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Eye Conditions

 •20/20 Vision
•Sight Conditions
 •Short-sightedness
 •Long-sightedness
 •Presbyopia
 •Astigmatism
20/20 Vision
Having 20/20 vision is how we explain perfect vision, where a prescription is not required to see clearly and comfortably. The fraction 20/20 is understood as follows: the bottom half of the fraction represents the distance, in feet, at which a perfect sighted person is able to see a target seen by another perfect sighted person at 20 feet. However, if you have trouble seeing things in the distance, you might see at 20 feet what a perfect sighted person sees at 40 feet. So, this means that your vision is measured as 20/40.

Assuming you have perfect sight when you are looking at an object in the distance, light from the object will focus on your retinas very precisely. When seeing an object close-up, the focus is blurred very momentarily, but this is unnoticeable, because your eye has an automatic refocusing ability that makes the target clear. This refocusing ability is called "Accommodation," and it works by making the natural lens of the eye larger or more convex in shape. As we get older, we lose more and more of this ability, which is why things close-up start to blur after about 45 years of age.


Perfect Sight



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Sight Conditions

 SHORT-SIGHTEDNESS
Short-sighted, also known as near-sight or Myopia, means that the light focuses in front of your retinas or 'too short.' This makes it difficult to see objects in the distance whereas objects close-up are clearer. This occurs when light from the objects seen focus in front of the retina rather than on it. This is believed to happen when the eyeball is slightly too long, and is also known as Axial Myopia.


Short Sight


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LONG-SIGHTEDNESS
Long-sighted, also known as far-sight or Hyperopia, means the eyes focus "behind" or 'too long,' which makes it difficult to see objects close up rather than from a distance. This occurs when light from objects viewed will theoretically focus behind the retina rather than on it. However, because the eye is able to naturally fatten the lens and cause light to bend more, this error in focus is overcome. This explains why distance vision is usually good. When the same individual tries to look at something up close, much more effort is required, as light from a near object will fall much further back behind the retina. Near vision is therefore worse.


Short Sight


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PRESBYOPIA
As our eyes grow older the ability to focus clearly on anything close-up starts to diminish. Each lens of the eyes contain many fibers, which grow throughout life in the same way that hair and skin continue to grow. When the lenses are younger and have fewer fibers, they are more flexible and can change shape easily. When the lenses are older and have many more fibers, this flexibility is obviously lost, which causes near vision to blur.

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ASTIGMATISM
Astigmatism usually means that the shape of the eye is like that of an egg or a rugby ball. Two main areas of curvature are found: one is flatter and the other is steeper. This shape causes light to focus in two different positions where the more curved area focuses further forward and the less curved focuses further back. The effect on vision is to distort shapes so similar shaped characters become confused. For example, the letter 'G' may be confused with a 'C' and the number '2' may be mistaken for the letter 'Z'. Signs that you may have astigmatism are: slightly blurred vision, eye strain, and prone to headaches. Astigmatism can also cause short-sightedness or long-sightedness.


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