When a patient walks through the door, the eye care professional must immediately begin evaluating the integrity of that patient; the way s/he carries themselves, their speech pattern, facial features, clarity of their eyes, position of their eyes, signs of squinting, or excessive tearing. These careful observations could alert the practitioner to issues that need attention. The eyes, as we know are the gauges of the inner workings of the body.
The pupils, in particular, characterize the delicate intricacies of the brain, and any abnormalities could prove devastating.

Our basic ocular design is such that both eyes work together in synchrony with each other. That is to say that the eyes are supposed to focus at the same level, move together, process light at the same rate, and both pupils are supposed to react the same to light and accommodation. There are certain conditions that will prevent full symmetrical functioning. For example, the eyes may not move the same way resulting in an eye turn, or one eye may see better then the other resulting in decreased visual functioning. However, the pupils are always supposed to react the same way, at the same time. The one exception to this rule is if an individual is born with this anomaly. Putting that situation aside, all pupils must react identically. If there is a pupil asymmetry, a very serious neurological problem could exist, and that may be life threatening.

To understand how the pupils operate we must first examine the visual pathway. The pupillary reflex starts in the retina. Light enters the eye and is absorbed by the retinal neuroreceptors (similar to camera film); the light then travels through the optic chiasm, the area where the right nerves crosses over to the left, and vice versa. At this junction, the light is split into two pathways on its way to the Lateral Geniculate Body. This is sort of a way station for the optical images sent from the eyes. The next stop on its way is the Edinger-Westfall Nuclei. This is the site where the mechanism that makes the pupils dilate and constrict together is housed. A pupillary anomaly anywhere along this pathway will result in unequal pupillary responses. It should be noted that there are no good causes for a pathway alteration. All are medically serious.

Relative Afferent Pupillary Defects (RAPD) are a serious and troubling finding when examing patients. Most often the eye that has a pupil that does not react properly will have a problem in front of the optic chiasm behind the eye. Some literature has suggested that a dense cataract will prevent light from getting to the retina resulting in a RAPD. However, since even in very dense cataracts some light reaches the retina, most experts will exclude it as a source of a RAPD. The most common source of the problem is optic nerve disease. It should be noted that substantial retinal disease can also result in a RAPD.

Medical conditions such as hypertension and hypercholesterolemia can result in a chocking of the optical nerve blood vessels, which will cause a RAPD. Occasional blurring or fading of vision are common symptoms. These are systemic conditions that must be addressed not only because of the RAPD but as a warning sign of serious medical conditions that can become life threatening. Emboli (blood clots) released by an artery or even the heart can cause RAPD, and may find their way into the brain. Patients suffering from diabetes may have an increased likelihood of presenting the signs of RAPD. Any condition that will result in an inflamed optic nerve can cause an RAPD as well.

The bottom line is any asymmetry in pupil reactions should be addressed immediately, and the appropriate referral must be made in an expedient fashion. Patients noticing any difference in pupil size, or reaction need to contact their eye care professional immediately, without delay. A rapid, proper referral may save the life of an individual.