How do you test the function of each extraocular muscle in a patient with suspected eye movement issues?

Testing Extraocular Muscle Function

To test the medial rectus, have the patient adduct the eye (look toward the nose); for all other extraocular muscles, use a two-step sequential movement that first positions the eye to isolate the muscle, then tests its primary action. 1

Testing the Medial and Lateral Rectus Muscles

These muscles are straightforward to test because they cross only the vertical axis of the globe:

• Medial rectus: Ask the patient to adduct (look nasally). Inability to adduct indicates medial rectus or CN III (inferior division) dysfunction. 2, 1
• Lateral rectus: Ask the patient to abduct (look temporally). Inability to abduct indicates lateral rectus or CN VI dysfunction. 1

Testing the Superior and Inferior Rectus and Oblique Muscles

These four muscles cross all three axes of the globe (vertical, horizontal, and anteroposterior), so they produce three movements each: elevation/depression, abduction/adduction, and torsion. 1 The key principle is to use a two-step sequence: first abduct or adduct the eye to eliminate one muscle's ability to elevate or depress, then test the remaining muscle. 1

Superior Rectus

• First abduct the eye (look temporally), which positions the superior rectus so it no longer crosses the horizontal axis
• Then ask the patient to look up from the abducted position
• Inability to elevate from abduction indicates superior rectus or CN III (superior division) dysfunction 2, 1

Inferior Rectus

• First abduct the eye (look temporally)
• Then ask the patient to look down from the abducted position
• Inability to depress from abduction indicates inferior rectus or CN III (inferior division) dysfunction 2, 1

Superior Oblique

• First adduct the eye (look nasally), which positions the superior oblique so it no longer crosses the horizontal axis
• Then ask the patient to look down from the adducted position
• Inability to depress from adduction indicates superior oblique or CN IV dysfunction 1

Inferior Oblique

• First adduct the eye (look nasally)
• Then ask the patient to look up from the adducted position
• Inability to elevate from adduction indicates inferior oblique or CN III (inferior division) dysfunction 2, 1

Comprehensive Motility Assessment

The American Academy of Ophthalmology recommends evaluating both versions (binocular motility in all gaze positions) and ductions (monocular motility), noting any limitation, overaction, or incomitance. 2

• Versions: Observe both eyes moving together through the nine cardinal positions of gaze 2
• Ductions: Test each eye individually through full range of motion, which can distinguish paretic from restrictive causes 2
• Oculocephalic rotations (doll's-head maneuver): Particularly valuable in infants and young children to reveal normal ductions that may not be apparent on voluntary testing 2

Critical Clinical Pitfalls

• In thyroid eye disease, avoid assuming normal anatomical muscle positions, as muscle enlargement (particularly inferior and medial rectus) causes mechanical restriction that mimics weakness. 2 Forced duction testing confirms restriction versus true paresis. 2
• Partial CN III palsies with incomplete ptosis or partial extraocular muscle involvement cannot be assumed to be microvascular—neuroimaging with MRI/gadolinium and MRA or CTA is required to exclude compressive lesions. 2
• Active force generation testing in the office helps identify muscles with residual function (responsive to resection) versus completely paretic muscles (where resection is ineffective). 2