The only way to get a good view of all the structures in the eye is to dilate them, or open the pupil up very big. If the eyes weren’t dilated with eye drops and  we tried to look in them with a light, the pupils would just get very small making it very hard to see inside. It would be like trying to look through a keyhole, we would only see a small area, but when dilated, it opens up the door to the eye so we can view everything.