Moebius syndrome is now classified within the spectrum of congenital cranial dysinnervation disorders.1 The minimal criteria for diagnosis of this syndrome are congenital facial palsy and limitation in horizontal gaze.2,3 Patients present with a masked face, loss of the nasolabial folds, and lagophthalmus.2,3 Affected patients may have systemic problems, including anomalies of the tongue, limbs, and chest.2,3 Moebius syndrome is categorized into three subgroups according to ocular deviation and limitations in eye movements: pattern A (40% of cases who are orthotropic with limitations in both adduction and abduction), pattern B (50% of cases who are esotropic with severe abduction limitation), and pattern C (10% of cases who are exotropic with limitations in both abduction and adduction).4 Limited data are available on the results of strabismus surgery and most reports discuss patients with pattern B who are esotropic.5–8 In this case series, we describe three patients with pattern C Moebius syndrome and report the technique and outcomes of surgery on two of them. This study was approved by our institutional review board.
A 13-year-old boy was referred because of strabismus from birth. He was born to consanguineous parents and was the result of normal-term delivery. His mother did not have a history of drug use during pregnancy or threatened abortion. The patient's face was expressionless and masked with shallow nasolabial folds. He had mild mental retardation and mild pectus excavatus (Figure 1A).
Photographs of case 1. (A) Pectus excavatus. (B) Expressionless face and large angle exotropia. (C) Improvement in exotropia after strabismus surgeries. (D) Improvement in dry eye after puncti occlusion and tarsorrhaphy in the medial and lateral eyelids of both eyes.
Eye examination revealed decreased lacrimal lake and corneal scars in both eyes. Refractions were −2.25 −1.25 × 180° and −1.75 −1.50 × 10° in the right and left eyes, respectively. Corrected visual acuity in both eyes was 3/10. Both eyes had fixed exotropia of greater than 90 prism diopters associated with severe limitations in adduction and abduction but normal vertical movements (Figure 1B).
We performed bilateral lateral rectus disinsertion to free the forced duction test, which resulted in little improvement in exotropia. After 2 months, we performed bilateral medial rectus resection of 15 mm, which resulted in orthotropia in primary position that persisted up to 2 years (Figure 1C). We also cauterized all lacrimal puncti and performed lateral and medial tarsorrhaphy sequentially to control the dry eye and gain a smooth lacrimal lake, leading to an improved visual acuity of 6/10 (Figure 1D).
A 3-year-old boy was referred to our clinic because of congenital strabismus. He was the result of a non-consanguineous marriage and normal-term delivery. His mother had no history of drug use in pregnancy or threatened abortion. His face was masked and expressionless with significant drooling, and he had weak crying sounds and moderate mental retardation. Other examinations were normal.
Refractions were +1.50 −3.00 × 180° and +3.00 −4:00 × 180° in the right and left eyes, respectively. The patient did not cooperate during visual acuity examination. He had approximately 70 prism diopters of fixed exotropia in both eyes. Abduction and adduction were severely limited in both eyes, whereas vertical eye movements seemed normal. Both eyes had severe dry eye (Figure 2A).
Photographs of case 2. (A) Expressionless face and large angle exotropia. (B) Improvement in exotropia after strabismus surgeries and improvement in dry eye after puncti occlusion and tarsorrhaphy in the medial and lateral eyelids of both eyes.
We performed bilateral lateral rectus disinsertion to free the forced duction test as a first surgery. After 3 months, residual exotropia led to bilateral medial rectus resection of 6 mm, resulting in orthotropia that remained stable for 4 years. Because of severe dry eye, we performed occlusion of all lacrimal puncti and lateral and medial tarsorrhaphy sequentially (Figure 2B). In the patient's final examination, refraction was plano −3.50 × 20° and plano −3.50 × 170° in the right and left eyes, respectively, and the corrected visual acuity of both eyes was 6/10.
A 10-year-old girl was referred to our clinic because of strabismus from birth. She was the result of full-term normal vaginal delivery and her mother had no history of drug use during pregnancy or threatened abortion. She also had masked face and open mouth. Systemic evaluation revealed mental retardation, gait difficulty, and outwardly rotated feet (Figure 3A).
Photographs of case 3. (A) Outward rotated feet. (B) Expressionless face and large angle exotropia. (C) Severe lagophthalmus.
The patient had fixed exotropia of approximately 60 prism diopters in both eyes. Adduction and abduction in both eyes were limited, whereas vertical movements were normal (Figure 3B). She also had severe lagophthalmus and severe dry eye in both eyes (Figure 3C). Visual acuity of both eyes was 2/10. This patient did not undergo surgery.
Alignment in Moebius syndrome may be orthotropic (pattern A), esotropic (pattern B), or exotropic (pattern C).4 In all types, nuclei of the 7th and 6th cranial nerves are damaged. In pattern C, damage to the medial longitudinal fasciculus is more severe than that of the 6th nerve nucleus; therefore, adduction is more limited than abduction and affected patients are exotropic.3,4
In all three cases reported herein, horizontal gaze palsy was present but the patients had normal vertical eye movements. When the lateral recti were disinserted in the first two cases, improvement in exotropia was limited because the medial recti were also severely weak. In these cases, weakening the lateral recti may not be successful and resection of the medial recti may have a tethering effect and add to the effect of surgery.
Results of strabismus surgery in Moebius syndrome have rarely been reported.5–8 In one study on esotropic Moebius syndrome, the weakening of both medial recti was successful.5 It was noted that when the esotopia is greater than 50 prism diopters and abduction limitation is severe, transposition of the vertical recti with or without lateral fixation is necessary.6 Resection of the lateral rectus muscles has also been reported.7 We did not find any report on the results of surgery on patients with exotropic Moebius syndrome.
According to concurrent fibrosis and weakness of the extraocular muscles, finding an appropriate and predictable surgery in Moebius syndrome is difficult. On the other hand, because of reports of overcorrection,8 transposition of the vertical muscle may not be an appropriate approach.9,10 It seems logical to perform stepwise operations in these cases similar to those performed in our study.
Because of their masked face, difficulty speaking, and frequent apparent anomalies, patients with Moebius syndrome have low self-esteem and may also have behavioral and psychological abnormalities.11 In addition to improving binocular function, strabismus surgery can also improve patients' quality of life and social relations. This was seen clearly in our cases after surgery.
Lacrimal nuclei in the brain stem may be involved in Moebius syndrome4,12; thus, dry eye and its consequences in these patients require special attention. Such symptoms may lead to corneal scarring and irregularity, as observed in our patients.
Maximal weakening of the lateral rectus muscles followed by strengthening of the medial recti in exotropic Moebius syndrome can improve exotropia significantly. Most of these cases also need some measures to relieve the often associated severe dry eye.
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