Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5507_Библиотеки_им_академика_М_И_Перельмана.pdf
306 Theory and Practice of Squint and Orthoptics
INVESTIGATIONS OF INCOMITANT SQUINT
It should include: (1) evaluation from strabismic
point of view and (2) investigations to find out
the cause of incomitant squint, such as orbital
ultrasonography, orbital and skull computerized tomographic scanning and detailed
neurological investigations (which are beyond
the scope of this chapter).
A detailed work-up of a strabismic patient is
described on page 107. However, the salient
points relevant to the paralytic strabismus are
mentioned here in brief.
History
A detailed history should be taken with
reference to following points:
1. Subjective symptoms
• Diplopia. Enquiry should be made to ascertain:
Onset, constant/intermittent, distance at
which diplopia is noticed, relative position of
images, field where greatest separation of
images occurs, any change since onset, does
diplopia disappear, when eye is occluded.
• Confusion. It occurs due to formation of images
of the different objects on the corresponding
points of two retina.
• Other subjective symptoms which a patient with
paralytic strabismus may experience are:
Difficulty in focussing, headache, eye strain,
general asthenopic symptoms and discomfort
from abnormal head posture.
2. Objective symptoms
• Constant/intermittent deviation
• Abnormal head posture
• Ptosis, exophthalmos
3. Any attributed cause
4. Any previous ocular problems and treatment taken
5. General health
6. Family history
Inspection
1. Ocular posture
2.Abnormal head posture; note its exact
components
3. Facial asymmetry
4. Ptosis, exophthalmos
Cover test
It should be carried out for near and distance;
with and without abnormal head posture. The
cover test will detect:
1. Presence of any manifest or latent deviation.
2. Type of deviation
3.Incomitance—primary versus secondary
deviation
4. Normally fixing eye. Patient usually fixes with
the nonaffected eye; but this may be influenced by visual acuity or dominant eye.
Ocular movements
Investigation of ocular movements is carried out
while the patient watches a fixation target, i.e.
moved from the primary position into each of
the cardinal positions of gaze.
1. Version movements. The examiner compares
the movement of the two eyes in all positions of
gaze. Symmetric movement indicates that no
defect is present. Unequal movements are seen
in underactions, overactions and limitations.
2. Duction movements. Monocular movements
are of value only in differentiating between a
paresis and a total paralysis. Testing for ductions
also helps to detect mechanical limitation of
movements.
3. Doll's head movements and command move-
ments testing is of particular use in supranuclear
gaze palsies.
Measurement of deviation
1. Synoptophore method. Major amblyoscope is
the best instrument for measurement of deviation
in paralytic squint; since measurements are taken
to compare the size of the deviation in each of
the cardinal directions of gaze while each eye in
turn is used for fixation. To make the comparison
valid, it is extremely important that the fixation
object be moved an equal distance from the
primary position in each direction. For this,
synoptophore can be adjusted so that the
deviation can be measured while the patient is
looking at an equal angle from the primary
position in all directions of gaze.
2. Prism and cover test. It is an easy method,
while carried out with the help of a prism bar.
Measurements should be taken with and
without abnormal head posture for near and
Incomitant Strabismus
307
distance fixation, fixing either eye. Measurements can be made in all the cardinal directions,
but for comparison these are not considered very
accurate. Since it is not possible to measure at
an equal angle from the primary position in all
directions; as is possible with the synoptophore.
3. Measurement of torsional deviation can be
made with special slides on major amblyoscope,
or on adapted Lees screen.
Note. In a paresis or paralysis of an extraocular
muscle, the deviation will be greatest in the
direction of maximal singular action of the
muscle while the affected eye is fixating.
Diplopia test
For details, see page 128. Salient points are as
follows:
• Tested with red/green goggles and a linear
light, or without dissociation aids.
• Position of maximum vertical and horizontal
separation of images and position of maximum
torsion is noted.
• Distal image belongs to the affected eye.
• The results are recorded either by written
description or as diplopia chart. Diplopia
charts of paralysis of extraocular muscles of
right eye and left eye are shown in Figs 12.13
and 12.14, respectively.
Bielschowsky three-step test (B3ST)
The classical head tilt test was proposed by
Bielschowsky to differentiate between superior
oblique palsy in one eye and superior rectus
palsy in the contralateral side. However,
presently in practice is the three step test as
modified by Parks'. It is useful in diagnosing
the paresis of any cyclovertically acting muscle.
There are in total 8 cyclovertically acting
muscles; 4 work as depressors of the eyes, and
4 work as elevators. The two muscles on each
eye that are responsible for depression are the
inferior rectus and superior oblique, and the
two muscles on each eye that are responsible
for elevation are the superior rectus and the
inferior oblique.
As expected, at the onset of a cyclovertical
muscle palsy, there will be limitation in the field
of action of the paralysed muscle. Shortly
thereafter, an overaction in the field of the
antagonist muscle will be noted. With time, this
overaction will produce a contracture of the
antagonist. Thereafter, there will be spread of
comitance, so that the amount of deviation will
gradually increase and become approximately
the same in the all fields of gaze. At this point,
based on analysis of duction and version
movements of the eye, the diagnosis of
cyclovertical palsy becomes impossible. At this
juncture, the Parks' modification over Bielschowsky's
head tilt test can be quite useful. There are three
steps of this test, each of which eliminates half
of the remaining potential muscles, leaving only
one muscle to be blamed after the three steps.
Procedure Parks' modified Bielschowsky's of
three-step test
Step 1
• Perform cover-uncover test in primary
position and determine which eye is hypertropic. If the patient's presenting sign is a
hypodeviation, consider it hyperdeviation of
the opposite eye. Step 1 reduces the number
of affected muscles from 8 to 4.
• A right hypertropia (RHT) implies any of the
following:
– Weakness of depressors of right eye (RIR,
RSO), or
– Weakness of elevators of left eye (LIO, LSR).
• A left hypertropia (LHT) implies any of the
following:
– Weakness of depressors of left eye (LIR,
LSO), or
– Weakness of elevators of right eye (RIO,
RSR).
• Let us assume, for example, the patient being
examined has LHT. Draw an oval (with red
lines) around the two possible muscle pairs
responsible for LHT (Fig. 12.15A).
Step 2
• Determine whether hypertropia (HT) is larger
in right gaze or left gaze.
• If the LHT is larger in right gaze, it implies
weakness of any of the 4 vertically acting
muscles in right gaze:
– RSR, RIR
– LIO, LSO
308 Theory and Practice of Squint and Orthoptics
Fig. 12.13 Diplopia charts (patient's view) of paralysis of extraocular muscles of the right eye.
• If the LHT is larger in left gaze, it implies
weakness of any of the 4 vertically acting
muscles in left gaze, i.e.
– LSR, LIR
– RIO, RSO
Incomitant Strabismus
309
Fig. 12.14 Diplopia charts (patient's view) of paralysis of extraocular muscles of the left eye.
• Let us say, in the same patient having LHT,
the deviation is greater in right gaze. Draw
an oval (with green lines) around the two
possible muscle pairs (Fig. 12.15B).
• Note that at this point, the paretic muscle must
be either the LSO or RSR muscle, since they
are the only muscles encircled twice
(Fig. 12.15B).
310 Theory and Practice of Squint and Orthoptics
Fig. 12.15 Parks modified Bielschowsky's three-step test (B3ST) in a patient with left superior oblique paralysis.
(A) step 1; (B) step 2; (C) step 3 (for explanation, see text).
Step 3
• Determine, if the HT is larger, when measured
during head tilt to the left or right. For proper
measurement, the base of the prism should be
held parallel to the floor of the orbit and not
parallel to the floor of the room. The Maddox
rod and correcting prism should be held so
that the line and base are parallel to the floor
of orbit (Fig. 12.16).
• If the LHT is larger, when the head is tilted to
the right, this implicates any of four muscles
that act vertically in right tilt position, i.e.
either intorters of right eye (RSR, RSO) or
extorters of left eye (LIR, LIO).
Fig. 12.16 Measurement of deviation using Maddox rod
and prism in a patient with right hypertropia. Note, head is
tilted to the right and base of the prism is held parallel to the
floor of the orbit. Maddox rod is held in such a way that the
red line seen is also parallel to the floor of the orbit.
• If the LHT is larger, when the head is tilted to
the left, this implicates any of the four muscles
that act vertically in left tilt position, i.e. either
intorters of left eye (LSR, LSO) or extorters of
right eye (RIR, RIO).
• Now, for the same individual, suppose that the
vertical deviation is quite large, when the head
is tilted to the left and is almost absent, when
the head is tilted to the right. Draw an oval (with
blue lines) around the muscle implicated, i.e.
(LSR, LSO, RIR, RIO) (Fig. 12.15C).
• Note that at this point, the LSO is the only
muscle, i.e. surrounded by three ovals and
is connected by the line that represents head
tilt to the right (Fig. 12.15C).
Incomitant Strabismus
311
Summary of the test shown in Fig. 12.15:
Step 1: LHT (LIR, LSO, RSR or RIO)
Step 2: Worse in right gaze (RSR or LSO)
Step 3: Worse in left tilt (LSO)
Results of B3ST in paralysis of various
cyclovertically acting muscles are summarized
in Table 12.3.
Limitations of Park modified three-step test
This test is quite useful in general, but it is not
always diagnostic and can be misleading,
especially during following conditions:
• In cases of long-standing paresis.
• When more than one muscles are paretic, e.g.
– Bilateral fourth nerve palsy
– Multiple other muscle weakness
• In cases with restrictions.
– Superior rectus overaction
– Superior rectus contracture
– Inferior restriction
• Dissociated vertical deviation (DVD)
• Pulley heterotopia
• Superior rectus palsy
• Skew deviation
• Prior extraocular muscle surgery
Quantitative measurement of extraocular
muscle actions
The quantitative measurement of extraocular
muscle action is most essential to comment
about the paretic muscles and the pathological
sequelae of the paralysis, viz. overaction,
contracture and secondary inhibitional palsy.
Commonly employed tests to have a graphic
record of the relative power of extraocular
muscles in all directions of gaze are as follows:
• Hess screen test
• Lees screen test
• Lancaster red and green test
These tests are based on haploscopic principle
and described in detail on page 129.
Uses of haploscopic tests
These tests are repeatable and their uses are as
follows:
• Diagnose underactions and overactions of
extraocular muscles and provide a good
pictorial representation of muscle actions.
• Diagnose A- and V-phenomena.
• Diagnose mechanical/neurological palsy
• Diagnose congenital/acquired palsy
•Aid in plan of surgery—preoperatively
• Show effect of surgery—postoperatively.
• Provide an accurate and permanent record of
change in state of ocular movements in
subsequent visits and thereby form part of
serial record of progress of palsy.
• Measure torsional movement with linear
pointer (Dulley and Harden) or cyclotiltmeter
(Brown).
Table 12.3 Results of Bielschowsky three-step head tilt
test in paralysis of cyclovertically acting muscles
Paralysed Bielschowsky head tilt test
muscle
RSO RHT Left Right
RIR RHT Right Left
LIO RHT Right Right
LSR RHT Left Left
LSO LHT Right Left
LIR LHT Left Right
RIO LHT Left Left
RSR LHT Right Right
Step 1 Step 2 Step 3
(hypertropia (HT worse (HT worse
in primary in left or on left or
gaze) right gaze) right tilt)
Field of binocular fixation
It must be tested, wherever applicable, i.e. if
patient has some field of binocular single vision.
It provides, useful and repeatable information.
The area of binocular single vision is opposite
to the direction in which ocular motility is
impaired.
The aim of treatment of muscle paralysis is to
provide comfortable field of binocular fixation,
i.e. the central field and lower quadrants.
For details of the test, see page 134.
Other tests
Other tests which can be carried out, if
necessary, includes forced duction test, EMG,
EOG, orbital ultrasonography and computerized
tomographic scanning.
312 Theory and Practice of Squint and Orthoptics
DIFFERENTIAL DIAGNOSIS OF
INCOMITANT SQUINT
Differential diagnosis to be considered in
patients with incomitant squint in general are
as follows:
• Comitant (non-paralytic) versus incomitant
(paralytic) squint.
• Congenital versus acquired palsies.
• Paralytic versus restrictive incomitant squint.
long-standing paralysis, there occurs spread of
comitance and thus it becomes extremely difficult and at times even impossible to differentiate such a condition from the comitant squint.
Anyshow, for a ready reference, the differences
between paralytic and non-paralytic squint are
depicted in Table 12.4.
Congenital versus acquired ocular palsy
Many a time, patients with congenital paralysis
of an extraocular muscle may remain asympto-
Comitant (non-paralytic) versus
incomitant (paralytic) squint
As mentioned earlier, by and large, there arises
no problem in differentiating comitant (nonparalytic) squint from the paralytic (incomitant)
squint of recent onset. However, in patients with
Table 12.4 Differences between paralytic and non-paralytic squint
S. no. Feature Paralytic squint Non-paralytic squint
1. Age of onset Any age Usually in childhood
2. Type of onset Usually sudden, rarely may be slow Usually gradual
or since birth
3. History of head Common Uncommon
injury
4. Diplopia Usually present Usually absent
5. Ocular movements Limited in the direction of paralysed Usually full
muscle
6. False projection It is common in palsy of recent onset, False projection is negative
i.e. patient cannot correctly locate the
object in space, when asked to do so
in direction of paralyzed muscle. There
occurs past pointing
7. Head posture A particular abnormal head posture may Normal
be present, depending upon the muscle
paralysed
8. Nausea and vertigo Usually present, due to confusion, Absent
diplopia and false projection
9. Primary versus Secondary deviation is more than Secondary deviation is equal
secondary primary deviation to primary deviation
deviation
10. Sensory adaptations Uncommon Common
(ARC, suppression,
amblyopia)
11. Cyclotropia Common with cyclovertical paresis Uncommon, except in A- and
12. Muscle sequelae Present in old cases Absent
13. Neurological May be present Usually absent
findings or
systemic diseases
matic for decades because of either a strong fusion
mechanism or by an unnoticed slight abnormal
head posture. Such a patient, when reaches adult
life, the chances are that, unless the latent
deviation is small one, decompensation will begin
to occur, especially between the ages of 30 and
V-patterns
Incomitant Strabismus
313
40 years. The patient may notice that he/she is
beginning to suffer from an intermittent diplopia,
especially if he/she is tired, overworked, or
suffering from ill health. Some of these patients
may develop intermittent squint without diplopia
due to suppression of the image of the deviating
eye. Such patients may experience difficulty in
focussing or have a feeling of using only one eye.
Under these circumstances, one needs to
differentiate between cases of congenital
paralysis with recent decompensation and those
of acquired paralysis of recent onset. It is very
essential, since in the former the treatment is
invariably operative while the latter requires a
diligent search for its cause by a complete
medical and neuro-ophthalmologic evaluation
and the appropriate treatment. Some of the chief
differences between the congenital and acquired
ocular palsies are summarized in Table. 12.5.
Paralytic versus restrictive incomitant squint
Incomitant ocular deviations are known both
due to palsies as well as restrictions of
extraocular muscles and are often confused
with one another by even experienced
examiners. Though, these are two distinct
problems but mere measurement obtained with
prism and alternate cover tests with either eye
fixing do not differentiate between them, since
in both, the secondary deviation is typically
greater than the primary deviation. However,
a differentiation between the two is most
important for the successful treatment of
incomitant deviation. It is unequivocal to state
that the restrictions must be relieved first,
before any other therapy, whether surgical or
non-surgical to be effective.
Commonly employed tests to differentiate
between palsies and restrictions are as follows:
1. Passive forced duction test (traction test)
As mentioned above, detection of associated
restriction is most important for the successful
therapy of an incomitant squint. Therefore, it is
mandatory to carry out forced duction test (FDT)
before any surgical therapy is undertaken.
Table 12.5 Differences between congenital and acquired ocular palsies
S.no. Feature Congenital ocular palsy Recent acquired ocular palsy
1. Onset of symptoms Usually indefinite and intermittent Usually definite and sudden
2. Diplopia Rare, intermittent diplopia in Almost invariably present, but may
decompensation be limited to paretic field
3. Primary deviation May be intermittent or constant Usually constant
angle of deviation may be large; Angle of deviation may be small and
but symptoms may be only slight yet the symptoms may be pronounced
4. Secondary deviation Only slightly greater than the Usually much greater than the
primary deviation (due to primary deviation
spread of comitance)
5. Past pointing Usually absent Present
6. Abnormal head posture May persist on covering paretic Disappears on covering paretic eye
eye because of secondary scolio-
sis and contracture of neck muscles
7. Facial asymmetry Common with torticollis of long Absent
standing
8. Amblyopia May be present Absent
9. Forced duction test May be positive due to Negative
contracture of antagonist
10. Abnormal head posture May be present Absent
in old photographs
314 Theory and Practice of Squint and Orthoptics
Steps of the forced duction test (FDT)
i. Anaesthesia. In adults and cooperative elder
children, FDT can be performed preoperatively
under topical anaesthesia with 4% xylocaine
instilled every 4 minutes for 4 times. In small
and uncooperative children, FDT is done under
general anaesthesia during surgery, taking an
account of following points:
– To remove the effect of tonic innervational
factors, the FDT should be performed, when
patient has reached stage 3 of anaesthesia.
– If succinylcholine is to be used, preferably the
FDT should be performed while the patient
has received an inhalation anaesthetic by
mask, but before intubation. Otherwise one
will have to wait for at least 20 minutes till
the contraction of the extraocular muscles
caused by succinylcholine is over.
– Pancuronium, a nondepolarizing muscle
relaxant, that does not alter the FDT, should
be preferred over succinylcholine.
ii. Grasping of the globe. After proper anaesthesia,
the globe should be grasped near the limbus
with either a forceps without teeth or Pierse
forceps to avoid tearing of the conjunctiva.
Preferably, the globe should be held with the
help of two forceps at right angle to the axis in
which restriction is to be tested.
For example, in a patient with divergent
squint (Fig. 12.17A), to distinguish between
lateral rectus paralysis and mechanical
restriction involving the medial aspect of the
globe, the forceps should be applied at 6 and 12
O'clock positions (Fig. 12.17B).
iii. Passive rotation of the globe. After grasping,
the globe should be rotated passively towards
the direction of action of suspected weak muscle,
e.g. into abduction in patients with lateral rectus
weakness versus mechanical restriction involving
medial aspect of the globe (Fig. 12.17C), taking
following precautions:
– When FDT is being performed under topical
anaesthesia, patient should be instructed to
look at his/her hand held in the direction in
which the eye is to be rotated by the forceps.
This will help in avoiding the effect of tonic
innervational factor.
– Care should be taken not to push the globe
into the orbit posteriorly, since this may
conceal a restriction of the movement resulting
in a false negative FDT.
• To test the restrictions in the field of action
of recti, the globe should be rotated, up,
down, medially or laterally.
• To test the restrictions in the field of action
of oblique muscles, the globe should be
rotated both down and in, and up and in.
Note. FDT should be repeated at the time of
surgery and also after completion of the surgery.
Interpretation of the results of FDT
1. Forced duction test is labelled negative, if
no resistance is encountered during passive
rotation and the examiner can rotate the
globe to its full extent. A negative FDT implies
that the motility defect is clearly caused by
paralysis of the weak muscle.
2. Positive FDT is labelled, if a resistance is
encountered during passive rotation of the
globe. With a feeling of resistance, if the
examiner can rotate the globe no further than
the patient voluntarily can, the motility defect
is purely due to mechanical restriction.
However, with a feeling of resistance, if the
examiner can passively rotate the globe beyond
where the patient can voluntarily rotate it, but
not to its full extent, the motility defect is a
combination of mechanical restriction and
agonist muscle weakness.
The restriction noted in the positive FDT
may be one of the following types:
i. Leash restriction is caused by the mechanical
factors such as marked scarring of Tenon's
capsule and conjunctiva, contracture of an
extraocular muscle and/or entrapment of
muscle or its facial sheath on the side of globe
opposite the limited field of rotation.
The globe can be passively rotated
freely up to a point after which tethering
effect of restriction does not allow the globe
to move further any more. Such a restriction
is not only felt but can also be seen as a taut
string of conjunctiva (String sign).
ii. Reverse leash restriction. The tethering effect
of restriction is similar to leash restriction as
described above. However, the mechanical
Incomitant Strabismus
315
Fig. 12.17 Technique of forced duction test (for explanation, see text).
factors responsible for tethering are marked
shortening of conjunctiva and Tenon's
capsule, marked posterior scarring of orbital
tissues or a tight posterior fixation suture
used in Faden's operation on the same side
of globe in which rotation is limited.
iii. Elastic restriction is caused by an early
contracture of a muscle following paresis of
its agonist, co-contraction of extraocular
muscles due to effect of succinylcholine and
orbital cellulitis. In contrast to the leash and
reverse leash restriction (in which globe can
be rotated to a point after which tethering
effect of restriction does not allow the globe
to move further any more), in elastic
restriction, there occurs a partial resistance
over the entire range of ocular movement
which can be overcome by an increased force.
2. Exaggerated traction test
It is a modified forced duction test which is
performed to estimate the tightness in superior
oblique (SO) and inferior oblique (IO) muscles.
Procedure. For checking tightness of RSO, the
eyeball is grasped near the limbus at 6 and 9
O'clock positions, as described in FDT. To
perform this test, the eyeball is first pushed in
the orbit and then elevated, adducted and rolled
back and forth by extorting and intorting the
globe across the tendon. During this manoeuvre,