What is considered a normal direct pupil diameter in millimeters?

• A. 1-2 mm
• B. 3-5 mm
• C. 6-8 mm
• D. 7-9 mm

Answer: (B)

Pupillary size is controlled by the autonomic nervous system and reflects how the eye adapts to light. In a person with normal function and typical lighting, the direct response to a light source should constrict the pupil to about 3 to 5 millimeters. This resting range fits with the way the eye balances light entry for clear vision without overdoing it. When you test, you illuminate one eye and observe both the direct response (that eye) and the consensual response (the other eye); both should constrict to a similar size within that 3–5 mm range. Remember, lighting matters: in bright light pupils tend to be smaller, roughly 2–4 mm, while in dim light they dilate to around 4–8 mm. If a pupil is noticeably smaller or larger than the normal range, or if the two pupils aren’t equal, it can indicate an issue needing evaluation.