Which pupillary finding can accompany optic neuritis?

• A. Normal pupillary reaction
• B. Constricted pupils
• C. Dilated but nonreactive pupils
• D. Fixed and dilated pupils

Answer: (D)

Pupillary light reflex hinges on the afferent input from the retina through the optic nerve to the midbrain. In optic neuritis, this afferent pathway is inflamed and disrupted, so the light signal fails to elicit constriction. When the inflammation is pronounced, the affected pupil may not constrict at all in response to light, appearing fixed and dilated. This reflects a severe loss of the light reflex from the damaged optic nerve. The other patterns—normal reaction, constricted pupils, or a dilated pupil that still responds—fit less with an optic nerve issue, whereas a fixed and dilated pupil fits the scenario where the reflex is essentially absent due to optic nerve involvement.