When light is shone into a pupil, what response is expected? (alternate wording)

• A. the opposite pupil should dilate
• B. the pupil should become larger in size
• C. both pupils should dilate together
• D. the pupil should become smaller

Answer: (D)

Shining light into a pupil triggers the pupillary light reflex, where the iris sphincter muscle contracts to make the pupil smaller. This direct constriction happens in the illuminated eye, and a similar constriction often occurs in the other eye as well (the consensual response). Therefore, the expected outcome is the pupil becoming smaller in bright light. Dilation would occur in low light, not when bright light is shone; the other options describe dilation or inappropriate responses, which don’t fit this reflex.