Why Is Eye Dilation Necessary During an Eye Exam?

This article will walk you through the eye dilation process and answer the question why is eye dilation necessary?  Most eye doctors feel it is really important to include a dilation with every comprehensive eye exam. Generally, after the check-in process, you will be taken back to a pre-testing room, where the exam process will begin with a thorough case history. It’s helpful to have a list of medications and really know your family history quite well just to give the doctor a better overall picture of your health, and it also helps with the final diagnosis.

In most cases, the exam will start off with checking your vision at distance and up close. They are going to check your pupils and your peripheral vision. From there, they are going to read your glasses if you wear them, so make sure you bring them. Also, if you’re a contact lens wearer it’s very important that you bring in either an old prescription or if you have a box that would be helpful. During the final process, the doctor is going to get you the most accurate prescription he or she can.

To check your prescription, the technician will work with what is called an autorefractor.  This is a computerized measurement of what your prescription may be.  The technician will look at your glasses and the autorefraction numbers to start your refraction process in order to come up with the most accurate prescription for you.

The doctor will verify those results once you’re in the room with a doctor, to give you the final prescription.  After the refraction process, the next step will be to check your eye pressure, and that’s where you’ll experience your first set of eye drops.   The first drop will numb your eyes so they can lightly touch the eye and measure its pressure.  It is a painless process.

After the glaucoma test is measured, the next step will be to dilate the eyes.  There is no pain in the process of dilation of the eyes because the first drop from the eye pressure test will numb your eyes.  Actually, your eyes will feel numb, heavy, and sticky for about 20 minutes.

Eye Dilation Process

Most optometrists will use two sets of eye drops to dilate the pupil.  One set will help relax the focus of the eyes and keep the pupils from seeing smaller bright lights. As we know bright light will make the pupils constrict, and this drop freezes that muscle’s ability. They will then use a second eye drop which also extends the ability to dilate the eye muscle as well.  So basically they will use two medications to allow them a better, broader look into your eye.

Each patient will dilate at a different rate. Patients with light eyes, such as blue eyes or green eyes, are going to dilate quicker.  Patients with really dark eyes, like brown eyes or dark pigmented eyes, will dilate slower. In general, the dilation process for most patients will be between 20 and 30 minutes.

Once the drops are placed into your eyes you are often brought out to the doctor’s waiting area where you will wait for the full dilation to take effect.  Again, that process is about 20-30 minutes for full dilation.

How Long Does Eye Dilation Drops Last in Children?

With children, doctors will use a different formula for dilating their eyes. The medication is a bit stronger so the child will relax, or focus more because sometimes children can trick doctors during the exam process. By “trick” we mean that while determining vision or prescription, children can be really good at focusing their eyes making it seem like their vision is OK when really they need the assistance of glasses or contacts.  So this stronger medicine allows the child to relax and gives the doctor a much more accurate prescription.

Oftentimes parents don’t feel that their child needs to be dilated because they’re not at risk for certain eye diseases or conditions just based on their age.  However, it is absolutely vital, especially for a first-time exam, for the doctor to get as much information as possible to give your child the best possible prescription.  The dilation will last anywhere from 4-24 hours but usually towards the lower end.

Difference in Dilation and Not Dilating During an Eye Exam

If an optometrist did not dilate your pupils during a routine eye exam when they went to shine a light in your eyes the pupil would constrict.  As a result of the pupil being smaller, the doctor would only be able to get about a 25 – 30 percent view of the inside of your eye.  If there’s a cataract or there’s a scar on the front window, the eye limits the doctor’s view even more. That’s why it’s recommended that all patients have dilated pupils when having their eyes examined.

It gives the doctor a much deeper view into the eyes and gives them a better look to diagnose cataracts or if you will need cataract surgery.  It helps them look at the optic nerve to help diagnose glaucoma, and it helps them get a better view of the macula, where you can develop macular degeneration. It allows them to look deeper at the periphery of the retina, to look for any signs of risk factors for retinal detachments, or the rare chance of eye tumors or things of that nature.


During a routine eye exam, it’s not uncommon for optometrists to discover early signs of a retinal detachment.  Even though you come in seeing 20/20 the doctor will be able to catch the detachment early enough so that it can be fixed and prevent a vision loss in the future.

Normal eye pressure is between 11 and 22 but can be very tricky.  Years ago anyone with a pressure of 20 or higher would be considered to have glaucoma. However, we know that’s not true today because the thickness of the front window of the eye can affect eye pressure.  Somebody with a pressure of 11 or 12 can still have glaucoma.

Someone with a pressure of 25 or 26 can be found to have normal health and not have glaucoma.  So eye pressure is just one small piece of the whole picture and that’s where the dilation helps doctors look at the optic nerve.  The optic nerve is what gets damaged with glaucoma, and so with the combination of dilation and eye pressure, doctors can help diagnose that sooner.

If you have any questions about eye dilation feel free to contact any of the eye doctors or optometrists listed in our directory and they will be glad to help you.  Or, contact your primary eye care provider.

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