Anisocoria

Anisocoria

🔑 Key concept

• Anisocoria = unequal pupil size
• Range: physiologic (benign) → life-threatening (eg. aneurysm, CN III palsy)
• การ approach ที่ดีช่วยลด unnecessary imaging ได้

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🧬 Neuroanatomy ที่ต้องรู้

1. Parasympathetic (constriction)

• Pathway: Retina → Pretectal nucleus → Edinger-Westphal → CN III → ciliary ganglion → sphincter pupillae
• Function: miosis (pupil constriction)
• Lesion → mydriasis (pupil ใหญ่)

2. Sympathetic (dilation)

• 3-neuron pathway:
• Hypothalamus → C8–T2
• → superior cervical ganglion
• → along internal carotid → eye
• Function: mydriasis (pupil dilation)
• Lesion → miosis (pupil เล็ก) (Horner syndrome)

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🔍 Clinical approach (สำคัญที่สุด)

🧭 Step 1: identify abnormal pupil

Finding	Interpretation
Anisocoria ↑ in dark	small pupil abnormal → sympathetic defect
Anisocoria ↑ in light	large pupil abnormal → parasympathetic defect

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👁️ Examination essentials

• ตรวจใน dim light
• ดู:
• size, shape, symmetry
• light reflex + consensual
• near reflex
• Key findings:
• Dilation lag → Horner
• RAPD → optic nerve (ไม่ทำให้ anisocoria)

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⚠️ Red flags

• Ptosis + diplopia + large pupil → CN III palsy (aneurysm until proven otherwise)
• Painful red eye + mydriasis → acute glaucoma
• New Horner → rule out carotid dissection / lung apex tumor

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📚 Major causes

1. 🟢 Physiologic anisocoria

• พบ ~20%
• ต่าง <0.4 mm
• ไม่มี dilation lag
• stable / intermittent
  → benign

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2. 🔵 Small pupil abnormal (miosis)

👉 Sympathetic problem

✔️ Common causes

• Horner syndrome
• triad: miosis + ptosis + anhidrosis
• worse in dark
• dilation lag
• Ocular causes (iritis, surgery)
• Pharmacologic (pilocarpine)

✔️ Diagnosis

• Apraclonidine test → pupil dilates (reversal)

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3. 🔴 Large pupil abnormal (mydriasis)

👉 Parasympathetic problem

✔️ Causes

(A) Third nerve palsy

• mydriasis + ptosis + ophthalmoplegia
  👉 Emergency (rule out aneurysm)

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(B) Adie (tonic pupil)

• Light-near dissociation
• Slow redilation
• hypersensitive to dilute pilocarpine

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(C) Pharmacologic mydriasis

• anticholinergic (atropine, scopolamine)
• sympathomimetic (phenylephrine)
• no ptosis/diplopia
• no response to 1% pilocarpine

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(D) Traumatic / structural

• irregular pupil
• history trauma/surgery

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🧪 Pharmacologic testing (high-yield)

Test	Interpretation
Apraclonidine	Horner → dilation
Dilute pilocarpine (0.1%)	Adie → constrict
1% pilocarpine	pharmacologic → no response

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🧠 Clinical pearls

• Isolated mydriasis ≠ CN III palsy (almost alwaysมี EOM deficit)
• RAPD ไม่ทำให้ anisocoria
• CT brain routine ใน ED ไม่ช่วยใน isolated mydriasis
• ดู old photos → key for physiologic anisocoria

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🧾 Practical algorithm (จำง่าย)

1.       Confirm anisocoria

2.       Compare in light vs dark

3.       Identify abnormal pupil

4.       Look for:

o   ptosis / diplopia

o   pain / red eye

o   drug exposure

5.       Decide:

o   emergency (CN III, acute glaucoma, carotid dissection)

o   vs benign

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