Congenital absence of the inferior rectus muscle--diagnosis and management.

Background: Congenital absence of the inferior rectus muscle is a rare cause of apparent inferior rectus palsy especially in the absence of associated cranial facial anomalies.
Methods: We report three cases of isolated congenital absence of the inferior rectus muscle and its successful surgical management.
Results: Failure of the normal embryologic development of the mesodermal complex around the eye can lead to agenesis of the extraocular muscles. In apparent palsies of the inferior rectus muscle and no definite cause, a high index of suspicion and orbital imaging can confirm the diagnosis of congenitally absent inferior rectus preoperatively. Surgical correction may involve inferior transposition of the horizontal rectus muscles.
Conclusions: Although rare, congenital absence of the inferior rectus muscle is a possible cause of apparent inferior rectus muscle palsy particularly in the absence of another identifiable cause. Strabismus surgery in conjunction with intramuscular botulinum toxin injection can offer significant improvement in function and cosmesis of these patients.