The pupil is the black, central point of the eye that sits in a sea of striated color called the iris. While appearing as solid as anything else, the pupil is actually an opening roughly 2-4 mm wide in ambient light, but the pupil doesn’t remain constant, it is actively opening and closing in response to the amount of light it is exposed to.

When the pupil is subject to dim light or darkness it opens or dilates; when exposed to bright light the pupil closes or constricts. In both cases, the pupil is actively responding to the environmental conditions it is exposed to thus enhancing a person’s vision under those specific conditions.

In darkness, the pupil will dilate from approximately 2-4 mm up to 4-8 mm in diameter, allowing for as much light as possible to enter the eye and increase a person’s ability to see in low light conditions.

Not only does the pupil allow a person to see the world around them, but when fully dilated and with the proper instruments and training, the pupil allows an optometrist to see the world within the eye.

Pupil Dilation and Constriction

Our eyes are constantly adjusting to different light conditions as we move through thew world. As conditions change slowly, our eyes adjust to allow for generally uninterrupted clarity of vision, but if conditions change quickly, it can take a few minutes for our eyes to adjust.

The iris is more than just a colorful display but also contains the sphincter or circular muscle that contract to close or constrict the pupil, and the iris dilator or radial muscle that opens, enlarges, or dilates the pupil.

Unlike other muscles in the body like the bicep in the arm or quadricep in the thigh, the muscles in the eye cannot as easily be controlled simply by flexing. The muscles in the iris, like cardiac muscles in the heart, are automatic or involuntary muscles controlled by the autonomic nervous system. While they are not simply controlled like arm muscles, they can be induced to expand or contract with an outside stimulus.

Optometrist Eye Dilation

Under professional clinical conditions, an optometrist can treat a person’s eyes with mydriatics, specialty eye drops that relax the eye muscles and stimulate the iris to enlarge or dilate the pupil. The effects of the eye drops, dilation, usually last 4-6 hours and means that during that time your eyes will be particularly sensitive to light. Under the influence of the eye drops, the automatic control of the pupil is temporarily suppressed.

Dilation allows your eye doctor to perform a much more comprehensive eye exam by providing them a better view of the back of your eye. With that unrestricted access, your eye doctor can better diagnose common diseases and eye conditions, possibly at their earliest stage, including diabetes, high blood pressure, macular degeneration, retinal detachment, glaucoma, and others.

Comprehensive eye exams that included dilation are an essential part of routine eye care. The 4-6 hours of light sensitivity or mildly blurry vision afterwards is well worth the diagnostic advantage, but just to be on the safe side, consider having a friend or loved one give you a ride home afterwards!