23.5 Practice Drills and Readiness Markers
Key Takeaways
- Drill the LR6 SO4 rule and the yoke-pair grid until recall is automatic and gaze-position independent.
- Be able to convert a complaint (diplopia direction) into a muscle, nerve, and expected cover-test finding.
- Practice reading a nine-position motility grid and the -4 to 0 grading scale at speed.
- Readiness means stable, correct answers on mixed motility items after a one-day break.
23.5 Practice Drills and Readiness Markers
Motility is high-yield and fast-moving on the COA exam, so the goal is automatic recall plus the ability to map a symptom to a muscle, nerve, and expected test result. Build short, mixed drills rather than rereading notes.
Drill 1 — innervation flash recall
Cover the cranial-nerve column and recite it: LR = VI, SO = IV, MR/SR/IR/IO = III. Then reverse it: given a nerve, list its muscles. CN III drives four EOMs plus the levator (lid) and the pupil sphincter, which is why a complete third-nerve palsy produces ptosis and a dilated pupil. CN IV is the only nerve that exits the brainstem dorsally and crosses, and it serves a single muscle.
Drill 2 — yoke-muscle map
Reproduce the six-cardinal grid from memory, naming the yoke pair for each gaze direction (e.g., right gaze = right LR + left MR). Then answer: "In the down-and-left position, which two muscles are tested?" Answer: right SO and left IR.
Drill 3 — complaint-to-finding conversion
| Complaint / sign | Muscle | Nerve | Expected cover-test result |
|---|---|---|---|
| Horizontal diplopia, can't abduct | Lateral rectus | VI | Esotropia, worse in field of action |
| Vertical diplopia worse reading, head tilt | Superior oblique | IV | Hypertropia, worse on down-and-in |
| Ptosis, down-and-out, dilated pupil | Multiple | III | Large deviation, limited adduction/elevation |
| Crossing worse at near, hyperopic child | (Accommodative) | — | Esotropia larger at near; correct first |
Drill 4 — grading and charting
Practice reading the -4 to 0 scale: 0 is full movement, -1 mild underaction, -4 no movement past midline; obliques can be +1 to +4 for overaction. Sketch a blank nine-position grid and fill in a hypothetical CN VI palsy (-3 in the abducting field, 0 elsewhere). Speed here saves time on chart-reading items.
Drill 5 — sensory tests
Quiz the Worth 4-Dot outcomes (4 = fusion, 2 red = left suppression, 3 green = right suppression, 5 = diplopia) and stereopsis units (seconds of arc, smaller is better). Pair each with the glasses convention (red over the right eye).
Readiness markers
| Marker | What good performance looks like |
|---|---|
| Recall | Recite LR6 SO4 and the yoke grid with no notes, in under 30 seconds. |
| Recognition | Identify the responsible nerve from a diplopia description alone. |
| Application | Choose the correct test and predict the cover-test/prism result. |
| Distractor control | Explain why monocular diplopia or a reversed prism base is wrong. |
| Retention | Score steadily on mixed motility items after a one-day break. |
The domain is ready when you can answer mixed motility questions without the topic label, justify each answer by the muscle and nerve involved, and still perform after a day away. A sharp drop after a break signals recognition-only memory that needs more active recall.
Drill 6 — paralytic versus restrictive sorting
Make a two-column sort. On one side list paralytic causes (CN III, IV, VI palsies), on the other restrictive causes (blowout fracture with inferior-rectus entrapment, thyroid eye disease, scarring). For each, state the distinguishing test: a forced duction is free in a palsy and resists in restriction. Add the bedside clue for each — pupil and ptosis for CN III, head tilt for CN IV, abduction loss for CN VI, trauma and cheek numbness for a blowout, lid retraction and proptosis for thyroid disease. This sort is the highest-yield application drill in the chapter.
Drill 7 — Hering and Sherrington recall
State both laws and one consequence of each: Hering's law of equal innervation → secondary deviation is larger than primary; Sherrington's law of reciprocal innervation → the antagonist relaxes when the agonist contracts. Being able to predict the larger deviation under each fixation condition is a common comparison-item skill.
Drill 8 — directional vocabulary speed round
Flash these and answer instantly: eso = in, exo = out, hyper = up, hypo = down; esotropia neutralized base-out, exotropia base-in, hypertropia base-down over the higher eye. Mixing these up is the single most common motility error, so over-practice them.
A weeklong readiness plan
| Day | Focus |
|---|---|
| 1 | Innervation and the EOM action table |
| 2 | Yoke-muscle grid and the nine positions |
| 3 | Cover-uncover vs alternating cover; phoria vs tropia |
| 4 | Prism base directions and PACT magnitude |
| 5 | Sensory tests: Worth 4-Dot and stereopsis units |
| 6 | Paralytic vs restrictive sorting and forced ductions |
| 7 | Mixed timed set, then re-test after one day off |
If the day-7 mixed set holds steady after the break and every miss can be traced to a named muscle, nerve, or directional rule, the motility domain is exam-ready. Persistent misses concentrated in one row of these drills tell you exactly where to spend the last review hour.
In addition to four extraocular muscles, the oculomotor nerve (CN III) also supplies which structures, explaining why a complete CN III palsy causes ptosis and a dilated pupil?