This is a dilating drop used during an eye exam to better view the retina. This drop works by stimulating the sympathetic system in order to dilate the pupil. It doesn’t cause cycloplegia so there is less problems with blurry vision when dilated. However, this drop does not dilate the pupil enough when used by itself, so it’s usually used in conjunction with a cycloplegic like tropicamide. This medication is now being used in over-the-counter decongestants like Sudafed as a replacement for the original pseudoephedrine (which you have to sign for to insure you are not a methamphetamine junkie).