When the imagination is perfect the mind is always perfectly relaxed,
and as it is impossible to relax and imagine a letter perfectly, and
at the same time strain and see it imperfectly, it follows that when
one imagines that one sees a letter perfectly one actually does see
it, as demonstrated by the retinoscope, no matter how great an error
of refraction the eye may previously have had. The sight, therefore,
may often be improved very quickly by the aid of the imagination. To
use this method the patient may proceed as follows:

Look at a letter at the distance at which it is seen best. Close and
cover the eyes so as to exclude all the light, and remember it. Do
this alternately until the memory is nearly equal to the sight. Next,
after remembering the letter with the eyes closed and covered, and
while still holding the mental picture of it, look at a blank surface
a foot or more to the side of it, at the distance at which you wish to
see it. Again close and cover the eyes and remember the letter, and on
opening them look a little nearer to it. Gradually reduce the distance
between the point of fixation and the letter, until able to look
directly at it and imagine it as well as it is remembered with the
eyes closed and covered. The letter will then be seen perfectly, and
other letters in its neighborhood will come out. If unable to remember
the whole letter, you may be able to imagine a black period as forming
part of it. If you can do this, the letter will also be seen
perfectly...]

- Dr. W. H. Bates, December 1919