Botulinum toxin augmentation as a sequential procedure for residual esotropia in traumatic sixth nerve palsy

Dear Editor, W e want to describe the surgical outcome of a patient with residual esotropia due to sixth nerve palsy with re-resection of the lateral rectus combined with botulinum toxin injection to previously recessed ipsilateral medial rectus. Sixth nerve palsy may be vasculopathic, traumatic, neoplastic, idiopathic and congenital in origin. In acute traumatic cases, greater abduction deficit at onset and bilaterality may negatively contribute to recovery rate. Many surgical approaches have been proposed to be effective in the treatment of chronic cases. Botulinum toxin may be used in combination to surgery in order to regain binocular single vision and to warrant good ocular alignment. We report a case with chronic sixth nerve palsy which was successfully treated with botulinum toxin and repeated surgery. A 45-year-old female presented with double vision after a motor vehicle accident 8y ago. On examination, visual acuity in both eyes was 6/6. The anterior and posterior segment evaluation disclosed no abnormality. She had a previous history of unilateral recession and resection surgery (left medial rectus recession of 7.5 mm and left lateral rectus resection of 9 mm) one year prior to her current presentation. She had 52 prism diopters (PD) left residual esotropia, face turn to the the left, diplopia in primary position and on the left gaze, -4 limitation in abduction on the left eye (Figure 1). Ocular movements were normal on the right eye. She had severe hypotension and bradycardia which required pacemaker application. A surgical exploration exhibited that left medial rectus insertion was at 13.5 mm from limbus and its forced duction test was strongly positive. She was submitted to ipsilateral re-resection of the lateral rectus (5 mm more) combined with 4 units of botulinum toxin A injection (Botox, Allergan, USA) to the medial rectus under direct visualization. At first day postoperatively, the left upper eyelid was ptotic, the patient had 12 PD esotropia in primary position and -3 limitation in left abduction. Six months after the operation, marked improvement of the ocular alignment in primary position was observed (Figure 2). The patient had 12 PD left esotropia and -3 limitation in abduction on the left eye. She was still diplopic on the primary position but single vision was achieved with 10 PD prismatic spectacle correction in primary position. The management of chronic sixth nerve palsy is challenging in terms of many contributing factors such as large angle deviation, disabling diplopia and contracture of the ipsilateral medial rectus which all complicate the treatment course individually. Various surgical procedures comprise recessionresection, augmented/unaugmented single/double vertical muscle transpositions with/without simultaneous weakening of the ipsilateral medial rectus and botulinum toxin injection to adress complete/incomplete sixth nerve palsy. Data on forced duction test and the extent of abduction deficit are among the main determinants of the type of surgery and in