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Vitamin A in Sight

Source: Creative Commons, Kander

Retinal, one of the parts of rhodopsin, is a special form of Vitamin A. One of the sources of Vitamin A in our diet is carrots so there is a strong belief that eating carrots will help you see better in the dark.

Retinal is essential for the functioning of the eye, in particular the rods in the eye. Rods provide black and white vision and respond in dim light, while cones provide colour vision and respond to bright light.

During the day, the incoming light is strong enough that what little retinal is around will be activated to start the process of vision. At night, when there is a lack of retinal, it becomes difficult for the rods to sense the small amount of light around and this results in poor night vision.

Geneticist Phillip Simon and horticulturalist Clinton Peters at the University of Wisconsin have developed a new variety of carrot called the Beta III. This ‘supercarrot’ contains three to five times the concentration of Vitamin A in normal carrots. This Beta III carrot is designed to combat the blindness caused in developing countries by a lack of Vitamin A.

“Worldwide each year Vitamin A deficiency causes 10 million cases of night blindness and one million cases of cloudy vision.” Dr Phillip Simon. 

However, lack of Vitamin A in your diet not only affects night vision, but can cause poor immune responses and has been linked to anaemia.

Good sources of Vitamin A include green leafy plants, yellow fruits such as golden mangoes, palm oils and of course carrots. Other foods that have been artificially fortified with Vitamin A include margarine, wheat, rice, edible oils, and sugar.

Interestingly, eating large amounts of carrots will only improve your eyesight if you don’t already have enough Vitamin A in your diet. A professor at Melbourne University in Australia has this to say about the carrot myth:

“No amount of carrots will improve your eyesight if you already have a well-balanced diet.” Professor Algis Vingrys of Melbourne University

If you are interested in learning more about Vitamin A and its role in sight, refer to the World Health Organisation’s Sight and Light Manual on Vitamin A, available at: http://www.who.int/ncd/vision2020_actionplan/documents/00allman.pdf

Other interesting articles are available from ABC news’ and Hubnews’ websites: http://www.abc.net.au/health/talkinghealth/factbuster/stories/2008/03/19/2176569.htm  http://aufait.hubpages.com/hub/What-Do-Carrots-and-Chocolate-Have-In-Common

Historical Aside

The idea that carrots help you to see in the dark was promoted by Britain’s Air Ministry during World War II. This tale served a two-fold purpose.

Firstly, it prompted people to eat more home-grown vegetables when few other food supplies were available.

But the main purpose was to disguise Britain’s new and secret Airborne Interception Radar technology, used to target enemy bombers before they reached the English Channel.

Britain’s increased success was attributed by both the public and the enemy to increased carrot consumption by British pilots, rather than new technology developments.

 

What is colour blindness?

Remember how cones in the eye are responsible for colour vision?

Colour blindness is caused by a problem with blue, red or green light-receptive cone cells in the eye. The spectrum of colours that we see is made up of different amounts of blue, red and green light.

If for example the green light-sensitive cones in the eye do not work properly, it is difficult to tell the difference between colours such as oranges, greens, browns and pale reds.

A Red-Green colour blind person would not be able to see the number 6 in this picture.

Some people suffer from a rare eye condition called monochromatism, where a person only sees in black, white and grey.

There are thought to be a number of causes of colour blindness:

  • Genetic problems
  • Trauma that causes retina and brain damage 
  • Long term alcoholism and diabetes 
  • Side effect or taking some drugs or medication.

Colour blindness is usually untreatable.

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