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This Week's Experiment - #329 Astigmatism
This week's experiment has to do with your eyes. Do you wear glasses? If
not, you probably know someone that does. There are different reasons for
wearing glasses. I am nearsighted, which means that I can see things up close,
but need glasses to let me see things far away. Other people are
farsighted, which is just the opposite. They can see distant objects, but need
glasses
to see up close.
You can take a quick glance at a pair of glasses and tell
whether they are for someone that is nearsighted or farsighted. Hold the
glasses in your hand, a few inches above a page with some writing. Looking
through the lens, if the writing looks smaller, the glasses are for someone that
is nearsighted. If the writing looks larger, then they are for someone that
is farsighted.
While you have the glasses in your hand, you can also check for astigmatism.
To do that, rotate the glasses as you look through them. If the writing is
distorted as you rotate the glasses, then the glasses are for someone with
astigmatism.
What is astigmatism? Ideally, the shape of your eye is nice and round. If
it is not, then it causes a distortion. Besides looking at glasses, you can
also detect an astigmatism by using your eyes. Go to either of these websites:
http://www.eyecareindia.com/subcontents.asp?
sectionid=6&subcontentid=39
http://library.thinkquest.org/C005949/fun/astigmatism.htm
If you have astigmatism, some of the lines will look
darker
and bolder than others. If you turn your head, you will find
that different lines now look bolder. The difference is not on the page.
It is in your eyes.
(Note: The following experiment requires a graphic created by Robert Krampf that does not appear to be online anymore. It's possible that the experiment can be done with the graphics from the above websites, but I haven't tested them.)
If you do not have astigmatism, you can still see what it is like. You just
need glasses to do it. Not eye glasses, but drinking glasses. You will
need:
the graphic from the website
a straight sided, clear, drinking glass
water
Fill the glass with water and hold it in front of the graphic. Look through
the glass and you will see that the horizontal lines look darker than the
vertical ones. This is what happens with astigmatism. Of course, the
distortion in a person's eyes is not nearly as much as you get through the
glass, but
it should give you an idea of what an astigmatism is.
Have a marvelous week.
These experiments are from Robert Krampf - The Happy Scientist
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