A lesion of the pretectal area would most likely produce which change in the pupillary response?

• A. Impaired direct and consensual light responses with preserved near response.
• B. Near response preserved with impaired light reflex.
• C. Pupils become constricted in all lighting.
• D. Pupillary responses are normal.

Answer: (A)

The light reflex pathway relies on the pretectal area receiving input from the retina and sending signals bilaterally to the Edinger-Westphal nuclei to drive pupillary constriction. A lesion in the pretectal region disrupts this light-driven signal to both EW nuclei, so both direct and consensual pupillary constrictions in response to light are lost. The near response, which involves focusing on a close object and the associated constriction, uses a slightly different route that can bypass the pretectal nucleus, so it remains intact. Therefore, you get impaired light responses in both eyes but preserved near response. The other options don’t fit because they describe scenarios not matching the disruption of the light reflex with sparing of the near reflex.