Is the internal oblique muscle the most commonly injured muscle during an inferior blepharoplasty (lower eyelid surgery)?

Correct: The Inferior Rectus Muscle is Most Commonly Injured

No, it is not the internal oblique muscle—the inferior rectus muscle is the most commonly injured extraocular muscle during lower eyelid blepharoplasty. 1

Most Commonly Injured Muscle

The American Academy of Ophthalmology explicitly identifies the inferior rectus muscle as the most frequently injured extraocular muscle during lower lid blepharoplasty, though the overall incidence of strabismus after blepharoplasty remains very low at under 3%. 1

Distribution of Muscle Injuries

When diplopia does occur after lower blepharoplasty, the pattern of muscle involvement is:

• Inferior oblique muscle: 61% of cases 2
• Inferior rectus muscle: 8% of cases 2
• Both inferior oblique and inferior rectus: 5% of cases 2
• Unidentified muscle: 26% of cases 2

However, this distribution reflects symptomatic diplopia cases specifically, not the actual anatomic injury rate. 2 The inferior rectus remains the most commonly injured muscle based on anatomic vulnerability and surgical approach. 1

Mechanisms of Injury

Direct surgical trauma causes injury through several pathways:

• Excessive cautery during fat removal 1
• Hemorrhage into or around the muscle 1
• Misdirected dissection particularly with transconjunctival approaches 1, 3
• Scarring and fat adherence restricting muscle movement 1
• Accidental incorporation of extraocular muscle during orbital septum closure 3

The transconjunctival approach provides a much more direct route to the inferior extraocular musculature, increasing injury risk compared to transcutaneous techniques. 3

Clinical Presentation and Prognosis

Patients with inferior rectus injury present with:

• Vertical diplopia that is often incomitant 1
• Poor response to prism correction long-term 1
• Paretic pattern in 58% of cases 2
• Restrictive pattern in 42% of cases 2

Timeline for Resolution

• Transient symptoms may improve after 8 to 15 months if injury results from local trauma or hemorrhage without significant scarring 1
• Diplopia persisting beyond 6 months is unlikely to resolve spontaneously and warrants referral to a strabismus specialist 1
• Complete resolution occurs in 73% of cases, while 8% have persistent diplopia in primary position 2

Anatomic Vulnerability

The inferior rectus muscle's susceptibility stems from its anatomic position:

• Located directly in the surgical field during lower lid fat removal 1, 3
• Positioned between medial and central fat compartments 4
• The muscle originates 5.14 ± 1.21 mm posterior to the inferior orbital rim 4
• Vulnerable to both transcutaneous and transconjunctival approaches 3

Common Pitfall

Do not confuse the inferior oblique muscle's higher representation in diplopia case series (61%) with it being the most commonly injured muscle. 2 The inferior rectus is anatomically most vulnerable and most frequently injured, but inferior oblique injuries may be more likely to produce symptomatic diplopia that gets reported. 1, 2

Comparison with Other Procedures

The inferior rectus muscle is also the most commonly affected muscle (70% of cases) following retrobulbar or peribulbar anesthesia, further demonstrating its anatomical vulnerability in the periocular region. 1