To report a congenital monocular elevation deficiency (MED) associated with inferior rectus anomaly.

A 3-year-old, otherwise healthy boy presented with left hypotropia. He showed chin-up and left head turn with left pseudoptosis. On examination, there was a left hypertropia of 60 prism diopters (PD) and esotropia in primary position. Upgaze -4 limitation in abduction and -3 from primary position, poor Bell's phenomenon, and normal vertical saccadic velocity until midline were observed. On orbital CT, thin and nasally displaced left inferior rectus showing enlargement at its posterior segments near the orbital apex was observed. Forced duction test at surgery revealed a strong positive restriction and thin, taut, fibrotic inferior rectus was inserted and displaced nasally.

Left inferior rectus recession of 5.5 mm with 2.0 mm of temporal transposition improved elevation deficiency, but consecutive exotropia and hypotropia remained. Knapp procedure combined with left lateral rectus recession of 5.5 mm and left medial rectus resection of 4.5 mm, and right superior rectus recession of 9.5 mm were additionally performed. Pseudoptosis and chin elevation resolved but left hypotropia 10PD, and exotropia 6PD remained. Elevation restriction in primary position and abduction were improved but still persisted. This case indicated that MED may accompany congenital inferior rectus anomaly. If severe inferior rectus restriction is observed during the forced duction test, a structural anomaly of the inferior rectus causing motility defects of MED.