How to Determine if the Upper Eyelid Elevator Muscle is Weak

Weakness of the levator palpebrae superioris muscle typically refers to ptosis, which can be assessed through tests such as the levator function test, measurement of palpebral fissure height and degree of ptosis in primary gaze, and the neostigmine test.

1. Levator Function Test

This method primarily evaluates levator palpebrae superioris muscle strength by applying digital pressure on the supraorbital ridge while measuring the excursion of the upper eyelid margin. Generally, a lid margin excursion of ≤4 mm indicates poor muscle strength; 5–7 mm indicates moderate strength; and ≥10 mm is considered normal.

2. Measurement of Palpebral Fissure Height and Degree of Ptosis in Primary Gaze

This method helps determine the severity of ptosis. For example, when the patient gazes straight ahead with eyes naturally open, mild ptosis is characterized by the upper eyelid margin covering more than 3 mm of the superior corneal limbus; in severe cases, it may cover over half the cornea or even the entire cornea.

3. Neostigmine Test

This test involves subcutaneous or intramuscular injection of neostigmine, followed by observation for improvement in ptosis. Improvement suggests that the ptosis may be attributable to myasthenia gravis.