Diplopia

Diplopia

🔹 Definition & Key Concept

• Diplopia = เห็นภาพซ้อน
• แยกให้ได้ก่อน:
• Binocular diplopia → หายเมื่อปิดตาข้างใดข้างหนึ่ง → ocular misalignment / neurologic cause
• Monocular diplopia → ยังเป็นแม้ปิดอีกข้าง → ocular/refractive problem

👉 Clinical pearl:
Binocular = neuromuscular / nerve → ต้องคิด serious cause

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🔹 Neuroanatomy (high-yield)

Muscle	Function	Nerve
Lateral rectus	Abduction	CN VI
Medial rectus	Adduction	CN III
Superior oblique	Intorsion	CN IV
Others	Elevation/Depression	CN III

👉 Rule:

• CN III → most muscles
• CN IV → superior oblique
• CN VI → lateral rectus

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🔹 Clinical Approach

1. Characterize diplopia

✔️ Direction

• Horizontal → medial/lateral rectus (CN III, VI)
• Vertical → oblique / vertical rectus (CN III, IV)
• Oblique/torsional → oblique muscle

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✔️ Worse gaze position

👉 “Worst direction = field of action ของ muscle ที่เสีย”

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✔️ Distance vs Near

• Worse at distance → CN VI palsy
• Worse at near → medial rectus problem

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✔️ Head position

• Head tilt/turn → compensatory → clue muscle involved

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2. Associated symptoms

🚨 Red flags

• Painful diplopia
• Severe headache (think aneurysm)
• Neurologic deficits
• Multiple cranial nerves involved

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3. Course

• Sudden → ischemic / vascular
• Fluctuating → myasthenia gravis
• Progressive → tumor / compressive lesion

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🔹 Examination

✔️ Essential

• Visual acuity
• Pupils (anisocoria!)
• Extraocular movement
• Cranial nerves

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🔴 Critical finding

• CN III palsy + pupil dilated = aneurysm until proven otherwise

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✔️ Simple bedside rules

• Diplopia worse looking right → right lateral rectus (CN VI)
• Ptosis + EOM defect → CN III
• Vertical diplopia + head tilt → CN IV

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🔹 Localization Framework

1. Neurogenic

• CN III, IV, VI palsy
• Brainstem lesion
• Internuclear ophthalmoplegia (MLF lesion)

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2. Neuromuscular junction

• Myasthenia gravis
• Fluctuating
• Fatigable
• Pupils normal

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3. Myopathic / restrictive

• Thyroid eye disease
• Orbital myositis

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4. Mechanical

• Orbital fracture
• Muscle entrapment

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🔹 Key Etiologies

1. CN III palsy

• Ptosis + “down and out”
• ± pupil involvement
• Pupil involved → suspect aneurysm → emergency imaging

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2. CN IV palsy

• Vertical diplopia
• Worse looking down
• Compensatory head tilt

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3. CN VI palsy

• Horizontal diplopia
• Worse looking far
• Common in ↑ICP / microvascular disease

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4. Myasthenia gravis

• Variable diplopia
• Fatigue-related
• Ptosis switching sides
• Pupils spared

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5. Thyroid ophthalmopathy

• Restrictive → worst opposite direction
• Proptosis
• Inferior rectus most common

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6. Internuclear ophthalmoplegia (INO)

• Impaired adduction + contralateral nystagmus
• Cause: stroke / MS

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7. Painful ophthalmoplegia (ต้องคิด serious)

• Aneurysm
• Tumor (cavernous sinus)
• Tolosa-Hunt syndrome
• Orbital inflammation

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🔹 Diagnostic Strategy (practical)

Step 1:

👉 Mono vs binocular

Step 2:

👉 Localize muscle/nerve from gaze pattern

Step 3:

👉 Look for red flags:

• Pain
• Pupil involvement
• Multiple CN

Step 4:

👉 Decide imaging

• MRI/MRA/CT if:
• CN III palsy (especially pupil involved)
• Painful diplopia
• Multiple CN
• Progressive

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🔻 Clinical Pearls (high-yield)

• Diplopia = neurologic symptom until proven otherwise
• Pupil-involving CN III palsy = aneurysm
• MG → pupil always normal
• Thyroid eye → restrictive (not weak)
• Worst gaze = field of weak muscle
• CN VI palsy → think ↑ICP / DM

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