Which extraocular muscle can cause diplopia (double vision)?

Which Extraocular Muscles Can Cause Diplopia

Any of the extraocular muscles can cause diplopia when affected, including the superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, and inferior oblique muscles. 1

Mechanism of Diplopia from Extraocular Muscle Dysfunction

Diplopia (double vision) occurs when there is misalignment between the eyes, preventing proper fusion of images. This misalignment can result from:

• Paresis (weakness) of one or more extraocular muscles
• Restriction of extraocular muscles
• Mechanical factors affecting muscle function
• Neurological issues affecting the cranial nerves that control these muscles

Specific Muscles and Associated Patterns of Diplopia

Rectus Muscles

• Superior Rectus: When affected, causes vertical diplopia that worsens in upgaze
• Inferior Rectus: Most commonly injured by regional anesthesia during eye procedures, causing vertical diplopia worse in downgaze 1, 2
• Medial Rectus: When affected, causes horizontal diplopia worse when looking toward the nose
• Lateral Rectus: When affected, causes horizontal diplopia worse when looking away from the nose

Oblique Muscles

• Superior Oblique: Causes vertical and torsional diplopia, typically worse in downgaze and when looking toward the nose 3
• Inferior Oblique: Can cause vertical and torsional diplopia, typically worse in upgaze

Common Clinical Scenarios

Third Nerve Palsy

Third nerve palsy affects multiple extraocular muscles including:

• Superior rectus
• Inferior rectus
• Medial rectus
• Inferior oblique

This results in the characteristic "down and out" position of the eye with ptosis (drooping eyelid) 3. Patients typically experience vertical and horizontal diplopia.

Fourth Nerve Palsy

Affects the superior oblique muscle, causing:

• Vertical diplopia worse on looking down and toward the nose
• Characteristic head tilt away from the affected side 3

Sixth Nerve Palsy

Affects the lateral rectus muscle, causing:

• Horizontal diplopia worse at distance and when looking toward the affected side
• Esotropia (inward deviation) of the affected eye 3

Iatrogenic Causes of Diplopia

Extraocular muscle dysfunction can occur following various ophthalmic procedures:

• Anesthetic myotoxicity: Superior and inferior rectus muscles are most commonly injured during retrobulbar or peribulbar anesthesia 1, 2
• Cataract surgery: 0.23% incidence of secondary strabismus with retrobulbar block anesthesia 1
• Blepharoplasty: Can damage the inferior rectus and inferior oblique muscles equally (transconjunctival approach) 4
• Orbital floor fracture repair: Can affect inferior rectus function 5

Risk Factors for Iatrogenic Diplopia

• Injection by a non-ophthalmologist
• Left eye injection (possibly due to right-handed surgeons having more difficult access)
• Absence of hyaluronidase in the anesthetic block 1
• Direct muscle or nerve trauma
• Anesthetic toxicity
• Periocular hemorrhage 2

Management Considerations

Treatment depends on the cause and may include:

• Treating underlying causes (e.g., microvascular disease, aneurysm)
• Temporary measures: occlusion, prisms, botulinum toxin
• Surgical correction when appropriate, typically after waiting 6-12 months for spontaneous recovery in cases like third nerve palsy 3

Diplopia from microvascular causes often resolves spontaneously within 3-6 months, while other causes may require specific interventions 6.