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Asked by luke9897 to Amy, Drew, Julia, Kimberley, Sara on 20 Jun 2011. This question was also asked by caitlink0406.
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Julia Griffen answered on 17 Jun 2011:
Hey Luke…
I’m pretty blind (short sighted) and wear contact lenses and glasses…
People that wear glasses struggle to focus on things, everything just seems fuzzy.
Poor sight is caused by weakening of muscles in your eyes that control your lense which allows you to focus on things, either way away of close…. If you notice when your looking at something close to you, the rest of your vision is blurred…
Astigmatism is a specific type of poor vision caused by the eye balls becoming shaped like rugby balls rather than footballs.
People that are shortsighted can see things close but not far away, generally have this from a young age and it will worsen.
People with longsight can’t see things close up and generally develops at the age of 50 +.. hence old people often need reading glasses.
Lazer eye surgery actually cuts a small bit of lense off of your current lense to refocus it… gross huh..
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Sara Imari Walker answered on 17 Jun 2011:
Hello Luke and Cailtin! Our eyes work like a lens. The pupil is the dark part at the center of our eyes that lets light in. The iris (the colored portion of the eye – mine are brown!) that surrounds the pupil expands and contracts to regulate the amount of light passing through. The light rays then pass through the lens, which actually changes shape so it can further bend the rays and focus them on the retina at the back of the eye. The retina is where all the light-harvesting cells are located, there are two kinds rods and cones. The cones are concentrated at the center of the retina and are the cells that provide clear sharp vision (with lots of color details) under bright light conditions. In rods are on the outside and provide our peripheral vision, and allow us to see in dim light at night. So, to relate back to Julia’s great description of how eyes go wrong – if your muscle in your eye don’t work right (i.e. you don’t have good control of your iris), the light hitting the back of your eye on your retina will not be focused correctly. The rods and cones can only detect the light they receive so you end up with poor vision. Glasses (or contacts) can correct this. They act as an additional lens, that corrects for either lack of contraction or too much contraction in you own eye – so the glasses actually help to focus the light on the back of your retina. Pretty cool to be able to compensate all the complex machinery of the eye with a simple glass lens, don’t you think?
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Amy MacQueen answered on 20 Jun 2011:
In many cases people need glasses because their eyes are not quite the ideal shape to give perfect vision. Ideally light should enter the eye by the pupil and come to a focus on the retina where there are cells which detect light. If the eyeball is too short light will focus behind the retina and things, especially those close to the eye will appear out of focus – this is the case when someone is long-sighted. The reverse is true if the eye is too long – light will focus in front of the retina meaning objects are out of focus especially those far away causing short-sightedness. Glasses are an extra lens outside the eye which either spread out the light rays or bring them closer together allowing them to be brought to a focus on the retina and objects to be seen in focus.
Pretty amazing really… 🙂
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