[...Optimums and Pessimums

In nearly all cases of imperfect sight due to errors of refraction
there is some object, or objects, which can be regarded with normal
vision. Such objects I have called optimums. On the other hand, there
are some objects which persons with normal eyes and ordinarily normal
sight always see imperfectly, an error of refraction being produced
when they are regarded, as demonstrated by the retinoscope. Such
objects I have called pessimums. An object becomes an optimum, or a
pessimum, according to the effect it produces upon the mind, and in
some cases this effect is easily accounted for.

For many children their mother's face is an optimum, and the face of a
stranger a pessimum. A dressmaker was always able to thread a No.10
needle with a fine thread of silk without glasses, although she had to
put on glasses to sew on buttons, because she could not see the holes.
She was a teacher of dressmaking, and thought the children stupid
because they could not tell the difference between two different
shades of black. She could match colors without comparing the samples.
Yet she could not see a black line in a photographic copy of the Bible
which was no finer than a thread of silk, and she could not remember a
black period. An employee in a cooperage factory, who had been engaged
for years in picking out defective barrels as they went rapidly past
him on an inclined plane, was able to continue his work after his
sight for most other objects had become very defective, while persons
with much better sight for the Snellen test card were unable to detect
the defective barrels. The familiarity of these various objects made
it possible for the subjects to look at them without strain - that is,
without trying to seem them. Therefore the barrels were to the cooper
optimums; while the needle's eye and the colors of silk and fabrics
were optimums to the dressmaker. Unfamiliar objects, on the contrary,
are always pessimums.

In other cases there is no accounting for the idiosyncrasy of the mind
which makes one object a pessimum and another an optimum. It is also
impossible to account for the fact that an object may be an optimum
for one eye and not for the other, or an optimum at one time and at
one distance and not at others. Among these unaccountable optimums one
often finds a particular letter on the Snellen test card. One patient,
for instance, was able to see the letter K on the forty, fifteen and
ten lines, but could see none of the other letters on these lines,
although most patients would see some of them, on account of the
simpilicity of their outlines, better than they would such a letter as
K.

Pessimums may be as curious and unaccountable as optimums. The letter
V is so simple in its outlines that many people can see it when they
cannot see others on the same line. Yet some people are unable to
distinguish it at any distance. although able to read other letters in
the same word, or on the same line of the Snellen test card. Some
people again will not only be unable to recognize the letter V in a
word. but also to read any word that contains it, the pessimum
lowering their sight not only for itself but for other objects. Some
letters, or objects, become pessimums only in particular situations. A
letter, for instance, may be a pessimum when located at the end, or at
the beginning of a line or sentence, and not in other places. When the
attention of the patient is called to the fact that a letter seen in
one location ought logically to be seen equally well in others, the
letter often ceases to be a pessimum in any situation.

A pessimum, like an optimum, may be lost and later become manifest. It
may vary according to the light and distance. An object which is a
pessimum in a moderate light may not be so when the light is increased
or diminished. A pessimum at twenty feet may not be one at two feet,
or thirty feet, and an object which is a pessimum when directly
regarded may be seen with normal vision in the eccentric field - that
is, when not directly regarded.

For most people the Snellen test card is a pessimum. If you can see
the Snellen test card with normal vision, you can see almost anything
else in the world. Patients who cannot see the letters on the Snellen
test card can often see other objects of the same size and at the same
distance with normal sight. When letters which are seen imperfectly,
or even letters which cannot be seen at all, or which the patient is
not conscious of seeing, are regarded, the error of refraction is
increased. The patient may regard a blank white card without any error
of refraction; but if he regards the lower part of a Snellen test
card, which appears to him to be just as blank as the blank card, an
error of refraction can always be demonstrated, and if the visible
letters of the card are covered the result is the same. The pessimum
may, in short, be letters or objects which the patient is not
conscious of seeing. This phenomenon is very common. When the card is
seen in the eccentric field it may have the effect of lowering the
vision for the point directly regarded. For instance, a patient may
regard an area of green wall-paper at the distance, and see the color
as well as at the near-point; but if a Snellen test card on which the
letters are either seen imperfectly, or not seen at all, is placed in
the neighborhood of the area being regarded, the retinoscope may
indicate an error of refraction. When the vision improves,the number
of letters on the card which are pessimums diminishes and the number
of optimums increases, until the whole card becomes an optimum.

A pessittium, like an optimum, is a manifestation of the mind. It is
something associated with a strain to see, just as an optimum is
something which has no such association. It is not caused by the error
of refraction, but always produces an error of refraction; and when
the strain has been relieved it ceases to be a pessimum and becomes an
optimum...]

- Dr. W. H. Bates, December 1919