Why Do My Eyes Have to Be Dilated for an Eye Exam?

When you go to the ophthalmologist for an eye exam, the doctor doesn’t just test to see how accurate your vision is. A comprehensive exam, which you should have once a year, includes looking at the interior and exterior eye structures to determine if you’re developing any eye diseases or other problems. To accurately examine those structures, the doctor needs to dilate your eyes.

At Retina Specialists, our team of expert ophthalmologists is passionate about making sure your vision is clear and your eyes stay healthy. That’s why they stress the importance of getting a comprehensive dilated exam, both for your yearly visit and following any kind of injury.

Here’s why dilation is so important.

The parts of the eye

To understand how healthy vision works and what can go wrong, it helps to know something about the structure and function of the eye. The easiest way to describe it is to follow light’s path. 

Incoming light first hits the eye’s surface, which is covered with a membrane that’s clear, curved, and tough. The clear area is what lets the light through, while the curved area (cornea) protects the eye and focuses the light.

The focused light moves through:

• The anterior chamber, a space filled with fluid called the aqueous humor
• The pupil, an opening in the chamber
• The lens, which fine-tunes the focusing
• The vitreous, another fluid-filled chamber

Finally, it strikes the light-sensitive tissue in the back of the eye (retina).

The retina converts the light waves into electrical signals, then sends them to the brain through the optic nerve. Your brain decodes the image, at which point you can “see” it.

The retina also contains a central region known as the macula, which makes up only 2% of the retinal tissue. This part is what registers your clear, central vision.

Why do my eyes have to be dilated?

A refraction is a test that simply evaluates your visual acuity, and your eyes don’t have to be dilated to give accurate results. The doctor may prescribe glasses or contact lenses if you need correction. 

A comprehensive eye exam, though, not only evaluates vision, but also the health of your inner and outer eye. Dilation is a critical part of the exam, because it allows the ophthalmologist to closely inspect the inner eye and determine if there’s any structural problem or disease.

When exposed to light, your pupil’s normal reaction is to get smaller. That means if your doctor shines a light into your eye, the pupil constricts, and he won’t be able to see a thing. To prevent the pupil constricting, we use special eye drops that force it to stay open so we can see the eyeball in its entirety, all the way back to the retina, macula, and optic nerve.

During a dilated exam, we can detect problems like the development of an eye tumor, trauma, or malformed structures. 

We can also diagnose and monitor a number of eye diseases:

• Torn or detached retina: Area of the retina pulls away from the connecting tissue, leading to vision loss
• Diabetic retinopathy: Blood vessels leak or grow abnormally on the retina
• Detached vitreous humor: often age-related, causes eye floaters (spots in vision)
• Glaucoma: damage to the optic nerve
• Macular degeneration (AMD): Protein buildup and unusual blood vessel growth destroy the macula and central vision
• Cataract: clouding of lens

Since most of these conditions don’t produce symptoms until they’re advanced, you may be unaware you need medical help unless you get your eyes dilated.

How will dilation affect my vision?

When we put dilating drops in your eyes, it usually takes 15-30 minutes for your pupils to open completely, and you can expect to remain dilated for about 4-6 hours, though everybody’s response is a bit different.

Dilating drops don't usually affect your distance vision, but they do make it hard for your eyes to focus on things close up. That means reading from a book or your phone, sewing, and other near-vision tasks will be difficult for a bit. You can avoid missing work by making your appointment for later in the day.

Dilating drops also increase your light sensitivity, since the pupils stay open. Definitely bring sunglasses with you to reduce the glare when you go outside, and try not to look at any bright lights. Also avoid driving, both because of the glare and because your vision will be a bit fuzzy.

If you haven’t had a comprehensive dilated eye exam for a while, it’s time to come into Retina Specialists so we can make sure your eyes remain healthy and clear. Call any of our five Texas offices — in Dallas, DeSoto, Plano, Mesquite, and Waxahachie — to make an appointment, or book online.