Sensory evaluation of squint

1. SENSORY EVALUATION OF
SQUINT
Dr Laltanpuia Chhangte
GMC College, UK

2. INTRODUCTION
 Normal binocular development
 Binocular single vision
 Sensory adaptations
 Tests for sensory system

3. NORMAL BINOCULAR DEVELOPMENT
 Binocular sensitivity and binocular fusion are
absent at birth.
 Afferent from each eye segregate in LGN and 4c
layer of ocular dominance coloumns(ODC) of
striate cortex .
 Horizontal binocular connections develop between
ODC’s of each side are weak at birthand become
sharply defined at 3-6 months of age.
 Stereopsis emerge in humans during the first 3-5
months of post natal age.

4. BINOCULAR SINGLE VISION
 Normal binocular single vision (BSV) involves
the simultaneous use of both eyes with bifoveal
fixation, so that each eye contributes to a common
single perception of the object of regard.
 This represents the highest form of binocular
cooperation.

5. NORMAL BINOCULAR VISION

6. BSV

7. CORRESPONDING RETINAL POINTS
 Every retinal point or area has a
partner in the fellow retina with
which it shares relative subjective
visual direction.
 Image from each eye is
superimposed on each other in
occipital cortex to obtain
binocular single vision.

8. HOROPTER
 Imaginary plane in external space, relative to both the
observer's eyes for a given fixation target, all points on
which stimulate corresponding retinal elements and are
therefore seen singly and in the same plane.
 This plane passes through the intersection of the visual
axes and therefore includes the point of fixation in BSV.

10. PANUM’S FUSIONAL AREA
 The region around the horopter that’s allows single
vision.
 Object stimulates slightly non- corresponding points
 Objects are not only seen single, but are seen
stereoscopically.

11. PANNUM’S AREA

13. PHYSIOLOGICAL DIPLOPIA
 The diplopia elicited by an object off the Panum’s
fusional area

14. GRADES OF BSV
 1 – simultaneous perception
 2 - superimposition
 3 – flat fusion
 4 - Stereopsis

15. SIMULTANEOUS PERCEPTION
 Is the most elementary type of binocularity
 Occurs when the visual cortex perceives separate
stimuli from the two eyes at the same time and
concerns itself essentially with the absence of
suppression.

16.  The two different pictures are seen simultaneously in
the same direction
 Differing targets are the superimposed into one
2 - SUPERIMPOSITION

17.  Cortical unification of visual stimuli into a single percept
after simultaneous stimulation of corresponding retinal
areas.
 Ability of the two eye to produce a composite picture
from two similar pictures ,each of which is incomplete
in one small different detail.
 The objects must be similar in shape and size
3 – SENSORY FUSION

19. 4 - STEREOPSIS
 It is the ability to fuse images that stimulate horizontally
disparate retinal elements within Panum’s fusional area
resulting in binocular appreciation of visual object in
depth i.e. in the third dimension
 Stereopsis occurs when
 Retinal disparity is large enough for simple fusion but small
enough not to cause diplopia

21. ABNORMAL BINOCULAR VISION
 Sensory adaptation
 Confusion
 Diplopia
 Supression
 Ecccentric fixation
 Anomalous retinal correspondence (ARC)

22. CONFUSION
 Simultaneous appreciation of two superimposed but
dissimilar images caused by stimulation of
corresponding retinal points (usually the foveae) by
images of different objects .

23. CONFUSION

24. DIPLOPIA
 Simultaneous appreciation of two images of the
same object in different positions and results from
images of the same object falling on non-
corresponding retinal points.

25. DIPLOPIA
Diplopia. (A) Homonymous (uncrossed) diplopia in right esotropia with
normal retinal correspondence; (B) heteronymous (crossed) diplopia in
right exotropia with normal retinal correspondence

26. SUPPRESSION
 Cortical inhibition of visual sensation that originates
from spatially abnormal eye to eliminate the
problem of visual confusion and diplopia.
 Pathologic suppression results from strabismic
misalignment of the visual axis
 Physiologic suppression occur in eyes with BSV

27. PATIENT WITHOUT
SUPPRESSION

28. TYPES OF SUPPRESSION
 Central v/s peripheral
 Monocular v/s alternating
 Facultative v/s obligatory

29. TYPES OF SUPPRESSION
1 Central or peripheral.
 In central suppression the image from the fovea of the deviating eye is
inhibited to avoid confusion.
 Diplopia is eradicated by the process of peripheral suppression, in which
the image from the peripheral retina of the deviating eye is inhibited.
2 Monocular or alternating
 . Suppression is monocular when the image from the dominant eye
always predominates over the image from the deviating (or more
ametropic) eye, so that the image from the latter is constantly
suppressed. This type of suppression leads to amblyopia.
 When suppression alternates (switches from one eye to the other)
amblyopia is less likely to develop.
3 Facultative or obligatory.
 Facultative suppression occurs only when the eyes are misaligned eg-
intermittent exotropia.
 Obligatory suppression is present at all times, irrespective of whether the
eyes are deviated or straight.

30. ABNORMAL RETINAL
CORRESPONDENCE
 Describes a condition in which originally non-
corresponding retinal areas of the two eyes co-
operate to produce a form of binocular single vision.
 The fovea of the fixating eye acquired an
anomalous common visual direction with a
peripheral element in the deviating eye.

31. TYPES OF ARC
 HARMONIOUS (HARC) – if the angle of anomaly =
angle of strabismus
 UNHARMONIOUS (UN-HARC) – if angle of
anomaly is greater than zero but less than the
angle of deviation
 PARADOXICAL (PARC) – if angle of anomaly is in
the opposite direction

32. ECCENTRIC FIXATION
 The fovea has lost its principal visual direction
 Looking straight at an object stimulates non
foveolar retinal area
 Types
 Foveal off-center ---1 degree or less (> 0 degrees)
 Parafoveal---3 degrees or less (> 1 degree)
 Paramacular---5 degrees or less (> 3 degrees)
 Peripheral---Greater than 5 degrees

33. TESTS FOR SENSORY ANOMALIES
 Visual acuity
 Worth four dot test
 Bagolini’s test
 4 prism base out test
 Synaptophore
 After image test
 Visuoscopy
 Test for stereopsis

34. Visual acuity
Fixation behaviour test
 Test is performed by seating the child comfortably in
mothers lap
 Object, usually a bright colored toy is slowly moved to the
right and to the left.
 If the baby can hold fixation on the target and follow it
when the target moves, the visual acuity noted as fix and
follow behaviour.
 Each eye is tested separately.

35. CSM method rating monocular fixation
• Done with one eye fixating on a target (examiner’s light)
held at 40 cm (other eye occluded)
• Vision is noted as CSM if-
• C (central) –if each eye fixates centrally, the light
reflex is seen in the center of the pupil.
• S (steady) – holds steady fixation on the target when
it is moved.
• M (maintained)- continues to stay fixated on the target
even if occlusion is removed from the fellow eye.

36. 2 . Preferential looking test-
 Two fields are shown to infant ,one
has a striped pattern and the other
one is homogenous
 Examiner is hidden behind the
screen and is able to look through
a hole in the screen at the infants
eye.
 Infant tends to look more at the
striped pattern.
 It is 6/240 in newborn
6/60 at 3 months
6/6 at 36 months

37. Visually evoked response(VER)
 VER refers to electro-encephalographic
recordings made from the occipital lobe in
response to visual stimuli
 It tells about the integrity of macular & visual
pathway.
 Pattern reversal VER is recorded using
patterned stimulus as in checkerboard.
 Flash VER is recorded using flash light as
stimulus.
 It is 6/120 at 1 month
6/60 at 2 months
6/6-6/12 at 1 year

38. VISUAL ACUITY
 At age 2 years, picture naming test such as the
crowded Kay pictures
 At age 3 years, most children will be able to
undertake the matching of letter optotypes as in the
Keeler logMAR
 Older children –Snellen’s, LogMar chart

39. WORTH FOUR-DOT TEST
 a gross test which provides
information only about the status
of peripheral binocular
cooperation
 Can be used for distant and near
fixation.
 Harmonious ARC= 4 lights
(Deviation)
 2 lights (Left suppression)
 3 lights (right suppression
 5 lights (Diplopia)

40. BAGOLINI STRIATED GLASSES
 The Bagolini lenses have fine
barely visible striations, oriented
at 135 degrees before the right
eye and 45 degrees before the
left eye.
 Patient is askesd to fixate at
small light.
 Each eye perceives an oblique
line.

41. BAGOLINI STRIATED GLASSES
 If the two streaks intersect at
their centres in the form of an
oblique cross (an ‘X’), the patient
has BSV if the eyes are straight,
or harmonious ARC in the
presence of manifest strabismus.
 If the two lines are seen but they
do not form a cross, diplopia is
present.
 If only one streak is seen, there
is no simultaneous perception
and suppression is present.
 In theory, if a small gap is seen
in one of the streaks, a central
suppression scotoma

42. 4 PRISM BASE OUT TEST
 Usually determines
whether a patient has
bifoveal fixation or a
small suppression
scotoma.
 A 4 prism dioptre base
out prism is placed
infront of one eye & a
biphasic movement of
the fellow eye is noted.

43. 4 Δ prism test in bifoveal fixation. (A) Shift of both eyes away from the
prism base; (B) fusional refixation movement of the left eye
4 PRISM BASE OUT TEST

44. 4 PRISM BASE OUT TEST
4 Δ prism test in left microtropia with a central suppression
scotoma. (A) No movement of either eye; (B) both eyes move to
the left but there is absence of re-fixation

45.  an instrument for the
assessment of strabismus
and the grade of binocular
vision
SYNOPTOPHORE

47. AFTER-IMAGE METHOD (HERING-BEILSCHOWSKY
TEST)
 In clinical practice the test is performed by using a
battery-powered camera flash to produce a vertical
afterimage in one eye and a horizontal afterimage in the
other eye
 Resulting afterimage is that of a line with a break in its
middle, which represents the fovea

48. 4/6/2007
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HERING-BEILSCHOWSKY AFTER
IMAGE TEST

49.  The patient fixates steadily the central mark, first with
one eye while the slit is horizontal and then with the
other eye while the slit is vertical
 In a darkened room or with the eyes closed, the patient
sees the two successively imprinted as positive
afterimages (bright lines)
 In a lighted room or with the eyes open, negative
afterimages (dark lines) will be seen

50.  Then open eyes and look at a plain surface and see if
lines cross
 In NRC the after images will coincide
 In ARC the after images will be separated

52. 52
VISUOSCOPY
Test of eccentric fixation
Available in ophthalmoscope

53. 4/6/2007
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54. TESTS FOR STEREOPSIS
1. TITMUS STEREOTEST
 The Titmus test consists of a three-
dimensional Polaroid vectograph
consisting of two plates in the form of
a booklet viewed through Polaroid
spectacles.
 The test is performed at a distance
of 40 cm.
 Fly is a test of gross stereopsis
(3000 seconds of arc), and is
especially useful for young
children.
 The fly should appear to stand out
from the page and the child is
encouraged to pick up the tip of one
of its wings between finger and
thumb.
 In the absence of gross stereopsis
the fly will appear as an ordinary flat
photograph.
 .

55. 1. TITMUS STEREOTEST
 Circles comprise a graded series which tests
fine depth perception. Each of the nine squares
contains four circles.
 One of the circles in each square has a degree of
disparity and will appear forward of the plane of
reference in the presence of normal stereopsis. The
disparities measured range from 800 to 40 seconds
of arc.

56. 2. TNO RANDOM DOTS STEREOTEST
 The TNO random dot test consists of
seven plates of randomly distributed
paired red and green dots which are
viewed with complementary red-
green spectacles.
 Within each plate the dots of one
colour forming the target shape
(squares, crosses etc.) are displaced
horizontally in relation to their paired
dots of the other colour so that they
have a different retinal disparity from
those outside the target.
 Some control shapes are visible
even without red-green spectacles
while the test targets are only visible
to an individual with stereopsis, while
wearing red-green spectacles (Fig.
18.19B).

57. . TNO RANDOM DOTS STEREOTEST
• The first three plates are used to establish the
presence of stereoscopic vision and subsequent
plates to quantify it.
• Because there are no monocular clues, the
TNO test provides a truer positive measurement of
stereopsis than the Titmus test, but can give false
negative errors when fusion is poor.
• The disparities measured range from 480 to
15 seconds of arc tested at 40 cm.
 Most children are able to do this (and the Frisby
test) from about 4 years of age.

58. 3. LANG STEREOTEST
 Consists of card, approx.
the size of a average
post card in which random
dots are incorporated in
paragraph
 Cylindrical lenses
laminated onto the surface
of the card are used for
dissociation of the eyes

59.  Lang test

60. LANG STEREOTEST
 Displacement of the dots creates disparity and the
patient is asked to name or point to a simple shape,
such as a star, on the card
 The Lang test can often be used to assess
stereopsis in very young children and babies, who
may reach out to touch the pictures.

61. THANK YOU