Extraocular muscle dynamics in diplopia from enophthalmos

The mechanism of diplopia from enophthalmos is not well understood. We describe a 55-year-old man who underwent a left transorbital craniotomy for clipping of a basilar aneurysm. The lateral orbital wall was not reconstructed properly, resulting in 8 mm of left enophthalmos. Months after surgery the patient developed diplopia with ocular excursions, although he remained orthotropic in primary gaze. The left eye was limited in elevation, adduction, and abduction. These findings were confirmed by eye movement recordings, which showed ocular separation increasing with gaze eccentricity. A CT scan demonstrated a defect in the sphenoid and frontal bones, profound enophthalmos, and shortening of the rectus muscles. Slack in the extraocular muscles reduced the force generated by each muscle, causing diplopia with ocular rotation. This case underscores the value of careful orbital wall reconstruction after orbitotomy and suggests a mechanism for diplopia produced by postoperative enophthalmos.