Did you know that your pupils respond to other factors beyond the amount of light necessary for good vision? They do!
Change in pupil size is involuntary. Our iris muscles are responsible for the dilation and constriction of the pupil, and the iris muscles are controlled by the autonomic nervous system. The autonomic nervous system controls automatic actions we experience daily, such as breathing, and is responsible for triggering involuntary responses to a variety of information and stimuli.
Not only do our pupils dilate in response to light, but they can also change due to:
seeing/looking at images of people we're attracted to,
some emotions such as fear, surprise, or anxiety (associated with fight or flight response),
medication or substance use, and
neurological condition or eye or brain injuries.
Pay attention to your pupils, people! You can learn a thing or two about your experiences from them... And don't worry - my eyes were dilated for an eye exam; it's all good here.