Mondo Knows Facts
Light in one eye makes both pupils shrink
Signals cross in the brainstem so each pupil responds to light entering either eye Retinal signals travel to the pretectal area of the midbrain, which drives both Edinger-Westphal nuclei. Each nucleus sends parasympathetic fibres that constrict its own pupil. The result is a direct response in the lit eye and a consensual response in the other, a standard test of brainstem wiring. It sits in Mondo's human body collection, one of 200 facts that each trace back to the reference below.
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Facts that can change over time are reviewed and updated. If something here looks wrong, Mondo would rather know than be confidently incorrect.
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Tags: pupil, reflex, vision
Light in one eye makes both pupils shrink: the short answers
- Where does this come from, and can I check it?
- Signals cross in the brainstem so each pupil responds to light entering either eye. The figure is taken from Merck Manual, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
- Is this really a human body fact?
- Yes. It sits on the Human Body shelf, one of 2,600 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
- What else can I read about it?
- The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.