Extraocular Movement Examination

The extraocular movement (EOM) examination evaluates the six extraocular muscles and their controlling cranial nerves (III, IV, VI), identifying motility disturbances from neurologic, muscular, or orbital causes. A systematic approach across all cardinal positions of gaze is what allows subtle restrictions and diplopia patterns to be localized rather than just noted.

The exam proceeds in a fixed sequence: primary position first (alignment, ptosis, nystagmus), then smooth pursuit through the six cardinal positions — right/up, right/horizontal, right/down, left/up, left/horizontal, left/down — pausing briefly at each extreme to check for nystagmus, then convergence testing (normal near point within 10 cm). If diplopia is present, the single most important branch point is whether it resolves with one eye covered: diplopia that persists despite monocular occlusion is monocular, pointing toward an ocular media cause such as corneal irregularity, lens subluxation, or macular disease rather than a neurologic one, while diplopia that resolves with occlusion is binocular and reflects true ocular misalignment.¹ A systematic history-and-exam approach to diplopia — and explicitly asking about it, since patients don't always volunteer the symptom — is what allows this localization to happen reliably.¹

Once binocular diplopia is confirmed, the pattern of restriction differentiates mechanical from neurogenic causes. Restriction limited to a single cranial nerve's distribution suggests a nerve palsy: CN III palsy produces limited adduction, elevation, and depression, often with ptosis; CN IV palsy produces vertical diplopia worse on downgaze and head tilt toward the affected side; CN VI palsy produces horizontal diplopia worse on gaze toward the affected side with limited abduction. Pupil involvement in a CN III palsy is a specific red flag — it raises concern for a compressive, potentially aneurysmal lesion and warrants urgent neuroimaging, distinct from the typically pupil-sparing microvascular CN III palsies seen in diabetic or hypertensive patients (and atypical features in an apparently microvascular case still warrant imaging).

Restriction that is multi-directional, painful, or accompanied by proptosis and conjunctival chemosis points toward a mechanical or orbital process rather than an isolated nerve palsy — orbital inflammatory, infectious, or infiltrative disease can restrict movement in a pattern that mimics a nerve palsy, and differentiating the two may require forced duction testing or imaging when the underlying cause is unclear. Painful restriction with significant orbital signs should prompt consideration of urgent imaging to rule out orbital cellulitis or abscess, since this can threaten vision if management is delayed.

Bilateral CN VI palsies are a distinct pattern worth recognizing on their own — rather than reflecting two isolated nerve lesions, bilateral involvement should raise concern for a diffuse process such as elevated intracranial pressure. Fatigability or variability in restriction over the course of the exam (or across the day) raises suspicion for myasthenia gravis rather than a fixed structural lesion.