Myopia, or
"nearsightedness", is a common vision problem. It is caused by the
inability of light to focus on the retina because the eye is either too
long or the curvature of the cornea is too steep. If either of these
conditions exists, light focuses in front of the retina and the image on
the retina is blurry. Glasses and contact lenses correct myopia by
bending light rays in such a way that the rays focus on the retina.
What is Hyperopia?
Hyperopia or "farsightedness" is a condition in
which the eye is too short or the curvature of the cornea too flat for
light to focus on the retina. Instead, light, if it could, would focus
behind the retina. The result of this is a blurry image on the retina.
Unlike myopia, under certain conditions the eyes can compensate for
small amounts of hyperopia and so often people that are farsighted may
not feel like they need glasses or contacts because they can see objects
clearly. As with myopia, contact lenses and glasses correct hyperopia.
What is Astigmatism
Astigmatism occurs when the cornea (the clear
part at the front of your eye that provides most of the focusing power
of the eye) is oval instead of round. The best analogy is to think of an
eye with astigmatism being shaped like a football and an eye without
astigmatism being shaped like a basketball. Because of the oval shape of
the cornea light rays are bent unevenly causing a distorted image.
Glasses and contact lenses correct astigmatism.
What is Presbyopia?
Presbyopia is the condition that everyone dreads which usually
presents around age 40. It is the need to wear reading glasses or
bifocals when focusing on objects that are close. It is caused by the
natural changes that occur in the lens of the eye. As we get older, the
lens starts to lose it's ability to change shape and thus it loses the
ability to change focus. As mentioned earlier, presbyopia is corrected
with reading glasses, bifocals, or contact lenses. Many people falsely
believe that once they reach the point of needing reading glasses they
can no longer wear contact lenses. There are several contact lens
options available to presbyopes. Contact your optometrist for more
information.
Clear normal vision
Cataracts: Blurry vision all
over
Glaucoma: Tunnel
vision
Diabetes: Scattered
loss of vision
Myopia, or
"nearsightedness", is a common vision problem. It is caused by the
inability of light to focus on the retina because the eye is either too
long or the curvature of the cornea is too steep. If either of these
conditions exists, light focuses in front of the retina and the image on
the retina is blurry. Glasses and contact lenses correct myopia by
bending light rays in such a way that the rays focus on the retina. 
Hyperopia or "farsightedness" is a condition in
which the eye is too short or the curvature of the cornea too flat for
light to focus on the retina. Instead, light, if it could, would focus
behind the retina. The result of this is a blurry image on the retina.
Unlike myopia, under certain conditions the eyes can compensate for
small amounts of hyperopia and so often people that are farsighted may
not feel like they need glasses or contacts because they can see objects
clearly. As with myopia, contact lenses and glasses correct hyperopia.
Astigmatism occurs when the cornea (the clear
part at the front of your eye that provides most of the focusing power
of the eye) is oval instead of round. The best analogy is to think of an
eye with astigmatism being shaped like a football and an eye without
astigmatism being shaped like a basketball. Because of the oval shape of
the cornea light rays are bent unevenly causing a distorted image.
Glasses and contact lenses correct astigmatism. 
Clear normal vision
Cataracts: Blurry vision all
over
Glaucoma: Tunnel
vision 
Diabetes: Scattered
loss of vision 
Macular Degeneration:
Blurry central vision