Cranial Nerve Palsies - Eye Movers & Shakers
📌 $LR_6SO_4R_3$
| Nerve | Muscles Affected | Eye Position / Ptosis | Diplopia Worsens | Key Signs / Causes |
|---|---|---|---|---|
| III | All EOMs (exc. SO, LR), Levator; Pupil (comp.) | Down & out; Ptosis | All gazes | Pupil sparing (DM); Involving (PCOM aneurysm); Trauma |
| IV | SO | Hypertropia, extorsion | Vertical; Downgaze, head tilt to paretic side | Compensatory head tilt away from paretic side; Trauma, Congenital |
| VI | LR | Esotropia (inward) | Horizontal; Ipsilateral gaze | Failure to abduct; Microvascular (DM, HTN), ↑ICP |
⭐ Pupil sparing CN III: microvascular (DM). Pupil involved: compression (aneurysm).
Optic Nerve Issues - Vision's Vital Wire
| Feature | Papilledema | Optic Neuritis (ON) | AION (Arteritic/Non-Arteritic) |
|---|---|---|---|
| Onset | Gradual | Acute/Subacute | Sudden |
| Pain | Usually No (headache common) | Yes, esp. on eye movement | Often No (jaw claudication in arteritic) |
| Vision Loss | Late (transient obscurations) | ↓Acuity, color, field defects | Severe, altitudinal common |
| Fundus | Bilateral disc edema, blurred margins, venous engorgement. RAPD absent initially. | Unilateral disc swelling (or normal if retrobulbar), RAPD present. | Pale disc edema (chalky white in arteritic), RAPD present. |
| Associations | ↑ICP (tumor, hydrocephalus) | MS, viral infections | GCA (arteritic), vascular risk factors (NAION) |
⭐ Pain on eye movement is a classic symptom of optic neuritis.
Pupillary Signs - Windows to Neuro
Pupillary signs: key neuro clues.
- Relative Afferent Pupillary Defect (RAPD / Marcus Gunn Pupil): Optic nerve lesion; swinging flashlight test.
- Horner's Syndrome: Sympathetic lesion. 📌 PAM HORNer (Ptosis, Anhidrosis, Miosis).
- Adie's Tonic Pupil: Ciliary ganglion/postgang. parasymp. damage. Dilated pupil, poor light rxn, LND (light-near dissociation), vermiform iris.
- Argyll Robertson Pupil: Neurosyphilis. Bilateral small pupils, no light rxn, brisk near (LND).
⭐ Argyll Robertson pupils: "Prostitute's Pupil" - accommodate but don't react to light.
Pupil Comparison:
| Feature | Horner's Syndrome | Adie's Tonic Pupil | Argyll Robertson Pupil | CNIII Palsy (Pupil) |
|---|---|---|---|---|
| Size | Miosis | Mydriasis | Miosis (irreg) | Mydriasis |
| Light Rxn | Normal/↓ | Poor/Absent | Absent | Absent |
| Near Rxn | Normal | Slow (LND) | Brisk (LND) | Poor/Absent |
| Key Signs | Ptosis, Anhidrosis | Vermiform, ↓DTRs | Bilateral | Ptosis, EOM palsy |
| %%{init: {'flowchart': {'htmlLabels': true}}}%% | ||||
| flowchart TD |
Start["👁️ Light Reaction
• Check pupil reflex• Good vs Poor RXN"]
Compare["⚖️ Compare Anisocoria
• Test dark vs light• Measure asymmetry"]
DilationLag["📸 Dilation Lag
• Look for slow dil• Use flash photos"]
Cocaine["💊 Cocaine Test
• Use 4 to 10 pct• Check for dilation"]
Simple["✅ Simple Anisocoria
• Physiological var• Normal finding"]
Horners["🩺 Horner Syndrome
• Sympathetic loss• Ptosis/Miosis/AnH"]
Hydroxy["💊 Hydroxyamphetamine
• Use 1 pct drops• Localization test"]
PreHorners["🩺 Pre/Central Horner
• Central/Pregang• Pupil dilates"]
PostHorners["🩺 Post-gang Horner
• Distal lesion• No dilation"]
ExamineIris["🔬 Iris Sphincter
• Slit lamp exam• Look for trauma"]
Cholinergic["💊 Supersensitivity
• Methachol/Pilo• Parasymp. test"]
Adies["🩺 Adies Tonic Pupil
• Sensitivity found• Sector palsy"]
Antichol["💊 Blockade Test
• Pilo 1 pct drops• Test constriction"]
IIRD["🩺 CN III Palsy
• Pupil constricts• Nerve lesion"]
Atropinic["💊 Atropinic Mydriasis
• Fail to constrict• Pharmacologic"]
IrisDamage["⚠️ Iris Damage
• Structural loss• Trauma/torn margin"]
%% Connections Start -->|Good reaction| Compare Start -->|One eye poor| ExamineIris
Compare -->|More in dark| DilationLag Compare -->|More in light| ExamineIris
DilationLag -->|No lag| Simple DilationLag -->|Lag found| Cocaine DilationLag -->|Lag found| Horners
Cocaine -->|Both dilate| Simple Cocaine -->|Fail dilate| Horners
Horners --> Hydroxy Hydroxy -->|Dilates| PreHorners Hydroxy -->|No dilation| PostHorners
ExamineIris --> Cholinergic ExamineIris -->|Sector palsy| Adies ExamineIris -->|Torn margin| IrisDamage
Cholinergic -->|Sensitive| Adies Cholinergic -->|Not sensitive| Antichol Cholinergic -->|Immobile| Antichol
Antichol -->|Constricts| IIRD Antichol -->|Fail constr.| Atropinic Antichol -->|Fail constr.| IrisDamage
%% Styles style Start fill:#FEF8EC, stroke:#FBECCA, stroke-width:1.5px, rx:12, ry:12, color:#854D0E style Compare fill:#FEF8EC, stroke:#FBECCA, stroke-width:1.5px, rx:12, ry:12, color:#854D0E style DilationLag fill:#FFF7ED, stroke:#FFEED5, stroke-width:1.5px, rx:12, ry:12, color:#C2410C style Cocaine fill:#F1FCF5, stroke:#BEF4D8, stroke-width:1.5px, rx:12, ry:12, color:#166534 style Hydroxy fill:#F1FCF5, stroke:#BEF4D8, stroke-width:1.5px, rx:12, ry:12, color:#166534 style Cholinergic fill:#F1FCF5, stroke:#BEF4D8, stroke-width:1.5px, rx:12, ry:12, color:#166534 style Antichol fill:#F1FCF5, stroke:#BEF4D8, stroke-width:1.5px, rx:12, ry:12, color:#166534 style ExamineIris fill:#FFF7ED, stroke:#FFEED5, stroke-width:1.5px, rx:12, ry:12, color:#C2410C style Simple fill:#F6F5F5, stroke:#E7E6E6, stroke-width:1.5px, rx:12, ry:12, color:#525252 style Horners fill:#F7F5FD, stroke:#F0EDFA, stroke-width:1.5px, rx:12, ry:12, color:#6B21A8 style PreHorners fill:#F7F5FD, stroke:#F0EDFA, stroke-width:1.5px, rx:12, ry:12, color:#6B21A8 style PostHorners fill:#F7F5FD, stroke:#F0EDFA, stroke-width:1.5px, rx:12, ry:12, color:#6B21A8 style Adies fill:#F7F5FD, stroke:#F0EDFA, stroke-width:1.5px, rx:12, ry:12, color:#6B21A8 style IIRD fill:#F7F5FD, stroke:#F0EDFA, stroke-width:1.5px, rx:12, ry:12, color:#6B21A8 style Atropinic fill:#F1FCF5, stroke:#BEF4D8, stroke-width:1.5px, rx:12, ry:12, color:#166534 style IrisDamage fill:#FDF4F3, stroke:#FCE6E4, stroke-width:1.5px, rx:12, ry:12, color:#B91C1C
**Light-Near Dissociation (LND) Flowchart:**
```mermaid
%%{init: {'flowchart': {'htmlLabels': true}}}%%
flowchart TD
Start["<b>📋 LND Present</b><br><span style='display:block; text-align:left; color:#555'>• Light-near dissoc.</span><span style='display:block; text-align:left; color:#555'>• Pupillary reflex</span>"]
CheckSmall["<b>📋 Pupil Size Check</b><br><span style='display:block; text-align:left; color:#555'>• Small and irregular</span><span style='display:block; text-align:left; color:#555'>• Shape assessment</span>"]
Argyll["<b>🩺 Argyll Robertson</b><br><span style='display:block; text-align:left; color:#555'>• Neurosyphilis link</span><span style='display:block; text-align:left; color:#555'>• Prostitute pupil</span>"]
CheckDilated["<b>📋 Iris Inspection</b><br><span style='display:block; text-align:left; color:#555'>• Unilateral dilated</span><span style='display:block; text-align:left; color:#555'>• Vermiform iris</span>"]
Adie["<b>🩺 Adie Tonic Pupil</b><br><span style='display:block; text-align:left; color:#555'>• Ciliary ganglion</span><span style='display:block; text-align:left; color:#555'>• Slow constriction</span>"]
Midbrain["<b>🩺 Dorsal Midbrain</b><br><span style='display:block; text-align:left; color:#555'>• Parinaud syndrome</span><span style='display:block; text-align:left; color:#555'>• Other LND causes</span>"]
Start --> CheckSmall
CheckSmall -->|Yes| Argyll
CheckSmall -->|No| CheckDilated
CheckDilated -->|Yes| Adie
CheckDilated -->|No| Midbrain
style Start fill:#FEF8EC, stroke:#FBECCA, stroke-width:1.5px, rx:12, ry:12, color:#854D0E
style CheckSmall fill:#FEF8EC, stroke:#FBECCA, stroke-width:1.5px, rx:12, ry:12, color:#854D0E
style CheckDilated fill:#FEF8EC, stroke:#FBECCA, stroke-width:1.5px, rx:12, ry:12, color:#854D0E
style Argyll fill:#F7F5FD, stroke:#F0EDFA, stroke-width:1.5px, rx:12, ry:12, color:#6B21A8
style Adie fill:#F7F5FD, stroke:#F0EDFA, stroke-width:1.5px, rx:12, ry:12, color:#6B21A8
style Midbrain fill:#F7F5FD, stroke:#F0EDFA, stroke-width:1.5px, rx:12, ry:12, color:#6B21A8
Gaze & Field Defects - Tracking Trouble
- Internuclear Ophthalmoplegia (INO): Medial Longitudinal Fasciculus (MLF) lesion. Results in ipsilateral adduction deficit (eye cannot move inwards) and contralateral abducting nystagmus (jerky eye movement in the outwardly looking eye).
- Nystagmus: Involuntary, rhythmic eye oscillations.
- Types:
- Jerk: Slow drift, fast corrective saccade (e.g., gaze-evoked, vestibular).
- Pendular: Sinusoidal, equal velocity (e.g., congenital, acquired - MS).
- Types:
- Visual Field Defects: Localize lesions along the optic pathway.
- Common Defects & Lesion Sites:
Lesion Site Defect Type Optic Nerve Ipsilateral scotoma / total blindness Optic Chiasm Bitemporal hemianopia Optic Tract Contralateral homonymous hemianopia Optic Radiations Contralateral quadrantanopia (📌 PITS: Parietal-Inferior, Temporal-Superior) Visual Cortex Contralateral homonymous hemianopia (often macular sparing) -
⭐ Bitemporal hemianopia classically indicates a lesion at the optic chiasm.
High‑Yield Points - ⚡ Biggest Takeaways
- Optic neuritis: key in MS; painful vision loss, RAPD, Uhthoff's.
- Papilledema: bilateral disc swelling from ↑ICP; vision initially normal.
- IIIrd nerve palsy: pupil involved = compression; pupil spared = ischemia.
- VIth nerve palsy: horizontal diplopia, worse ipsilaterally; common in ↑ICP.
- INO: MLF lesion; ipsilateral adduction deficit, contralateral nystagmus; MS/stroke.
- Horner's syndrome: ptosis, miosis, anhydrosis; sympathetic pathway lesion.
- Visual fields: bitemporal hemianopia (chiasm); homonymous hemianopia (post-chiasm).