The eyes serve an important role in your healthcare beyond allowing you to see: they show changes going on in deeper areas of the body and are often the first place these systemic diseases are noticed. Most vital of all, the eyes are the windows to the brain, and can tell our eye doctor important information about how pathways in your brain are working. One of the main ways they do this is through the pupils, the dark hole in the middle of the colored portion of the eye, the iris. Read on to learn about how the pupils work and what information they can provide about your health.
Pupillary Pathways and Functions
The pupillary responses are governed by the brain in response to several signals. One signal is light. When you shine light on the eye, the pupil constricts and becomes smaller in order to let less light into the eye. The opposite happens when we are in the dark: the pupils increase in size to let more light in, and this is part of dark adaptation. Another less known signal to the pupils is looking at something up close. When we hold an object close to us (i.e. a book), our eyes change their level of focusing to see it clearly, move inwards to keep it single, and constrict the pupils to provide easier focusing. If any of these responses are not intact, our eye doctor will investigate further for the possible cause.
Examination and Diagnosis of the Pupil
Our eye doctor will check the relative sizes of your pupils and their responses to light as part of your eye examination. If the pupils are quite different in size and this has not been noticed before, it can be an important sign of disease affecting either the iris of one eye or the neural pathway from brain to iris in that eye. If the pupils are the same size but one or both are not properly responsive to light, this is a sign of disease in the retina at the back of the eye or the optic nerve, which carries signals from the eye to the brain.
Conditions That Affect the Pupils
As explained above, anything affecting the brain or the eyes can affect the pupillary size and response to light or near work. These can include blockages of blood vessels that feed the retina or optic nerve, infections or inflammations of these structures, tumors, or glaucoma. Syphilis, diabetes, genetic conditions, and shingles can also do this. Illicit drugs, prescribed medications, or over the counter medications can also cause changes in the pupils. This can include eye drops given to you by our eye doctor or systemic medications given you by another doctor. Examples include opiates, nicotine, anti-allergy, anti-depression, anti-seizure, or antipsychotic medications; caffeine, marijuana, LSD, cocaine, etc.
There are some conditions affecting the pupils that require urgent medical attention. One of these is called a third nerve palsy, where one pupil is completely dilated with that eye also turned down and out with minimal movement possible. This may be due to a compressive tumor or aneurysm in the brain, requiring a trip to the hospital immediately. Head trauma, concussion, stroke, and swelling in the brain can also cause issues with pupils. Overall, if you are noticing changes to your pupil sizes or how they respond, get them checked with our eye doctor.