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
106 Theory and Practice of Squint and Orthoptics
7. Lancaster WB. "Terminology," with extended
comments on the position of rest and fixation. In
Allen, JH, editor: Strabismus ophthalmic symposium
I, St. Louis, 1950, Mosby -Year Book, Inc.
8. Lyle TK, Wybar, KC. Lyle and Jackson's practical
orthoptics in the treatment of squint (and other
anomalies of binocular vision), ed. 5, Springfield,
III, 1967, Charles C Thomas, Publisher.
9. Paul TO, Hardage LK: The heritability of
strabismus, Ophthalmic Genet. 15:1, 1994.
10. Scobee RG. Anatomic factors in the etiology of
heterotropia, Am. J. Ophthalmol. 31:781, 1948.
11. Worth C. Squint, its causes, pathology and
treatment, ed. 6, London, 1929, Bailliere, Tindall
and Cox.
6
Evaluation of a Case of Strabismus
and Orthoptic Instruments including
Computer-based Orthoptic Programs
EVALUATION OF A CASE OF STRABISMUS
History, vision evaluation and preliminary
examination
History
Vision evaluation
Preliminary examination
Inspection
•
Pupillary reactions
•
Media and fundus examination
•
Refraction
•
Motor evaluation
Cover tests
Direct cover test
•
Cover uncover test
•
Alternate cover test
•
Quantitative measurement of angle of deviation
• Bruckner pupillary red reflex test
Hirschberg corneal reflex test
•
Prism and alternate cover test
•
Prism reflex test (Krimsky's test)
•
Perimeter method
•
Maddox rod test
•
Synoptophore method
•
Double prism test
•
• Haploscopic test
Assessment of ocular movements
Ductions
•
Versions
•
Vergences
•
Assessment of accommodation and
AC/A ratio
Heterophoria method
•
Gradient method
•
Fixation disparity method
•
Haploscopic methods
•
Assessment for extraocular muscle paresis
Diplopia charting
•
Quantitative measurement of action of extraocu-
•
lar muscles
– Lancaster red-green test
– Hess screen test
– Lees screen test
Field of binocular fixation
•
Bielschowsky phenomenon test
•
Bielschowsky head tilt test
•
Sensory evaluation: Assessment for binocular
cooperation and sensory anomalies
Tests for fixation behaviour
•
Tests for the state of retinal correspondence
•
Tests for binocular vision
•
Tests for suppression and amblyopia
•
ORTHOPTIC INSTRUMENTS
Conventional Orthoptic Instruments
Synoptophore
•
Livingston binocular gauge
•
Visuscope
•
Euthyscope
•
Computer Based Orthoptic Programs
• Computerised orthoptic diagnostic programs
• Computer based vision therapy and neurovision
therapy programs
• Computer based combined diagnostic and
therapeutic programs
EVALUATION OF
A CASE OF STRABISMUS
To avoid repetition, the subject of evaluation
is discussed even before the clinical
description of different varieties of the
squint. Though the list of tests is exhaustive,
all of these may not be required in every case.
An experienced strabismologist chooses a set
of tests to be performed in a particular
patient.
Main components of evaluation of a case of
strabismus are:
I. History, vision evaluation and preliminary
examination
• History
• Vision evaluation
• Preliminary examination
108 Theory and Practice of Squint and Orthoptics
II. Motor evaluation
• Head posture evaluation
• Evaluation for ocular deviation
– Cover tests
– Corneal reflex tests
– Subjective tests for measurement of deviation
– Measurement for cyclodeviation
• Assessment for ocular movements
– Evaluation of ductions
– Evaluation of versions
– Evaluation of vergence
• Assessment of accommodation, and AC/A
ratio
• Assessment for extraocular muscle paresis
III. Sensory evaluation
• Tests for fusion,
• Tests for binocularity and diplopia
• Tests for fixation
• Tests for status of retinal correspondance
• Tests for suppression and amblyopia
• Tests for stereopsis.
In general, for a systematic evaluation,
following approach may be adopted.
HISTORY, VISION EVALUATION AND
PRELIMINARY EXAMINATION
HISTORY
A detailed and meticulous history taking before
beginning the examination is very important in
the management of a case of squint. A complete
history taken should contain the following
information.
1. Age of the patient
2. History of present illness. Information about
deviation of eye should include:
• Time when first noticed. It is desirable to
document the age of onset of deviation or
symptoms. All available old photographs of
the child are invaluable for this purpose.
• Onset, sudden or gradual.
• Constant or intermittent deviation.
• Unilateral or alternating deviation.
• If alternating, which eye more frequently
fixates (dominant eye).
• Alleged cause, if any, such as trauma, illness,
psychologic disturbance, change in occupation,
increase in close work, etc.
• Abnormal head posture (ask to demonstrate).
• Associated symptoms such as diplopia,
blurred vision, headache, asthenopia.
• Any history of closing or covering one eye
in bright light indicates intermittent squint.
3. Birth history. It is especially important in
cases of childhood onset deviations. Enquiry
should be made regarding:
• Problems during pregnancy and
• Problems during delivery
4. Family history. History regarding any of the
following disorders in grandparents, parents,
siblings or even in uncles, aunts and cousins is
important;
• Strabismus
• Refractive errors
• Lazy eye
• Other ocular defects
5. Past history
• General ill health
• Any systemic disease
• Any ocular defect
6. History of previous treatment
a. Optical treatment
• When and how long?
• Were glasses worn constantly?
• Effect of glasses on the deviation.
• Date of last refraction.
b. Orthoptic treatment.
• Occlusion. Type, when, how long, effect
on vision.
• Exercises. When, type, how long, effect
on deviation.
c. Surgical treatment
• When performed?
• Eye operated: Right, left or both.
• Muscle touched. Medial, lateral or both
(if known).
• Patient's/parents' opinion about the result
of surgery.
VISION EVALUATION
Testing of visual acuity of each eye separately
is critical in evaluation of any patient with
strabismus. Visual acuity should be tested
without glasses and with glasses (if worn); and
for near and distance vision.
109Evaluation of a Case of Strabismus and Orthoptic Instruments
Methods of testing visual acuity in infants,
preschool age children and in school-age
children as well as adults have been described
in Chapter 3 (see pages 38–54). However, for a
ready reference, these are enumerated below.
Methods of estimating visual acuity in infants
1. Fixation behaviour test
2. Preferential looking test
3. Optokinetic nystagmus
4. Visually evoked response
5. CSM method
Methods of estimating visual acuity in
preschool-age children
1. Marble game test
2. Hand chart
3. Illiterate E-game test
4. Allen's preschool vision test
5. Sheridan-Gardiner test
Methods of estimating visual acuity in schoolage children and adults
1. Snellen's test types
2. E-chart
3. Landolt's broken-C chart
Visual acuity in patients with nystagmus. In
patients with nystagmus, visual acuity may be
better with both eyes open than with one eye
occluded. In order to assess this situation, it may
be helpful to place a +5.00D sphere lens in front
of the eye not being tested, and then reverse this
in order to test the other eye.
PRELIMINARY EXAMINATION
Inspection
Large degree squint (convergent or divergent)
is obvious on inspection.
Epicanthus, when observed in infants, may be
the cause of pseudoesotropia.
Facial asymmetries may also create the
impression of pseudostrabismus especially
hypertropia.
Abnormal head posture (AHP) when present,
becomes obvious during initial inspection of the
patient. Infact observation for AHP should
always be made without any instructions to the
patient, otherwise a lot of information may be
lost after the patient becomes concious of being
examined. As described in detail on page 302,
observation should be made for all the three
components of head posture, i.e.
• Chin elevation or depression (vertical
component),
• Face turn to right or left (horizontal
component), and
• Head tilt to right or left shoulder (torsional
component)
Interpupillary distance (IPD) should also be
inspected and measured. Unusually, narrow
IPD may be the cause of pseudoesotropia and
an exceptionally wide IPD may be a cause of
pseudoexotropia.
Inspection during pen light examination may
sometimes erroneously reveal strabismus owing
to presence of a large angle kappa. A large
positive angle kappa may be a cause of
pseudoexotropia and a large negative angle
kappa may be a cause of pseudoesotropia. For
details of angle kappa and its measurement, see
page 200.
Pupillary reactions
Light reflexes may be abnormal in patients with
sensory deviations due to diseases of retina and
optic nerve and in squint due to pupil involving
third nerva paralysis.
Media and fundus examination
It may reveal associated diseases of the ocular
media, retina or optic nerve. Fundus should also
be evaluated for presence of torsion (extorsion
or intorsion).
Refraction
It is most important, because a refractive error
may be responsible for the symptoms of the
patient or for the deviation itself. Refraction is
performed before complete squint check-up.
Preferably, refraction should be performed
under full cycloplegia especially in children. The
commonly used cycloplegics are as follows:
1. Atropine is indicated in children below the
age of 5 years. It is used as 1% ointment thrice
daily for 3 consecutive days before performing
retinoscopy. Its effect lasts for 10–20 days.
2. Homatropine is used as 2% drops. One drop
is often instilled every 10 minutes for 6 times
and the retinoscopy is performed after 1 to
2 hours. Its effect lasts for 24–28 hours. It is used
110 Theory and Practice of Squint and Orthoptics
for most of the hypermetropic individuals
between 7 and 35 years of age.
3. Cyclopentolate is a short-acting cycloplegic.
Its effects last for 6 to 18 hours. It is used as 1%
eyedrops in patients between 7 and 35 years.
One drop of cyclopentolate is instilled every 10
minutes for 3 times (Havener's recommended
dose) and the retinoscopy is performed 1 to 1½
hours later after estimating the residual
accommodation, which should not exceed one
dioptre.
MOTOR EVALUATION
EVALUATION FOR OCULAR DEVIATION
COVER TESTS
Prerequisites for cover tests
• Patient should be co-operative enough to
fixate a target.
• Should have sufficient vision to see the target.
• Should have central fixation in both eyes.
• Latent nystagmus should not be present.
Methods of cover tests
The cover tests should be performed with and
without glasses at distance (6 m) and at near
(33 cm). The patient is asked to fixate a 6/12
visual acuity symbol or any object that keeps
patient's attention, such as a small picture or a
toy (especially in small children), with one eye.
This is to prevent the use of accommodation,
when torch light is used (which is a common
practice). The other eye is then covered with the
help of an occluder or palm of the hand. The
interpretations are made as described below.
Fig. 6.1 Direct cover test depicting left exotropia.
No movement of the uncovered eye on covering the
seemingly fixating eye indicates any of the
following:
• No squint (pseudostrabismus)
• Gross eccentric fixation (there may be very
small or no movement of redress in the
uncovered deviated eye)
• No vision in the deviated uncovered eye.
Cover-uncover test
Aim. To establish the presence and type of heterophoria
(latent deviation).
Procedure (Fig. 6.2). It is performed, when direct
cover test has established that no manifest
deviation is present. To perform it, one eye is
covered with an occluder and the other is made
Direct cover test
Aim. To confirm the presence of a manifest squint.
Procedure. To perform this test, patient is first
asked to fixate (Fig. 6.1) a point with both eyes
open. The normal looking eye is covered while
observing the movement of the uncovered eye.
In the presence of manifest squint, the
uncovered eye will move in the opposite
direction to take fixation. For example, when an
exotropia is present, the eye taking up fixation
will move towards nose and in the presence of
esotropia, it will move towards the temple.
Fig. 6.2 Cover-uncover test depicting exophoria. Note
orthophoria in primary position (A) and immediate inward
movement of right eye on removal of the cover (B and C).
111Evaluation of a Case of Strabismus and Orthoptic Instruments
to fixate an object. In the presence of heterophoria, the eye under cover will deviate (since
covering one eye of a patient with normal
binocular vision interrupts fusion). After a few
seconds, the cover is quickly removed and the
movement of the eye (which was under cover)
is observed. Direction of the movement of the
eyeball tells the type of heterophoria (e.g. the
eyeball will move towards the nose in the
presence of exophoria and towards the temple
in the presence of esophoria) and the speed of
movement tells whether recovery is slow or
rapid.
Alternate cover test
Aim. To establish whether the squint is unilateral
or alternate and also to differentiate concomitant
squint from paralytic squint (where secondary
deviation is greater than primary deviation).
Procedure (Fig. 6.3). To perform this test, patient
is asked to fixate an object alternately with each
eye. It is important to place occluder alternately
in front of each eye several times to dissociate
the eyes and to maximize the deviation. Further,
the occluder should be quickly transferred from
one eye to other to prevent fusion from
occurring. Observations made are as follows:
In the presence of an alternate squint, either
eye fixates and the opposite eye under cover
deviates and maintains the position of deviation
on removing the cover; but in the presence of a
unilateral squint, after removal of the cover,
always the normal looking eye takes up fixation
and the squinting eye deviates.
To differentiate concomitant squint from
paralytic squint, observation about the degree
of deviation in the eye under cover is made
while performing the alternate cover test. In
concomitant squint, primary deviation is equal
to secondary deviation (deviation of the normal
eye under cover); while in paralytic squint,
secondary deviation is much more than the
primary deviation.
Limitations of cover tests
Following deviations may be either overlooked
or cannot possibly be diagnosed with cover tests:
• A small heterophoria
• A small angle esotropia (of less than 5)
• A microtropia
• A monofixation syndrome
• A cyclodeviation
QUANTITATIVE MEASUREMENT
OF ANGLE OF DEVIATION
Various methods for quantitative measurement
of angle of deviation can be grouped as under:
Objective tests for heterotropia
• Hirschberg corneal reflex test
• Prism and cover test (prism bar cover test)
• Prism reflex test (Krimsky's corneal reflex test)
• Synoptophore test
• Perimeter method
Subjective tests for heterotropia
• Maddox rod test
• Synoptophore test
• Diplopia test
• Hess/Lees screen test
Objective tests for heterophoria
• Prism and cover test
Subjective tests for heterophoria
• Maddox rod test
• Maddox wing test
• Double prism testFig. 6.3 Alternate cover test depicting alternate exotropia.
112 Theory and Practice of Squint and Orthoptics
Tests based on corneal reflex
• Hirschberg corneal reflex test
• Prism and cover test (prism bar cover test)
• Prism reflex test (Krimsky's corneal reflex test)
• Perimeter method
• Synoptophore method
• Bruckner test
Dissimilar image tests
• Maddox rod test for heterophoria or hetero-
tropia
• Double Maddox rod test for cyclodeviations
• Red glass test
Dissimilar target tests
• Major amblyoscope test
• Lancaster red-green projection test
• Hess screen test
Bruckner pupillary red reflex test
This is a screening test and does not measure
the size of deviation. It is performed with the
help of a direct ophthalmoscope. Patient is made
to look into the light and examiner compares
the brightness of pupillary red reflex of both eyes
obtained simultaneously,
• In orthophoria, the Bruckner red reflex is
symmetric in the two eyes.
• In strabismus, the reflex is brighter in the
deviated eye.
• In ocular pathologic conditions such as large
anisometropia, gross retinal pathology, large
retinal detachment, media opacities (corneal,
lenticular or vitreal), the red reflex is altered
in the affected eye.
Hirschberg corneal reflex test
It is a rough but handy method to estimate the
angle of manifest squint. In this test, patient is
asked to fixate at a point light held at a distance
of 33 cm and the deviation of corneal reflex from
the centre of pupil is noted in the squinting eye.
Hirschberg reported that each 1 mm decentration of corneal reflex corresponds to 7° (14)
of deviation of the visual axis. Thus, roughly the
angle of squint is 15 degree (about 30 prism
dioptres) and 45 degree (about 90 prism
dioptres) when the corneal light reflex falls on
the border of pupil and limbus, respectively
(Fig. 6.4).
Fig. 6.4 Hirschberg corneal reflex test depicting ortho-
position (A); right exotropia (B) 15°; (C) 30°; (D) 45° and
right esotropia (E:15°, F:30°, G:45°).
Prism and alternate cover test
(prism bar cover test, i.e. PBCT)
In practice, this test is most popular and a simple
method of measuring the angle of deviation
objectively in various diagnostic positions of gaze.
Prisms of increasing strength with apex towards
the deviation are placed in front of one eye and
the patient is asked to fixate a target with the
other eye. For large deviations, a loose prism of
30 or 45 prism dioptre is placed in front of one
113Evaluation of a Case of Strabismus and Orthoptic Instruments
Fig. 6.5 Prism and cover test with its optical principle. (A) right esotropia; (B) image of the object fixated by left eye is
projected on major half of retina of the right eye; (C and D) when left eye is covered, right eye moves outwards to take over
fixation and under the cover left eye performs an inward movement of equal amplitude following Hering's law of equal
innervation; (E and F) when cover is transferred to right eye, the left eye moves outwards to takeover fixation and under
the cover right eye performs an inward movement; (G and H) a prism base-out is held before the right eye and cover is
transferred to the left eye. There is still outward movement of the right eye when taking over fixation; (I and J) cover is again
transferred and a prism of greater power is held before the right eye; (K and L) transfer of cover to the left eye does not
show any outward movement of the right eye indicating that it is the end point of the prism and cover test. At this juncture,
prism of sufficient power offsets the nasal displacement and the right eye will no longer change its position when left eye
is covered. The power of this prism equals the deviation.
eye and the prism bar is used in front of the other
eye.
• When horizontal and vertical deviations co-exist,
the prisms are placed horizontally in front
of one eye and vertically in front of the other
eye.
• Alternate cover test is then performed till there
is no recovery movement of the eye under
cover (Fig. 6.5). This will tell the amount of
deviation in prism diopters.
Both heterophoria as well as heterotropia can be
measured objectively by this method.
114 Theory and Practice of Squint and Orthoptics
Test should be performed for distance and near
fixation, using an accommodative target.
Test should be performed, preferably in all the
nine diagnostic positions of gaze. In Boyce-
Smith deviometer (Fig. 6.6), nine prefixed
retroilluminated slides (accommodative targets)
positioned 35° from the primary position are
used to perform cover and prism test in
diagnostic positions of gaze.
One great advantage of using a deviometer is
that the prism and cover test can be performed
in diagnostic positions under exactly the same
conditions on different occasions and thus
permit meaningful comparison of test results (e.g.
preoperative and postoperative).
Comparison of prism and cover test performed
in primary position, straight up position and
straight down position is very useful in
detecting the 'A', 'V' and 'X' pattern
heterotropias.
Test should be repeated by holding the prism and
occluder before the other eye to detect any
difference between right and left fixation, which
would indicate incomitance.
Uses of prism and cover test
A carefully performed PBCT can provide
following useful information:
1. Nature of deviation of esotropia (basic or
convergence excess or divergence insufficiency
type) and exotropia (basic or convergence
insufficiency or divergence excess type) can be
known from the results of near and distance
measurements.
2. Accommodative element of deviation can be
known from measuring deviation for far and
near with and without glasses (including
bifocals, if any).
3. Incomitance, if any, can be detected by
performing the test in 9 cardinal positions of gaze.
4. A-V patterns can be detected by measuring the
deviation in upgaze of 25° and downgaze of 35°.
5. Primary versus secondary deviation can be
detected by measuring the deviation with right
and left eye fixating alternately.
6. Divergence excess versus simulated divergence
excess exotropia can be differentiated by
measuring the deviation before and after
prolonged occlusion.
Fig. 6.6 The Boyce-Smith deviometer.
Limitations of prism and cover test
• Since, this test requires an accurate fixation,
so it cannot be performed, if the deviating eye
is blind or has gross eccentric fixation.
• The optical qualities of the prisms also limit
the test accuracy. The stronger the prism, the
greater the error.
• The spectacle lenses with power more than
±5D introduce a significant artifact in
measurement of deviation. Plus lenses
decrease and minus lenses increase the
measured deviation.
• The presence of manifest as well as latent
nystagmus hinders the accurate measurements by prism and cover test.
• Test accuracy is also limited by the minimum
movement of redress that the examiner can
detect with naked eye.
Prism reflex test (Krimsky's corneal reflex test)
Prism reflex test first described by Krimsky has
become universally accepted as a practical
method of estimating the size of the angle of
115Evaluation of a Case of Strabismus and Orthoptic Instruments
squint in patients with a blind or deeply
amblyopic eye with or without eccentric
fixation.
To perform the test, patient is asked to fixate
on a point light and prisms of increasing
strength (with apex towards the direction of
manifest squint) are placed in front of the
normal fixating eye till the corneal reflex is
centered in the squinting eye (Fig. 6.7). The
power of prism required to centre the light reflex
in the squinting eye equals the amount of squint
in prism dioptres. To avoid errors from parallax,
the examiner must observe the corneal reflex
with one eye by sitting directly in front of the
deviating eye while keeping his other eye closed.
In an alternative method, prism of increasing
power can be placed in front of the deviating
eye until the corneal reflexion is centred.
Fig. 6.7 The Krimsky's corneal reflex test. (A) right exotro-
pia; (B and C) prism base-in of increasing powers are
placed in front of the fixing left eye till the corneal reflex
centres in the right eye (C); (D) optical principle of the prism
reflex test.
However, since the observation of the corneal
reflexion through prisms is difficult, therefore,
the method described above is preferred.
Advantages of Krimsky's test
• Since the test requires only that the patient
fixate the light, being entirely objective
otherwise, it is useful in testing small children.
• It is quicker to perform than the prism cover test.
• It can be used in patients in whom the
deviating eye has a low visual acuity or has
lost central fixation.
Limitations of the Krimsky's test
• Since the angle kappa is included in the
measurement, the test is inaccurate.
• It is impossible to perform the test for distance
fixation, since the position of the examiner's
head required to obtain an accurate observation prevents the patient from seeing the
fixation light.
Simultaneous prism cover test
Aim. The aim of this test is to measure only the tropia
without dissociating the phoria.
This special cover test is used to measure the
tropia component of patient with small tropia
<10 PD and a larger phoria (i.e. monofixation
syndrome). It is not useful for larger tropia
(>10 PD), which does not permit fusion and,
therefore, does not have an associated phoria.
Procedure. This test is performed as below:
• Hirschberg corneal reflex test is performed to
estimate the approximate size of tropia
(Fig 6.8A).
• Simultaneous prism cover test is then performed
by placing the prism of the size of tropia in
front of deviating eye and an occluder in front
of the fixating eye (Fig. 6.8B). The power of
prism with which the deviated eye does not
show refixation shift equals the tropia.
Note. For patients with monofixation syndrome,
the amount of tropia is measured with simultaneous prism cover test and the total angle
(tropia plus phoria) is measured with the
alternate prism cover test.
Perimeter method
Patient is asked to fixate at O-mark on the arc
perimeter with normal eye and a flash light is