From Jasti V Ramanamma Children’s Eye Care Center (RK, RB), and the Department of Ophthalmic Pathology (GKV), L. V. Prasad Eye Institute, Hyderabad, India.
The authors have no financial or proprietary interest in the materials presented herein.
Address correspondence to Ramesh Kekunnaya, MD, FRCS, Pediatric Ophthalmology, L. V. Prasad Eye Institute, Road No. 2 Banjara Hills, L. V. Prasad Marg, Hyderabad, AP 500 034, India. E-mail: firstname.lastname@example.org
Typical features of congenital fibrosis of extraocular muscle syndrome type 3 include severe hypotropia with limitation of elevation, ptosis, and enophthalmos of the affected eye. We present a similar case with descriptive clinical, pathological, and radiological features. All of these revealed a dysplastic inferior rectus muscle, which did not fit into any typical pattern of disorders of extraocular muscles.
A 20-month-old boy was brought to the Pediatric Ophthalmology Service because the parents had noticed non-progressive downward deviation of the right eye since 10 months of age. The right eye also appeared smaller in size, which had been noticed since birth. The family, personal, social, and medical history was unremarkable with no maternal drug intake or history of consanguinity. A general physical examination showed that the child was otherwise healthy.
His visual acuity was no fixation movement in the right eye and 20/63 at 55 cm (90% reliability) with Teller acuity chart in the left eye. Cycloplegic refraction showed +2.00 diopter sphere / +1.50 @ 90° and +1.25 diopter sphere in the left eye. On ocular motility evaluation, he had approximately 15° of chin elevation. Right hypotropia measured 45 prism diopters (PD) with Krimsky’s test. The right eye was not elevating even up to midline in straight, adducted, and abducted positions (Fig. 1). Ocular movements were full in the left eye. He had enophthalmos (Fig. 1) of the right eye with pseudoptosis of the right upper eyelid. Enophthalmos could not be measured objectively. The anterior segment, pupillary reaction, and funduscopy were normal in both eyes. A provisional diagnosis of congenital fibrosis of the inferior rectus muscle, enophthalmos syndrome, and amblyopia (right) was made.
Figure 1. Preoperative Nine-Gaze Photographs Showing Large Right Hypotropia, Retraction of the Globe, and Elevation Deficit in the Right Eye.
An ultrasound B-scan ruled out the possibility of myocysticercosis. A computed tomography (CT) scan of the orbit showed gross thinning of the anterior (one-third) and diffuse thickening in the posterior part of the muscle belly (Fig. 2). There appeared to be a few adhesions between the superior rectus muscle and the sclera in the posterior aspect. CT scan of the brain and left orbit was normal. Systemic work-up included complete blood cell count and thyroid profile (T3, T4, and TSH), both of which were normal.
Figure 2. (A) Computed Tomography Scan (coronal View) Showing Inferior Rectus Muscle Enlargement. (B) Computed Tomography Scan (reconstructed Sagittal View) Showing Enlargement of the Posterior Aspect of the Inferior Rectus Muscle.
The child underwent strabismus surgery in the right eye in an attempt to increase the binocular field. A forced duction test revealed a severely tight right inferior rectus muscle. We could not get the eye to move even to the midline. The inferior rectus muscle was hooked. A second hook could not be passed to stretch the muscle, so as to pass the suture to secure the muscle for recession. Because of this situation, an intraoperative decision was made to perform a free tenotomy. A small tenectomy was also performed, assuming that pathological examination would aid in the diagnosis and keeping in view the atypical features. At the same time, the visible portion of the inferior rectus muscle was inspected for any gross anomaly and the excised inferior rectus muscle tissue was sent for histopathologic examination. Inferior oblique and superior rectus muscles were found to be normal. There were no adhesions between the superior rectus muscle and sclera. Forced duction test became negative in all directions. Further surgery was deferred assuming that the situation would improve. The histopathology report showed muscle tendon and replacement of muscle by fibrous tissue (Fig. 3).
Figure 3. Section from the Excised Muscle Shows Fibrosis and Tendon-Like Structures but Lacks the Presence of Muscle Fibers (hematoxylin–Eosin, Original Magnification ×400).
At 3 months postoperatively, there was right hypotropia of 6 PD and exotropia of 8 PD in the primary position (Fig. 4). Elevation improved minimally. Enophthalmos reduced significantly and the abnormal head posture was eliminated. Figure 5 shows the transected right inferior rectus muscle. The patient was given glasses to correct the refractive error and was asked to continue part-time occlusion therapy for amblyopia of the right eye.
Figure 4. Postoperative Nine-Gaze Photographs Showing Improved Alignment, Retraction, and Motility.
Figure 5. Postoperative Computed Tomography (reconstructed Sagittal View) Scan Showing Transected Inferior Rectus Muscle.
Enlargement of the extraocular muscles may result from a variety of neoplastic, inflammatory, or infiltrative processes, or from the blockage of orbital venous drainage.1,2 Although enlargement of the extraocular muscles is uncommon in children, there are a few reported cases. Burroughs et al. described a case of congenital muscle enlargement, possibly due to euthyroid ophthalmopathy.3 Dickson et al. reported another case of extraocular muscle enlargement wherein the etiology was uncertain.4 In both of these cases, muscle enlargement uniformly involved the whole muscle belly, sparing the tendinous portion of the muscle. In the patient described here, the enlargement of the muscle involved only the posterior part of the belly. In addition there was retraction of the globe. This kind of enlargement was unique to this case. Histopathologic examination of the muscle tissue showed a fibrous change. There could be two possibilities here: tendons had replaced the muscular part or the actual muscle tissue may not have been included in the biopsy.
On clinical examination, retraction of the globe and positive results on forced duction test were suggestive of a tight inferior rectus muscle, which could be part of congenital unilateral fibrosis, blepharoptosis, and enophthalmos syndrome. Congenital unilateral fibrosis, blepharoptosis, and enophthalmos syndrome is one of the rare types of congenital fibrosis of the extraocular muscles.5,6 There have been multiple hypotheses on the causes of fibrosis in this group of patients. However, this seems to be characterized by a primary orbital fibrotic process and there is no evidence of a genetic association. There is some evidence that this could be an acquired condition, secondary to prenatal5 or perinatal orbital inflammation, associated with prenatal trauma,7 or secondary to inflammation induced by a sinus tumor.8 This condition should be differentiated from the paretic form of double elevator palsy, a frequent cause of monocular hypotropia with limited elevation in infants and children, by resistance to the forced duction test in the upward condition and absence of Bell’s phenomenon in congenital unilateral fibrosis.9 The amount of severe retraction also suggests more restrictive pathology. In our case, the tightness of the inferior rectus muscle was the primary cause of elevation limitation because the elevation improved after surgical release of the tight inferior rectus muscle.
The classic concept that congenital fibrosis of the extraocular muscles is due to primary myopathy is changing. Engle et al. suggested that congenital fibrosis of the extraocular muscles is a primary disorder of extraocular muscle lower motor neuron development, leading to hypoplasia or atrophy of the extraocular muscles they innervate and to secondary contracture of their antagonists.10 There is further magnetic resonance imaging evidence for the same.11 The affected muscles showed hypoplastic changes uniformly involving the whole muscle. In our case, magnetic resonance imaging could not be performed because of economical issues. However, on CT scan the posterior part of the inferior rectus muscle was thickened, which is not typical of congenital fibrosis of the extraocular muscles.
Surgical options recommended for the hypotropia caused by inferior rectus pathology include large recession, tenectomy, free tenotomy, or transposition of the horizontal muscles.9,12 Although inferior rectus recession was planned, we had to perform free tenotomy because the muscle was tight, following which the restriction was immediately eliminated. Postoperatively, the primary position alignment was good. Elimination of abnormal head posture suggests good binocularity and probably improvement in the binocular visual field. Preoperatively, there was no fixation movement in the right eye. This could be due to restriction per se and also to a component of amblyopia. Thus, part-time patching therapy was advised for further possible visual benefit and would be monitored accordingly.
The pattern of inferior rectus enlargement as seen on the CT scan was unique to this case and the constellation of findings does not follow any previously reported pattern of disorders of extraocular muscle abnormality.
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