What is the size of a small pupil?

• A. 5-7 mm
• B. <5 mm
• C. >7 mm
• D. 8-10 mm

Answer: (B)

Pupil size is described by how wide the pupil opens in millimeters, and it changes with lighting. A small pupil is the range under 5 millimeters in diameter. In bright light, the pupil constricts toward this small size, often around 2–4 mm for many adults, while it can broaden to 5–7 mm or more in dim light. In exam contexts and practical lens work, the threshold used for “small” is less than 5 mm. So the best answer is that a small pupil is under 5 millimeters. The other ranges describe average (about 5–7 mm) or large pupils (over 7 mm).