What is dilation? Why does my doctor dilate my eyes?

Dilation, also known as mydriasis, is a process by which the pupil of the eye is temporarily enlarged with special eye drops (mydriatic). Dilating your pupil allows the eye doctor to get a better view of the inside of your eye — particularly your vitreous and retina. The doctor uses special equipment, like an ophthalmoscope or a fundus camera to visualize the inside of the eye through your dilated pupil.

Watch the “How vision works” animation

There are two types of muscles in the iris that are responsible for pupil size: the sphincter muscle (pupil contraction) and the dilator muscle. The different available dilation eye drops work by either relaxing the eye’s sphincter muscle or stimulating the dilator muscles. Either one of these actions will lead to enlargement of the pupil.

How to use eye drops.

Also see “Interactive Human Eye” animation