Neuro-Ophthalmology
Neuro-Ophthalmology
What Do You Need to Know?
- Pupil-involving CN III palsy: PComm aneurysm until proven otherwise — pupil fibers travel superficially on CN III, compressed by aneurysm before microvascular ischemia reaches them
- RAPD: localizes to optic nerve (or massive retinal disease) — NEVER caused by cataracts, refractive error, or media opacity
- INO: MLF lesion → ipsilateral adduction deficit + contralateral abducting nystagmus; young bilateral = MS, old unilateral = stroke
- GCA: start glucocorticoids BEFORE temporal artery biopsy. Use IV pulse methylprednisolone for threatened vision loss / cranial ischemia; high-dose oral prednisone is standard for active GCA without cranial ischemia (per 2021 ACR/VF). Jaw claudication is the most specific symptom.
- ONTT: low-dose oral prednisone alone increases optic neuritis recurrence — do not use. High-dose oral corticosteroids bioequivalent to IV methylprednisolone have similar short-term outcomes in typical ON (modern data).
- Horner syndrome + ipsilateral pain: carotid dissection until proven otherwise (3rd-order neuron)
- Visual field defects: more congruous = more posterior; macular sparing = occipital lobe (best explained by bilateral cortical representation + large cortical magnification of the macula; the classical "dual PCA/MCA blood supply" teaching is not well supported by anatomic data)
🚩 Don’t Miss — Test-Day Priorities
- Pupil-involving CN III palsy: PComm aneurysm → urgent CTA/angiography; SAH risk — never call it microvascular until imaging is clean
- Painful Horner + neck pain: carotid dissection until proven otherwise → urgent CTA neck/MRA; apraclonidine reverses anisocoria to confirm Horner
- Suspected GCA: start glucocorticoids immediately BEFORE temporal artery biopsy — IV pulse methylprednisolone for threatened vision/cranial ischemia, high-dose oral prednisone for active GCA without cranial ischemia (2021 ACR/VF). Tocilizumab is steroid-sparing; fellow eye blinds within days if untreated
- Optic neuritis (ONTT): IV methylprednisolone speeds recovery and delays MS conversion at 2 yr; low-dose oral prednisone alone (as used in ONTT) INCREASES recurrence — do not use. High-dose oral corticosteroids bioequivalent to IV MP have similar short-term outcomes.
- Atypical ON (bilateral, severe, painless, recurrent, NLP) → send AQP4-IgG and MOG-IgG; treat as NMOSD until proven otherwise (plasma exchange if steroid-refractory)
- Bilateral INO in a young patient: MS until proven otherwise; unilateral INO in older vasculopath → brainstem stroke
- Vertical supranuclear gaze palsy + preserved VOR (doll’s eyes): PSP — downgaze affected first; pair with axial rigidity and early falls
- Spasmus nutans (child: head bobbing + nystagmus + torticollis) → MRI to rule out chiasm/hypothalamic glioma — do NOT call it benign without imaging
- IIH with vision threat: escalate beyond acetazolamide — ONSF, CSF shunt, or venous sinus stenting; transient visual obscurations & enlarging blind spot are red flags
- Foster Kennedy syndrome (unilateral optic atrophy + contralateral papilledema) → frontal mass (olfactory groove meningioma) until imaged
- Ocular myasthenia: fatigable ptosis + variable diplopia, normal pupils; ice pack test improves ptosis; check anti-AChR and screen for thymoma
🔍 Buzzwords & Pathognomonic FindingsClinical · Visual field / pupils / gaze · Workup / treatment
Clinical phenotype
- Painful monocular vision loss + red desaturation in a young woman → optic neuritis (MS)
- Jaw claudication + scalp tenderness + new headache age >50 + chalky-white swollen disc → arteritic AION (GCA)
- Vasculopath wakes with altitudinal field defect + crowded "disc at risk" → NAION
- Young male, bilateral subacute painless central vision loss + telangiectatic peripapillary microangiopathy + maternal inheritance → LHON (m.11778G>A)
- Down-and-out eye with dilated pupil after sudden headache → PComm aneurysm CN III palsy
- Vertical diplopia worse going downstairs + compensatory head tilt → CN IV (trochlear) palsy
- Proptosis + lid lag + EOM enlargement sparing tendon insertions → thyroid (Graves) ophthalmopathy
- Fatigable ptosis + Cogan twitch + ice-pack improvement → ocular myasthenia gravis
- Obese young woman + headache + pulsatile tinnitus + transient visual obscurations → idiopathic intracranial hypertension
Pupil / VF / gaze findings
- RAPD (Marcus-Gunn pupil) + central scotoma → optic nerve lesion (ON/AION)
- Mild ptosis + miosis + anhidrosis → Horner syndrome (painful + neck → carotid dissection)
- Dilated pupil + sluggish to light + brisk to near + slow redilation + tendon areflexia → Adie tonic pupil (Holmes-Adie)
- Small irregular pupils that accommodate but do not react ("prostitute pupil") → Argyll Robertson (neurosyphilis / DM)
- Ipsilateral adduction failure + contralateral abducting nystagmus + preserved convergence → INO (MLF lesion)
- Ipsilateral conjugate gaze palsy + ipsilateral INO → one-and-a-half syndrome (paramedian pontine + MLF)
- Vertical supranuclear gaze palsy with intact VOR/doll’s eyes → PSP
- Homonymous hemianopia with macular sparing → occipital cortex (PCA) stroke
- "Pie in the sky" superior quadrantanopia → temporal lobe (Meyer loop); "pie on the floor" → parietal optic radiations
- Bitemporal hemianopia → chiasm (pituitary adenoma / craniopharyngioma); junctional scotoma → anterior chiasm / distal optic nerve
- Downbeat nystagmus → cervicomedullary junction (Chiari, MS, lithium/AED toxicity); upbeat → brainstem
- Pendular nystagmus + palatal tremor → oculopalatal myoclonus (hypertrophic olivary degeneration / Mollaret triangle)
- See-saw nystagmus → parasellar / chiasmal lesion; periodic alternating nystagmus → cerebellar (nodulus/uvula)
- Unilateral optic atrophy + contralateral papilledema → Foster Kennedy syndrome (frontal mass)
- Cortical blindness + denial/confabulation → Anton syndrome (bilateral occipital); simultanagnosia + optic ataxia + ocular apraxia → Balint (bilateral parieto-occipital watershed)
Workup / treatment
- ESR ≥50, CRP elevated, platelets ≥400K in patient >50 with new visual loss → start glucocorticoids immediately (IV pulse methylprednisolone if vision threatened / cranial ischemia; otherwise high-dose oral prednisone), then temporal artery biopsy
- Apraclonidine reverses anisocoria (dilates the miotic pupil) → confirms Horner syndrome
- Low-dose pilocarpine (0.125%) constricts a dilated tonic pupil → denervation supersensitivity — Adie pupil
- AQP4-IgG serum (cell-based assay) → NMOSD; MOG-IgG serum → MOGAD; oligoclonal bands → MS
- MRI orbits with fat suppression + gadolinium → optic neuritis (short-segment enhancement = MS; long-segment/perineural = MOGAD; chiasmal = NMOSD)
- LP opening pressure >25 cm H₂O with normal CSF in obese young woman → IIH → acetazolamide + topiramate + weight loss; ONSF / CSF shunt / venous stenting for vision threat
- Empty sella, posterior globe flattening, distended optic nerve sheath, transverse sinus stenosis on MRV → IIH imaging signature
- Pupil-involving CN III palsy → urgent CTA / catheter angiogram for PComm aneurysm
- Anti-AChR / anti-MuSK + chest CT for thymoma; ice pack + edrophonium (historical) → ocular myasthenia workup; treat with pyridostigmine ± steroids
- RPR/VDRL + FTA-ABS + CSF VDRL → Argyll Robertson / neurosyphilis
- Mitochondrial DNA testing (m.11778G>A, m.14484T>C, m.3460G>A) → LHON; idebenone trialed
Optic Neuritis
Typical vs Atypical Optic Neuritis
| Feature | Typical ON (MS-associated) | Atypical ON |
|---|---|---|
| Age | 20–45 years | Any age (children, >50) |
| Pain | Periorbital, worse with eye movement (92%) | May be painless or severe |
| Vision loss | Mild–moderate; central scotoma | Severe (NLP possible in NMOSD) |
| Laterality | Unilateral | Bilateral (NMOSD, MOGAD, sarcoid) |
| Disc appearance | 66% retrobulbar (normal disc); 33% disc edema | Disc edema more common (MOGAD, NMOSD) |
| Recovery | Good (>90% recover to 20/40 by 1 year) | Poor recovery (NMOSD); good in MOGAD |
| MRI orbits | Short-segment enhancement (<50% nerve length) | Long-segment or perineural enhancement |
| Key associations | MS (50% develop MS within 15 yr) | NMOSD, MOGAD, sarcoid, syphilis, lupus |
MS vs NMOSD vs MOGAD Optic Neuritis
| Feature | MS | NMOSD (AQP4+) | MOGAD |
|---|---|---|---|
| Severity | Mild–moderate | Severe (often ≤20/200) | Moderate–severe |
| Bilateral | Rare (unilateral) | Simultaneous or sequential bilateral | Often bilateral (especially children) |
| Disc edema | Uncommon (retrobulbar) | Common | Very common (prominent edema) |
| Enhancement pattern | Short segment, no perineural | Posterior/chiasmal involvement | Anterior, long segment, perineural sheath |
| Recovery | Excellent | Poor without treatment | Excellent (often complete) |
| Recurrence | Common | Very common (attack-driven damage) | Common; relapsing form exists |
| OCT (RNFL) | Mild thinning | Severe thinning | Variable |
| Antibody | Oligoclonal bands (CSF) | AQP4-IgG (serum) | MOG-IgG (serum) |
Treatment — ONTT Key Findings
- IV methylprednisolone (3 days) → oral taper: faster recovery; no difference in final visual outcome at 1 year
- Low-dose oral prednisone alone (as used in ONTT): INCREASED recurrence rate — should not be used. High-dose oral corticosteroids bioequivalent to IV methylprednisolone have similar short-term outcomes in typical optic neuritis.
- Observation: acceptable for mild cases; equivalent long-term visual outcome to IV steroids
- MS risk: ≥1 brain MRI lesion at presentation → 72% MS risk at 15 yr; 0 lesions → 25%
💎 Board Pearl
- ONTT: low-dose oral prednisone alone increases recurrence — the #1 tested fact from this trial. High-dose oral corticosteroids bioequivalent to IV MP are acceptable (similar short-term outcomes).
- RAPD is the hallmark of optic neuritis — if absent, reconsider the diagnosis
- Uhthoff phenomenon: transient visual worsening with heat/exercise (demyelinated nerve conducts worse when warm)
Ischemic Optic Neuropathy
Arteritic (AION) vs Non-Arteritic (NAION)
| Feature | AION (Giant Cell Arteritis) | NAION |
|---|---|---|
| Age | ≥50 (mean ~70) | ≥50 (mean ~60) |
| Onset | Sudden, may be preceded by amaurosis fugax | Sudden, often noticed on waking |
| Pain | Headache, jaw claudication, scalp tenderness | Usually painless |
| Disc appearance | Pale (chalky white), edematous | Hyperemic (swollen, not pale), sectoral edema |
| Visual field | Altitudinal or diffuse; often severe (counting fingers/NLP) | Inferior altitudinal most common; mild–moderate |
| ESR/CRP | Markedly elevated; ESR ≥50 (often ≥100) | Normal |
| Platelets | Often elevated (≥400K) | Normal |
| Pathology | Granulomatous arteritis of posterior ciliary arteries | Small vessel ischemia of short posterior ciliary arteries |
| Cup-to-disc ratio | Any | Small cup — "disc at risk" (≤0.2) |
| Fellow eye risk | Very high without steroids (50% within days–weeks) | 15–20% over 5 years |
| Treatment | Threatened vision / cranial ischemia: IV pulse methylprednisolone → high-dose oral prednisone taper. Active GCA without cranial ischemia: high-dose oral prednisone is standard (2021 ACR/VF). Tocilizumab for steroid-sparing. | No proven acute treatment; optimize vascular risk factors and OSA. Aspirin can be used for standard vascular indications, but fellow-eye prevention is unproven. |
| Biopsy | Temporal artery biopsy (gold standard); ≥1.5–2 cm specimen (post-fixation shrinkage); skip lesions possible — contralateral biopsy if first negative and suspicion high | Not indicated |
| Prognosis | Poor if untreated; stable if treated | Stable; modest spontaneous improvement in ~40% |
GCA Red Flags — Symptom Specificity
| Symptom | Sensitivity | Specificity | Notes |
|---|---|---|---|
| Jaw claudication | ~34% | Highest (~95%) | Most specific symptom; masseter ischemia from maxillary artery involvement |
| Scalp tenderness | ~40% | High | Over temporal arteries; pain with hair combing |
| PMR | ~40–50% | Moderate | Proximal shoulder/hip girdle stiffness and pain; overlapping condition |
| New headache | ~75% | Low | Most sensitive; temporal predominance |
| Visual symptoms | ~25–50% | Moderate | Amaurosis fugax, diplopia, permanent vision loss |
NAION Key Points
- Disc at risk: small cup-to-disc ratio (≤0.2) — crowded optic disc with no room for edema
- Risk factors: HTN, DM, OSA, nocturnal hypotension, PDE5 inhibitors (sildenafil)
- No proven treatment: IONDT showed optic nerve sheath decompression NOT beneficial (may worsen)
- Fellow eye: 15–20% risk within 5 years; counsel patients
⚠ Warning
Start glucocorticoids for suspected GCA BEFORE temporal artery biopsy — biopsy remains positive for ≥2 weeks after starting steroids. IV pulse methylprednisolone for threatened vision loss or cranial ischemia; high-dose oral prednisone is standard for active GCA without cranial ischemia (2021 ACR/VF). Never delay treatment to wait for biopsy.
💎 Board Pearl
- Chalky white disc edema = AION (GCA); hyperemic disc edema = NAION
- Jaw claudication is the most specific symptom for GCA; new headache is the most sensitive
- ESR formula ceiling: men = age/2; women = (age + 10)/2 — GCA values far exceed these
Hereditary & Other Optic Neuropathies
Leber's Hereditary Optic Neuropathy (LHON)
| Feature | Details |
|---|---|
| Demographics | Young men (3:1 to 9:1 male predominance); typically 15–35 yr |
| Inheritance | Mitochondrial (maternal transmission); incomplete penetrance |
| Mutations | m.11778G>A (most common, ~70%), m.3460G>A, m.14484T>C |
| Presentation | Painless, sequential bilateral central scotoma (second eye affected within weeks–months); dyschromatopsia |
| Acute fundus | Pseudoedema with peripapillary telangiectasia (no true leakage on FA) → progresses to optic atrophy |
| Prognosis | Most cases progress to severe vision loss; m.14484 has best recovery potential |
Riddoch Phenomenon
- Definition: Preserved motion perception within a hemianopic field despite loss of static visual perception
- Localization: V1 (primary visual cortex) lesion with sparing of V5/MT (motion area) and its extrastriate inputs
- Significance: A form of "blindsight"; patient cannot see static objects but can detect moving ones in the blind field
💎 Board Pearl
- LHON: young man, painless sequential bilateral central scotoma, mtDNA m.11778G>A — pseudoedema (no FA leakage) → atrophy
- Riddoch phenomenon: motion preserved in hemianopic field — V1 lesion with intact V5/MT
Papilledema & Idiopathic Intracranial Hypertension
Papilledema vs Pseudopapilledema
| Feature | Papilledema (True) | Pseudopapilledema |
|---|---|---|
| Disc margins | Blurred, obscured (especially nasal first) | Irregular but distinct; anomalous elevation |
| Vessels | Obscured at disc margin; venous engorgement | Visible, not obscured; normal caliber |
| Hemorrhages | Peripapillary splinter hemorrhages, cotton-wool spots | Absent |
| Blind spot | Enlarged | Normal or mildly enlarged |
| Visual acuity | Preserved early (loss = late/severe) | Normal |
| Venous pulsations | Absent (elevated ICP abolishes them) | Present (normal) |
| Fluorescein angiography | Disc leakage, capillary dilation | Autofluorescence of drusen; no leakage |
| Common causes | Raised ICP (tumor, IIH, CVT, hydrocephalus) | Optic disc drusen (most common), hyperopia, tilted disc |
IIH — Modified Dandy Criteria
- A. Papilledema present
- B. Normal neurologic exam (except CN VI palsy allowed)
- C. Normal brain MRI (or with supportive signs only)
- D. Normal CSF composition
- E. Elevated LP opening pressure: >25 cm H2O in adults; >28 cm H2O in children (non-sedated, non-obese)
IIH MRI Supportive Signs
| MRI Finding | Significance |
|---|---|
| Empty sella | Chronic elevated ICP flattens pituitary |
| Optic nerve sheath distension | Perioptic CSF expansion — most sensitive sign |
| Posterior globe flattening | Pressure transmitted to back of eye |
| Transverse sinus stenosis | Bilateral; cause vs. consequence debated; target for stenting |
| Optic nerve tortuosity | Increased perioptic CSF causes kinking |
IIH Treatment Ladder
| Step | Intervention | Key Points |
|---|---|---|
| 1 | Weight loss | 5–10% weight loss can resolve symptoms; only disease-modifying treatment |
| 2 | Acetazolamide | Carbonic anhydrase inhibitor; reduces CSF production; IIHTT trial: improves visual field and papilledema |
| 3 | Topiramate | Weak carbonic anhydrase inhibitor + weight loss effect; useful adjunct |
| 4 | Serial LPs | Temporizing; rarely used long-term |
| 5 | LP shunt (VPS or LPS) | Fulminant or refractory cases; high revision rate |
| 6 | ONSF (optic nerve sheath fenestration) | Primarily for visual decline without headache; local CSF decompression around nerve |
| 7 | Venous sinus stenting | For documented transverse sinus stenosis with pressure gradient ≥8 mmHg |
Medications Causing Pseudotumor (Raised ICP)
| Drug | Mnemonic Clue |
|---|---|
| Tetracyclines (minocycline, doxycycline) | Most commonly tested; acne patients on tetracyclines |
| Vitamin A / retinoids (isotretinoin) | Acne treatment — double risk with tetracyclines |
| Growth hormone | Pediatric patients |
| Lithium | Psychiatric patients |
| Corticosteroid withdrawal | Not initiation — withdrawal causes rebound ICP elevation |
💎 Board Pearl
- Papilledema preserves visual acuity until late — early loss of acuity suggests optic neuritis, AION, or other optic neuropathy, NOT papilledema
- CN VI palsy in IIH is a false localizing sign (long intracranial course, stretched by raised ICP) — does not localize to a focal lesion
- Optic disc drusen are the #1 cause of pseudopapilledema — best confirmed with autofluorescence or B-scan ultrasound
Third Nerve Palsy (CN III)
Pupil-Involving vs Pupil-Sparing CN III Palsy
| Feature | Pupil-Involving | Pupil-Sparing |
|---|---|---|
| Pupil | Fixed, dilated (mydriasis) | Normal and reactive |
| Most likely etiology | Compressive — PComm aneurysm (#1) | Microvascular (diabetes, HTN) |
| Mechanism | Pupillary parasympathetic fibers travel superficially on CN III → compressed first | Ischemia affects the central core of the nerve (vasa nervorum supplies core preferentially); peripherally located pupillary parasympathetic fibers are spared by virtue of pial collateral supply |
| Urgency | EMERGENCY — CTA/MRA/DSA immediately | Observe 3 months; image if no improvement or other features develop |
| Pain | Often severe (aneurysm stretching CN III) | Can be painful (diabetic CN III can cause pain) |
| Recovery | Depends on intervention (aneurysm repair) | Spontaneous recovery in 3 months (~95%) |
| Age | Any age; younger patients = higher suspicion | Typically >50 with vascular risk factors |
Complete CN III Palsy — Signs
- Eye position: "down and out" (unopposed lateral rectus + superior oblique)
- Ptosis: complete (levator palpebrae involved)
- Pupils: dilated, unreactive (if pupil-involving)
- Muscles affected: MR, SR, IR, IO, levator palpebrae, pupillary sphincter, ciliary muscle
- Spared: SO (CN IV) and LR (CN VI)
Aberrant Regeneration of CN III
- Misdirected reinnervation after compressive (NOT microvascular) CN III injury
- Signs: lid-gaze dyskinesis (lid elevates on downgaze or adduction), pseudo-Argyll Robertson (pseudo-LND from misdirected adduction fibers to pupillary sphincter)
- Primary aberrant regeneration (without preceding CN III palsy) → suggests slowly compressive lesion (cavernous sinus meningioma)
- If aberrant regeneration follows a "microvascular" CN III → reconsider diagnosis; image for compressive lesion
CN III Fascicular Syndromes (Midbrain)
| Syndrome | Lesion Site | CN III + Additional Findings |
|---|---|---|
| Weber | Cerebral peduncle (ventral midbrain) | Ipsilateral CN III + contralateral hemiparesis |
| Benedikt | Red nucleus / tegmentum | Ipsilateral CN III + contralateral tremor/choreoathetosis |
| Claude | Red nucleus + superior cerebellar peduncle | Ipsilateral CN III + contralateral ataxia |
| Nothnagel | Superior cerebellar peduncle / tectum | Ipsilateral CN III + ipsilateral cerebellar ataxia |
Nuclear CN III Anatomy — Localization Pearls
| Subnucleus | Anatomy | Lesion Effect |
|---|---|---|
| Edinger-Westphal (EW) nuclei | Paired (NOT midline) | Unilateral nuclear lesion → ipsilateral mydriasis |
| Central caudal subnucleus | Single midline structure innervating BOTH levators | Single midline lesion → bilateral ptosis |
| Superior rectus subnucleus | Crossed (innervates contralateral SR) | Unilateral nuclear lesion → contralateral SR weakness |
💎 Board Pearl
- A nuclear CN III lesion produces a unique constellation: ipsilateral CN III findings + contralateral SR weakness + bilateral ptosis (central caudal nucleus is midline)
💎 Board Pearl
- Rule of the pupil: pupil-involving CN III = PComm aneurysm until proven otherwise; pupil-sparing = microvascular
- Aberrant regeneration never occurs after microvascular CN III palsy — if present, image for compression
- A "complete" pupil-sparing CN III palsy is extremely rare with aneurysm — but incomplete pupil-sparing or progressive palsy still warrants imaging
Fourth & Sixth Nerve Palsies
CN IV (Trochlear Nerve) Palsy
| Feature | Details |
|---|---|
| Muscle | Superior oblique (intorts + depresses in adduction + abducts) |
| Deviation | Hypertropia of affected eye |
| Worse on | Contralateral gaze + ipsilateral head tilt (Parks-Bielschowsky three-step test) |
| Head posture | Contralateral head tilt (compensatory — away from affected side) |
| #1 cause of bilateral CN IV | Head trauma (bilateral because nerves decussate in anterior medullary velum) |
| Congenital CN IV | Most common congenital cranial nerve palsy; long-standing head tilt in old photos; large vertical fusional amplitude |
| Other causes | Microvascular (DM/HTN), tumor, cavernous sinus lesion |
Parks-Bielschowsky Three-Step Test
- Step 1: Which eye is hypertropic? (identifies 4 muscles)
- Step 2: Is hypertropia worse in right or left gaze? (narrows to 2 muscles)
- Step 3: Is hypertropia worse with right or left head tilt? (identifies the paretic muscle)
- Example: right hypertropia + worse in left gaze + worse with right head tilt = right CN IV palsy (right SO)
CN VI (Abducens Nerve) Palsy
| Feature | Details |
|---|---|
| Muscle | Lateral rectus (abduction) |
| Presentation | Horizontal diplopia worse at distance; esotropia |
| Most common cause of diplopia | CN VI palsy overall |
| False localizing sign | Long intracranial course → vulnerable to raised ICP (stretched over clivus/petrous apex) |
| Common causes | Microvascular (adults), raised ICP, post-viral (children), tumor, trauma |
CN VI Nuclear vs Fascicular vs Peripheral
| Level | Key Features | Why |
|---|---|---|
| Nuclear | Ipsilateral gaze palsy (both eyes cannot look ipsilaterally) | CN VI nucleus contains motor neurons for LR AND interneurons for contralateral MLF → full gaze palsy |
| Fascicular | Ipsilateral LR palsy + additional pontine signs (CN VII, Horner, hemiparesis) | Fascicle traverses pons near CN VII, sympathetics, corticospinal tract |
| Peripheral | Isolated LR palsy | No adjacent structures involved |
Bilateral CN VI Palsy — Differential
| Cause | Clue |
|---|---|
| Raised ICP | Papilledema, headache; false localizing sign |
| Wernicke encephalopathy | Confusion, ataxia, ophthalmoplegia; thiamine deficiency |
| Meningitis (infectious/carcinomatous) | Fever, neck stiffness; CSF analysis abnormal |
| Clivus lesion (chordoma, metastasis) | CN VI travels over clivus; bilateral involvement |
| NMOSD | Area postrema involvement; AQP4+ serology |
| Trauma | History of head injury |
💎 Board Pearl
- CN IV is the only cranial nerve to exit the brainstem dorsally, fully decussate before exiting, and has the longest intracranial course — explains vulnerability to trauma
- CN VI nuclear lesion → ipsilateral gaze palsy (not just LR weakness) because interneurons for contralateral MLF originate in CN VI nucleus
- Look at old photographs for head tilt — long-standing tilt suggests congenital CN IV palsy
INO & Supranuclear Gaze Disorders
Internuclear Ophthalmoplegia (INO)
| Feature | Details |
|---|---|
| Lesion | MLF (medial longitudinal fasciculus) between CN VI nucleus and contralateral CN III nucleus |
| Ipsilateral eye | Adduction deficit (weak medial rectus activation via MLF) |
| Contralateral eye | Abducting nystagmus (compensatory overshoot) |
| Convergence | Preserved (separate supranuclear pathway, not through MLF) |
| Named for | Side of the adduction deficit (i.e., side of MLF lesion) |
INO Etiologies
| Age/Pattern | Most Likely Cause |
|---|---|
| Young + bilateral INO | MS (demyelination of MLF) |
| Older + unilateral INO | Brainstem stroke (small perforator infarct) |
One-and-a-Half Syndrome
- Lesion: ipsilateral PPRF (or CN VI nucleus) + ipsilateral MLF
- Result: ipsilateral gaze palsy ("one") + ipsilateral INO ("half")
- Only movement remaining: contralateral eye abduction
- Localization: dorsal pontine tegmentum (often lacunar infarct or MS plaque)
- Eight-and-a-half syndrome: one-and-a-half + ipsilateral peripheral CN VII palsy (facial colliculus involvement)
Parinaud Syndrome (Dorsal Midbrain Syndrome)
| Feature | Detail |
|---|---|
| Upgaze palsy | Cannot look up voluntarily (supranuclear — doll's eyes may overcome) |
| Convergence-retraction nystagmus | Attempted upgaze → eyes converge and retract into orbits |
| Light-near dissociation | Pupils react to near but not to light (pretectal input disrupted) |
| Eyelid retraction | Collier sign (posterior commissure involvement) |
| Causes | Pinealoma (children), stroke, hydrocephalus (aqueductal), MS |
Supranuclear Gaze Pathways
| Structure | Function | Lesion Effect |
|---|---|---|
| PPRF | Horizontal saccade generator (ipsilateral) | Ipsilateral horizontal gaze palsy |
| CN VI nucleus | LR motor neurons + MLF interneurons | Ipsilateral gaze palsy (both eyes) — same as PPRF but nuclear |
| MLF | CN VI nucleus → contralateral CN III (adduction signal) | INO (ipsilateral adduction failure) |
| riMLF | Vertical saccade generator (bilateral input) | Upgaze or downgaze palsy; bilateral lesion → complete vertical gaze palsy |
| FEF (frontal eye field) | Contralateral saccades | Eyes deviate toward lesion ("eyes look at the lesion" in stroke); away from lesion in seizure |
PSP vs Parinaud — Vertical Gaze Palsy
| Feature | PSP | Parinaud |
|---|---|---|
| Direction | Downgaze affected first (then upgaze) | Upgaze affected first |
| Type | Supranuclear (overcome by VOR early) | Supranuclear (overcome by doll's eyes) |
| Pupils | Small, poorly reactive | Light-near dissociation, mid-dilated |
| Convergence-retraction nystagmus | Absent | Present |
| Associated features | Falls, axial rigidity, frontal dementia | Eyelid retraction (Collier sign) |
| Etiology | Tauopathy (4R tau) | Pinealoma, hydrocephalus, stroke |
💎 Board Pearl
- INO is named for the side of the adduction deficit (= side of the MLF lesion)
- One-and-a-half syndrome: only the contralateral eye can abduct — everything else is paralyzed
- FEF stroke: eyes deviate toward the lesion; FEF seizure: eyes deviate away from the focus
Pupil Disorders
Horner Syndrome
| Feature | Details |
|---|---|
| Triad | Miosis + ptosis (1–2 mm) + anhidrosis (variable) |
| Dilation lag | Affected pupil dilates more slowly in darkness (best early sign) |
| Ptosis | Mild (1–2 mm); Müller muscle (sympathetic) — NOT complete ptosis |
| Inverse ptosis | Lower lid elevation (inferior tarsal muscle denervation) → apparent enophthalmos |
Horner Localization — Three-Neuron Arc
| Order | Pathway | Key Causes | Anhidrosis |
|---|---|---|---|
| 1st order (central) | Hypothalamus → C8–T2 (ciliospinal center of Budge) | Lateral medullary stroke (Wallenberg), hypothalamic lesion, spinal cord lesion | Ipsilateral body + face |
| 2nd order (preganglionic) | C8–T2 → superior cervical ganglion (travels over lung apex, along subclavian artery) | Pancoast tumor (lung apex), thyroid surgery, neck surgery, trauma | Ipsilateral face |
| 3rd order (postganglionic) | Superior cervical ganglion → eye (travels along ICA → cavernous sinus → long ciliary nerves) | Carotid dissection (#1 to test), cavernous sinus lesion, cluster headache | None (fibers diverge before ganglion) |
Pharmacologic Testing
| Drop | Mechanism | Result in Horner | What It Tells You |
|---|---|---|---|
| Cocaine 4–10% | Blocks NE reuptake (needs intact NE release) | Affected pupil fails to dilate (anisocoria increases) | Confirms Horner syndrome (any order) |
| Apraclonidine 0.5–1% | Weak α1 / strong α2 agonist; dilates the denervated (supersensitive) pupil via α1 activity → reversal of anisocoria | Affected pupil dilates (reversal of anisocoria) | Confirms Horner (alternative to cocaine) |
| Hydroxyamphetamine 1% | Releases stored NE from postganglionic terminal | No dilation = 3rd-order (postganglionic); dilates = 1st or 2nd order | Localizes: postganglionic vs pre/central |
Adie Tonic Pupil
| Feature | Details |
|---|---|
| Lesion | Ciliary ganglion or short ciliary nerves (parasympathetic) |
| Pupil | Dilated, poor/absent light reaction, tonic near response (slow constriction, slow redilation) |
| Vermiform movements | Segmental iris sphincter contractions on slit lamp (pathognomonic) |
| Light-near dissociation | Near response preserved (more fibers devoted to accommodation → more likely to regenerate) |
| Denervation supersensitivity | Dilute pilocarpine 0.1% (or 0.125%) constricts Adie pupil but NOT normal pupil |
| Holmes-Adie syndrome | Adie pupil + absent deep tendon reflexes (areflexia) |
| Demographics | Young women; idiopathic, viral, post-surgical |
Argyll Robertson Pupil
- Features: bilateral, small, irregular pupils; NO light reaction, intact near response (light-near dissociation)
- Mnemonic: "Accommodates but doesn't React" — ARP = Argyll Robertson Pupil
- Classic association: neurosyphilis
- Localization: Lesion in the ROSTRAL midbrain periaqueductal gray (NOT pretectal — pretectal disruption causes Parinaud's mid-dilated light-near dissociation). Light fibers from pretectal olivary nucleus to Edinger-Westphal are interrupted, sparing the more ventral near-response pathway
- Also seen in: diabetes (rare), sarcoid, Lyme, MS
RAPD (Marcus Gunn Pupil)
| Feature | Details |
|---|---|
| Test | Swinging flashlight test — affected eye paradoxically dilates when light swings to it |
| Mechanism | Reduced afferent input from affected optic nerve → less consensual signal when stimulated |
| Localizes to | Optic nerve disease (or massive asymmetric retinal disease) |
| NOT caused by | Cataracts, refractive error, amblyopia, media opacity, macular degeneration |
| Bilateral optic nerve disease | No RAPD if symmetric; still have bilaterally sluggish pupils |
| Optic tract lesion | RAPD contralateral to the lesion (contralateral eye has more crossing nasal fibers) |
Light-Near Dissociation — Differential
| Condition | Pupil Size | Unilateral/Bilateral |
|---|---|---|
| Argyll Robertson | Small, irregular | Bilateral |
| Adie tonic pupil | Large (dilated) | Usually unilateral |
| Parinaud syndrome | Mid-dilated | Bilateral |
| Aberrant CN III regeneration | Variable | Unilateral |
| Severe afferent disease (bilateral optic neuropathy) | Large | Bilateral |
💎 Board Pearl
- Horner + ipsilateral neck/face pain in a young patient = carotid dissection until proven otherwise (CTA neck immediately)
- RAPD localizes to the optic nerve — if a patient has decreased vision + no RAPD, the optic nerve is NOT the problem
- Dilute pilocarpine 0.1% (or 0.125%) constricts Adie pupil (denervation supersensitivity) but not normal pupils — confirmatory test
Nystagmus
Peripheral vs Central Nystagmus
| Feature | Peripheral | Central |
|---|---|---|
| Direction | Unidirectional (fast phase away from lesion); mixed horizontal-torsional | Direction-changing, pure vertical, or pure torsional |
| Fixation | Suppressed by visual fixation | NOT suppressed (may worsen) |
| Vertigo | Severe | Mild or absent |
| Hearing loss/tinnitus | May be present | Usually absent |
| Dix-Hallpike | Fatigable, latency 2–20 s, transient (<60 s) | Non-fatigable, no latency, persistent |
| Associated signs | None (isolated vestibular) | Skew deviation, INO, cerebellar signs, diplopia |
| Duration | Days to weeks (self-limited) | Variable; may be persistent |
Nystagmus by Direction — Localization
| Nystagmus Type | Localization | Key Causes |
|---|---|---|
| Downbeat | Cervicomedullary junction (craniocervical) | Chiari malformation (#1), MS, lithium, anticonvulsants, B12 deficiency, spinocerebellar degeneration |
| Upbeat | Pontomedullary tegmentum or caudal medulla (perihypoglossal nuclei, NPH); also anterior vermis | Wernicke encephalopathy, medullary infarct, MS, drug toxicity |
| Gaze-evoked | Cerebellum (flocculus) or drug effect | Most common type; phenytoin, carbamazepine, alcohol, cerebellar lesion |
| Periodic alternating (PAN) | Cervicomedullary junction / nodulus | Chiari, MS, spinocerebellar ataxia; treat with baclofen |
| See-saw | Parasellar region / diencephalon | Craniopharyngioma, pituitary tumor, septo-optic dysplasia |
| Convergence-retraction | Dorsal midbrain (posterior commissure) | Parinaud syndrome (pinealoma, hydrocephalus) |
| Opsoclonus | Cerebellar (disinhibition of fastigial nucleus) | Paraneoplastic: neuroblastoma (children), breast/ovary (adults); anti-Ri, anti-Hu; post-infectious |
| Ocular flutter | Same as opsoclonus (horizontal only) | Same etiology as opsoclonus; horizontal saccadic oscillation without intersaccadic interval |
Key Nystagmus Patterns
- Downbeat nystagmus: think Chiari I first — get MRI craniocervical junction; also screen for medications
- Opsoclonus-myoclonus-ataxia (OMA): in children → neuroblastoma workup (urine catecholamines, abdominal imaging); in adults → breast, ovary, lung
- Acquired pendular nystagmus: MS (demyelination of cerebellar/brainstem connections), oculopalatal tremor (hypertrophic olivary degeneration)
- Oculopalatal tremor: rhythmic palatal + pendular nystagmus; hypertrophic olivary degeneration (MRI: T2 bright inferior olive); Guillain-Mollaret triangle lesion
💎 Board Pearl
- Downbeat nystagmus = craniocervical junction until proven otherwise — Chiari I is the #1 structural cause
- PAN (periodic alternating nystagmus) is treated with baclofen — commonly tested
- Opsoclonus in a child = neuroblastoma workup; in an adult = breast, ovary, lung paraneoplastic screen + anti-Ri/anti-Hu
Visual Field Defects — Localization
Visual Pathway Localization
| Lesion Site | Visual Field Defect | Key Features |
|---|---|---|
| Optic nerve | Ipsilateral monocular vision loss (central scotoma, altitudinal, arcuate) | RAPD present; optic neuritis, AION, NAION, compression |
| Optic chiasm | Bitemporal hemianopia | Pituitary adenoma compresses chiasm from BELOW → SUPERIOR bitemporal quadrants lost first (inferior crossing fibers compressed first); progresses to involve inferior fields. Craniopharyngioma compresses from ABOVE → inferior bitemporal quadrants first |
| Junction (nerve + chiasm) | Junctional scotoma: ipsilateral central scotoma + contralateral superior temporal defect | Wilbrand’s knee (inferior nasal fibers loop into contralateral optic nerve) |
| Optic tract | Contralateral homonymous hemianopia (incongruous) | RAPD contralateral to lesion; incongruous because fibers not yet fully organized |
| LGN | Contralateral homonymous hemianopia (sector defects possible) | Dual blood supply (PCA + anterior choroidal) → unique sector patterns; sectoranopia |
| Temporal lobe (Meyer’s loop) | Contralateral superior quadrantanopia (“pie in the sky”) | Inferior retinal fibers (= superior visual field) loop through temporal lobe |
| Parietal lobe | Contralateral inferior quadrantanopia (“pie on the floor”) | Superior retinal fibers (= inferior visual field) travel through parietal lobe; may have OKN asymmetry |
| Occipital lobe | Contralateral homonymous hemianopia (congruous) | Most congruous; macular sparing best explained by bilateral cortical representation + large cortical magnification of macula (classical "dual PCA/MCA blood supply" teaching not well supported); PCA stroke most common cause |
High-Yield Localization Rules
- More posterior = more congruous: tract (incongruous) → radiations (moderate) → occipital (congruous)
- Macular sparing: in PCA stroke; best explained by bilateral cortical representation of the macula + the very large cortical area devoted to macular vision at the occipital pole. The classical "dual PCA/MCA blood supply" teaching is widely taught but not well supported by anatomic/angiographic data (Osborn; Caplan).
- Temporal lobe = "pie in the sky" (superior quadrantanopia) — Meyer’s loop
- Parietal lobe = "pie on the floor" (inferior quadrantanopia)
- Optic tract = RAPD contralateral to the lesion (more crossed nasal fibers = contralateral eye has relatively more afferent input loss)
- Retrochiasmal lesions do NOT cause RAPD (with the exception of optic tract lesions)
Special Visual Field Patterns
| Pattern | Localization | Key Association |
|---|---|---|
| Junctional scotoma | Optic nerve–chiasm junction | Ipsilateral central scotoma + contralateral superior temporal defect (Wilbrand’s knee) |
| Bitemporal hemianopia | Optic chiasm | Pituitary adenoma; may cause bitemporal visual field "sliding" (loss of binocular fusion) |
| Homonymous hemianopia with macular sparing | Occipital lobe (PCA territory) | PCA stroke; macular sparing best explained by bilateral cortical representation + large cortical magnification of macula (classical "MCA collateral / dual blood supply" teaching not well supported) |
| Bilateral occipital | Cortical blindness | Anton syndrome = denial of blindness (bilateral V1 + association cortex involvement); normal pupillary reflexes (subcortical reflex intact) |
| Checkerboard pattern (bilateral homonymous hemianopia) | Bilateral occipital | Bilateral PCA strokes; "top of the basilar" syndrome |
| Monocular temporal crescent | Contralateral anterior occipital lobe | Only the most anterior occipital cortex represents far temporal monocular field; spared in tip-of-occipital lesions |
Clinical Pearl
- Cortical blindness (bilateral occipital) has normal pupillary reflexes (pretectal light reflex pathway is subcortical and intact) — distinguishes from bilateral optic nerve disease
- OKN asymmetry (optokinetic nystagmus): impaired with drum rotating toward the side of a deep parietal lesion — helps lateralize the lesion in hemianopia
💎 Board Pearl
- Bitemporal hemianopia = chiasm; pituitary adenoma compresses from BELOW → SUPERIOR bitemporal quadrants lost first (inferior crossing fibers hit first); craniopharyngioma compresses from ABOVE → inferior bitemporal quadrants first
- Macular sparing = occipital lobe (best explained by bilateral cortical representation + large cortical magnification of the macula; the classical "dual PCA/MCA blood supply" teaching is not well supported by anatomic data); never seen with optic tract or LGN lesions
- Anton syndrome: patient is cortically blind but denies blindness and confabulates visual experiences — bilateral occipital infarcts (bilateral V1 + association cortex involvement)
High-Yield Comparison Table
Master Quick-Reference: Neuro-Ophthalmology
| Condition | Key Finding | Localization | Board Buzzword |
|---|---|---|---|
| Optic neuritis (MS) | Painful vision loss, RAPD, retrobulbar | Optic nerve | ONTT — low-dose oral pred alone increases recurrence; high-dose oral bioequivalent to IV MP is acceptable |
| NMOSD optic neuritis | Severe bilateral vision loss, poor recovery | Optic nerve (posterior/chiasmal) | AQP4-IgG; longitudinal enhancement |
| AION (GCA) | Chalky white disc edema, jaw claudication | Posterior ciliary arteries | Glucocorticoids before biopsy (IV pulse if cranial ischemia, otherwise high-dose oral); skip lesions |
| NAION | Hyperemic disc, inferior altitudinal defect | Short posterior ciliary arteries | Disc at risk (small cup); no proven treatment |
| Papilledema | Bilateral disc edema, preserved acuity early | Raised ICP | Absent venous pulsations |
| IIH | Obese female, headache, papilledema, elevated OP | Diffuse (increased ICP) | Acetazolamide; weight loss; CN VI false localizing |
| CN III (PComm aneurysm) | Pupil-involving, "down and out," ptosis | PComm / CN III | Pupil-involving = aneurysm until proven otherwise |
| CN III (microvascular) | Pupil-sparing, painful, resolves in 3 months | CN III (central ischemia) | Diabetes/HTN; no aberrant regeneration |
| Weber syndrome | CN III + contralateral hemiparesis | Ventral midbrain (cerebral peduncle) | Ipsi CN III + contra hemiparesis |
| CN IV palsy | Hypertropia, worse contralateral gaze + ipsi head tilt | Trochlear nerve | Trauma #1 bilateral; Bielschowsky test |
| CN VI palsy | Esotropia, LR weakness, horizontal diplopia | Abducens nerve | False localizing sign (raised ICP) |
| INO | Ipsilateral adduction deficit + contralateral abducting nystagmus | MLF (brainstem) | Young bilateral = MS; old unilateral = stroke |
| One-and-a-half syndrome | Only contralateral eye abducts | Pons (PPRF + MLF) | Ipsilateral gaze palsy + ipsilateral INO |
| Parinaud syndrome | Upgaze palsy, convergence-retraction nystagmus, Collier sign | Dorsal midbrain | Pinealoma; light-near dissociation |
| Horner syndrome | Miosis, ptosis (1–2 mm), anhidrosis | Sympathetic chain (3 orders) | 3rd order + pain = carotid dissection |
| Adie tonic pupil | Dilated pupil, poor light reaction, vermiform movements | Ciliary ganglion | Dilute pilocarpine 0.1% (or 0.125%) constricts Adie |
| Argyll Robertson | Small, irregular, light-near dissociation | Rostral midbrain periaqueductal gray (NOT pretectal — pretectal = Parinaud) | "Accommodates but doesn't React" = syphilis |
| RAPD | Paradoxical dilation on swinging flashlight | Optic nerve | Never from cataracts or media opacity |
| Downbeat nystagmus | Nystagmus beating downward | Craniocervical junction | Chiari malformation #1 |
| PAN | Alternating nystagmus direction periodically | Cervicomedullary junction / nodulus | Treat with baclofen |
| Opsoclonus | Involuntary chaotic multidirectional saccades | Cerebellum (fastigial disinhibition) | Neuroblastoma (child); breast/ovary (adult) |
| See-saw nystagmus | One eye rises + intorts while other falls + extorts | Parasellar region | Craniopharyngioma; pituitary tumor |
| Bitemporal hemianopia | Loss of temporal fields bilaterally | Optic chiasm | Pituitary adenoma |
| "Pie in the sky" | Contralateral superior quadrantanopia | Temporal lobe (Meyer’s loop) | Inferior retinal fibers loop through temporal lobe |
| Macular sparing hemianopia | Congruous hemianopia with central vision preserved | Occipital lobe | Bilateral cortical macular representation + large cortical magnification (classical "dual PCA/MCA" teaching not well supported) |
| Cortical blindness | Bilateral vision loss, normal pupils | Bilateral occipital lobes | Anton syndrome (denial of blindness) |
💎 Board Pearl
- Neuro-ophthalmology board questions are all about localization — know the anatomy, and the answer follows
- If a question describes pupil abnormality + pain → think CN III (aneurysm) or Horner (dissection) — both are emergencies
- Any vertical gaze palsy: downgaze first = PSP; upgaze first = dorsal midbrain (Parinaud)
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