I know it is the custom with a great many if not the majority of opticians to fit a customer without knowing whether he has presbyopia, hypermetropia, or any of the other errors of refraction. Their method is first to try a convex, and if this does not improve, a concave, etc., until the proper one is found. This, of course, amounts to the same thing if the right glass is found. But in practice it will be found both time saving and more satisfactory to first decide with what error you have to deal. It is very simple, and, where you have no other means of diagnosing (such as the ophthalmoscope), it does away with the necessity of trying so many lenses before the proper one is found. You should have a distance test card placed at a distance of twenty feet from the person you are examining, and in a good light. A distance test card consists of letters of various sizes which it has been found can be seen at certain distances by people with good vision. Thus the largest letter is marked with a cc, meaning that this should be seen at two hundred feet, and another line, XX, at twenty feet, which is the proper distance for testing vision for distance, for the reason that a normal eye is at rest when looking at any object twenty feet from it or beyond, and the rays coming from it are parallel and come to a focus on the retina. You must also have a near vision test card with lines that should be seen by a normal eye from ten to seventy-two inches, and a card of radiating lines for astigmatism. With this preparation you are ready to proceed. To illustrate, the first customer comes and tells you that up to six months ago he had very good vision, but he finds now that, especially at night, he has trouble in reading or writing, and that he finds he can see better a little farther away. His head aches and eyes smart. You will of course say that this is a very simple case. It must be old sight (presbyopia). Probably it is if he is old enough (45), but you must prove this for yourself, without asking his age, which is embarrassing in the case of a lady. If you direct him to the distance card twenty feet away, and find that he can see every one down to and including the one marked XX, his vision is up to the standard for distance, and you know that he can have no astigmatism worth correcting, nor any near sight, as both of these affect vision for distance, but he may have far sight or old sight or both combined. You must find which it is.