The iris (the coloured part of the eye) plays an important role in the proper functioning of the eye, as it's primary job is to regulate how much (or how little) light enters the eye. This is controlled by muscles in the iris which will constrict or enlarge the pupil. Nerve impulses travel down the optic nerve after light enters the eye, which affects the size of the pupil. The pupil changes involuntarily, which is known as the pupil reflex.
However, there are a range of other emotional or physical environmental triggers which can cause your pupils to change in size which include...
1. Lighting conditions
Just as a camera requires the correct amount of light to capture vivid images - your eyes also need the correct amount of light to see properly. During the day less light is needed to see things around you, which is why the iris narrows and the pupil constricts and gets visibly smaller. Conversely, in darker conditions, the pupil will enlarge as your eye will try to let in more light to see things you otherwise would have easily seen during the daytime.
When focusing your eyes on a near object your pupils will constrict to increase the depth of focus in the eye by blocking the light scattered by the periphery of the cornea. Conversely, when you when you look at something further out into the distance, the diameter of your pupil will increase and muscles will relax in order to stretch the ligaments inside your eyes. This will pull on the lens, causing it to flatten and create a thinner contour allowing you to see distant objects in focus.
A few medicines can affect the muscles that control your pupils; preventing your pupils from getting smaller when the light shines in. Similarly, in order for the eye doctor to view the back of the eye during an eye exam, dilation eye drops work by relaxing the muscles in the iris that are responsible for constricting the pupils.
For example, 'Atropine' is a medication that enlarges the pupil and comes from a plant called Belladonna which is Italian for 'beautiful woman' (because historically the herb was used by women to make them appear more seductive).
4. Drug Use
Certain illegal drug can temporarily affect the ability of the iris to contract, which is why enlarged pupils can sometimes be an indication that someone has used illegal drugs. Marijuana is a good example of this, as it triggers a release of dopamine, which excites the adrenergic receptors and induces mydriasis (dilation of the pupils). On the other hand, narcotics are known to cause "pinpoint pupils".
5. Love at first sight? Or lust?
Studies have shown that pupil dilation correlates with arousal. When our gaze falls on a someone of interest to us, the brain releases a surge of dopamine, which triggers a pupil dilation. For those who have darker coloured irises, this pupil size change would be less noticeable.
For this reason, often in advertising, the models' are photoshopped to have enlarged pupils, making the models look more attractive and alluring. This is because the ability to decode pupil dilation is hardwired in our brains and subconsciously when looking into a pair of enlarged pupils in advertising (or in person), we think that we are looking at eyes that find us attractive.
6. Tricky Tasks
According to some studies, the harder your brain works, (for example when you're calculating a tricky equation) the more your pupils will enlarge. Furthermore, the more difficult you find the task, the wider your pupil will get.
If you wanted others to think you find algebra a breeze, don't worry, your secret is most likely safe! Even if you found the task absolutely mind-boggling, this pupil dilation is barely noticeable with the changes generally less than half a millimetre. Your pupils will return to their normal size when you have finished or given up on the task.
7. Fight or Flight
During periods of extreme stress, anxiety attacks or fear, often your pupils will dilate in response to the rush of adrenalin in your body. When your body goes into 'survival mode', this physical response is triggered to allow more light into the eyes, enabling you to see better and remove yourself from the potential danger.
While the saying "the eyes are the window the soul" may not be scientifically accurate, studies have shown that eyes can, in fact, be a window into someone's emotions and feelings. Since pupils are part of our body language that we have no control over, the size of a person’s pupils can reflect one's state of mind, giving another person a strong impression of sexual attraction, fear, sympathy or hostility.
Pupils can change dramatically not only with different emotions, but also are can be affected by medications, lighting conditions and by what you have ingested. However, there can be more serious reasons for changes in pupil size, such as an injury to the brain and certain rare conditions, like Horner's Syndrome. Pupil size changes and variations can be normal and in many cases are harmless, which can occur for varying reasons. A past physical injury to the eye can affect the pupil size too, just look at David Bowie's left eye for example.
Cause for Concern?
If you have noticed a recent significant change in the size or shape of one or both of your pupils, there could be an underlying issue, in which case, we highly recommend you book an appointment with an ophthalmologist to have it checked out. To book an appointment with one of our expertly trained ophthalmologists, give us a call on 09 529 24 81.