Vision Testing (20/20)
OVERVIEW
The
vision
test
is
one
of
the
simplest
yet
most
important
components
of
the
eye
exam. In
order
for
eye
doctors
to 
compare
results,
it’s
always
done
at
a
standardized
distance
of
twenty
feet. Old-fashioned
offices
had
rooms
that
were
twenty
feet
long. Today,
mirrors
are
used
to
reflect
the
image
so
the
room
can
be
shorter;
but
the
image
still
looks
like
it
is
twenty
feet
away. The
charts
are
standardized
too
and
doctors
around
the
world
use
the
same
basic
format. But
what
do
those
numbers
mean?
Each line of the eye chart is assigned a notation in the form of a fraction that represents your visual acuity. The numerator is the distance in feet the patient is from the eye chart. The denominator represents the distance an eye with “normal” vision can read the same line. Interpreting the numbers is simple. If you can read the 20/40 line, you’re able to see at 20 feet what a normal eye could see at 40. And if your vision is 20/16? You’re above average because you can see an object from 20 feet that a normal eye sees at 16!
St. Luke's Cataract & Laser
Institute provides this on-line information for educational and
communication purposes only and it should not be construed as
personal medical advice. Information published on this St.
Luke's website is not intended to replace, supplant, or augment a
consultation with an eye care professional regarding the
viewer/user's own medical care. St. Luke's disclaims any and
all liability for injury or other damages that could result from use
of the information obtained from this site.