To Dilate or Not To Dilate: There Is No Question

Irritating part of annual exam key to early detection of problems

By A.Paul Chous, MA, OD, FAAO


One of the least pleasurable but most important parts of an eye examination is having your eyes dilated. Patients frequently complain about the increased light sensitivity and blurred vision that invariably, if only temporarily, follows having the eye doctor place drops in their eyes. Believe me, I understand how you feel. I have had to have my eyes dilated at least once a year for the last 37 years! However, I think that if each of us with diabetes understands why dilation of our pupils is so important in detecting eye disease and preventing any loss of our vision, we will actually welcome (or, at least, less grudgingly accept) the annual ritual.


The pupil is like an open "window" looking to the inside of our eyes. It naturally opens (dilates) and closes (constricts) to precisely control the amount of light entering, controlled by two sets of muscles in the colored part of the eye, the iris. In order to examine the inside of an eyeball, a lighted instrument must be used to allow your doctor to see what is inside. Without dilating drops, when your eye doctor examines the inside of your eye, the pupil automatically gets smaller, giving her a much smaller "window" through which to see. Dilating the pupil with eye drop medicines (which temporarily stimulate the iris dilator muscles and block the iris constrictor muscles) makes that window much larger, and ensures that you will get a more thorough eye exam. Put another way, if you have serious eye disease caused by diabetes, the odds of it being detected and treated are much greater if your pupils are dilated and much lower if they are not.

The typical pupil is 3-4mm (1/6 of an inch) in diameter in normal room lighting, whereas a dilated pupil is 7-8mm. This difference yields a three to seven times greater area through which to examine the internal eye. Remember, the pupil is essentially an open circle – this means that the area of the pupil equals its radius squared multiplied by pi (forgive me if I have stirred any bad memories of junior high school geometry!). This means that the entire retina can be visualized through a dilated pupil with relative ease, while examination of the entire retina is very difficult, at best, through undilated pupils. Perhaps even more important is the fact that dilated pupils allow your eye doctor to see three-dimensional, stereo views of the retina and optic nerve, something critical in the detection and treatment of diabetic retinopathy and glaucoma, two potentially blinding eye diseases for which every single patient with diabetes is at significant risk.

The undeniable "standard of care" for examining the eyes of patients with diabetes includes dilation of the pupils to allow detailed examination of the retina and other ocular structures. Current guidelines recommend that all type 1 patients receive dilated eye examination within 3-5 years after diagnosis and each year thereafter, and that all type 2 patients be dilated upon diagnosis and each subsequent year. Upon diagnosis of diabetic retinopathy in particular, the frequency of subsequent dilated examinations may be greater, depending upon the degree of severity. It should be noted that many patients with diabetes have smaller than average pupils (high blood sugar can impair the nerves controlling the iris dilator muscles), a factor that makes dilated examination all the more obligatory.

It must also be noted that people with diabetes are no less susceptible to many "non-diabetic" eye diseases than the general population (e.g. age-related macular degeneration and retinal tear/detachment), that much eye pathology is age-related, and that a majority of patients with diabetes are over the age of 60 years. For all these reasons, routine dilated examination of all patients is indicated, but most especially for those with diabetes. Nonetheless, recent analysis demonstrates that as many as 40% of persons with diabetes do not receive annual dilated eye exams. This is tragic statistic because blindness caused by diabetes is almost entirely preventable if problems are caught and treated early. Always remember that many eye diseases, including those caused by diabetes, often cause no symptoms whatsoever until permanent damage has already occurred.

Most visually bothersome effects of dilation dissipate within two to three hours, and patients should not drive until they feel safe to do so. Is this inconvenient? Yes. Is it less "inconvenient" than losing your vision because a serious problem is not detected in time? Absolutely. So bring your dark glasses and a driver, see your eye doctor every year, insist that your eyes be dilated, and be glad when they are. For those of us who have diabetes and want to keep our vision, it is simply the easiest and most important thing that we possibly could do.

For more information on diabetic eye disease, consult Dr. Chous' book Diabetic Eye Disease: Lessons From a Diabetic Eye Doctor, Fairwood Press, Seattle, 2003.

Read more about Dr. Chous here.

Visit Dr. Chous' website here.

NOTE: The information is not intended to be a replacement or substitute for consultation with a qualified medical professional or for professional medical advice related to diabetes or another medical condition. Please contact your physician or medical professional with any questions and concerns about your medical condition.

Last Modified Date: June 28, 2013

All content on is created and reviewed in compliance with our editorial policy.

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by Brenda Bell
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