to report the clinical features of patients with torsional diplopia due to acquired trochlear nerve palsy and the results of HI surgery in these patients.

Introduction

The Harada-Ito (HI) procedure is a strabismus surgical technique developed to treat torsional diplopia caused by excyclotorsion resulting from superior oblique (SO) muscle palsy. The main indication for the procedure is acquired trochlear nerve palsy following closed head injury, particularly due to traffic accidents.¹ In acquired SO palsy, torsional diplopia occurs as a result of weakened intorsional effect and the greater extorsional effect of the inferior oblique (IO) muscle. The HI procedure is an effective surgical method, especially in cases of bilateral SO palsy with a large amount of torsion.² In the original technique described by Harada and Ito⁴ in 1964, the anterior fibers are advanced anteriorly without disinsertion.³ In 1974, Fells modified the technique and described the form that is commonly used today.^3,5 In this modified technique, the SO muscle tendon is bisected and the anterior fibers are disinserted and transposed anterolaterally to increase the intorsional effect.⁵ The procedure can be applied unilaterally or bilaterally, depending on amount of torsion and laterality. In 1981, Metz and Lerner described the use of an adjustable suture technique with this procedure.⁶

Although there are internationally published studies concerning HI surgery, to the best of our knowledge there is no nationally published study on this subject. The existing publications are mostly from retrospective studies and the surgical techniques are usually described in these reports in writing or illustrations.^1,2,3,4,5,6 In this study, we aimed to report the clinical features and outcomes of HI surgery in three patients who developed torsional diplopia due to acquired trochlear nerve palsy. In addition, one of our patients was evaluated with pre- and postoperative tests together with images showing the technique in order to make this rarely practiced surgical procedure more comprehensible.

The medical records of three patients who underwent the HI procedure due to torsional diplopia were retrospectively evaluated. Written consent forms were obtained from all patients prior to surgery. Medical procedures, data collection, and all stages of the study were carried out according to the Declaration of Helsinki and ethics committee approval was obtained.

For all patients, detailed medical history, examination findings, and the etiology, clinical presentation, and duration of disease were recorded. Visual acuity, anterior and posterior segment findings, eye movements, angle of deviation, abnormal head positions, oblique muscle functions, and amount of torsion were assessed pre- and postoperatively. Deviation was measured with a prism cover test, torsion was measured by double Maddox rod test, and extraocular muscle function was assessed using a Hess screen. Diagnosis of SO palsy was made based on limited depression on adduction, IO hyperfunction, V-pattern, hypertropia, abnormal head position, excyclotorsion findings, and medical history. Patients who had symptoms for at least six months underwent surgical treatment.

All patients underwent Fells’ modified HI procedure. A conjunctival incision was made in the superotemporal quadrant 8 mm from the limbus, the superior rectus (SR) muscle was isolated and the SO muscle was exposed from the lateral side. The SO tendon was split longitudinally 10 mm posterior from the insertion. The anterior fibers were separated from the insertion by suspending with 6.0 vicryl suture. The lateral rectus (LR) muscle was then isolated using a muscle hook and the anterior fibers of the SO tendon were sutured to the sclera adjacent to the superior margin 8 mm posterior to the LR insertion.

Discussion

The long intracranial course of the trochlear nerve makes it especially prone to injury in closed head traumas. Acquired trochlear nerve palsy may cause symptomatic excyclotorsion, also referred to as torsional diplopia, which is rarely seen in congenital cases.⁷ Managing patients with this complaint is difficult. The main goal of surgical treatment in these patients is to provide single vision in primary and downgaze and to correct abnormal head position.⁷ While various surgical techniques have been described for the treatment of SO palsy due to acquired trochlear nerve injury, the modified HI procedure is very effective in reducing excyclotorsion and treating torsional diplopia.⁷ In the modified HI technique, the anterior fibers of the SO muscle are transposed anterotemporally, strengthening the intorsion effect of the muscle.²

In our study, HI surgery was successfully performed on five eyes of three patients with torsional diplopia. Postoperative diplopia was not observed with distant or near fixation in the primary gaze position. However, surgical success rates of 43-68% have been reported in previous studies.^2,3 Preoperatively, our patients exhibited abnormal head positions they had developed to prevent diplopia and achieve fusion. We found that in all cases, head position was improved and fusion achieved postoperatively. Bradfield et al.⁸ demonstrated that the presence of fusion prior to surgery was associated with surgical success.

Another factor determining surgical success is preoperative amount of torsion. Bradfield et al.⁸ reported that surgical success increased as the amount of torsion decreased. Torsion usually does not exceed 10 degrees in unilateral SO palsy; as in our third case, patients with complaints of diplopia occurring immediately after head trauma later report unilateral hypertropia.¹ In these patients, SR recession or IO muscle weakening to correct hypertropia can be performed concurrently with the HI procedure to correct torsion. Our third patient, whose right eye was hypertropic in addition to having 10 degrees of torsion, underwent HI surgery and concurrent SR recession due to the absence of IO hyperfunction. Patients with more than 10 degrees of excyclotorsion are usually symptomatic, as in our other 2 cases. Such patients have a chin down head position, and bilateral SO muscle palsy should be suspected.² Together with a history of head trauma, examination findings of V-pattern, more than 10 degrees of excyclotorsion, and left hypertropia in right gaze and right hypertropia in left gaze are suggestive of bilateral SO palsy.¹ Managing bilateral acquired SO palsy may be difficult because of the considerable amount of torsion, but bilateral HI surgery can successfully reduce extorsion and alleviate symptoms in these patients.² To improve the success of surgical treatment, the HI procedure should be used in patients with primary complaints of torsion in particular.

Taking into account coexisting vertical and horizontal deviations, V-pattern, and IO hyperfunction during surgical planning influences surgical success. Tendon transposition of the rectus muscles, inferior or superior rectus recession, and IO muscle weakening surgery to correct V-pattern can also be performed together with the HI procedure.

As with our second patient, there are patients who postoperatively develop limitation of movement in the IO muscle field and diplopia on upgaze, similar to Brown’s syndrome.⁸ Patients undergoing surgery should be informed about complications such as iatrogenic restriction and under- or overcorrection. As in our first case, intorsion may develop in the early postoperative period following HI surgery for symptomatic extorsion. Intorsion usually regresses during follow-up. Postoperative recurrence of symptomatic extorsion has been reported in several studies; therefore, an overcorrection of up to 10 degrees of intorsion is recommended.^2,3,9 Residual excyclotropia occurring later in the postoperative period, as in our second case, is common.^1,3,9 It has been reported that patients with acquired cyclotropia exhibit retinal sensory reorientation to overcome torsion and are only symptomatic in dissociated environments.¹⁰

Limitations of our study include the fact that it was a retrospective chart review. In addition, statistical analyses could not be done due to the small number of patients and paucity of data, and follow-up was short.

In conclusion, HI surgery successfully treated torsional diplopia, especially in primary gaze position, in all three of our patients. Preoperative amount of torsion and the presence of fusion can affect surgical success. Prior to surgery, patients should be informed that diplopia may persist postoperatively, especially in downgaze, that this may necessitate an additional intervention or the use of prisms, and that iatrogenic Brown’s syndrome may develop and cause diplopia in upward gaze.