Reading Snellen Eye Chart for Astigmatism Posted: 05-26-07 03:25am
Hello. A concerned bio student here. I
recently did a lab on senses and in one of
our sessions we did the Snellen eye chart
and took an astigmatism test which
consisted of covering one eye and staring
at the center of a wheel whose peripheries
were labelled much like a clock. I
registered 20/15 for Snellen and for the
astigmatism I registered for my right eye
4' o clock - 10 'o clock astigmatism and
my left eye at 2 'o clock - 8 'o clock
astigmatism. I found this quite peculiar
and asked my professor who I found out had
the exact same values in the same eyes. I
would just like to gain some insight on
this and understand what is the
significance of this type of result if
any, thank you.
The Snellen eye chart has defined standard
vision as the ability to recognize an
optotypes when the eye has subtended 5
minutes of arc. That's why the line
designated for 20/20 vision is the
smallest line that a person with normal
acuity can read at a distance of twenty
feet. The scale is for rating vision goes
from 20/20 up to 20/200. The biggest
letter on a eye chart represents acuity
20/200, the value considered for a person
to be legally blind. Astigmatism results
from a deformation of the cornea wherein
vertical and horizontal focusing occurs at
two different points. You can consult an
ophtalmologist for a check up.
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