Dilation Drops 101

What You Should Know About Dilating Your Eyes

A thorough eye examination contains several tests to help your eye doctor evaluate your eyes and vision. Part of the eye examination that helps your doctor assess the overall health of your eyes is the dilated funds examination or dilation of the pupils.

Dilating eye drops

Special eye drops are used during an eye exam to make the pupil of the eye grow larger. The pupil is the opening or hole in the middle of the iris that controls the amount of incoming light.

Pupil size is controlled by two different systems in the body, one acting to constrict the pupil and the other to make it larger. Therefore, two different types of medicinal eye drops are used for dilating the pupil. They are available as a combined eye drop and as separate drops. They are also available in spray form, which is easier to administer in people that are extra sensitive.

Some dilating drops also act to relax or temporarily paralyze the muscle that allows the eye to focus on near objects. Drops that accomplish this are called cycloplegic eye drops. These drops are used more in children to improve the accuracy of checking the child's overall vision. Sometimes the cycloplegic effect is simply a side effect of a dilating drop and other times the cycloplegia is the purpose of administering the drop.

Why does the doctor need to use dilating drops?

Although some parts of the inside of the eye can be viewed by looking through an undilated pupil, the view is similar to shining a flashlight into a tiny keyhole.

Dilating the eye is like opening the door and turning the lights on. A dilated pupil allows a much better view into the eye to diagnose abnormalities and eye diseases. Some dilating drops produce a cycloplegic effect that relaxes the focusing muscle. You might think this would be counterintuitive when measuring a child’s need for vision correction, but it calms down the visual system so the doctor can measure only the raw data with little influence from the child.

Do eye doctors use dilating or cycloplegic drops for anything else?

Yes. The cycloplegic effect of dilating drops is used to treat eye inflammation after eye surgery or for inflammatory eye conditions such as iritis or uveitis. Pediatric eye doctors use them to treat amblyopia, a condition commonly called "lazy eye" in which a child develops reduced vision for a variety of reasons. These types of drops are given for a much longer duration, sometimes even months.

How long will the dilation last?

Eye drops administered during an eye examination will usually keep your pupils dilated anywhere from 3-4 hours to 24 hours. Dilating drops are available in different strengths. Eye doctors tend to use stronger dilating drops when performing eye examinations on children or prescribing them for the treatment of inflammation or amblyopia. The duration of dilation also depends on the individual. People with light colored eyes will stay dilated longer than those with dark brown eyes. The pigment in darker eyes binds the dilating drug, lessening its effects.

What are the side effects of dilating or cycloplegic eye drops?

Because dilating drops enlarge the pupil, you will become light sensitive. Protective sunglasses should be worn outdoors for a few hours post-dilation. Because some dilating drops relax the focusing muscle, your vision may also be blurred at a close or near distance. These side effects gradually disappear over a few hours. While rare, some dilating drops cause some children to become disoriented or even hyperactive for a short time. Side other rare side effects include fever, dry mouth, flushing of the face, and rapid pulse.

Does dilating the eyes hurt?

Some dilating drops may cause temporary burning or stinging upon instillation. Occasionally, eye doctors will first apply an anesthetic numbing eye drop that sometimes stings as well. This drop acts not only to lessen the stinging and burning of the dilating drops but also to allow the dilating drops to penetrate the eye better, causing a better dilating effect.

Source: Eskridge, Boyd.  Clinical Procedures in Optometry, J.B. Lippincott Company, 1991.

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