Managing Hypoplasia of the Inferior Rectus Muscle by Inferior Oblique Anterior Transposition in Children

Congenital anomalies of inferior rectus and its surgical outcomes

Congenital inferior rectus hypoplasia and aplasia is a rare abnormality of the extraocular muscles, and it is the second most common after superior oblique muscle aplasia. It has been reported either in isolation or with coexisting ocular or systemic associations. We describe here cases of inferior rectus hypoplasia/aplasia, their clinical features, and surgical approach to achieve satisfactory outcomes. We retrospectively reviewed medical records from January 2009 to December 2020 of patients with vertical strabismus due to inferior rectus hypoplasia/aplasia at a tertiary eye care center. Those who underwent surgical intervention with an adequate follow up postoperatively were included in the study. Three patients who presented with congenital hypertropia and diagnosed of inferior rectus aplasia/hypoplasia and who underwent strabismus surgery were identified. Diagnosis was based on clinical examination and orbital imaging. Coexisting horizontal deviation was present in two patients. None of the patients had any other ocular, cranial, or systemic anomalies. All patients had isolated inferior aplasia/hypoplasia with normal other extraocular muscles on orbital imaging. Intraoperatively, ipsilateral superior rectus was tight in all patients. All underwent ipsilateral superior rectus recession, whereas two patients with large vertical strabismus required additional inferior oblique anteronasal transposition in the same eye. Satisfactory outcomes were achieved in all three patients without the need for resurgery. Moderate to large vertical A pattern strabismus and limitation of infraduction are common clinical findings. Orbital imaging helps not only in diagnosis but also in surgical planning. Weakening of antagonist superior rectus with anteronasal transposition of inferior oblique not only gives good surgical outcomes but also avoids potential complications related to vertical transposition of either horizontal rectus muscle.

Small-angle hypertropia in a case of inferior rectus aplasia: an intraoperative surprise

Introduction: The clinical features of congenital inferior rectus (IR) aplasia are similar to IR paresis/palsy, and they include hypertropia, limitation of downgaze - especially in abduction, incyclotorsion, A-pattern strabismus, and abnormal head posture.Case report: A 22-year-old man presented with a right face turn, small-angle hypertropia (14 prism diopters) in the right eye, and limitation of downgaze that passed the midline; no diplopia was present and supraduction was normal in that eye. Double Maddox rod revealed 12 degrees of incyclotorsion for the right eye. The Titmus test revealed a stereo acuity of 400 seconds of arc. Based on the preoperative clinical findings, a presumptive diagnosis of IR paresis was made and a surgical plan for performing superior rectus muscle recession and IR muscle resection was devised. Intraoperatively, forced duction test was positive in depression. To our surprise, after performing a 4 mm recession of the superior rectus muscle, we found that the IR muscle was absent. We then revised the surgical plan and performed a 6 mm resection and anterior transposition of the inferior oblique (IO) muscle. Post-operatively, the patient was orthophoric in the primary position without diplopia, and his abnormal head posture was significantly improved.Conclusion: The amount of primary position hypertropia and severity of downgaze limitation are not adequate for differentiating congenital IR aplasia from IR paresis/palsy. Orbital imaging including CT, MRI or anterior segment optical coherence tomography (AS-OCT, UBM) is helpful to distinguish these two entities preoperatively.

Clinical and imaging features of congenital and acquired isolated inferior rectus muscle hypofunction

BACKGROUND

Inferior rectus (IR) underaction may arise from various causes that are distinguishable through imaging. We investigated clinical and imaging characteristics of congenital and acquired causes of IR underaction.

METHODS

Cases of IR underaction were selected from data prospectively collected in a study of orbital imaging in strabismic patients.

RESULTS

Review identified 3 cases of congenital IR underaction (2 with bilateral IR aplasia and 1 with unilateral IR hypoplasia), 12 acquired cases, including 4 due to denervation (2 idiopathic, 1 after multiple strabismus surgeries, 1 after head trauma), and 8 cases of direct IR damage (5 with orbital trauma and 3 with previous surgery, including 2 sinus surgery and 1 laser blepharoplasty). Of the 23 cases, 11 adults had high-resolution magnetic resonance imaging, and 2 children had computed tomography. Imaging identified the anatomic diagnosis in congenital cases; in acquired cases, imaging helped to identify atrophy and exclude alternative orbital causes; and in direct mechanical damage, imaging clarified the mechanism of underaction, extent of IR damaged, and the degree of retained contractility. Patients with congenital IR absence or hypoplasia exhibited A pattern exotropia that was typically absent in isolated acquired denervation or direct IR damage.

CONCLUSIONS

Orbital imaging demonstrates a variety of abnormalities in patients with congenital or acquired IR hypofunction, helping to clarify the underlying mechanism and guide management.