numerator the distance at which each eye and both together can
easily see. If the regular Snellen card is used containing letters
of different size, place in the denominator the number of the
lowest line each eye and both eyes together can read easily, and
in the numerator the number of feet from card to eye.

8. Explain the result to the child, to his fellows, to his
parents. If the left eye reads 10/20 and the right eye 10/30, it
means that neither eye is normal, and that reading small type is a
constant strain, even though unnoticed. The right eye must be
within ten feet to read what it should read at twenty feet. The
left eye must be within ten feet to read what it should read at
thirty feet. If the two eyes read at ten, it means that in working
together they successfully strain for a result that is not worth
what it is costing. When eyes thus unconsciously see what they are
not intended to see, it is only a matter of time when stomach and
nervous system will announce that the strain can no longer be
borne. Indigestion, dislike of study, restlessness follow. If,
however, the eyes are so near the normal that their story reads
12/10 or 8/10, the strain will be negligible _for the present_.
If, on the other hand, the only difficulty is a confusion of _x_
and _z_ with _c_ and _g_, it means that there is a strain due to
astigmatism, and that the child should be sent to an oculist.

9. Teach children and parents (and practice what you preach) the
urgent importance of periodic reexamination, just as you would
teach them to visit a dentist twice a year. This is needed by
those who wear eyeglasses, and more particularly by those who have
recently put them on. Moreover, as shown below, it is needed by
children able to pass satisfactorily the Snellen test.

10. Acquire the habit of reading the eye for evidence of temperate
or intemperate living, sleeping, eating, dancing, drinking, and
smoking. Inflamed eyes are _results_,--signals of danger. "The
organ may be faultless in construction and in its work poor,
because of nerve exhaustion, or, in a less and more easily
recoverable degree, nerve fatigue." If unusual eye conditions are
not readily explained by mode of living or by eye tests, an
oculist should be consulted.

The limits of the card test must be constantly kept in mind: (1) it
does not register eye sickness due to dust, smoke, or disease germs;