Which of the following is NOT a typical cause of a hyperphoria?

• A. CN 3 palsy
• B. Duane's retraction syndrome
• C. CN 4 palsy
• D. Thyroid eye disease

Answer: (B)

Hyperphoria is a latent vertical misalignment that becomes evident when fusion is disrupted, often arising from conditions that alter vertical muscle balance or Restriction. When the eye is affected by a third-nerve palsy, the vertical misalignment tends to present as a vertical deviation because the nerve loss leaves the eye pulled downward by unopposed muscles, creating a hypertropic tendency in the other eye that the system tries to compensate for. A fourth-nerve palsy produces hypertropia of the affected eye, especially on certain gaze positions, again yielding a vertical misalignment that appears as a hyperphoria under dissociating tests. Thyroid eye disease can cause restrictive changes in the vertical orbit, leading to vertical misalignment as well, and thus hyperphoria.

Duane’s retraction syndrome centers on abnormal innervation leading to co-contraction of horizontal recti, globe retraction, and limited abduction with possible upshoots or downshoots on adduction. Its primary pattern is horizontal misalignment with characteristic lid and globe movements, not a typical vertical phoria. That’s why it isn’t considered a typical cause of hyperphoria.