The Eye in its Relation to Health
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By Chalmer Prentice, M.D.
Chicago, A.C. McClurg & Company, 1895
Transcription (c) A. Wik, 2004

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        | Chapter XI |  pages 165-170
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ORTHOPHORIA: Regular or correct tending
of the optic axes.
  Heterophoria:  Different tending of the optic
axes.
  Esophoria:  Inward tending of the optic axes.
  Exophoria: Outward tending of the optic axes.
  Hyperphoria:  Upward tending of the optic
axes.
  Cataphoria:  Downward tending of the optic
axes.*
  The above terms have heretofore been used
in a relative sense; namely, esophoria, a relative
tending of the optic axes toward each
other; exophoria, a relative tending from
each other; hyperphoria, in which the one
axis is relatively higher than the other;
and cataphoria, in which it is lower.  A person
with but one eye may have any one of the above
conditions.  The optic axis of a single eye may
turn inward, outward, upward or downward from
what would be a normal position, giving rise to
considerable disturbance and strain, especially if

[   * We are indebted to Dr. George T. Stevens, of New York, for the ]
[ above nomenclature.                                                ]

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a glass is worn, in which case the clearest vision
is sought through its center, necessitating the
holding of the eye in a normal position.  If a
glass is not worn, the head is usually thrown into
that position which most relieves the strain.  If
the upper muscle is short, the chin is thrown
down and the forehead forward; if the lower, the
chin is thrown up and the head back; but if the
short muscle is the outer or the inner, the eye
rather than the head is usually turned so as to
relieve the strain.  These conditions are quite
common in persons with but one eye, so I think
it would be well to discriminate between relative
and individual heterophoria.
  By considering only the relative position of
the two eyes, we are likely to overlook some
grave defect in the ocular muscles, for it is pos-
sible for both of the superior or both of the in-
ferior muscles to be short in connection with a
relative deviation or a relative balance.  Short-
ness of the external of one eye and the internal
of the other may exist, and still a relative balance
be maintained.  We may often fall short in our
investigation by taking into consideration only
the relative position of the lines of sight.  There
are cases that should require months of careful in-
vestigation before safe conclusions can be drawn.
  Defective length and defective attachment of
the oblique muscles will sometimes be found.  I

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have met with two cases of this kind in which
there was a very manifest turning of the ball on
its antero-posterior axis when an effort was made
to move the eye laterally.  With the assistance
of Dr. C. S. Hamilton, of Toronto, I operated on
one of these cases by making a complete division
of the superior oblique muscle at its ocular
attachment with the result that the twisting
movements of the eye ceased and there was
very marked improvement in the nervous symp-
toms from which the patient had suffered previ-
ously.
  From the fact of the convergence and diver-
gence necessary for the accommodations for vari-
ous distances, defects are much more likely to be
manifest in the external and internal muscles than
in the superior and inferior muscles, because
during their functions there is never any devi-
ation from a horizontal plane.  Both eyes
move upward and downward simultaneously and
equally, and through such constant use the
nerve-impulses to these muscles establish a very
fixed horizontalizing tendency.


		DIFFUSION TESTS.

  Place a red or highly colored plain glass before
one eye.  The dissimilarity in color in some cases
will disclose a lack of parallelism of the lines of
sight.

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  A plus lens of 10 dioptres, more or less,
covered with a disc with a small opening in its
center which permits one eye to see only directly
through the center of the lens, renders two lights
so dissimilar in shape that diffusion will some-
times occur.
  The Maddox rod placed before one eye dis-
torts a light into a long beam of light, while the
same object seen by the other eye retains its
natural shape, and any manifest deviation can be
discovered.
  Another ingenious instrument for creating dif-
fusion, is Mr. Brayton's Optomyometer, which
consists of two hollow tubes about eighteen inches
in length, through which the eyes of the patient
look at a plain, smooth curtain or surface.  When
diffusion takes place two round spaces appear.
These cylinders or barrels are so arranged that they
can then be moved from their parallelism into a
position that brings the two objects together, the
degrees of deviation being measured by a pointer
on the instrument.  The fusion stimulus can be
decreased in this instrument by adding any one
of the above mentioned three implements to one
of the eye barrels.
  Direct the patient to look steadily at a light
or some fixed object, covering one eye with a
card.  After a minute or two, suddenly change
the card over to the opposite eye and inquire of

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the patient if any apparent change occurred in the
position of the light.  Sometimes by this test we
are able to see the eye move as it fixes itself on
the light when the card is changed.
  Place before the eyes enough prism, base in,
to create diplopia, being careful that the axes of
the prisms are horizontal and the head of the
patient erect, and a single light or object appears
as two, the object on the right side being seen by
the right eye, and that on the left by the left.  If
either object appears lower than the other, the
indication is that the eye on the same side is
higher.
  Place sufficient prism, base down, before one
of the eyes to create diplopia, being careful that
the axes of the prisms are vertical and the head
erect, thus making a single light or object appear
as two.  If the lights are relatively vertical, there
is an apparent balance; but if with the prism
base down, before the left eye the upper object is
to the left, there is a manifest convergence of the
eyes; if to the right, a divergence.
  Two prisms held together, base to base, by an
eyeglass rim, if placed before the center of the
pupil of the eye, with their axes horizontal, create
for that eye two apparent objects.  The other eye
will see the real object between these two, if the
prisms are of sufficient strength.  If the middle
object seen with the uncovered eye is higher than

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the other two, then that eye is lower; and con-
versely, if the object is lower the eye is higher.
If the prisms are not of sufficient strength, the
uncovered eye may fuse its object with one of the
other two images.  By now turning the axes of
this prism vertical, the two apparent objects are
seen by one eye, one above the other, and any
deviation of the middle or third object indicates
a deviation in the lateral muscles.
  This double prism test has no advantage over
the single prism test, if indeed it does not possess
one disadvantage, namely that of multiplying the
objects; for the fact of there being two exactly in
the horizontal plane offers a higher stimulus for
the other eye to horizontalize, or bring its image
into the vertical plane.  There being two appar-
ent sports exactly vertical, the stimulus to verti-
calize by the lateral muscles is emphasized.*


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[  * See horizontalizing and verticalizing tendencies, pages ]
[ 37 and 38.                                                 ]





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        | End of Chapter XI |  pages 165-170
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