When your pupil is small, your doctor’s view of the retina and optic nerve is restricted to the central region of the retina. Because of this limitation, the health of your retina and optic nerve can’t be fully known. A dilated eye exam “is critical to preventing and treating eye conditions that could potentially lead to vision loss,” states ophthalmologist Yvonne Ou, M.D. of BrightFocus Foundation.*

What is pupil dilation?

Dilation occurs when the hole at the center of the iris enlarges to allow in more light. This happens naturally or in response to different stimuli. During an eye exam, eye drops are administered to dilate the pupils.

Eye exams with and without dilation provide doctors with useful information, but Ou says a complete examination of the optic nerve is “crucial,” and that can only be accomplished with pupil dilation. It’s important to understand both, however.

Why we need an undilated eye exam

There are multiple reasons for keeping the pupils undilated during a comprehensive eye examination:

• Visual testing, along with possible measurement for eyeglasses
• Measuring pupil light response to see that our visual pathway is working properly
• Gonioscopy to ensure that your fluid drainage angle isn’t narrowing or closed, causing pressure buildup and risk of developing or worsening glaucoma
• Field of vision testing, part of a glaucoma test, involving peripheral (side) vision
• Examining other frontal eye structures, like the iris

Why we need a dilated eye exam

A dilated eye exam is needed to help your doctor diagnose a variety of major conditions, including:

• Glaucoma and other optic nerve-related diseases
• Age-related macular degeneration (AMD) and diabetic retinopathy
• Retinal tears and detachments, eye tumors, and other conditions

Getting a dilated eye exam

To see the entire retina, the pupils are dilated using eye drops. It usually takes 15-30 minutes for pupils to reach full dilation. 

Once dilated, the eyes will be sensitive to light, since more light is entering the eye. Wearing sunglasses is recommended. If you don’t have any, your doctor may offer you a disposable pair. Temporarily blurry vision, especially while reading, is also possible, as is a feeling of tightness in the eyelid. 

Since it generally takes four to six (4-6) hours for the dilation to subside, Ou advises first-timers and people with impaired vision from dilation to arrange a ride home. (Eye drops for reversing dilation after an exam are no longer available.)

How often should a dilated eye exam be done?

Experts advise everyone aged 60 years and older to have a comprehensive dilated eye exam each year. For African Americans, the starting age is 40 due to the higher risk of glaucoma.

For diabetics:

• Type 1 diabetics should get their eyes examined no later than five (5) years after diagnosis.
• Type 2 diabetics should have their eyes examined at the time of diagnosis.
• Diabetic women considering pregnancy should have an eye exam before conceiving, or at the beginning of their first trimester.

“Pupil dilation is very important at revealing the status of your optic nerve and retina,” says Ou, so that potentially harmful eye problems can be prevented and detected early.

*Ou, Y. (2021, July 5). The Dilated Eye Exam: Why It’s So Important. BrightFocus Foundation. https://www.brightfocus.org/glaucoma/article/dilated-eye-exam-why-its-so-important