There are many factors that can cause dilated eyes. And till now, I didn' t find any good treatment for the dilated eyes. If you want to undilate it, you shall know what causes it, and then treat it differently according to the causes. Usually, some drugs can cause the eyes to dilate, if so, you may have to wait your eyes recover themselves. Also, the lighting can also cause dilate the eyes to help you focus better. If so, you can stay in a brighter light.