During a comprehensive eye exam, your pupils will be dilated with special drops. This will not hurt. Dilation enlarges your pupils to allow the eye doctor to evaluate the inside of your eye. Special instruments and lights are used to examine the internal structures of your eye, such as your retina and optic nerve, looking for irregularities like swelling or leaking.
The effects of dilation last several hours and can make your eyes slightly sensitive to light. It is a good idea to have someone drive you home and to bring sunglasses to wear on the ride home.