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Letters to the Editors
Congenital Bilateral Medial
Rectus Muscle Aplasia
To the Editors:
Ocular motility problems related to congenital
abnormalities of the extraocular muscles are rare.
Such congenital abnormalities may present in a
spectrum from accessory additional rectus muscles
to the absence of extraocular muscles.1-5 Absence of
one or more extraocular muscles is a rare condition
usually seen in association with craniofacial syndromes. We present a case of bilateral medial rectus
muscle aplasia with a constant exodeviation in the
absence of associated cranial facial anomalies.
An 8-year-old girl presented to our clinic with
abnormal eye movement since the age of 8 months.
She was otherwise healthy. On examination, the patient’s best-corrected visual acuity was 20/20, with a
refraction of -1.75 -2.0 ⫻ 180° in the right eye and
16/20 with a refraction of -1.0 -1.5 ⫻ 180° in the
left eye. No abnormal head position or chin depression was observed. A 30 prism diopter (PD) exotropia was present in primary and near gazes and a
25 PD exotropia was present in distance gaze. She
showed mild overaction of both inferior oblique
muscles and moderate limitation of adduction in
both eyes. On down gaze, a 10 PD exotropia was
present that increased to 40 PD on up gaze. A significant V-pattern exodeviation of 40 PD exotropia on
up gaze was present. The remaining ocular examination was entirely normal. A computed tomography
(CT) scan of the orbits was performed before surgery, but all extraocular muscles appeared normal.
Surgical correction with bilateral inferior oblique
muscle myectomy, resection of the medial rectus
muscle, and recession of the lateral rectus muscle of
the left eye was planned.
Bilateral inferior oblique muscle myectomy was
performed. The left medial rectus muscle showed
thin fibrous tissue and was biopsied (Figure 1A).
Medial rectus muscle exploration of the right eye was
performed and showed marked fibrotic tissue (Figure 1B). A biopsy of the right medial rectus muscle
was also performed. After the biopsies, bilateral
lateral rectus muscle recession was performed. The
lateral rectus muscles were visible and appeared to
be normal. The biopsy results of both medial rectus
muscles showed fibrous tissues with scattered vasculatures and an absence of muscle fiber (Figures 1C
and 1D). After surgery, the patient was orthophoric
in primary gaze with glasses, and the V-pattern was
greatly diminished. She continued to do well for 3
years after the surgery.
Orbital CT or magnetic resonance imaging can
Figure 1. (A) Intraoperative photograph of the left eye with the left medial rectus muscle showing marked
thin fibrotic tissue. (B) The right medial rectus muscle showing marked
fibrotic tissue. (C) Left medial rectus
muscle. (D) Histologic section of the
right medial rectus muscle showing
fibrous tissue with scattered vasculature and the absence of muscle fibers
(hematoxylin–eosin, original magnification ⫻200).
Copyright © SLACK Incorporated
Letters to the Editors
aid in the diagnosis of congenitally absent extraocular muscles before surgery and can allow for effective surgical planning to correct the congenital abnormality. However, in our patient, although all of
the extraocular muscles appeared normal throughout the coronal orbital CT scans, bilateral medial
rectus muscle aplasia was found intraoperatively.
The unusual findings in the presented case suggest
that developmental abnormalities of the extraocular
muscles should be considered in the differential diagnosis for constant exotropia.
1. Cuttone JM, Brazis PT, Miller MT, et al. Absence of the superior
rectus muscle in Apert’s syndrome. J Pediatr Ophthalmol Strabismus. 1979;16:349-354.
2. Carruthers JD. Strabismus in craniofacial dysostosis. Graefes Arch
Clin Exp Ophthalmol. 1988;226:230-234.
3. Lin PY, Yen MY. Congenital absence of bilateral inferior rectus muscles: a case report. J Pediatr Ophthalmol Strabismus.
4. Astle WF, Hill VE, Ells AL, et al. Congenital absence of the
inferior rectus muscle-diagnosis and management. J AAPOS.
5. Özkan SB, Özsunar Dayanir Y, Gökçe Balci Y. Hypoplastic inferior rectus muscle in association with accessory extraocular muscle
and globe retraction. J AAPOS. 2007;11:488-490.
Dong-Wook Lee, MD
Sam Lee, MD
Min Ahn, MD, PhD
Jeonbuk, South Korea
The authors have no financial or proprietary interest in
the materials presented herein.
Journal of Pediatric Ophthalmology & Strabismus • Vol. 50, No. 3, 2013
doi: 10.3928/01913913-20130416-01