Why doctors dilate your eyes (and why they might not)

The point of getting an eye exam is for your doctor to examine your entire eye inside and out. One important way to do that is through dilation. 

You might not need to have your eyes dilated at every visit. Here’s everything you need to know about what to expect and how it can help keep your eyes healthy. 

To perform a dilated eye exam, your eye doctor will place dilating drops into your eyes. The treatment temporarily enlarges your pupils (the round black opening of the eye).^{1, 2} These effects may last from 4 to 24 hours.¹

Usually, shining a light into your eyes causes your pupils to become small. That prevents your doctor from seeing into your eyes fully.¹ Enlarging the pupil lets more light enter the eye so that your doctor can get a good look at the back of the eye. That allows your optometrist to examine your eyes for signs of damage or disease.^{1, 2}

Without dilation, “it’s like looking through a peephole when you want to look through a big window,” says Chantal Cousineau-Krieger, M.D., an ophthalmologist at the National Eye Institute. Think of eye dilation like a doorway. Opening a door wide lets more light into a dark room.³

There are 2 important reasons that your eyes get dilated, says Jeffrey Walline, O.D., the associate dean for research at Ohio State University’s College of Optometry.

First, some eye diseases have no warning signs or symptoms until the disease is advanced.² At that point, the damage may already be done. Getting a dilated eye exam is the only way for your doctor to see the entire back of your eye. That helps them confirm whether your eyes are healthy. 

“There’s only one place in the body that we can look directly into the blood vessels, and that’s in the back of the eye,” says Dr. Walline.

These common eye diseases can be spotted in their early stages, during a dilated eye exam:^{2, 4}

• Glaucoma (a group of diseases that damages the optic nerve, the nerve in the back of the eye) 
• Diabetic eye disease (a group of eye problems that can affect people with high blood sugar) 
• Age-related macular degeneration (slow breakdown of light-sensitive tissue in the eye)  

In young children, optometrists may dilate their eyes to figure out their prescription.¹ Dilating drops help relax the focusing muscles of the eye.  

“If we give them those dilating drops, it doesn’t allow them to focus their eyes, so we get a true idea of what their prescription is,” says Dr. Walline.

Not necessarily. The frequency of dilated eye exams depends on your risk factors for eye disease. According to the American Academy of Ophthalmology, 1 in 3 Americans will have a vision-impairing eye disease by age 65.⁵ The earlier these diseases are found, the more likely you are to keep your vision.⁵

Most people with diabetes or high blood pressure need a dilated exam at least once a year.⁵ It’s important for adults to get a baseline eye exam with dilation at age 40.⁵

“If the person has been established as a very healthy person and has no problems, then the eye doctor might dilate their eyes every other year,” says Dr. Walline.

Once your doctor dilates your pupils, things will look and feel a bit strange for a little while. You can expect:⁶

• Blurry vision
• Difficulty focusing on close-up objects
• Extra sensitivity to light

The effects of dilating drops may last only a few hours — or several hours. It depends on how each patient’s eyes react to the drops.⁶

Light eyes (such as blue, green or hazel) usually dilate faster than brown eyes.⁶

“Patients with light irises (the colored part around the pupil) tend to dilate very quickly and stay dilated longer,” says Dr. Krieger. “Patients with dark varieties tend to take longer to dilate, and the dilation wears off more quickly.”

Since your vision may be blurry for some time, make sure to plan ahead. Take steps to make your eye appointment comfortable, such as:

• Asking a friend to drive you to and from the visit
• Bringing sunglasses
• Being patient as your vision returns to normal

Talk to your eye doctor about how often you should get a dilated exam. It’s the best way to find out what’s right for your vision needs.