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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.  Sight Conditions 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.  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.  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. 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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