23.3 Scenario Practice for Ocular Motility Testing
Key Takeaways
- Diplopia that resolves when one eye is covered is binocular and usually motility/EOM in origin.
- A 'down and out' eye with ptosis and a dilated pupil is a classic CN III palsy pattern.
- Esotropia worse at near with high hyperopia suggests accommodative esotropia; check the AC/A response.
- Always test corrected with the patient's habitual glasses and at both distance and near.
23.3 Scenario Practice for Ocular Motility Testing
Motility scenario questions give a complaint plus a clue, then ask which test, which muscle, or which documentation step is correct. Practice this method: name the symptom, decide monocular vs binocular, localize the muscle/nerve, choose the test, and predict the chart entry.
First fork: monocular or binocular diplopia
The single most useful question is, "Does the double vision go away when one eye is covered?"
- Resolves with either eye covered → binocular diplopia. This is a misalignment problem (EOM weakness, nerve palsy, restriction). It belongs in the motility workup.
- Persists with the fellow eye covered → monocular diplopia. This is optical (uncorrected astigmatism, cataract, dry eye, dislocated lens) and is not a motility issue. A common trap answer pushes a motility workup for monocular diplopia.
Scenario A — sudden binocular horizontal diplopia
A 58-year-old reports horizontal double vision, worse looking to the right; the right eye does not abduct fully past midline (graded -3 in right gaze). Isolated abduction deficit = lateral rectus = CN VI (abducens) palsy. The COA should document the limitation in the nine-position grid, note that diplopia is worse in the field of the weak muscle, and measure the deviation with prism cover test (it will be an esotropia, larger in right gaze).
Scenario B — ptosis with a 'down and out' eye
A patient presents with a droopy right lid, the right eye resting down and out, and a dilated right pupil. The intact muscles are the superior oblique (CN IV) and lateral rectus (CN VI), so this is a CN III (oculomotor) palsy. Pupil involvement is a red-flag clue the COA must report promptly because it raises concern for an aneurysm.
| Clue in the stem | Localizes to |
|---|---|
| Eye won't abduct, horizontal diplopia | CN VI / lateral rectus |
| Vertical diplopia, worse reading/down-and-in, head tilt | CN IV / superior oblique |
| Ptosis + down-and-out + dilated pupil | CN III / multiple muscles |
| Limited up-gaze after orbital trauma | IR entrapment (blowout fracture) |
Scenario C — child with crossing worse at near
A 4-year-old has eyes that cross more when focusing on near objects and is significantly hyperopic. This pattern suggests accommodative esotropia: accommodating to overcome hyperopia drives excess convergence. The correct workflow is to test with the full hyperopic correction in place and compare the distance and near deviation (the accommodative convergence/accommodation, or AC/A, relationship). The trap answer recommends surgery before refractive correction is tried.
Documentation discipline
For every scenario, the defensible chart entry records the test used, the eye, the position(s) of gaze affected, the grade or prism measurement, and whether correction was worn. Recording "diplopia" without the test or direction is an incomplete answer the exam will mark wrong.
Scenario D — vertical diplopia after a fist injury
A patient struck in the eye reports vertical double vision and cannot look up with the affected eye; there may be numbness of the cheek. This is the pattern of an orbital floor (blowout) fracture with inferior rectus entrapment: the muscle is mechanically tethered, so up-gaze is restricted even though the nerve is intact. The distinguishing feature from a nerve palsy is that the deficit is restrictive (mechanical), often confirmed by forced duction testing performed by the physician. The COA documents the limited elevation, the gaze position, and the history of trauma, and reports promptly.
Scenario E — eyelid retraction and limited up-gaze in an adult
An adult with lid retraction, bulging eyes, and trouble elevating in up-gaze suggests thyroid eye disease (Graves orbitopathy), where the inferior rectus is most commonly affected by restriction and fibrosis. Like the blowout fracture, this is restrictive, not paralytic, and the COA should note the symmetric or asymmetric pattern and any associated lid signs.
Reading-method summary
| Step | Question to answer |
|---|---|
| Symptom | Is the diplopia horizontal, vertical, or torsional? |
| Laterality | Does covering one eye resolve it? (binocular vs monocular) |
| Localize | Which muscle and nerve explain the pattern? |
| Mechanism | Is it paralytic (nerve) or restrictive (mechanical)? |
| Test | Versions, cover, prism, forced ductions, sensory? |
| Document | Test, eye, gaze position, magnitude, correction worn |
Run every scenario item through these six prompts and the tempting-but-incomplete distractor usually exposes itself, because it skips either laterality (monocular vs binocular) or mechanism (paralytic vs restrictive).
Scenario F — intermittent outward drift in a tired child
A parent reports one eye drifts outward when the child is tired, daydreaming, or sick, but looks straight most of the time. This is the classic picture of an intermittent exotropia, a deviation controlled by fusion much of the day and breaking down with fatigue or inattention. The right workflow measures the deviation at distance and near (intermittent exotropia is often larger at distance) and assesses how well fusion is maintained.
The trap answer treats it as a constant tropia or recommends immediate surgery; the defensible answer documents frequency, the breakdown triggers, and the distance-versus-near magnitude so the physician can judge control.
A patient reports vertical double vision that worsens when reading and improves with a head tilt toward the opposite shoulder. Which muscle is most likely weak?