Claud Worth Charles Henry May.

A manual of diseases of the eye online

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disuse (amblyopia ex anopsia), and may finally become very-
pronounced. There are no asthenopic symptoms.

Etiology. — Concomitant squint is generally the result of an
interference with the normal fusion of the macular images of
the two eyes, dependent upon a defect of the fusion faculty. In
the infant, the motor co-ordinations of the ey^ serve to main-
tain an approximate parallelism of the visual axes. The
fusion faculty soon begins to develop and is complete before
the sixth year; this establishes a desire for binocular vision
which keeps the eyes straight. " Sometimes, however, owing
to a congenital defect, the fusion faculty develops later than
it should, or it develops very imperfectly, or it may never
develop at all. Then there is nothing but the motor co-
ordinations to preserve the normal relative directions of the
eyes, and anything which disturbs the balance of these co-
ordinations will cause a permanent squint " (Worth).

In the presence of a defect of the fusion faculty, the eyes
are in a state of unstable equilibriumy ready to squint on slight
provocation. Such exciting causes may be (1) disturbance in
the relation between accommodation and convergence by
errors of refraction, (2) anisometropia, (3) imperfect vision in
one eye due to congenital amblyopia, opacities of the media,
and intraocular diseases, (4) disparity in the length or thick-
ness of opposing muscles.


In this form of squint (esotropia) there is deviation inward
of the visual Hne of one eye (Fig. 339). It is generally asso-
ciated with hyperopia, with or without hyperopic astigma-
tism; rarely it occurs in myopia and in emmetropia. It usu-

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ally commences in early life, between the first and fourth years,
when the child begins to use his accommodation for near
objects, such as toys and pic-
tures; rarely it is congenital.
At first the squint may be
noticed only at times (period-
ic), with near vision, or when
there is any interference with

the general health; but it is Fig. SSS.— convergent strabismus.

apt to become constant for

both near and distant vision; occasionally it disappears


The acuteness of vision in the squinting eye often presents
considerable reduction, and there may be marked amblyopia.
Whether the squint precedes and is the cause of the amblyo-
pia, or whether the amblyopia is originally present and is the
cause of the squint, is one of the imsettled questions in oph-
thalmology; probably in most instances the amblyopia is ac-
quired /rom disv^se of the squinting eye.

The frequent association of convergent squint and hyperopia
depends upon the close connection between accommodation
and convergence. A child who is hyperopic must use some ac-
commodation for distance, and more for near vision. Accom-
modation and convergence being associated, he must increase
his convergence with increase of accommodation. In looking
at a near object, the stimulus to converge corresponds not
only to the amount present in the emmetrope, but includes an
additional and abnormal amount called for by the extra ac-
commodation required to compensate for his hyperopia.
Hence the point of convergence is nearer than the distance
accommodated for and convergent squint results.

Treatment comprises (1) the correction of refractive errors
by glasses, (2) exercise of the squinting eye by occluding its
fellow, (3) instillation of atropine, (4) the training of the
fusion sense (orthoptic training), and (5) operation.

Non-Operative Treatment. — ^The error of refraction should
be estimated under homatropine or atropine, and convex glasses
correcting very nearly the total hyperopia (also the astigma-

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tism, if present) prescribed for constant wear. In slight cases,
especially if periodic, this sometimes effects a cure. Glasses
may be worn by children of two years and upward. It is
sometimes advisable to keep the eyes under the influence of
atropine for a week when the glasses are first worn.

The fixing eye should be covered by a patch or bandage for
one hour, three times a day, or the occlusion may be continu-
ous. This compels the squinting eye to fix, exercises it, pre-
vents amblyopia from disuse, and restores, as far as possible,
the sight of the deviating eye if amblyopia already exists.

Atropine should be instilled into the fixing eye so that the
latter cannot be used for near vision, thus compelling the
child to employ the squinting eye for seeing close objects. One
drop of a 1-per-cent. solution or ointment is used every morn-
ing; the practice may be kept up for months.

Orthoptic Training of binocular perception and the sense of
fusion may be undertaken with stereoscopes, but most success-
fully with the amblyoscope (Fig. 340).

This instrument consists of two brass tubes joined by a hinge, each
provided with a mirror and a convex lens. The object-dides are devices

Fig. 340. — ^Worth's Amblyoscope.

drawn on translucent paper gummed on glass, or printed on celluloid
squares (Fig. 341). The two halves of the instrument can be brought

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together to suit a convergence up to 60°, or separated to suit a diver-
gence of 30°. Each object-slide is lighted by a separate electric lamp,
the brilliancy of which can be regulated, thus increasing or diminishing
the illumination of either of the pictures.

The Amblyoscope is used as follows: The instrument is
adapted roughly to the angle of the child's squint and the ex-
ercises are begun by an attempt to develop dmvUanecms per-
ceptiortj by increasing the illumination before the squinting





Fig. 341. — Object>slides uaed with Worth's Amblyoscope.

eye and adjusting the relative brilliancy of the lights, imtil the
objects of both slides are seen simultaneously; then the child
is taught to fuse the images; finally the amplitude of fusion is
increased, and the sense of perspective taught.

Non-operative treatment is successful in a large proportion
of cases of convergent concomitant squint, if used sufficiently
early. The earlier such treatment is begun, the better the
results; after the sixth year it is not usually effective.

Operative Treatment. — If non-operative measures do not
overcome the deviation after a lengthy trial, operation is indi-
cated. It is not customary to operate before the seventh year;
it is generally advisable to postpone operation until the child
is old enough to allow local anaesthesia and to aid by its co-
operation, since the results are better and more certain under
such circumstances. In cases in which it was foimd impos-
sible to develop the fusion faculty, operation relieves the dis-
figurement but fails to give binocular single vision.

Two operative procedures, tenotomy of an internal rectus,
and advancement of an external rectus, are employed either
singly or in combination. Tenotomy of an internal rectus
consists in a division of this muscle at its insertion, allowing
the eye to rotate outward. In advancement, the tendon is sep-

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arated at its insertion, often shortened, and the cut end secured
to the eyeball nearer the cornea than the original insertion.

The choice of operation depends upon the amount of squint,
the lateral excursions of both eyes, the amount of amblyopia
in the squinting eye, and upon other conditions brought out
by careful examination. The relative advantages of tenot-
omy and advancement have been much discussed. Tenotomy
is much the easier operation, quickly performed, inflicting little
if any pain when done under local anaesthesia, and causing but
slight inconvenience to the patient. Advancement, on the
other hand, is more difficult, takes longer, is not entirely free
from pain, may require a general anaesthetic, and the patient
is confined to the house for several days. A good general rule
is to resort to tenotomy when there is considerable overaction
of the internal recti with normal power of the extemi, and to
advance one or both extemi when there is relaxation of these
muscles with decided limitation in abduction; but advance-
ment has certain advantages over tenotomy which make it the
more satisfactory operation in general, and the one preferred
probably by most ophthalmic surgeons. Deviations of more
than 25 "* are best corrected by an advancement of the external
rectus and a tenotomy of the internal rectus.

The esiimMion of the result likely to follow operative treat-
ment requires considerable judgment and exi)erience. A free
tenotomy of one internal rectus will usually diminish an inter-
nal squint to the extent of about 13° (3 to 4 mm.). An ad-
vancement, if successfully carried out, will produce any degree
of rotation of the globe. As a rule, only one internal rectus
should be divided at a time, imless the squint be very marked,
since it is difficult to gauge the after-efifect correctly. The
full effects of such operations frequently are seen only after
several months; if too much has been done, there will be di-
vergence. In young children, a general anaesthetic is often
required; in older children, local anaesthesia will suffice.


This form of squint exists when one eye fixes an object and
the other deviates outward (Fig. 342). It is usually associated

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with myopia, but may occur with other errors of refraction.
It is also observed after tenotomy for the cure of internal
squint, and when the fiision
faculty is defective or the
sight in one eye is deficient or
abolished, as in opacities of
the media, ocular disease and
injury, and in blindness; in

.1 1 . , . . Pig. 342. — Divergent Strabismus.

these cases, bmocular vision

being impossible, there is no need for convergence. Di-
vergent squint is much less frequent than convergent.

Association with Myopia, — ^In myopia little or no accom-
modation is needed for near vision; consequently, there is an
habitual deficiency of the stimulus for convergence, and a ten-
dency to relax the internal recti muscles. Again, the exces-
sive convergence necessary to see near objects within the far
point causes fatigue of the intemi, giving rise to muscular
asthenopia (p. 348); to relieve this, one of the internal recti
muscles relaxes, and the eye turns out, especially if the sight
in this eye is defective. Another predisposing cause is the
increased antero-posterior diameter of the eyeball, which me-
chanically limits convergence.

Unlike convergent squint, the condition is infrequent in
very young children. It develops during youth, when near-
sightedness is established, and the tendency increases with the
degree of myopia; when the latter reaches a high degree, the
far point is so close, that it is impossible to maintain the neces-
sary convergence, and divergence becomes inevitable. At
first the squint is manifest only during near use of the eyes
(periodic); but it usually progresses and is present in distant
as well as with near vision (constant).

Treatment. — In recent cases, when the squint is still peri-
odic and the patient's vision is good, we may cure the squint
by giving thefuU correcting lenses. In other cases, especially
those of long duration, operation is indicated. The best results
are obtained from advancement of one or both internal recti.



Fig. 347. — Large and
Small Squint Hooks.

Fig. 348. — Curved
Strabismus Scissors.

Fig. 350. — ^Advancement Forceps.

Figs. 843 to 350. — ^Instruments Required for Tenotomy and Advancement of the

External Ocular Muscles.

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The following description applies to tenotomy of the right
internal rectus. The methods of operating employed most
frequently are the subconjunctival and the open.

Instruments Required. — (1) Eye speculum (Fig. 346); (2)
fixation forceps (Fig. 343); (3) toothed forceps (Fig. 344);
(4) blunt-pointed, curved strabismus scissors (Fig. 348); (6)
two squmt hooks (Fig. 347); (6) needle holder (Fig. 349);
(7) fine curved and half-curved needles (Fig. 346); and thin
black silk.

The Subconjunctival Method. — The speculum is introduced
and the eyeball drawn outward, if necessary, by an assistant.
The conjunctiva over the lowest portion of the insertion of the
muscle, together with the sub-
conjimctival tissue and Ten-
on's capsule, is seized with
the toothed forceps, raised
and divided with scissors; the
first cut divides the conjunc-
tiva, the second Tenon's cap-
sule. Keeping the fold raised
with the forceps, a strabis-
mus hook is introduced

., , ,, . , Fig. 351.— Tenotomy of the Internal Rectus.

through the openmg, passed

beneath the tendon, and pushed upward until its point is seen
through the conjunctiva at the upper border of the muscle.
The hook is transferred to the left hand and raised so as to
lift the tendon. The scissors are taken in the right hand and
introduced, one branch between the tendon and conjimctiva,
and the other between the tendon and sclera; the tendon is
divided close to the sclera by two or more small cuts. The
hook is reintroduced to make sure that no portion of the ten-
don has been left undivided. If the tendon has been com-
pletely divided, the hook can be advanced to the cornea with-
out resistance; if not, the undivided fibres must be cut with
scissors. The hook is again introduced and swept from be-
hind forward, above, and below, to ascertain whether there
are any uncut fibres of attachment to the sclera which, if

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found, must be severed. The conjunctival wound is closed
with one or two vertical sutures.

The Open Method, — The steps are the same as in the preced-
ing operation except that the muscle is exposed. The con-
junctiva is incised about 2 nmi. from the corneal margin, and
dissected backward and downward beyond the lower border
of the muscle. The hook is inserted beneath the fully exposed
tendon, which is raised and divided close to the sclera (Fig.
351). The wound is closed by two vertical sutures.

After-Treatment. — The result of the operation should be
noted after completion (if done under local anaesthesia). It
may be necessary to lessen the effect by a suture which
stitches the muscle forward to the insertion of the tendon ; or to
increavse the effect by again introducing the hook and dividing
the upper and lower expansions of the insertion of the tendon.

There should always be some convergence (5®) left after the
operation since, although the primary result usually dimin-
ishes for a few days, the subsequent effect increases for a niun-
ber of months; hence if the inmiediate correction be perfect,
there is apt to be subsequent divergence.

If we desire to increase the effect of the operation, atropine
is instilled and both eyes bandaged for a few days; otherwise
this is unnecessary. There is usually no great reaction; the
eye will be congested, but not painful. The bandage can be
left off in a day or two. Sometimes there is slight defonnity
caused by a sinking of the caruncle, the result of free division of
Tenon's capsule. Infection occurs in rare instances, empha-
sizing the necessity for strict asepsis.


Operations designed to increase the action of an ocular
muscle and to strengthen its power of rotation are of three
varieties: 1. Advancement, which brings the attachment of
the muscle further forward; 2. resection, in which a piece of
the muscle is cut out, thus shortening the muscle; 3. muscle-
tucking, in which a permanent fold is made in the muscle
and thus the latter is shortened. Sometimes two of these
methods are combined.

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Advancement. — In slight deviations it will be suflBcient to
advance the muscle without tenotomizing its opponent; for
squints of greater degree, it is best to include a tenotomy upon
the opposing muscle. • Many methods of advancement have
been designed; the Worth operation, which the author usually
employs with sUght modifications, is performed as follows:

The instruments required are the same as those needed for
tenotomy with the addition of advancement forceps (Fig.
350). General ansesthesia is sometimes required, but in
most instances, local anaesthesia is suflBcient. After inser-
tion of the speculum, the conjunctiva is grasped with the
toothed forceps and a curved vertical incision is made,
rather more than half-an-inch in length, with its convexity
close to the corneal margin; a similar incision is made through
Tenon's capsule; the conjunctiva and capsule then retract or
are pushed and dissected back, so as to expose the muscle well.

A tenotomy hook is now passed under the muscle so as to
free it suflBciently and then one blade of an advancement
forceps takes the place of the hook, the other blade being
clasped upon muscle, capsule of Tenon and conjunctiva
with their relations undisturbed except for the retraction of
the membranes (Fig. 352). The tendon and a few small
fibrous bands are now divided at the insertion into the scle-
rotic. The part of the sclera near the cornea intended for the
new insertion of the advanced muscle is carefully cleaned of
all loose tissue so as to favor firm union. The advancement
forceps holding tendon, capsule and conjunctiva can now be
lifted up so as to get a good view of the underside of the muscle.

Two sutures of black No. 2 braided silk, with a needle at
each end, and a third with rather lighter silk armed with a
single needle, are required. One of the needles is passed in-
wards about 2 mm. behind the advancement forceps through
conjunctiva, capsule and muscle at A', and the other on the
same suture at B'; the first needle is continued forward
under muscle and advancement forceps; the second is made
to pierce muscle, capsule and conjunctiva coming out at D.
The other double armed suture, A.B., at the lower margin
of the muscle, is then similarly dealt with.

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The anterior parts of the muscle, capsule and conjunctiva
are then cut off with scissors behind where they are grasped
by the advancement forceps. The position of the loops of
silk and the amount of tissue removed vary with the degree
of rotation required; if only a small effect is desired, it may
not be necessary to remove any tissue at all.

Fig. 862. — ^Worth's Operation of Advancement of an
Ocular Muade.

One needle of each of the two sutures is then inserted into
the sclera near the corneal margin (G', G) ; this step requires
considerable skill; the needle is made to enter the sclera
about one-eighth inch from the limbus and penetrates one-
half the thickness of the sclera, care being taken not to
pierce the whole thickness. Each suture is tied at H after
gradual tightening. The third suture is then passed through
conjunctiva, capsule and muscle and then through sclera
exactly in the horizontal plane, midway between the two
main sutures, affording additional protection and helping
to keep the edges of the wound in apposition; if there are
any gaps in the line of junction these are closed with addi-
tionl fine sutures.

The immediate effect is the permanent result and over-
correction is not necessary. Both eyes are bandaged for
three or four days, the operated eye for a week; stitches are
removed on the eighth day. Worth keeps the patient in
bed, with both eyes bandaged, for ten dajrs, and leaves the
sutures in for this period.

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Resection. — One of the best muscle-resection operations is
that devised by Reese, which is performed as follows: A
vertical incision is made in the conjmictiva 6 mm. from the
limbus; at the upper and lower limits of this incision an
opening into the tissue anterior to the sclera is made so that
a squint hook can be passed under the muscle; all conjunc-
tival and subconjunctival tissue is dissected back to the
canthus so that the muscle is completely bared; one blade
of an advancement forceps is then inserted under and the
other over the muscle, 3 mm. from its insertion, and the
instrument is clamped. The tendon is divided 2 mm. from
its insertion, leaving a stump.

Three sutures are necessary. The middle suture consists
of No. 3 braided silk with a needle on each end; both needles
are passed through the under surface of the muscle, 4 mm.
back of the point of resection and then through the dissected
edge of the conjunctiva, so as to form a loop 2 mm. broad,
in the central part of the muscle, on its scleral surface. This
central suture is reinforced by an upper and a lower suture
of No. 5 twisted silk; the single needle of each of these
sutures passes first through the upper and lower part of the
dissected conjunctiva and then includes the superior and
inferior border of the muscle respectively, slightly posterior
to the loop of the middle suture.

The muscle is cut 2 mm. in front of the loop. The two
needles of the middle suture are brought out through the
center of the stump, 2 ami. apart, and the other two needles
through the upper and lower edges of the stmnp, all including
the conjunctiva as they pass from behind forward. All
three sutures are then tied. The middle suture is removed
in ten days, the others can be removed after forty-eight
hours. The eye operated upon only is bandaged anH '^ - «— ^^
for five days.

Tendon-Tucking. — Many operations for produc
manent folding of the muscle have been advocate
muscle and tendon are exposed, freed from all attf
to the sclera, and then a portion of the muscle is fok
itself, often by the means of a specially-constructe

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or triple hook; the folds of tendon are then sewn together
with catgut, and thus a permanent shortening of the muscle
is produced.


Heterophoria (Insufficiency) is a condition in which the
eyes have a constant tendency to deviate, but are forced into
simultaneous fixation of an object by special exertion. If this
effort were not made, there would be a slight deviation and
double images. So as to seeing binocular vision and avoid
diplopia, an excessive amount of innervation is employed to
maintain proper though /orced balance. When one eye is cov-
ered, diplopia cannot occur; hence the eye will deviate; its
direction now represents the position of rest. The condition
differs from concomitant squint; in the latter affection, the
deviation is due to an absence of the power of binocular fixa-
tion and cannot be overcome by increased innervation.

Varieties. — ^The following terms are employed for designat-
ing the various forms of normal and faulty muscular balance:

Orthophoria, perfect muscle balance.

Heterophoria, imperfect muscle balance.

i?xopAona, tendency to deviate outward (latent divergence).

Esophoria, tendency to deviate inward (latent convergence).

Hyperphoria, a tendency of one eye to deviate upward; right
hyperphoria, when the right eye tends to deviate upward; left
hyperphoria, when the left eye tends to deviate upward.

Hyperexophoria and hyperesophoria, a combination of hy-
perphoria with exophoria and esophoria respectively.

Cyclophoria, want of equilibrium of the oblique muscles.

Etiology. — ^The chief cause is some error of refraction, espe-
cially when accompanied by some disturbance in the normal
relationship between accommodation and convergence. Another
very common cause is general lack of muscular tone seen in
delicate individuals and in convalescence. Much less fre-
quently, certain anatomical conditions, such as a defect or
weakness, or abnormality in size or insertion of one of the
muscles, is responsible. The condition is very common.

Symptoms. — ^In slight degrees of heterophoria, there are

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very often no symptoms whatever. In more pronounced forms,
the symptoms of muscular asthenopia are present: Headache,
various neuralgias, mental dulness, pain in the eyes, indis-
tinctness or " running together " of print, diplopia, vertigo,
and irritable condition of the lids. In exophoria, these symp-

Online LibraryClaud Worth Charles Henry MayA manual of diseases of the eye → online text (page 31 of 36)