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The dilated eye exam is a medical exam that checks for eye conditions and diseases in their early stages.

Before the eye dilation test begins, the eye doctor — either an ophthalmologist or an optometrist — will administer the dilating eye drops. According to the American Academy of Ophthalmology, eye dilation then takes effect within 20–30 minutes. However, people with blue or green eyes will experience dilation faster than people with brown eyes.

The dilated eye exam may include a few additional tests, such as:

• Pupil response test: The doctor shines a small flashlight into the eyes to see how the pupils react to the light.
• Eye muscle function test: The doctor asks the person to follow a moving object with their eyes. This movement allows the doctor to check for problems with the muscles surrounding the eyes.
• Visual acuity test: The doctor asks the person to read letters up close and at a distance. The results indicate how clearly a person can see.
• Visual field test: The person holds their eyes still while reporting how well they can see objects in their periphery. This test assesses a person's peripheral vision.
• Tonometry test: A special machine quickly puffs a small amount of air into the eye. This technique measures the pressure within the eye.

While the dilated eye exam may be over rather quickly, the dilation itself continues. During this time, a person may experience the following effects of eye dilation:

• blurred vision
• sensitivity to bright lights, such as sunlight
• difficulty focusing on nearby objects

The duration of eye dilation can vary widely. According to the American Association for Pediatric Ophthalmology and Strabismus, the average dilation lasts from 4 to 24 hours.

However, several different factors affect how long the eyes remain dilated. These include:

• Eye color: People with lighter colored eyes tend to experience the effects of eye dilation for longer than those with darker colored eyes.
• Age: Younger children tend to have a very strong focus mechanism in the eye. Therefore, they require stronger drugs to dilate the pupils. As a result, a child's eyes may stay dilated for 24 hours or longer.
• Type of drug: The type of drug that a doctor uses to dilate the pupils will affect how long the eyes remain dilated. For example, a doctor may use weaker eye dilation drops when treating a person with nearsightedness because this helps limit side effects.

Some people feel comfortable enough to drive immediately after their eye exam.

However, doctors may recommend avoiding driving while the eyes remain dilated, especially if the person has not experienced the effects before.

Where possible, people should arrange for a friend or family member to drive them home after their eye exam.

Eye dilation can cause several side effects. The most immediate effect is stinging, which generally occurs when the eye dilation drops come into contact with the eyes. In some cases, doctors may apply numbing drops to the eye beforehand to prevent the stinging sensation.

Once the dilation drops take effect, the person may experience one or more of the following:

• blurred vision
• difficulty focusing on nearby objects
• light sensitivity

In very rare cases, a person may experience an allergic reaction to the eye dilation drops, which may result in red and swollen eyes. More severe allergic reactions could produce the following symptoms:

Managing side effects

People can take some steps to manage the effects of eye dilation. These include:

Wearing sunglasses: People can take a pair of sunglasses along to their eye appointment to wear after the eye exam. Wearing these will help protect eyes that are light-sensitive due to pupil dilation. Most eye doctors provide temporary sunglasses for their patients.

Avoiding close work: Close work, such as reading and focusing on a computer screen, can be difficult during eye dilation. People whose jobs involve these tasks should arrange a few extra hours off work, where possible.

Eye dilation can sometimes result in a temporary condition called cycloplegia. Cycloplegia is paralysis of the eye muscle that allows a person to focus.

For most people, cycloplegia occurs only while the eye dilation drops are taking effect. In rare cases, eye dilation may cause cycloplegia to last for several days. Although this can be very concerning, the condition is temporary and will go away with time.

Having certain preexisting eye conditions may also complicate the effects of eye dilation. Conditions such as a lazy eye, glaucoma, and cataracts can affect a person's vision. In some cases, these visual problems may worsen while the eye dilation drops are taking effect.

Eye dilation is necessary for several types of eye test. These tests are important for detecting various eye conditions and diseases in their early stages.

While the effects of eye dilation drops can be uncomfortable and unpleasant, they are temporary.

Most people can expect eye dilation to last somewhere between 4 and 24 hours. Generally, the effects last the longest in people with lighter colored eyes and in children who require stronger doses of eye dilation drops.

People who are concerned about the effects of eye dilation should speak with their eye doctor.