Modified horizontal muscle transposition without tenotomy and splitting for a case of inferior rectus and inferior oblique muscles aplasia with hemifacial microsomia.

Aplasia of the inferior rectus and inferior oblique muscles is extremely rare. Failure of the normal embryologic development of the inferior mesodermal complex can lead to agenesis of inferior rectus, inferior oblique, and lower sections of the lateral rectus muscles. This rare condition is usually seen in association with craniofacial syndromes or in conjunction with microcornea, microphthalmos, Axenfeld-Rieger syndrome, and coloboma. The usual treatment for this condition is a reverse Knapp procedure to improve the vertical alignment; however, this procedure can lead to complications, such as anterior segment ischemia, undercorrection, and torsional problems. To our knowledge, unilateral inferior rectus and inferior oblique muscle aplasia has not been described previously in a patient with congenital facial nerve palsy and optic nerve hypoplasia. In the present case, the patient was successfully treated with a modified minimally invasive horizontal rectus muscle transposition procedure.