When examining one eye, the other eye must be completely covered with an eye patch. But be careful not to oppress the eyeball. When checking, let the candidates see the largest line of marks first. If they can recognize it, point out the smaller marks step by step from top to bottom, from big to small, until they find the smallest line of marks that can be clearly recognized. If it is estimated that the patient's vision is still good, it is not necessary to start with the largest line mark, but may start with the smaller line mark as appropriate.