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Dilating Eye Drops

Fig. 1 Cyclopentolate (Cyclogyl), a commonly-used dilating/cycloplegic drop.

What are dilating eye drops?

Dilating eye drops contain medication to enlarge (dilate) the pupil of the eye. There are two types of drops: one type stimulates contraction of the muscles that enlarge the pupil (such as phenylephrine); the other type relaxes the muscles that make the pupil constrict (such as cyclopentolate). This latter drop also relaxes the muscles that focus the lens of the eye. The two medications are often used simultaneously, either as two separately administered drops or as a single combination drop. Sometimes the drops are administered via spray formulation [See figures 1 and 2].

Why are dilating drops necessary?

A large pupil is helpful to examine the interior of the eye which is essential to diagnose and treat eye diseases. Also, relaxing the focusing muscles of the eye allows for a more accurate determination of refractive error (need for glasses) in children. Finally, dilating eye drops are sometimes used to treat eye diseases, such as amblyopia and inflammation.

How long do dilating drops last?

Dilating eye drops used for examination of the eye can last from 4 to 24 hours, depending upon the strength of the drop and upon the individual patient. Children require stronger and longer lasting drops than do adults to accurately measure refractive error. Weaker drops are used for premature babies and neonates. Dilating eye drops are occasionally used to treat certain eye diseases, such as amblyopia and inflammation in the eye. These therapeutic dilating drops (atropine and homatropine) may have a longer duration of action, even up to 2 weeks. Despite the longer duration of action, daily administration of the drop may be necessary for treatment.

Fig. 2 Pharmacologically dilated pupil.

What are the side effects of dilating drops?

Light sensitivity and blurry vision (especially for near tasks) may be noticed. Both side effects gradually disappear. Sun glasses may be helpful after a dilated eye exam. Children can return to school, but teachers should be aware of blurred vision while reading Allergic reactions are rare with drops used for examination, but include lid swelling and red eyes. Side effects from atropine (which has a longer duration of action) include fever, dry mouth, flushing of the face, and a rapid pulse.

Do dilating eye drops burn or sting?

Like most eye drops, there is generally some stinging immediately after instillation. This is usually momentary. A topical anesthetic (numbing drop) can be used prior to the dilating drop to increase patient comfort.