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.
If, while he is still looking at the twenty-foot line, you place in
front of the eyes a weak convex and he tells you he sees just as well
with as without, it proves the existence of far-sight or
hypermetropia, and the strongest convex that still leaves vision as
good for distance as without any, corrects the manifest. But if the
weak convex blurs it, it shows that there is some defect in focusing,
if the near vision is below normal. You therefore know that you have a
case of old sight or presbyopia, requiring the weakest convex to
correct it, that will enable your customer to see the finest line on
the near card at the required distance.
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