Which finding is characteristic of optic neuritis?

Which finding is characteristic of optic neuritis?

• A. Loss of color vision
• B. Central scotoma
• C. Marcus-Gunn pupil
• D. Pain with eye movement

Answer: (C)

Optic neuritis damages the optic nerve and disrupts the afferent limb of the pupillary light reflex. This produces a relative afferent pupillary defect, known as a Marcus-Gunn pupil. In the swinging flashlight test, light shone in the affected eye elicits a reduced direct and consensual constriction (pupils don’t constrict as they should), and when the light is swung to the normal eye, the reflex is stronger. The key clue is this relative afferent defect, which points to optic nerve pathology. Clinically, patients often have unilateral vision loss with eye-movement–related pain and sometimes decreased color vision, but the Marcus-Gunn pupil is the characteristic finding indicating optic neuritis.

Optic neuritis damages the optic nerve and disrupts the afferent limb of the pupillary light reflex. This produces a relative afferent pupillary defect, known as a Marcus-Gunn pupil. In the swinging flashlight test, light shone in the affected eye elicits a reduced direct and consensual constriction (pupils don’t constrict as they should), and when the light is swung to the normal eye, the reflex is stronger. The key clue is this relative afferent defect, which points to optic nerve pathology. Clinically, patients often have unilateral vision loss with eye-movement–related pain and sometimes decreased color vision, but the Marcus-Gunn pupil is the characteristic finding indicating optic neuritis.