Which finding is most consistent with a neurogenic motility deficit?

• A. Negative forced duction
• B. Positive forced duction
• C. Mechanical restriction
• D. Orbital edema without restriction

Answer: (A)

The main idea is differentiating neurogenic versus mechanical problems with the forced duction test. In a neurogenic motility deficit, the muscle weakness isn’t due to a physical block, so when the examiner moves the eye passively there’s no resistance. That yields a negative forced duction result. If there were a mechanical restriction, such as scar tissue or a restricted pulley system, passive movement would be blocked and the forced duction would be positive. Orbital edema without restriction wouldn’t produce a motility deficit with a mechanical block either. So, the finding most consistent with a neurogenic motility deficit is a negative forced duction.