The human eye is not just the organ for vision, but it is truly a "window to the soul" of a person. Recent studies have suggested that pupillary evaluation can often reveal more than just the deterioration values of their sight and necessary lens power to fix their vision.

It is widely said that when you're with someone you love, your pupil will dilate in response to the chemicals racing in your brain. It's also well known that the pupil dilates in response to the adrenaline under stress, especially during "fight or flight" situations. Pupils are also known to dilate in response to arousal or activities requiring heavy concentration. During the Cold War, the Canadian government developed a prototype device called the "fruit machine" to detect homosexuality among employees through pupillary size measurement in response to racy images of men and women. And these are just surface examples of how pupil measurement can lead one to the emotional, mental and physiological state of a patient.

This article briefly discusses the nature of pupils and their surprisingly resourceful diagnostic powers when it comes to a person's mental, emotional, and physiological state.

Nature of the Pupil

The autonomic nervous system manages the continuous and involuntary turning of the pupil size. More specifically, it controls the iris to regulate the amount of light entering the eye, similar to a camera aperture.

The pupil is constantly responding to the changing balance of the sympathetic and parasympathetic nervous systems. It is influenced not only by light but also by anxiety, attraction, arousal, stress, trauma, and psychiatric and neurological conditions. Drugs and medications which induce or incite chemical, mental, emotional, and physiological responses in a person, including increased heart rate, blood flow, and perspiration, also result in changing pupillary sizes. Thus, when we think of the eye, and in direct relation, the pupil as a simple constant structure, we are not looking at the big picture but blinding ourselves to the reality that the pupil is constantly in flux.

Pupillary size measurement, which is a common practice at the optometrist and ophthalmologist's office, can reveal a lot more than just the power of your eye and what power lenses you'll need. Because of the nature of the eye and pupils specifically,  pupil diameter measurement can reveal what's going on in your nervous system and whether it's a disorder induced by mental, emotional, or physiological stress.

Pupillary Dynamics in Function

Today, a standard eye examination typically only generally and subjectively evaluates the pupil using standard penlight technologies to measure pupil size and conclude on obvious abnormalities or disorders such as anisocoria, fixed dilated pupil, and so on. These can always be more than just ocular disorders and may be symptoms of a serious neurological disorder buried underneath. Even in the case of physical injuries to the brain or a traumatic brain injury that can have varying effects on several organs, it can sometimes be detectable through pupil diameter measurement. Though the pupillary response in traumatic brain injury is often null, they are thus, more often than not, undetectable by ordinary penlight exams.

As technology progresses, there are more devices that can fine-tune and hone in on these significant pupillary dynamics every day. With a proper goal and roadmap, these can be incorporated into the regular medical sciences and help detect a lot of diseases and illnesses long before they fatally manifest in a patient. Below is a common pupillary dynamic as recognized by doctors today:

Pupillary Dynamics in Migraine or TBI (Traumatic Brain Injury)

Recent studies have revealed that patients suffering from migraines or TBI have slower pupil constriction and dilation speeds. Pupil measurement of such patients have shown that it responds to a light stimulus, but not as quickly as it should. It is theorized that these velocity issues could be the driving issue in some light sensitivity or accommodative problems usually seen in TBI patients.

Pupillary response to traumatic brain injury is often unpredictable, but some common ground rules can be established after repeated and mass observations, such as in the above example. Some TBI patients often have accommodative insufficiency (trouble engaging accommodation) and accommodative spasm, or difficulty relaxing, which is strange and uncharacteristic of age-related accommodation problems.

Potential Roadmap

In addition to employing proper technology and software for accurately measuring pupillary dynamics, an accommodative function needs to be added to the standard post-TBI oculomotor assessment. There are already pupillometry applications on several app-stores such as Reflex or Brightlamp, which are quick, easy-to-use apps that help diagnose pupillary function at a basic level even with difficult patients who cannot easily undergo a table-based pupillometric examination. The use of applications like these must be normalized among eye care specialists, eye researchers, optometrists and ophthalmologists, and such others in the medical professions.

Pupillary dynamics can also be an important metric for the systemic assessment of a patient's health. People with diabetes or high blood pressure become presbyopic faster, and in those cases, pupillometry could be a useful tool for screening or following their systemic health over time. With regular and routine pupillometric checkups by your local optometrist or ophthalmologist, your health remains in check, and your blood sugar levels remain regulated.

Before normalizing such practices, however, more in-depth research into the nuances of pupillary dynamics must be done. Treatments or therapies which are effective at normalizing pupil response must be practiced and assured of complete safety and absence of any side effects. Additionally, a robust set of normative values for pupil size must be established in pertinence with their dynamics at different ages and with different conditions. Although pupillometry is increasingly in use among modern neuro-optometrists and neurologists, the understanding of the role of pupil dynamics among the common masses is still lacking. There also needs to be drives of awareness and flexible measurement standards to build a stronger understanding of the role of pupil dynamics among normal and pathological populations.


The eye is still a mysterious organ, and we still lack a proper understanding of how vision and images actually work and are processed within our brains. Pupillary dynamics are only scratching the surface of harnessing the diagnostic power of pupils, but even that is a great leap in the ocular sciences. However, we are closer to making that theoretical leap into a practical one with modern and progressing technology.