them, that homonymous diplopia in typical convergent squint (not
paralytic) can only be corrected occasionally by one-sided tenotomy when
the deviation is slight. As a rule it is necessary to distribute the
operation between the eyes. A result seems attainable by means of simple
tenotomy on both sides, which is expressed by prism 20 deg. in the trial of
convergence. In future cases it would be desirable to determine during
correction of the anomalies of refraction (1) the weakest prism which is
able to unite the double images at about 5 m. distant (without red
glass); (2) the distance at which the double images stand apart from one
another during the trial of convergence with prisms deviating in a
vertical direction; and (3) the prism which brings the double images
immediately above one another in the case of objects about 5 m. off.
Next to the cases above discussed stand those where convergent squint
remains after paralysis of the abducens; at the same time slightly
defective mobility and a distinct moving apart of the double images
towards the affected side can usually be detected. In a few such cases I
could restrict myself to tenotomy of the internal rectus of the affected
eye, but in those cases which I was able to attend to more particularly,
double tenotomy was necessary, and did not always suffice. Here also the
advancement of the external rectus is suitably applied, which I should
like to illustrate by means of a few examples.
CASE 49.--Mr. B--, aet. 20, was seized by paralysis of the abducens of
the right eye in November, 1877. In April, 1878, convergent squint was
still present, and as it continued patient decided on an operation in
February, 1879. Both eyes are emmetropic and possess full visual
acuteness.
Immediately before the operation the double images were united at 4 to 5
m. in the horizontal plane by a prism of 39 deg.; towards the right their
deviation rather increased. The measurable deviation amounted to 4 mm.
in the right eye, the secondary deviation of the left to 5 mm. In order
to proceed carefully, I confined myself at first to tenotomy of the
internal rectus of the right eye. After the space of a week single
vision was present at the distance of 1 metre in the middle line and at
the height of the eyes; at about 5 m. homonymous double images corrected
by prism 12 deg., together with slight difference in height (= prism 4 deg.,
base upwards before the right eye). The area of double vision extended
from the limit of the right visual field to about 20 deg. the other side of
the middle line.
This result would have sufficed perfectly for a cosmetic tenotomy where
binocular fusion did not exist; the annoyance caused to patient by
diplopia, however, was only slightly relieved. I decided, therefore, on
a second operation, not without fearing an excessive result, and
performed tenotomy of the left internal rectus with a very small
conjunctival wound and by closing the wound by means of a suture. The
result was by no means excessive, for it was perfectly _nil_, apparently
even negative at first, for a few days after the operation the area of
single vision approached the eye to less than 0.5 m. and at 4 to 5 m. a
prism of 20 deg. was requisite for correction; however, eighteen days after
the tenotomy of the left internus everything was as before. Single
vision to 1 m. while prism 12 deg. corrected for a distance of 4 to 5 m. The
tenotomy then had no effect at all on the position of the eye; however,
the restriction of movement dependent on it, asserted itself in that the
double images were crossed on the limit of the right visual field (about
45 deg. towards the right). On the supposition that this insufficient result
might be caused by the suture of the conjunctival wound I decided to
repeat the separation of the internal rectus. The agglutination of the
muscle with the sclerotic is so slight for two to three weeks after the
operation that the strabismus hook perfectly suffices to sever the
connection; no suture was put in, but the result again was _nil_, and on
the day after the operation single vision was only present to 0.5 m. in
the middle line, just as after the previous tenotomy of the left
internal rectus. It was now clear that the result with respect to the
position of the eye was only unsuccessful because the antagonist did not
do its duty. I shortened the abducens (without touching the internus
again). The immediate effect, during the chloroform narcosis, was a
terrible divergence, but on the same evening it was less, and
twenty-four hours after the operation with a red glass, homonymous
double images were present close together at a distance of 4 m. Ten days
afterwards binocular single vision was insured, facultative divergence
= 3 deg. at 4 m., crossed double images towards the limits of both visual
fields, but only on moving the eyes in a lateral direction; no practical
use was made of this. If one could have diagnosed beforehand the
insufficiency of the externi assuredly present here, which was probably
the reason for the development of squint on the healing of the paralysis
of the abducens, one would have been able to combine shortening of the
right abducens with tenotomy of the internus in the first operation,
whereas the necessity for the advancement was only shown by the
abnormally slight effect of the tenotomy on the left side. According to
accounts received by letter the favorable result has continued.
We obtain a result more quickly by the immediate advancement of the
abducens. For example:
CASE 50.--Mr. K--, aet. 29, suffered from paresis of the right abducens
in the autumn of 1877. In December, 1878, convergent squint is present,
linear deviation 5 mm. (scarcely more on the left than on the right).
The defect of movement towards the side of the right abducens amounts to
about 2 or 3 mm. Diplopia is present in the whole visual field with
increase of the deviation towards the right. Emmetropia and full visual
acuteness on both sides. Tenotomy of the internal rectus and advancement
of the abducens of the right eye at the end of December. Three weeks
later single vision is present in the middle line; on the left limit of
the visual field crossed double images, on the right side homonymous
ones, beginning about 20 deg. from the middle line. The result was by no
means excessive.
In convergent squint with congenital paresis of the abducens, not much
can be attained without shortening the abducens. Of course only the
squint can be removed, not the paralysis, but if once a correct position
is attained for the middle line, cosmetic demands are satisfied; the
outward movement, which is absent, must be replaced by turning the
head.
The chief method for absolute divergent squint is the combination of
shortening with tenotomy of the externus. If the impulse for convergence
is once lost, so that an associated movement occurs in place of an
accommodative one on fixation of a point situated on the middle line, a
removal of the squint cannot be obtained by simple tenotomy of the
externi--another proof that a change of position of the eye is by no
means a necessary result of tenotomy.
Moreover, this slight aid given by tenotomy has its ground not solely in
the condition of the opposing recti muscles. In other practices I have
seen cases enough in which tenotomy of the externi, performed on account
of relative divergence, was followed by convergent squint, just as
injudicious division of the interni may induce divergent squint. It is
probable, therefore, that the faulty effect of simple tenotomy in
permanent absolute divergent squint depends on other causes, which, in
my opinion, are to be found in the obliques. The loop formed by the
obliques round the posterior circumference of the eye is most stretched,
when the visual line falls in with the muscular plane of the obliques in
a medial direction of the eyes. On the whole, then, it is proved that
the obliques are extended on turning the eyes inwards, but shortened on
turning the eyes outwards by means of their muscular action. In
divergent squint, if the movement inwards occurs but seldom or not at
all, the obliques consequently are not extended in a normal way--it
follows then that they lose in ductility, offer greater resistance to
the inward movement, and by means of their elastic tension continually
draw the posterior pole of the eye inwards and the cornea outwards. As
in strabotomy we cannot get at the obliques, it seems all the more
desirable to offer them stronger resistance by greater tension of the
internus by means of advancement. Certainly tenotomy of the external
rectus of the fixing eye is as a rule also necessary. A sufficient
result is usually thus obtained at once; if it is much lessened in the
course of one or two months there is nothing to prevent the repetition
of the tenotomy of one or the other external rectus.
The innervation for the movement of convergence is not always perfectly
lost; it withdraws itself from the influence of binocular fusion because
this is gradually forgotten while a convergence, even if an insufficient
one, unites itself with the effort of accommodation. If we ask such
patients to fix a large object lying near, a pencil, for example, they
cannot usually converge upon it, whilst if we ask them to read at the
same distance, a distinct convergent movement occurs; large objects are
sufficiently clearly recognised, even without distinct retinal images,
and the supposition that an effort of accommodation is present is only
justified if we employ sufficiently small objects at the examination, in
order to distinguish which, clear retinal images are necessary. Of
course we must have regard to the condition of refraction; myopes, who
use their far point for reading, want no accommodation, therefore no
convergent movement occurs, even if the impulse of innervation for it,
is not yet quite lost. However, the innervation for convergence may be
lost, without the internal recti losing in elastic tension. The
operative importance of this relation may be illustrated by an example.
CASE 51.--Bertha K--, aet. 10, has myopia 5 D. on both sides, visual
acuteness 12/20, and divergent strabismus. At 4 mm. the crossed diplopia
is corrected by prism 23 deg.; a convergent movement is no longer attained,
at most parallelism of the visual axes. Tenotomy of both interni on
October 2nd, 1873. The immediate result was convergent squint, with a
defect in movement outwards amounting to 4 to 5 mm. in both eyes. On
October 9th prism 37 deg. was still necessary to unite the homonymous double
images at a distance of 4 m.; single vision existed only to about 20 cm.
The area of single vision gradually extended itself; at the end of
October it was restored for distance also, facultative divergence
_nil_; however, relative divergence was present for near objects.
Naturally this was not the result of muscular weakness of the interni,
for they had proved their capabilities by a convergent squint,
fortunately only temporary, which made one anxious, but was solely the
result of a faulty innervation. The further course was also interesting.
After three years, in October, 1876, the myopia of the left eye amounted
to 8 D., that of the right 7 D., visual acuteness 1/2 on the right, on
the left 3/4 of the normal; a posterior staphyloma measuring about 1/3
of the diameter of the optic disc was present. The left eye was used for
near objects with relative divergence of the right and the occasional
occurrence of diplopia; there was convergence only to about 15 cm.
Facultative divergence _nil_.
We very frequently have the opportunity of seeing, that myopia increases
even after tenotomy of the externus, and if von Graefe's assertion that
the progress of myopia would be brought to a standstill by means of
tenotomy still finds believers, I should like to cite one example which
offers proof to the contrary.
In permanent divergent squint we shall have, as a rule, to combine
shortening of the internus of the squinting eye with tenotomy of both
externi, even if the convergent movement is still possible to a slight
degree. The result thus obtained differs somewhat; sometimes it suffices
at once, sometimes a repetition of the separation of the externi is
necessary later on. Two examples may illustrate this.
CASE 52.--Miss Marie M--, aet. 22, has squinted on the left side since
her third year, nominally after a keratitis, which left behind in the
left eye a nebula of the cornea of small circumference. The deviation
amounts to 8 mm. The visual power is much worse than the opacity of the
cornea leads us to suppose, with visual axes deviating inwards fingers
were only counted at a distance of about 1 m.
On the right myopia 1 D., V. = 4/5. A slight convergent movement is
still practicable. At the end of May, 1879, shortening of the left
internal rectus, tenotomy of both externi. The next day slight
convergence on viewing distant objects, correct position after four
days. In January, 1880, correct position of the eyes, convergence
possible to about 20 cm. While a correction of 8 mm. was immediately
obtained here, the same operation does not always permanently suffice
for slighter deviations.
CASE 53.--Ernest Sp--, aet. 11-1/2; divergent squint had been observed as
early as his second year. The deviation amounts to 5 or 6 mm., is
sometimes alternating, generally the left eye deviates. No convergent
movement on fixing a pencil about 25 cm. distant; the right eye is then
used for reading, the left one makes a distinct, but not a sufficient,
movement inwards. Emmetropia on both sides, visual acuteness nearly
perfect on the right, on the left 2/3 of the normal. Even with red glass
and prisms deviating in a vertical direction, double images not
perceived. On October 2nd, 1879, shortening of the left internal rectus,
tenotomy of both externi. A week later divergence was no longer present.
When reading, the left eye makes a distinct, perhaps rather too great,
movement of convergence, and yet six weeks after the operation, distinct
divergent squint was again present, even if to a slighter degree than
before; the left eye deviates 3 to 4 mm., the right 2 to 3 mm. outwards.
The result obtained amounted then to not more than about 3 mm. In the
middle of December the tenotomy of both externi was therefore repeated.
A week after the operation convergent squint of 2 mm. is present with
homonymous diplopia. A pencil made to approach on the middle line is
seen double to about 20 cm., on approaching nearer, double images are
not perceived in spite of distinct relative divergence. Double images at
a distance of 4 m. are corrected by prism 25 deg.; as, however, normal
binocular vision is not present, the value of this statement is very
questionable. Three weeks after the second operation the position of the
eyes was normal, and the slightest convergence was perceived only on
close investigation. Double images are no longer observed, however they
may still be brought to view.
In periodic divergent squint, if the deviation is considerable and
frequent, if at the same time the normal near point of convergence is
only attained with difficulty or not at all, we can hardly combine
shortening of the internus with tenotomy of the externus; more often
indeed, additional tenotomy of the externus of the other eye is
necessary in order to obtain a permanent cure. In exceptional cases
(when it seemed to me as if the squint depended more on insufficiency of
the internus than on preponderance of the externus) I have confined
myself to shortening the internus without separating the externus; I
will quote just one example of this.
CASE 54.--Ida K--, aet. 11. On the right, hypermetropia 3 D. with the
ophthalmoscope, visual acuteness 5/24. No. 0.3 is read with difficulty.
On the left, with the ophthalmoscope hypermetropia 4.5 D. with
asymmetric meridian. Single letters of 3.0 m. are recognised with convex
6.5 D. Fingers are counted at about 1-1/2 m. The choroid is slightly and
unequally pigmented, no ophthalmoscopically assignable reason exists for
the considerable visual defect. The left eye frequently deviates
outwards, convergence is attainable to 15 cm. On May 2nd, 1877,
shortening of the internus (without tenotomy of the externus). Two weeks
later slight convergent squint was present; in November, 1877, six
months after the operation, the position of the left eye was perfectly
normal.
Tenotomy of the externi suffices when the divergent deviation is
inconsiderable and does not occur often, if the normal near point of
convergence can still be reached, and binocular fusion is possible.
If we want to increase the effect of simple tenotomy of the externi,
this may be done just as well by practice of the associated movements of
the eyes as by practice of the convergence, of course for a short time
only after the operation. As long as the detached tendon of the external
rectus is not re-attached firmly with the sclerotic, all these movements
of the eyes help to strengthen the result of the tenotomy. In order to
practise convergence we can bring a suitable fixed point on to a mirror
and so make it possible for the patient himself to see the position of
his eyes, of course only in cases where binocular fusion is no longer
present. He who possesses a normal binocular vision is troubled in these
exercises by diplopia; but this is not the case in the suppression of
binocular fusion so frequent as a result of squint.
Periodic divergent squint is divided by no sharply defined limits from
those cases in which only a preponderance of the externi exists without
insufficiency of the interni. We frequently find very considerable
degrees of facultative divergence as a casual symptom, without the
occurrence of manifest divergence or the presence of asthenopic
troubles. If this is accompanied by weakness of the interni, absolute
divergence occurs on looking at near objects, sometimes for distance
also and certainly if we suppress binocular fusion by covering one eye
or render it difficult by colouring one visual field with a red glass.
In these cases the indications for the operation are given either by
asthenopia, by troublesome double images or by the disfigurement
inseparable from periodic squint; it will depend on the degree of the
facultative divergence, whether we confine the tenotomy of the externus
to one eye or whether we distribute it between both eyes.
Finally, it may be desirable to still say a few words as to the most
favorable period for the operation. The comprehension of the defective
sight often present in squint as caused by "non-use" has resulted in
the preposterous advice that tenotomy should be carried out as early as
possible. I can vouch for the fact that even the earliest tenotomy of
the ocular muscles is of no avail against congenital amblyopia. I have
repeatedly seen children on whom tenotomy had been performed in their
first year, usually with bad cosmetic result but with continuance of
defective sight of the squinting eye.
The final result of the operation is almost always very unsatisfactory
when performed on children before their fourth year. I can show a number
of good results in children on whom I operated between their fifth and
sixth year; however, the more I considered the subject, the more it
seemed to me advisable to raise the tests which must be imposed on the
patients. With children it is not so much a question of determining the
limit of age, but whether their intelligence is sufficiently developed
to render a reliable examination possible. A sufficient knowledge of
letters and the power of reading is necessary to an accurate trial of
vision; the entire bearing of the children must permit of the
ophthalmoscopic diagnosis of the weak condition and should raise no
scruples as to wearing spectacles which may be necessary after the
operation. Under any circumstances no harm is done by deferring the
operation until these conditions are fulfilled; the interval may be
filled up by practising the mobility of the eyes, which does more good
than the customary strabismus spectacles or even tying up the eye. If we
tie up the fixing eye, the squinting one is certainly put into fixation,
but the other squints instead, and of course it is just the same with
the plan, as childish as it is antiquated, of tying on a pierced walnut
shell before each eye.
Strabismus spectacles, _i. e._ those with a leather band to go round the
head, provided with leaden discs which cover one eye completely and
leave only a side aperture for the other, of course only induce a
transfer of the squint to the covered eye, together with practice of
the eye in a lateral direction; but apart from their unsightly
appearance they require a constant lateral direction of the eye, which
is followed even after a short time by fatigue of the muscles employed
and soon becomes unbearable. This is not the case if we cause the
mobility to be practised alternately and towards both sides; here we
must insist that the limits of the outward movement are really reached.
These exercises are at least rational and tend to increase the strength
of the antagonist, on which we must depend so much in the operation and
to diminish an insufficiency made worse by want of practice.
PRINTED BY ADLARD AND SON, BARTHOLOMEW CLOSE.
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