Eye
On this page 6 sections
Extraocular muscles
Rule: LR6 – SO4 – Rest3
| Nerve | Muscle |
|---|---|
| CN VI (abducens) | Lateral rectus |
| CN IV (trochlear) | Superior oblique |
| CN III (oculomotor) | Remaining four recti and inferior oblique; also levator palpebrae superioris |
Mnemonic: LR6, SO4, all the rest 3.
CN Palsies Table
| CN Palsy | Presentation |
|---|---|
| CN III | Ptosis + dilated pupil + eye down-and-out |
| CN IV | Impaired downward gaze in adduction; head tilt opposite side |
| CN VI | Cannot abduct eye (medially directed) |
- Vertical diplopia = CN IV or CN III.
- 4th nerve palsy = diplopia on seeing down (vertical).
- 3rd nerve palsy = diplopia seeing down + right/left (horizontal).
- 6th nerve palsy = diplopia seeing right or left (horizontal).
Pupil Abnormalities — FCPS High-Yield Notes
Quick reference table
| Finding | Most likely diagnosis |
|---|---|
| Ptosis + mydriasis ± diplopia | CN III palsy |
| Ptosis + miosis | Horner syndrome |
| Light reflex absent, accommodation preserved | Argyll–Robertson pupil |
| Dilated pupil with poor light response, tonic near response | Holmes–Adie pupil |
| Pinpoint pupils + respiratory depression | Opioid toxicity |
| Bilateral pinpoint pupils | Consider pontine hemorrhage or drugs |
| Anisocoria greater in bright light | Larger pupil is abnormal |
| Anisocoria greater in darkness | Smaller pupil is abnormal |
Horner syndrome
- Ptosis
- Anhidrosis
- Miosis
Caused by interruption of the sympathetic pathway. Possible causes include a Pancoast tumor, brainstem/spinal cord lesions, or carotid artery dissection. Facial flushing may occur.
CN III palsy
- Ptosis
- Eye typically “down and out”
- Diplopia
- Possible mydriasis if parasympathetic fibres are involved
Argyll–Robertson pupil
- Accommodation response preserved
- Light reflex absent or markedly impaired
- Classically associated with neurosyphilis
- Often bilateral, small and irregular pupils