OP10.1 | Extraocular Movement Examination: Uniocular and Binocular Technique — Summary & Reflection

KEY TAKEAWAYS

EOM Examination — Key Points:

• The six extraocular muscles are innervated by CN III (MR, SR, IR, IO, levator, pupil), CN IV (SO), and CN VI (LR) — remembered as LR6SO4.
• Ductions (monocular testing with fellow eye occluded) assess individual muscle excursion and isolate restriction or paresis. Versions (binocular, conjugate) expose yoke muscle imbalance.
• The cover/uncover test detects manifest deviation (tropia); the alternate cover test detects total deviation (tropia + phoria).
• The Hirschberg test gives an objective estimate of strabismus angle: 1 mm decentration ≈ 7° (≈15 prism dioptres); reflex at pupil margin ≈ 15°; iris margin ≈ 30–45°.
• Comitant deviation (equal in all gazes) = childhood/fusional type; incomitant (varies with gaze direction) = palsy or restriction.
• CN VI palsy: abduction failure, horizontal diplopia. CN IV palsy: depression-in-adduction failure, hypertropia, head tilt. CN III palsy: "down and out" eye, ptosis, ± dilated fixed pupil.
• Painful pupil-involved CN III palsy = aneurysm until proven otherwise. Pupil-sparing in a diabetic = microvascular (but never entirely reassuring if pain is present).
• Angle kappa can mimic strabismus — always confirm with the cover test.

REFLECT

Think about the last patient you saw with ocular symptoms. Could there have been an extraocular movement abnormality that you or your team might have missed? What would have been the consequence of missing a CN III palsy with pupil involvement — and what test would have detected it? As you attend your ophthalmology clinical postings, commit to performing a systematic EOM examination on every patient presenting with any ocular complaint, not just those with obvious diplopia. Record your findings using the standard notation. Over time, you will develop the pattern-recognition speed that experienced ophthalmologists use to identify CN palsies within the first few seconds of asking a patient to follow a light.