Roughly, forty percent of people wear contacts or glasses. Some scientists think that the cause is genetic and some think is because of our surroundings.
Scientists have been able to show that people who look out over long distances, like sailors, often do not have problems with short-sightedness or are not myopic (MY-OP-ICK). People such as tailors who have to focus their eyes close to their face often are myopic. It seems that muscles on the side of the eye will correct the eye and help it to see more clearly. If you were to travel to primitive parts of the world, you would see people who have excellent vision without the help of glasses.
Monkeys that have been taken from the wild and held in captivity have been shown to only focus on this close to them. They have become unable to focus far away. Scientists gave chickens glasses and showed that they could cause the chickens to be nearsighted (see things only close to their face, or beaks) for a short time. Imagine a chicken with glasses!
Another theory as to why animals are able to see well is because those that cannot do not live for very long. This is the survival of the fittest theory. That animals that are the strongest will survive the longest and make more animals that are the strongest.
Among domesticated animals, or animals taken from the wild, like cats and dogs, eye problems are likely as the animal gets older. Older domestic animals and humans typically get what are called cataracts (CAT-TER-ACTS). Cataracts are when the front part of the eye becomes cloudy and hard to see through. Have you ever seen an old dog with blue-grey hazy eyes? This is probably because of cataracts.
Little Lion Experiment:
Do you or people in your family wear glasses? Try on some of your family members' glasses and see if you can figure out if they are near- or far-sighted. Do not keep the glasses on too long; they might give you a headache!
Do you see a pattern in the age of the person wearing the glasses and the strength of the glasses? Do older people in the house have stronger glasses than younger people?
A good scientist always looks for trends in the results from their experiments.
Perform a search on the Web for information about the eye and vision problems. Pages like http://www.google.com or http://www.yahoo.com are good search engines. If you just search on eyes, you will get a lot of information.