[...The Memory Cure

When the sight is perfect, the memory is also perfect, because the
mind is perfectly relaxed. Therefore the sight may be improved by any
method that improves the memory. The easiest thing to remember is a
small black spot of no particular size and form; but when the sight is
imperfect it will be found impossible to remember it with the eyes
open and looking at letters, or other objects with definite outlines.
It may, however, be remembered for a few seconds or longer, when the
eyes are closed and covered, or when looking at a blank surface where
there is nothing particular to see. By cultivating the memory under
these favorable conditions, it gradually becomes possible to retain it
under unfavorable ones, that is, when the eyes are open and the mind
conscious of the impressions of sight. By alternately remembering the
period with the eyes closed and covered and then looking at the
Snellen test card, or other letters or objects; or by remembering it
when looking away from the card where there is nothing particular to
see, and then looking back; the patient becomes able, in a longer or
shorter time, to retain the memory when looking at the card, and thus
becomes able to read the letters with normal vision. Many children
have been cured very quickly by this method. Adults who have worn
glasses have greater difficulty. Even under favorable conditions, the
period cannot be remembered for more than a few seconds, unless one
shifts from one part of it to another. One can also shift from one
period, or other small black object, to another...]

- Dr. W. H. Bates, November 1919