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.
Keywords: Congenital hypertropia; IOANT; imaging in strabismus; inferior rectus hypoplasia.