7. If the card is stationary and the child moved, and if only one size of the letter is used, put in the denominator the number of feet at which the normal eye should see clearly, and in the 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 reëxamination, 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.