WHY IS PUPIL DILATION IMPORTANT?Dr. Carolina Valdivia answers a question about why pupil dilation is performed by ophthalmologists and other eye-care professionals for an eye examination.  A 38 year-old woman from Puerto Rico writes:Hi Dr. Valdivia. This is probably a stupid question, but I will ask it anyway. Why does my eye doctor put drops in my eyes to dilate my pupils when I visit him? This is very annoying to me because in Puerto Rico there is a lot of sun and when I go outside after my appointment the light makes my eyes hurt.
Rather than being trivial, your question is very important and is one about which I am sure that many other people have wondered. I perform a pupil dilation for an eye examination because doing so enables me to get the best look at that back of your eye. In technical terms this area is called the vitreous chamber. The process usually involves administering two types of eye drops: numbing eye drops followed by two different types of dilating eye drops. As you can see from the diagram below, widening (dilating) a patient's pupils increases the angle of observation. I am able to see a much greater area and have a clearer view of the back of your eye.
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 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 have an eye disease. Because the eye is such a sensitive structure, it often shows early signs of other disease conditions, such as high blood pressure (systemic hypertension), diabetes, and elevated cholesterol (hypercholesterolemia). Pupil dilation helps 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, known as the iridocorneal angle, in the anterior chamber of the eye is narrow. This can impede the normal flow of fluid, known as aqueous humor, in this part of the eye and raise intraocular pressure. Dilating pupils in eyes that already have narrow iridocorneal angles can cause the angles to narrow further and result in a pupillary block, which is a medical emergency. I determine if a patient has narrow iridocorneal angles with a test called gonioscopy. Unless there is an emergency, such as eye trauma, that requires immediate examination of the retina, I prefer to perform a peripheral iridotomy before dilating pupils in eyes that have narrow iridocorneal angles. Following an eye examination, your pupils typically will remain dilated for 3-5 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 once they leave my office. I have some disposable sunglasses that I provide 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 an eye examination far outweigh any short-term inconveniences. Most of these can be effectively managed, such as temporary sensitivity to light with sunglasses. If you have further questions, I will be happy to respond to them. Carolina Valdivia, MD
REFERENCE:Leitman MW. Manual for Eye Examination and Diagnosis, 7th Ed. Oxford, UK: Blackwell Publishing, 2007.
A number of visitors have written to me asking for recommendations pertaining to eye-care products and books for obtaining more information. I have joined with Amazon.com to create a dependable resource for books and products. You can find these materials at the Eye-Care Store. My goal in answering your questions is to provide you with information, clear up misconceptions, and to explain options so that you can have an informed conversation with your doctor. However, under no circumstances should my response to your question be considered a substitute for ongoing consultation and examination with your doctor. Since I have not examined you, I only can speak in terms of generalities, whereas your doctor has sufficient clinical details to evaluate your case specifically.
Return from Pupil Dilation to Other Eye Problems
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Thank you for your interest in glaucoma-eye-info.com. A professor of mine in medical school once told our class that the only stupid question is the one that you did not ask. I have followed this advice throughout my career. I hope that it will serve you as well as it has benefited me. 
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.