The pupil is mainly affected by the two groups of muscle innervations, when you are frightened or get emotional volatility, your pupils will become big because of sympathetic stimulation. In addition, it is normal for pupils become big when dim light enters eyes, so when you work at night, you‘d better choose a brighter lamp to prevent bigger pupils. Another reason is the excitement of the parasympathetic nerve, when you breathe deeply or does too much brain work, it will cause big pupils owning to the parasympathetic nerve. In this case, please give yourself enough time to take a break.
