What is an Adie’s pupil?

An Adie’s pupil is a dilated pupil, usually found incidentally, caused by paralysis of the parasympathetics that normally constrict the pupil. This usually occurs after a viral illness that hits the ciliary ganglion that sits behind the eye. It is harmless and in the absence of other neurologic signs, will not cause any problems except cosmetic.

The opposite of an Adie’s pupil would be a Horner’s pupil, where you get a constricted pupil from loss of sympathetic dilation. The sympathetic chain is quite long and so workup for a new Horner’s is much more involved.