In the fraction 20/20 - the numerator is
the distance in feet between the subject
and the eye chart. The denominator is
the distance frm which a normal person
can read the 8th line - 1 arc minute
Whole Number
Eye measurements are
usually in millimetres (mm)
Geometry
Circles &
Domes
Pupil
Iris
Sphere
Shape of an eyeball
Measurement
Angles
Angles of light
reflection in the
eye
1 minute of arc (1 minute
is 1/60 of a degree)
Diameter
Measuring the cross distance
of certain circular shapes in
the eye such as the iris
Radius
Circumference
Determining
dilation/constriction of
the pupil
They use trigonometry to
determine the height of letters
in an eye testing chart
Placing an eye chart on a wall involves specific
mathematic measurements such as angle of
where a letter is in relation to a person's eye
and distance of chart from the viewer
The minimum average
separation of two lines (depicted
in a letter) that a person can see
is an angle of 1 minute arc