Sara- Grade 10 - Duluth, Ontario, asks
From sleepy newborn babies to overworked business people to drowsy grandfathers after supper, pretty much everyone’s experienced the relief that rubbing their eyes brings. In fact, most people probably don’t even realize how often they rub their eyes when they’re tired, making it almost a reflexive action. So why do we do it?
Sometimes we rub our eyes to help relax the muscles around the eyes, which can become strained and fatigued, especially if we’ve been working at the computer or playing video games for too long. Rubbing the eyes also encourages the production and coating of the eyeballs with more tears, which may help if they’ve started to dry out.
While these are reactions that are helpful when we’re trying to stay awake and fighting off the urge to sleep, rubbing our eyes can also help relax and prepare us for sleep by slowing our heart rate by 5 to 13 beats per minute through activation of the oculocardiac reflex.
Did you know? A decrease in heart rate is known as bradycardia; irregular heart rates are known as arrhythmias
The oculocardiac reflex is similar to the knee jerk reflex you get when the doctor taps your knee, in that it’s an involuntary, or unconscious, response to a stimulus. In this case, the stimulus is the rubbing of the eyes, which causes an increase in the pressure in and around the eyeballs. The increased pressure is relayed to the brain via a specialized nerve, called the sensory trigeminal nerve, and results in signals being sent to the heart via another nerve, called the effector vagal nerve, resulting in a decrease in heart rate.
Did you know? Reflexes are carried out in the body by nerves. A sensory nerve senses the initial stimulus and transmits the information via an effector nerve to cause the final response. This circuit is known as a reflex arc.
Intentional lowering of the heart rate with the oculocardiac reflex is used by hypnotists, naturopathic or holistic healers and martial arts practitioners as method of relaxation. Prisons and hospitals have also been known to employ the oculocardiac reflex as a way to subdue violent or agitated inmates or patients.
However, care needs to be taken when deliberately inducing the oculocardiac reflex, as it can decrease the heart rate to dangerously low levels, or result in irregular heartbeats, to the point of causing fainting or, in rare cases, death. This is more likely to occur when sustained pressure to the eye is applied.
The oculocardiac reflex can cause problematic decreases in heart rate during eye surgery, particularly in otherwise healthy younger children. To prevent this, anaesthesiologists will often numb the trigeminal nerve using drugs. Interestingly, activation of the oculocardiac reflex is often thought to be linked to the high rate of vomiting after eye surgery.
Did you know? Anaesthesia (numbing) of the trigeminal nerve is often achieved by administering atropine, the same drug the ophthalmologist may use to dilate your pupils during a routine eye exam.
So, when we instinctively rub our tired eyes, it’s our bodies’ way of preparing us for sleep by mildly slowing down our heart rate and helping us relax, or wind down. Some people may rub their eyes even when they’re not tired, especially if they’re stressed, because it helps calm them down. Yet another example of the exquisite way our bodies work as a system!
Want to learn more?
Rubbing eyes Sleepy, rubby eyes
1. McMonnies CW (2008) Management of chronic habits of abnormal eye rubbing. Contact Lens & Anterior Eye 31:95-102.
2. Patil BB, Dowd TC (2000) Physiological functions of the eye. Curr. Anaesthesia & Critical Care 11:293-298.
3. Dewar KMS, Wishart HY (1976) The oculocardiac reflex. Proc. Roy. Soc. Med. 69:13-14.
This answer was researched and written by May Cheng. May studies the properties of cardiac potassium channels (proteins that help regulate your heartbeat) as part of her PhD training at the University of British Columbia. She also received her Master’s and Bachelor’s degrees from UBC. When she’s not in the lab, she enjoys researching her other great love – food.