What does Pupil Dilation Indicate?

While in school, the study of the human eye was perhaps our first introduction to the phenomenon of pupil dilation. We learned that our pupils (the black centers of the eye surrounded by the iris) dilated in conditions where there was near darkness or less light and our pupils dilated to let in more light.

So how does this natural, seemingly harmless physical response indicate complex emotions such as sexual arousal or expose the lies buried deep in your mind and let out your true feelings? Also, if you know that your eyes are indeed the window to your soul, can you then train your pupils and control the dilation to protect your case?

Let us take a deep dive and explore the depths of our eyes.

The normal dilation of pupils (also called mydriasis) is meant to control light, typically sunlight, such that it does not harm the retina. The dilation occurs when there's not enough light and the pupils constrict (constriction of pupils is called miosis) when there's too much bright light that may cause potential harm. But it's not just light that affects pupillary responses.

Your pupils may dilate for a short time in response to feelings of fear (especially in response to sudden stimuli), physical attraction to someone, etc. This minimal dilation is usually restored instantly when you have adjusted to the stimulus.

In addition, drugs (including illegal psychoactive drugs such as methamphetamine) and certain medications can also cause the pupils to dilate. This "induced" dilation can last longer and is usually more pronounced.

An ophthalmologist may have your eyes dilated using certain mydriatic eye drops just before examination. The eye doctor artificially dilates the pupils to look for signs of damage to the back of the eye or even symptoms that may indicate a disease.

Conditions such as multiple sclerosis, kidney disease, diabetes, brain trauma (after a fall or injury) and high blood pressure are often accurately indicated through pupil abnormalities. If a person has fallen from a considerable height, you will notice that the medical examiner will also investigate his/her pupillary reflexes to rule out brain injury, etc.

If you're a concerned parent wondering if your child is using illegal drugs, pupil dilation is a symptom of meth (methamphetamine), LSD, cocaine or marijuana use. If you observe your child has a zombie-like vacant expression with wide eyes and a fixed gaze, you could test him/her for drug use.

However, it is important to note that dilation of pupils for a relatively long span of time (more than a day) can also be due to medications such as antihistamines, diphenhydramine (Benadryl, Allermax, Allergia-C) or chlorpheniramine and other decongestants.

In addition, dilated pupils can also indicate poisoning such as benzene or chloroform poisoning or reaction to consumption of poisonous mushrooms. Seek medical assistance, if pupil dilation occurs for more than a day or two.

The evaluation of pupillary responses as an indicator of emotions is known as pupillometrics, the term coined by a biopsychologist from the University of Chicago, Eckhard Hess, in 1975.

Hess conducted research-oriented, pupillary response studies on various groups of people and concluded that pupil dilation indicates positive emotions whereas constriction of pupils generally denotes lack of interest or even unpleasantness.

You may actually find this conclusion useful if you're dating someone. For example, you can judge if the person you're seeing is truly interested in you by observing his/her eyes while talking. If the eyes are consistently large and the pupils are mostly dilated, it indicates attraction and interest!

But it's not just about romance, if you are sitting down to a much-awaited meal that has your favorite things plated up in front of you, your pupils will dilate.

These evaluations of pupillary responses find application in forensics and law enforcement. Electronic examination of pupils is done to detect fatigue, driving under the influence of alcohol and/or drug abuse in errant drivers.

These tests are quite cheap, non-invasive, fast and accurate and therefore, widely used for examining traffic offenders and in correctional facilities as pre-screening mechanisms.

More studies into the language of the eyes suggest that the direction of gaze and pupillary responses can jointly be used to interpret the levels of deception in a person's reactions. This technique finds application when law enforcement officials are interrogating a suspect.

Studies indicate that a rightward glance means the left brain is in use. The left brain is associated with logical functions like concocting a story, hence, a rightward glance might imply lying, a glance to the left means the person is recalling something and a downward glance typically means association with emotional memories.

This type of subject reading is not foolproof though, as some people could be telling a story by recalling something that happened long ago and therefore, they may not be necessarily lying! Besides, there are no consistencies with those who're left-handed using their right brain more often.

However, when used along with polygraph tests, etc., these techniques might bring more clarity in evaluating a suspect.

Computerized pupillometry which employs digital pupillographs and other devices to measure and record pupil size and movement are being increasingly used beyond the realms of research, as diagnostic tools. The conclusions from Hess's research are being used to study consumer behavior.

In fact, Hess also concluded that while dilated eyes mean positive interest in whatever is being shown, if subjects are shown images of people with dilated eyes, they find them more attractive.

This concept is at the center of various ad campaigns that show close-up pictures of attractive models with dilated or larger eyes. Next time when you're walking down the personal products aisle at the supermarket, pay close attention to the poster that advertises cosmetics, hair products or clothing.

As far as attraction to someone or something is concerned, pupil dilation occurs fairly consistently. Subject to certain conditions (such as drug abuse and presence of illnesses causing dilation), pupil dilation comes across as an important and effective indicator in psychoanalysis.

It is especially reliable when combined with other forms of deception response tracking (such as a polygraph test).

In forensic psychology, pupil dilation is being researched with primary focus on providing behavioral clues to deception. Researchers are trying to evaluate foolproof methods of measuring lie signs, and pupil dilation seems to be at the forefront of this measurement.

Although the results of such research seem to help forensics and law enforcement agencies, being able to evaluate people's reactions to their surroundings based on pupillary responses can open up vast possibilities in consumer research as well.

Imagine being able to read consumer behavior merely by observation without having to physically ask the questions or interviewing or surveying the consumers.

Pupil dilation is also being studied by experts in the field of neuroscience as an important phenomenon in understanding the brain and the central nervous system better. In fact, studies seem to show a link between the diameter of the pupil and cortical dopamine levels.

Researchers are also probing a connection between the properties of the pupil and pupillary responses with mental illnesses.

Another area of research is concentrated on further establishing a correlation between pupil dilation and increased mental efforts leading to what is called cognitive workload. These studies experiment with pupillometry in response to exposing their subjects to cognitive tasks involving memory, language processing, perception and reasoning.

The resulting conclusions are being applied in the fields of psycholinguistics such as language acquisition as well as in cognitive neuropsychology.

You can learn more about pupil dilation not just to know what pupil dilation indicates but also to become a mind reader. You could feel so powerful that you have the unique ability to see through people, well, at least most of the time.

Wouldn't it be great that you're able to spot a liar, locate the first signs of a disease or seek out a future life partner by exploring that black hole of information in someone's eye!