A patient has absent corneal reflex on the right side but winking (blink response) is present in the right eye when the left cornea is stimulated. Which specific part of the reflex arc is interrupted?

• A Efferent limb — right CN VII
• B Afferent limb — right CN VII
• C Efferent limb — right CN V
• D Afferent limb — right CN V (ophthalmic division) ✓

Explanation

The corneal reflex afferent is the nasociliary branch of V1 (ophthalmic division of trigeminal); the efferent is the facial nerve (CN VII) innervating orbicularis oculi. When the right cornea is touched and no blink occurs in either eye, the afferent (right V1) is damaged. When the LEFT cornea is touched and the RIGHT eye blinks, the right efferent (CN VII) is intact. Therefore, the right afferent (right V1/ophthalmic) is interrupted. If the right efferent were damaged, touching the right cornea would produce a blink only in the left eye (consensual) but not in the right (direct), while touching the left cornea would produce bilateral blinks.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.