[The progress of clinical research and treatment of monocular elevation deficiency]

Monocular elevation deficiency (MED) is a functional defect in upward eye movement caused by paralysis, restriction, or a combination of factors. The affected eye experiences limited movement in the upward, nasal, and temporal directions, often accompanied by downward deviation and ptosis. Previously known as double elevator palsy (DEP), MED can result from muscle paralysis responsible for upward movement, restriction of the inferior rectus muscle, or lesions in the supranuclear pathway. The Knapp procedure was once the most commonly used surgical approach for MED. However, in cases involving restriction of the inferior rectus muscle, a staged approach combining inferior rectus muscle weakening and subsequent Knapp procedure is necessary to avoid anterior segment ischemia. This has led to the development of alternative surgical techniques, such as single-rectus muscle transposition, partial tendon transposition, and muscle belly transposition. Differentiating MED subtypes based on the underlying paralysis or restriction etiology is crucial for determining the appropriate surgical plan. This review article summarizes the clinical features, classification, and available surgical options for MED, aiming to provide valuable insights for clinical research and treatment.