What is the term for the reaction in the pupils of the eyes when exposed to light?

The correct term for the reaction of the pupils in response to light is reactivity. When light is shone into the eyes, the pupils constrict (become smaller) to limit the amount of light entering the eye, which helps protect the retina and improves visual acuity. This reflexive response is known as the pupillary light reflex, indicating the pupils' reactivity or responsiveness to light.

In this context, contraction refers specifically to the narrowing of the pupils, while dilation refers to their widening, which occurs in low light conditions rather than in response to light exposure. Terms like "expansion" are not commonly used in this context and do not accurately describe the physiological process at play when light is introduced to the eyes. Therefore, recognizing the term "reactivity" is crucial, as it encompasses the functional aspect of how the pupils respond to changing light conditions.