Eyedrops are placed in the eye to cause the pupil to enlarge, allowing the doctor to view the inside of the eye more clearly.   It's a lot like looking into a room from a window as opposed to looking through a keyhole. 

Why should the pupils be dilated & who should have it done?

The eye doctor needs to be able to see clearly into the pupil in order to look for: any retinal changes (a hole, rips, tears, etc.), lens changes (cataracts) and optic nerve abnormalities (glaucoma).   EVERYONE should be dilated at some point. Patients who fall in the following categories should be monitored regularly -

Diabetes - High Blood Pressure - Stroke - Certain Medications - Past Eye Trauma - Headaches - Decreased Vision (unknown origin) - Cataracts (diagnosis / management) - Glaucoma (same) - Moderate to High Perscriptions - Prior Retinal Problems (or surgeries) - Past Head Trauma - 'Flashers' or 'Floaters' Present - High Cholesterol

The only side effect of this procedure is a sensitivity to light; sunglasses will be provided afterwards. Some patients report blurred vision when viewing objects close to them, but the distance vision remains as it was before dilation.  (Exceptions: uncorrected hyperopia & undiagnosed farsightedness.)

Dilation effects usually last two to four hours, so a driver is recommended to take you home.