Eye myths… fact or fiction?

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Eye myths… fact or fiction?

Eating carrots helps you see in the dark.

True! Carrots are full of vitamin A which is a precursor to an important chemical substance used by the light sensitive cells in the retina (the rods) for vision in low light / night time. If you are deficient in vitamin A, you can have problems with night vision.

[1] However, having an excess of the vitamin does not enhance your vision above what is normal. So eating carrots all day like Bugs Bunny will not give you superhuman eyesight but just ensure your visual system is working normally!

If you watch TV for too long, you will go cross-eyed.

Myth! Watching TV for a long period of time won’t cause you to become ‘cross-eyed’ but it can make your eyes quite tired, sore and red. This is because when you are concentrating on screen (TV, phone, computer etc), you blink less than normal which contributes to an increase in evaporation of your tears.[2] Your tears normally create a uniform film over the front surface of the eye to protect it. Watching a screen has been shown to reduce our blink rate meaning that the interval between blinks increases. This allows the atmosphere to evaporate our tears leading to dry eyes. The symptoms of dry eye include red, sore, gritty, tired, stingy and watery eyes. It is recommended that you spend a maximum of 30 minutes on a screen before taking a break to allow your eyes a chance to rest.

Wearing glasses will make your eyes dependent on them and your vision worse.

Myth! At least 2 or 3 of my patients will ask me whether this is true each and every day so it is a very popular myth. It is not at all true. However, most people will think their vision seems worse when they take their specs off compared to before they put their specs on. This has nothing to do with the eyes themselves but with your brain. Your eyes are the hardware of vision – receiving the light signals from the world around us; and the brain is the software of vision – interrupting the neural signs from the eyes to perceive and interpret the information. The brain very much prefers clear vision so once you put specs on, your brain quickly adapts to accepting the improved vision. Once you remove your specs, your brain does not like the same blur that was there before. Your brain becomes less tolerant of the blur but your eyes remain the same.[3] Vision, however, does change particularly with age, but this change will happen regardless of whether you wear specs a little, a lot or not at all.

Onions make you cry.

True! Onions contain acids and enzymes within their cells. This acid is kept separate from the enzymes, but chopping onions allows the acid and enzyme to mix. This causes the onion to release its juice and sulphur based gas. This gas wafts towards your eyes and reacts with your tear film, combining to form sulphuric acid.[4] The sulphuric acid causes your eyes to burn / sting which in turns stimulates your tear glands to produce more tears in an effort to dilute the noxious substance. This is how you inevitably end up crying while chopping onions! Try refrigerating the onion before chopping – this will help reduce the gas emitted from the onion and avoid the tears.

It is impossible to sneeze with your eyes open.

Myth. It is really only possible to keep your eyes while sneezing if you make a big concerted effort to do so or if you force your eyes open (ie hold your eyelids apart) as the natural response to sneezing is always closing your eyes. This happens due to an involuntary reflex. The nose and eyes are linked by the trigeminal nerve (one of the cranial nerves).[5] The stimulation for the sneeze sends a nerve signal up one nerve to the brain and down another nerve to the eyelids triggering a blink. So, much like a reflex to kick your foot out when the doctor taps on a tendon / nerve just under your knee, closing your eyes while sneezing just happens automatically.

If you have know any other eye myths you would like debunked (i.e. old wives tales or something your colleague at work told you), let us know and we will debunk away!

 

References

[1] Nutrition and eye health book

[2] Wimalasundera S. Computer vision syndrome. Galle Medical Journal. 2006;11(1):25-29.

[3] Cufflin MP, Mankowska A, Mallen EA. Effect of blur adaptation on blur sensitivity and discrimination in emmetropes and myopes. Invest Ophthalmol Visual Sci. 2007;48:2932–2939

[4] Nagata T. An onion enzyme that makes the eyes water. Nature. 2002;419:685.

[5] Birch, CA. Sneezing. Practitioner 1959;182:122-124.

By | 2018-06-28T07:03:00+00:00 24th February 2016|General Eye Interest, Just for fun|0 Comments

About the Author:

Lauren Herring
In her spare time, Lauren is a tea drinker, book reader, weekend market browser and wanderlusting holiday planner. Otherwise, she’s just a girl with a really cool day job.

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