Eye Health – Why is Pupil Dilation Important For an Eye Examination?

A woman from Puerto Rico recently asked me why her eye doctor administers drops to dilate her pupils during an examination. She mentioned that she found this to be very annoying because in Puerto Rico there is a lot of sun and, when she went outside after her appointment, the light made her eyes hurt.

This is a very important question and is one about which I am sure that many other people have wondered.
So … is pupil dilation really necessary?

Yes. As an eye-care professional, I have a dual responsibility: to ensure that you have the best visual acuity possible and to monitor your eye health. It is the second of these, monitoring eye health that requires administration of eye drops to dilate your pupils. The misunderstanding occurs because most people visiting an eye doctor are focused on the visual acuity aspect. Since pupil dilation is not needed to test visual acuity, it often is considered an unnecessary nuisance. However, as you soon will see, this is an indispensable tool that helps me to monitor the health of your eyes.

I perform pupil dilation for an eye examination because doing so enables me to get the best look at the back of your eye. In technical terms, this area is called the vitreous chamber. It is filled with a fluid called vitreous humor. The process usually involves administering two classes of eye drops: numbing drops followed by two different types of dilating drops.

Widening (dilating) a patients' pupils increases the angle in which I can observe the back of the eye. I examine this area by pointing a beam of light through the pupil. Normally, in the presence of bright light, the pupils constrict to allow less light to pass through to the retina. This would create an unacceptable situation in which I only would be able to see a small point in the back of your eye. However, with the pupils dilated, I am able to see a much greater area and have a clearer view of this region.

Once I have administered eye drops for pupil dilation, I examine the optic nerve and the blood vessels in your retina. Specifically, I look for changes in the optic nerve that could be an indication of glaucoma or other eye health problems, such as macular degeneration. I also evaluate the quality of the blood vessels, including the way that they cross each other. Changes in the optic nerve, retina, or blood vessels from one eye examination to the next could be a sign that you are developing an eye disease. The earlier that I am able to detect this, the better the outcome will be for your overall eye health.

Because the eye is such a sensitive structure , it also can show early signs of other disease conditions, such as high blood pressure (hypertension), diabetes, and elevated cholesterol (hypercholesterolemia). Pupil dilation can help me to identify these problems early. However, there are certain conditions for which pupil dilation is not recommended. Foremost among these is primary angle-closure glaucoma. In this condition, the angle formed by the iris and the cornea in the front part of the eye, known as the irideocorneal angle, is narrow. This can impede the normal flow of fluid, known as aqueous humor, in this region and rapidly raise the pressure inside your eye. Dilating pupils in eyes that already have narrow irideocorneal angles can cause the angles to narrow further and result in a pupillary block, which is a medical emergency.

Following an eye examination, your pupils typically will remain dilated for 3-4 hours. During this time, you will experience sensitivity to light and may have blurry vision, especially during reading and other work requiring close focus. For this reason, I always recommend that my patients bring sunglasses with them so that they are not bothered by light when they go outside. I provide disposable sunglasses to patients that have forgotten to bring their own, but these resemble the 3-D glasses that are given out at movie theaters and are not particularly stylish.

As you can see, the benefits of pupil dilation for monitoring eye health far outweigh any short-term inconveniences. Most of these can be effectively managed, such as temporary sensitivity to light with sunglasses.

Under no circumstances should you attempt to drive an automobile after an eye examination in which your pupils have been dilated. If public transportation is unavailable, I recommend that you arrange to have someone able to drive either accompany you to the exam or be available to pick you up when it is finished. Similarly, if you plan to go to work after the examination, you should not operate any machinery or do other work that requires fine focus.

Persons over 50 years of age that have diabetes, high blood pressure, and / or elevated cholesterol should have yearly eye examinations in which their pupils are dilated.