defect in the outward movement of the left eye. On looking to the left
homonymous diplopia is present, on looking to the front and the right
binocular single vision and no squint; on both sides emmetropia and full
acuity of vision.
CASE 9. Mr. V. W--, aet. 24, has likewise congenital paralysis of the
left abducens. No squint, but as soon as the left eye is used for
fixation in the left direction there occurs in the right one a strong
secondary movement inwards.
HYSTERICAL SQUINT.
In the hysterical form we see rather a rare variety of convergent
squint, which is conditional on contraction of the interni through
restriction of movement of the externi. Hysterical symptoms may at the
same time appear in the eyes or elsewhere, still this does not always
happen. As these cases are rare I will relate a few of those I have
observed. (These cases are not included in the above statistics.)
CASE 10. Anna R--, aet. 20, came under treatment in February, 1878,
stating that on the previous day she perceived blindness of the right
eye on waking; in the afternoon she felt particularly weary, and after
she had slept about an hour woke with blindness in both eyes. No
perception of light, good pupillary reaction, ophthalmoscopic report
normal. Patient was treated with copious enemata and dismissed on the
fifth day cured.
In February, 1880, she again came under treatment with blindness of both
eyes, also perceived the previous day on waking. Convergent strabismus
was present at the same time, of such a degree that the eyes converged
to a point 10 to 20 cm. distant. The outward movement was suspended in
both eyes. The attempt to turn the eye outwards is accompanied by short
convulsive movements, and followed by an immediate rebound to the
convergent position. She asserts her inability to see the movements of a
hand before her eyes, is able, however, to move about in a strange room,
unsteadily certainly, but with avoidance of obstacles; she sits down on
a chair indicated to her, &c. The position of the eyes proves that there
was no simulation in all this; it would be impossible for any person to
simulate a strong convergent squint continuously for four to five days.
Eight days after her admission the patient was dismissed with normal
movement of the eyes and good vision.
CASE 11. Miss Antonie E--, aet. 15, who has been treated by her family
physician for various hysterical disturbances, suffered since the middle
of December, 1879, from convergent strabismus with permanent but very
varying deviation, which is at times very slight, and sometimes amounted
to more than 7 mm. The movement outwards is in both eyes rendered
difficult, still the outer edge of the cornea is brought to the outer
angle of the lids with trouble and twitching movements. Homonymous
double images are present, their mutual distance is alike in the whole
field of vision, but is (six or eight weeks after the commencement of
the squint) signified as being slight; at the same time a difference in
height is present, the image of the left eye stands lower, prism 30 deg.,
base outwards, places the images just above one another. Nystagmus
occasionally occurs in monocular fixation (with exclusion of the other
eye). In due course a gradual improvement set in, the deviation and the
distance apart of the double images became slighter, the outward
movement better, and in the middle of April, 1880, four months after the
trouble began, no squint and no diplopia were present, the outward
movement normal, facultative divergence = 0.
The hysterical character of the visual disturbance showed itself when
the vision was tested. I will first observe that repeated investigations
with atropine showed emmetropia, while in the first investigation on the
left side, No. 36 at 5 m. was not recognised with the naked eye, but
only with weak concave glasses (with - .5 D. V. = 5/18). With the right
eye No. 0.8 was read fluently, from 0.75 she asserted she was unable to
recognise a word, with - 2 D. V. = 5/36. It would be wrong to conclude
from this myopia or spasm of the accommodation, for here, as in most
cases of hysterical weak sight, it could be shown that whatever glass
one chose to hold before the patient's eyes, was followed by an
improvement in the statements. The same improvement in visual acuteness
was repeatedly obtained in this case by a weak prism (3 deg.), held before
the fixing eye during monocular examination, and in the end, V. 5/12 was
obtained for the right eye, as against 5/6 with a prism of 3 deg.
Finally, on May 1st, full visual acuteness was present on both sides.
Field of vision and sense of colour normal.
CASE 12. Mrs. B--, aet. 30, previously treated for various hysterical
disturbances, has complained for about eight days of disordered vision,
the binocular nature of which was proved as patient had herself observed
that on closing one eye she could at once see clearly. Near objects to
15 cm. are seen distinctly. With all this, at the first examination it
was impossible to produce diplopia, either with the aid of a red glass
or prisms, &c., the images of first one eye, then the other were always
seen by turns. A few days later, on repeating the examination, double
images were perceived, they were homonymous with slight difference in
height (image of the right eye lower), the lateral displacement is
corrected by a prism of 28 deg. Micropsia of one image was also perceived.
On both sides the outward movement is rather difficult. Full visual
acuity on both sides--in the first examination slight myopia - .75 D. is
specified, afterwards emmetropia. The visual disturbance was removed by
goggles with faintly ground glass on the right side--preparations of
iron, bromide salts, shampooing with cold water and electricity were
used. In six weeks' time binocular single vision was again restored; the
facultative divergence = 0. With red glass and vertically deviating
prisms homonymous diplopia corrected by prism 3 deg. Field of vision and
sense of colour remained normal throughout.
DIVERGENT SQUINT.
If we want to draw a comparison between convergent and divergent squint,
we must consider only absolute divergent strabismus, for convergent
strabismus does not offer a parallel to relative divergent squint. In
absolute divergent squint the direction of the visual axes is such that
they would meet behind the patient's head; in the relative divergent
squint the axes of vision are parallel or slightly convergent, but they
do not cross at the point fixed by the one eye, but at a greater
distance off.
If we then only compare that which admits of comparison, we first find
out that divergent squint is rarer than the convergent form, and the
cause contained in the ocular muscles is here brought to light still
more clearly than there.
We must next distinguish between permanent and periodic squint, and we
see the latter so frequently continue as such, that we must not consider
the transition from this variety to the permanent one to be the rule.
In 183 cases of absolute divergent strabismus which appeared in my
private practice in the same space of time as the cases of convergent
squint above discussed I have been able to obtain exact determinations
of the refraction and visual acuteness. The weakness of the fixing eye
was the test for classing them among the statistics, and in patients who
had been long under observation, the first certain determination of
refraction, which was necessary, as several children are included who
came under treatment with divergent strabismus and emmetropia whilst
myopia developed itself later.
A. Divergent squint with hypermetropia.
(_a_) Permanent 4 cases. Visual acuteness of the squinting eye more than
1/7 1 case, V. less than 1/36 1 case, 2 excluded, one on account of
complication with detachment of retina, the other on account of
impossibility of testing vision.
(_b_) Periodic squint 5 cases. Among them 3 with double hypermetropia, 2
with emmetropia in one, and hypermetropia in the other eye. Visual
acuteness of more than 1/7 in 3 cases; V. = 1/9 1 case; V. = 1/36 1
case.
B. Divergent squint in emmetropia.
(_a_) Permanent 32 cases. Among them 10 with alternating strabismus and
anisometropia of at least 2 D. And in 9 cases emmetropia in one, myopia
in the other eye; once simple hypermetropic astigmatism in one, with
myopic astigmatism in the other eye. Visual acuteness of both eyes in
these 10 cases more than 1/7. In the 22 cases of monocular squint the
visual acuteness of the squinting eye amounted 8 times to more than 1/7
-, 10 times 1/12 to 1/36 (in 1 case V. = 1/36 with nystagmus of the
squinting eye when put into fixation). V. less than 1/36 in 3 cases; 6
cases excluded on account of complications.
(_b_) Periodic squint 28 cases. Among them 5 with anisometropia of at
least 2 D. (emmetropia in one, myopia in the other eye). Visual
acuteness of the squinting eye more than 1/7 in 27 cases, less than 1/7
to V. = 1/12 in 1 case.
C. Divergent squint in myopia to M. = 2 D.
(_a_) Permanent 24 cases (among them 6 with anisometropia of at least 2
D.). Visual acuteness of the squinting eye more than 1/7 in 15 cases. V.
less than 1/7 to V. = 1/12 2; V. less than 1/12 to V. = 1/36 3; V. less
than 1/36 2 cases; 2 cases excluded on account of complications (one on
account of atrophy of the optic nerve, the other on account of posterior
polar cataract).
(_b_) Periodic squint 23 cases. Among them 10 cases with anisometropia
of at least 2 D. Visual acuteness more than 1/7 in all 23 cases.
D. Divergent squint in myopia 2 D. to M. = 4 D.
(_a_) Permanent 17 cases. Among them 2 with anisometropia of more than 2
D. V. to 1/7 9 cases. V. < 1/7 to V. = 1/12 1 case. V. < 1/12 to V. =
1/36 2 cases. V. < 1/36 1 case. Four cases excluded (2 with choroiditis,
1 with congenital cataract, 1 with traumatic cataract).
(_b_) Periodic 8 cases. Among them 4 with anisometropia of at least 2 D.
V. to 1/7 7 cases. V. 1/36 1 case.
E. Divergent squint in myopia 4 D. to M. 6.5 D.
(_a_) Permanent 10 cases. V. more than 1/7 in 5; V. less than 1/36 in 3
cases, 2 excluded (one on account of large anterior synechia, one on
account of choroiditis of the macula lutea).
(_b_) Periodic 9 cases. Among them one with anisometropia of more than 2
D. V. more than 1/7 5 cases. V. = 1/9 1 case; 3 cases excluded on
account of complications.
F. Divergent squint in myopia more than 6.5 D.
(_a_) Permanent 8 cases. V. more than 1/7 4 cases, 4 excluded on account
of choroiditis of the macula lutea.
(_b_) Periodic 10 cases. V. to 1/7 9 cases; V. = 1/12 in one case.
_Table of Refraction and Visual Acuteness in Divergent Squint._
[Transcriber's note: Key created to make table fit page]
KEY:
A: Permanent.
B: V. to 1/7.
C: V. < 1/7 to V. = 1/12.
D: V. < 1/12 to V. = 1/36.
E: V. < 1/36.
F: Excluded.
G: Periodic.
H: V. to 1/7.
I: V. < 1/7 to V. = 1/12.
J: V. < 1/12 to V. = 1/36.
K: V. < 1/36.
L: Excluded.
-------------------+---+----+----+----+----+----+----+----+----+----+----+---
| A | B | C | D | E | F | G | H | I | J | K | L
-------------------+----+----+----+----+----+----+----+----+----+----+----+--
Hypermetropia | 4| 1 | -- | -- | 1 | 2 | 5 | 3 | 1 | 1 | -- | --
Emmetropia | 37| 18 | -- | 10 | 3 | 6 | 28 | 27 | 1 | -- | -- | --
Myopia to M. 2 D. | 24| 15 | 2 | 3 | 2 | 2 | 23 | 23 | -- | -- | -- | --
M. 2 D. to 4 D. | 17| 9 | 1 | 2 | 1 | 4 | 8 | 7 | -- | 1 | -- | --
M. 4 D. to 6.5 D. | 10| 5 | -- | -- | 3 | 2 | 9 | 5 | 1 | -- | -- | 3
M. more than 6.5 D.| 8| 4 | -- | -- | -- | 4 | 10 | 9 | 1 | -- | -- | --
-------------------+---+----+----+----+----+----+----+----+----+----+----+---
|100| 52 | 3 | 15 | 10 | 20 | 83 | 74 | 4 | 2 | -- | 3
-------------------+---+----+----+----+----+----+----+----+----+----+----+---
It follows then from this, that periodic absolute divergent squint is
just about as frequent as the permanent form and that both become more
rare as the degrees of myopia increase. As, however, in spite of this,
myopia is present in about 60 per cent. of all cases, the connection can
be no other than this, that myopia frequently unites itself with
insufficiency of the interni and preponderance of the externi; in this
respect, as in every other, myopia and hypermetropia are directly
opposed.
The setting up of a "hypermetropic divergent strabismus," dependent on
hypermetropia, seems to me only to show how much people have been
carried away by the idea that the cause of the squint must be given by
the state of refraction. Isler claims 17 to 29 per cent. of the cases
for hypermetropic divergent strabismus; of these, however, the half
possess only slight hypermetropia of 2 D. or less, which perfectly
agrees with the fact that the same observer has also found in convergent
squint a remarkably high percentage of the lower degrees of
hypermetropia.
Whether squint originates in the permanent or periodic form depends
chiefly on whether the movement of convergence is retained or lost.
There are cases of considerable divergent squint, in which the near
point of the convergence is scarcely removed, while on the other hand,
the physiological innervation for convergence may be lost, without
absolute divergence ever being brought about. In a number of emmetropic
or slightly myopic cases with absolute preponderance of the externi, the
physiological connection between accommodation and convergence is
maintained in a relaxed way; thus, for example, it is impossible to
converge voluntarily to a large object, as, for instance, a pencil held
in the vertical line, while accurate convergence immediately follows on
reading at the same distance; in other cases accommodation can be
exerted to the near point, without inducing the slightest impulse to
convergence. This circumstance is worthy of consideration for the
prognosis of the operation. A mere relaxing of the tie between
accommodation and convergence may be strengthened by practice, but if
the impulse to innervation is completely lost, it will scarcely be
possible to restore it again; as after complete laying aside of absolute
divergence the relative form still continues to exist.
Those cases deserve special consideration in which emmetropia is present
in one eye, in the other myopia. Slight degrees of one-sided myopia
reconcile themselves with the continuance of a normal binocular act of
vision. If the far point of the myopic eye lies at an inconvenient
proximity even for reading, then, as a rule, the emmetropic eye is used
for near as well as distant objects; if, on the contrary, the degree of
myopia answers to a range of vision convenient for working, and visual
acuteness is normal, then the temptation to use the emmetropic eye only
for distance and the myopic one only for near objects is so
overpowering, and the advantages on the other hand which would be
offered by clinging to binocular vision so slight, that a convenient
monocular vision is generally preferred. Even for objects which lie
nearer the eye than the far point of the myopic, and at the same time
farther than the near point of the emmetropic eye, for which, therefore,
both eyes could secure clear retinal images, binocular vision is not
used. In cases in which the patient can read with proper binocular
fixation, if one covers all but one line and then makes with prisms
double images standing one above another, it is the myopic eye alone
which almost invariably shows a clear retinal image.
The usual result of this is, first a relaxing of binocular vision, and
as together with this the motive for convergence, namely, the effort of
the accommodation ceases, the conditions for the commencement of
divergence are produced. Still the elastic tension of the ocular muscles
decides even here; if the interni preponderate, convergent squint
results, when the myopic eye is used for near objects, the emmetropic
for distant ones. If the externi preponderate, then permanent or
periodic divergent strabismus is caused. Nevertheless, in a remarkable
minority of cases the elastic tension of the ocular muscles is so
regulated that, despite relaxation of binocular fusion, neither
convergent squint nor absolute divergence occurs, but simple relative
divergence remains with employment of the myopic eye for near objects.
DYNAMIC SQUINT, INSUFFICIENCY OF THE INTERNI AND MUSCULAR ASTHENOPIA.
The habit of binocular single vision, when it has once reached its
normal development, governs the movements of our eyes to a great degree;
the desire to avoid double images makes itself continually felt; and
where this is not possible, an uncomfortable feeling of uncertainty
arises at every movement of the body. Double images are prevented as far
as possible by movements of the eyes, which we must designate as
voluntary when we are conscious of their occurrence.
If we follow a moving object with the eyes, the latter make
corresponding movements in order to keep the image in the centre of both
retinae. For example, if we look at a distant object which approaches in
the direction of one visual axis, this eye will necessarily remain
still, while the other will be put into convergence in proportion as the
object advances. If this did not happen, if this eye remained also
immovable, the retinal image would deviate outwards more and more from
the macula lutea and diplopia would arise. In order then to avoid
diplopia the macula lutea moves to where the retinal image is formed. We
can, however, move the images on the retina by the aid of prisms without
movement of the object. If, for example, we hold a prism before the eye
so that the base lies towards the temporal side, the retinal image will
be displaced towards the base of the prism, outwards then from the
macula, and double images will occur, which are at once removed by a
distinctly perceptible inward movement of the eye. In this way, by means
of a prism applied with the base inwards, outward deviation may be
produced, and even in a modified way deviations in height of the visual
axes by means of prisms with the base upwards or downwards. Here the
force of habit is apparent, for in the daily use of our eyes we
continually practise the inward movement of the visual axes; we can also
easily restore the customary degree of convergence by means of prisms
with the bases outwards; physiologically indeed, it is quite immaterial
whether an object is in a proximity to our eyes attainable by
convergence, which causes double images until it is binocularly fixed,
or whether by the aid of prisms we bring the retinal images of a distant
object to parts of the retinae which do not correspond. If we look at a
distant object fixed with parallel visual axes, under normal
circumstances, prisms of 6 deg. to 8 deg. with the base inwards can be overcome,
that is to say, as in weak prisms the deviation is equal to about half
of the prism, an absolute divergence of the visual axes of 3 deg. to 4 deg. may
be produced by which the double images are blended. It is immaterial
whether we apply a prism of, say 8 deg. to one eye, or prisms of 4 deg. with the
bases inwards to both. The facultative divergence thus attainable
remains the same, which speaks for the fact, that this monolateral
movement attainable by prisms is also combined with double innervation;
and of course in the eye remaining in unmoved fixation, with impulses to
innervation which are reciprocally abolished.
In the physiological use of our eyes we certainly never have occasion to
practise absolute divergence, but we constantly practise the transition
from the inward to the outward movement of the eyes, and experiments
with prisms teach us, that the innervation of the externi therewith
connected may even be carried somewhat beyond the physiological limits
of parallelism. Moreover, the extent of the "facultative" divergence
attainable by prisms shows a considerable latitude.
The case is similar with deviation in height of the visual axes. In
looking upwards or downwards the innervation of both eyes is usually
precisely the same, but on looking at any point when holding the head
obliquely, the difference in height of the eyes then present must be
balanced by a corresponding difference in the direction of the visual
axes. The same thing happens, if we hold a vertically deviating prism in
front of one eye in binocular vision; prisms of 2 deg. to 3 deg. may then be
overcome by difference in height of the eyes; rarely is a much greater
difference in height of the visual axes attainable. I have seen this
particularly in those cases where facultative divergence also was
greater than usual.
It happens especially in myopia that prisms of considerably more than 6 deg.
to 8 deg. are overcome by divergence, and certainly without causing any
inconvenience. Among the cases presented for examination, those, of
course, are most numerous where the patients have some complaint to
make, even if this have quite a different cause. In any case a divergent
position of the axes of vision corresponds to the balance of the
muscles, and this does not generally occur, for this reason, because
retaining binocular single vision necessitates a parallel or convergent
position of the eyes. Frequently, however, even a slight impediment to
binocular fusion, such as the application of a red glass to one eye,
suffices to procure preponderance in the elastic tensions of the
muscles, and to cause the fixed point to appear double. We can put a
stop to binocular single vision still more surely by applying to one eye
a prism with the base upwards or downwards. If the double images of a
point 4 to 5 meters distant show a crossed lateral position besides the
difference in height caused by the prism, we may assume that an
absolute divergent position of the eyes corresponds to the elastic
tension of the muscles; and the measure of the deviation will be given
by those prisms which, placed with the bases inwards before one or both
eyes, bring the double images perpendicularly over one another. As a
rule, in these cases the degree of divergence which occurs on cessation
of binocular single vision, is almost as great as the facultative
divergence, which may be reached in the interest of binocular single
vision.
V. Graefe designates as "dynamic squint" that condition in which the
position of divergence corresponding to the state of tension of the
muscles does not occur because binocular vision is retained. Without
clearly defined limits these conditions pass on into periodic squint,
when either diplopia occurs together with the divergence, or the habit
of binocular fusion becomes less frequent or is quite forgotten, while,
however, according to the varying state of the muscles sometimes normal
position, sometimes divergence, is present. A correct position of the
eyes is quite possible even without binocular fusion, then only the
regulator is wanting, which, in the varying play of the muscular forces,
ensures the balance of position and movement.
The older ophthalmologists had a parallel strabismus and probably
understood by that, what we now designate as relative divergence. The
connection between relative divergence and myopia, pointed out by
Donders, is universally admitted; on the other hand, in more modern
literature we scarcely find any intimation of the fact that a parallel
squint occurs, which is quite independent of myopia, and rests solely on
the fact that the impulse of innervation for convergence is lost. A few
examples may explain this condition.
CASE 13.--Auguste T--, aet. 28. On the left emmetropia, V. 12/20. On the
right the visual acuteness is variously given, but certainly does not
amount to more than 1/5 nor less than 1/10 of the normal.
Ophthalmoscopic report normal. The left eye is naturally the fixing one,
the right always remains parallel--for near objects double images are
present. A convergent movement is not attained, either for near objects,
or by means of prisms with bases outwards for distant ones. Prisms with
the bases inwards are not overcome; with vertically deviating prisms the
double images of distant objects stand perpendicularly above one
another.