the opening and closing of the pupil in response to light is an involuntary action controlled by the parasympathetic branch of the autonomic nervous system
The pupil controls the intensity of light entering into the eye.
The parasympathetic branch of the autonomic nervous system (PSNS) controls the constriction of the pupil and the sympathetic branch of the autonomic nervous system controls the dilation of the pupil.
It is an automatic action which translates to it being an involuntary action.
