Eyesight
Problems (Refractive Errors)Introduction: Eyesight
problems, medically termed "refractive
errors", are common. They can often develop within a few months
and they occur mostly in the early teenage years and in the mid 40's to 50's.
During the teenage years (ages between 10 and 13) the eye ball experiences a great
deal of growth and can genetically grow too long, this is often associated with
myopia.
In the 40's it is the aging process that leads to a relative shortening of the
eye ball and this is associated with far-sightedness
(hyperopia) that leads to the necessity of reading glasses. Signs
and Symptoms: With uncorrected myopia (nearsightedness)
your eyesight
would be blurred as shown in this link. Objects in front would be in focus,
but the objects in the distance would be blurred.
Myopia
is the visual condition in which only nearby objects appear in focus, much like
a camera permanently focused at a close distance (Nearsightedness = without glasses
or optical correction only near objects, typically when held very close to the
eyes, are sighted). Nearsightedness is caused by either the eye being too long
(axial myopia) or eye having too much refractive power (refractive myopia).
With hyperopia (farsightednes), however, the patient
sees the distance clearly. In this example seen through the eyes of a
patient with farsightedness the man up front is not in focus. Note that the tree
and the buildings in the background in the distance are clear and focused. The
patient has a problem reading a newspaper and the arms feel too short to be able
to focus on the print. Reading glasses help the patient to see the print in focus
again. With astigmatism the surface of the cornea in these
patients is not like a perfect globe, but rather like the asymmetric shape of
a rugby ball. This is illustrated
in this link. The vision before correction would look
like this(uncorrected astigmatism) , where the image not in focus in the
front or the back. All of it is blurred because the cornea has different curvatures.
However, after correction
for astigmatism the same image looks as shown in this link. The following
link explains more about the diagnostic
tests regarding astigmaitsm. Diagnostic
Tests: The simplest test to check the overall vision is a visual
acuity test. Using eye charts the doctor or optometrist will determine
which of the letters or numbers you can still accurately read (20/20 vision is
perfect) at a certain distance. Here is another
site that explains this. Treatment: Glasses
and contact lenses are that main conventional means of correcting
visual problems such as myopia, hyperopia and astigmatism. However, there
are operative methods (refractive
surgery) that can now be used, although they have their strengths
and weaknesses. It is tempting to throw away glasses and contact lenses and have
clear vision after refractive surgery (so the commercial goes). But there are
possible complications, such as a certain percentage of cataract and glaucoma
formation following these surgeries and a weakening of the cornea making the eye
more susceptible for rupture with physical trauma. Here is an image of the cornea
before and after laser surgery, which makes you realize that the cornea
is thinner after the procedure. If you would like to explore refractive surgeries,
discuss this with the eye surgeon carefully and weigh the pros and cons. For my
part I decided to continue to live with glasses.
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