Which extraocular muscle is primarily responsible for abduction of the eye and outward rotation of the eyeball?

Appeared in: RRB Nsg. Superintendent -29 April-2025 (shift-2nd)

Explanation

The lateral rectus muscle is responsible for moving the eye outward, away from the midline, a movement called abduction.
It is the only muscle innervated by the abducens nerve (Cranial Nerve VI).
The name of the nerve, 'abducens', directly relates to its function of abducting the eyeball.
A helpful mnemonic is LR6, indicating the Lateral Rectus is controlled by Cranial Nerve VI.

Option A: The inferior rectus muscle's primary action is depression, which moves the eye downward.
Option C: The superior rectus muscle's primary action is elevation, which moves the eye upward.
Option D: The medial rectus muscle's primary action is adduction, which moves the eye inward toward the nose.

Visual 1: Diagram: An illustration of the six extraocular muscles attached to the eyeball, showing their points of origin and insertion. This helps visualize how the contraction of each muscle produces a specific movement.
Visual 2: Mnemonic Chart: A chart displaying the mnemonic (SO₄LR₆)₃ to help remember the cranial nerve innervation for each muscle.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Actions and Innervation of Extraocular Muscles as background academic context rather than a clinical decision trigger.
Assessing the six cardinal fields of gaze is a fundamental nursing assessment to check the function of all extraocular muscles and their corresponding cranial nerves (III, IV, and VI).
A deficit in abduction (inability to move the eye outward) points to a potential lesion or palsy of the abducens nerve (CN VI). This can be an early sign of increased intracranial pressure.
What if? If a patient presented with an eye that is deviated inward (esotropia) and they cannot move it outward, the nurse would suspect a lateral rectus palsy. The priority would be to perform a full neurological assessment and notify the physician.

How to Approach the Question

First, identify the key action described in the question stem: 'abduction' (moving away from the midline).
Next, recall the primary function of each of the four rectus muscles provided in the options.
Associate the term 'abduction' with the lateral rectus muscle. The name of the innervating nerve, the 'abducens' nerve, is a strong clue.
Use the mnemonic (SO₄LR₆)₃ to confirm the innervation: Lateral Rectus is innervated by Cranial Nerve 6 (Abducens).
Eliminate the other options based on their primary actions: medial rectus (adduction), superior rectus (elevation), and inferior rectus (depression).

Concept Tested & Keywords

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Practise the full RRB Nsg. Superintendent -29 April-2025 (shift-2nd)

Attempt every question from this paper in a timed mock, then review the full solution for each one.