Why do you dilate my pupils?

Did you know? Patients frequently ask why it's necessary to dilate the pupils during a complete eye examination. It's simple, really. Imagine the difference between looking into a room through a keyhole, and looking in through a large window. If you really want to get a good view inside the room, the large window gives a much more complete view.

Similarly, dilating the pupil enables the ophthalmologist to view the entire back of the eye. What are we looking for? There are hundreds of things that can go wrong inside the eye, (many of which have no symptoms). We're checking to see if everything is normal. We look at the optic nerve, the blood vessels, and the retina, including the central retina, called the macula. If you have a specific complaint, like floaters, or a family history of glaucoma, or blurred central vision, obviously we will pay particular attention to the part of the eye which is most likely involved.

Here is a diagram which shows the advantage of a dilated pupil. The diagram is incorrect, though. With a dilated pupil, and the proper equipment and technique, the entire back of the eye can be examined (including the periphery), not just the part shown in the diagram.

 

(courtesy of the National Eye Institute) 

Did you also know? In 1823, a Dr. Purkinje was the first to ever look inside a living human eye, when he devised the optics to do so. It was not until 1850 that another ophthalmologist, Hermann von Helmholtz, invented the ophthalmoscope independently and publicized his device that other doctors finally were able to look inside the eye and more accurately diagnose its conditions. Read more about the history of the ophthalmoscope here.