1. Abnormal retinal correspondence and eccentric fixation
Rajeshwori Ngakhushi
2. Retinal Correspondence Retinal elements of the two eyes that
share a common subjective visual direction. All other retinal
elements are non- corresponding or disparate with respect to a
given retinal element in the fellow eye for a particular visual
direction.
3. Retinal correspondence is the inherent relationship between
paired retinal visual cells in the two eyes. Images from one object
stimulate both cells, which transmit the information to the brain,
permitting a single visual impression localized in the same
direction in space.
4. Specifically, the right nasal retina contains points that
correspond to their counterpart in the left temporal retina, and
vice versa. When stimulation of corresponding retinal points or
areas produces single vision, normal retinal correspondence is said
to be present.
5. Conversely, when stimulation of corresponding retinal points
produces diplopia OR when stimulation of noncorresponding retinal
points produces single vision, anomalous retinal correspondence is
present
6. Law of Sensory Correspondence It states that existence of
corresponding retinal elements with their common relative
subjective visual direction is the essence of binocular
vision.
7. Retinal Correspondence can be of two types: 1. Normal
Retinal Correspondence 2. Abnormal Retinal Correspondence
8. Normal Retinal Correspondence Retinal correspondence is
called normal when both the fovea have a common visual direction
and the retinal elements nasal to the fovea in one eye corresponds
to the retinal elements temporal to the fovea in the other
eye.
9. Abnormal Retinal Correspondence when the fovea of one eye
has a common visual direction with an extrafoveal area in the other
eye angle of squint is small and the extrafoveal point is close to
the fovea - to regain the binocular advantage, although
anomalous
10. This results in the eyes seeing binocularly single inspite
of a manifest squint. under binocular conditions the fovea and the
extafoveal point share the common subjective visual direction when
the normal eye is closed the extrafoveal element loses any
advantage over the fovea of that eye, which retains its primary
visual direction.
11. Concept of a Horopter From the Greek words horos (boundary)
and opter (observer). The term Horopter (the horizon of vision) was
introduced in 1613 by Aguilonius. locus of all object points that
are imaged on corresponding retinal elements at a given fixation
distance
12. Geometric Vieth Muller horopter According to this model of
horopter if corresponding points have a regular horizontal distance
from the retina the horopter would be a circle passing through the
center of rotation of the two eyes and the fixation point.
13. Empirical Horopter Curve slightly flatter than vieth muller
geometric horopter Hering-Hillebrand deviation - due to both neural
and optical factors - nasal hemi-retina at any given eccentricity
contains more photoreceptors per unit area than the temporal hemi
retina producing a deviation in the horopter mapping in the visual
cortex.
14. Panums Fusion Area Region in front and back of the horopter
in which single vision is present diplopia elicited by object
points off the horopter - Physiological diplopia
15. narrowest at the fixation point and becomes broader in the
periphery at a rate of 1-2 arc min per degree of visual field
eccentricity.
16. expands and contracts depending on the size, sharpness and
speed of the stimuli Panums area for the stimuli that are fuzzy and
slow moving is 20 times wider than it is for stimuli that are
sharply focused and rapidly moving.
17. Fusion Fusion is defined as the unification of visual
excitations from the corresponding retinal images into a single
visual percept. Sensory Fusion It is the ability to appreciate two
similar images, one with each eye and interpret them as one. Single
visual image is the hallmark of retinal
18. Motor Fusion It is the ability to align the eyes in such a
manner that sensory fusion can be maintained. The stimulus for
these fusional eye movements is retinal disparity outside panums
area and the eyes moving in opposite direction (vergence).
19. Diplopia simultaneous stimulation of non- corresponding or
disparate retinal elements by an object point causes this point to
be localized in two different subjective visual directions. Double
vision is the hallmark of retinal disparity.
20. Retinal Rivalry / Binocular Rivalry When dissimilar
contours are presented to corresponding retinal areas fusion
becomes impossible and retinal rivalry may be observed.
21. Simultaneous excitation of corresponding retinal areas by
dissimilar objects does not permit fusion and leads to
confusion
22. Test for Retinal Correspondence Clinically the tests used
can be based on either of the two principles: A) Assesment of
relationship between the fovea of the fixing eye and the retinal
area stimulated in the squinting eye. This includes: 1. Bagolini's
striated glasses test 2. red filter test 3. Synaptophore using SMP
slides for measuring the objective and subjective angles 4. Worth's
4 dot test
23. B) Assessment of the visual directions of the two foveas.
Included in this are: 1. After image test (Hering Bielschowsky) 2.
Cuppers binocular visuoscopy test (foveo-foveal test of
Cuppers)
24. 1. Bagolini's Striated Glasses Test patient fixates a small
light, after being provided with plano lenses with narrow fine
striations across one meridian (micro Maddox cylinders). lenses are
usually placed at 45 degree OS and 135 degree OD and the patient
fixates for distance or near.
25. The interpretation of this test is as follows- Crossing of
the lines at right angles to each other If cover test reveals no
shift and fixation is central, the patient has NRC If cover test
reveals a shift, harmonious ARC is present Single line represents
suppression
26. fixation light is seen as an elongated streak
27. 2. Red Filter Test place a red filter in front of the
habitually fixating eye while the patient is looking at a small
light source number of different responses can be elicited. patient
may report that two lights are seen, a red one and a white
one.
28. In esotropia the images appear in homonymous (uncrossed)
diplopia,
29. In exotropia the images appear in heteronymous (crossed)
diplopia This represents NRC.
30. patient may report that only one pinkish light in the
position of the white fixation light is seen This is clearly an
abnormal response in presence of heterophoria. This is termed
Harmonious ARC.
31. may report that the measured distance between the double
images proves to be smaller than expected from the magnitude of
deviation This represents unharmonious ARC.
32. 3. Measurement of Angle of Anomaly: The angle of anomaly
denotes the degree of shift in visual direction. It is determined
by calculating the difference between the objective and subjective
angles of deviation.
33. subjective angle of anomaly is the angle at which the
visual targets are superimposed. no further fixation movement of
the patients eye reading of both the arms is noted sum total of the
reading of both the arms gives the objective angle of anomaly SMP
slides is made arms of the synaptophore are set at zero moved by
the examiner while alternately flashing the light
34. The interpretation of this test is as follows- Angle of
Anomaly = Objective Angle Subjective Angle If Subjective Angle =
Objective Angle NRC If Subjective Angle < Objective Angle ARC If
Angle of Anomaly = Objective Angle Harmonious ARC (full sensory
adaptation) If Angle of Anomaly < Objective Angle Unharmonious
ARC
35. 4. Worth Four Dot Test: simple test utilizing red-green
color dissociation. consists of a box containing four panes of
glass, arranged in diamond formation, which are illuminated
internally. The two internal panes are green, the upper one is red
and lower one is white.
36. patient wears red and green goggles (as a convention red in
front of right and green in front of left). can be performed
separately for distance and near vision.
37. The interpretation of this test is as follows- four dots
normal binocular response with no manifest deviation (NRC with no
heterotropia) Harmonious ARC with manifest squint five dots
uncrossed diplopia with esotropia, red dots appear to the right
crossed diplopia with exotropia, red dots appear to the left of the
green dots 3 green dots suppression of right eye 2 red dots
suppression of left eye
38. 5. Hering Bielschowsky After- Image Test: highly
dissociating orthoptic test in which battery- powered camera flash
is used to produce a vertical after image in one eye and a
horizontal after image in the other eye. center of flash is covered
with a black mark (serves as a point of fixation and protects the
fovea).
39. Procedure Each eye fixates on the center black mark of a
glowing filament horizontally to the better eye vertically to the
poorer eye for 20 sec in a darkened room patient indicates the
relative position of the two gaps in the center of each afterimage
gaps correspond to the visual direction of each fovea if central
fixation is present.
40. Interpretation of results - Cross response: A symmetrical
cross with the central gaps superimposed indicates a normal
bifoveal correspondence. Asymmetrical crossing: In case of ARC the
horizontal and vertical lines have their center separated, the
amount of separation dependent on the angle of anomaly. Single line
with a gap: A single line with a gap indicates suppression in the
fellow
41. Displacement between the centres of the two after images is
proportional to the angle of anomaly Tan = dispalcement / distance
of testing
42. 6. Foveo-Foveal Test of Cuppers: Cuppers test for retinal
correspondence determines whether the two foveas have common or
different visual directions. It permits quantitative analysis of
the angle of anomaly when eccentric fixation is present.
43. Procedure - patient fixates with the normal eye on the
central light of a Maddox scale via a plano mirror the amblyopic
eye looks straight ahead visuoscope asterisk is projected onto the
fovea of the amblyopic eye figure of the Maddox scale on which the
patient sees the asterisk indicated the angle of anomaly.
44. Modification - To determine which parts of the peripheral
retina in the deviating eye have acquired a common visual direction
with the fovea of the fixating eye the patient is asked to guide
the Visuoscope until he sees the asterisk superimposed on the
central light of the Maddox
45. Abnormal retinal correspondence Abnormal retinal
correspondence is a physiological part of normal binocular vision
in many persons and is a natural accompaniment of the binocular
adjustment when the visual axes are not parallel in all positions.
It is a binocular condition and not a uniocular adaptation of
projection.
46. Anomalous retinal correspondence (ARC) is a neural
adaptation to eye misalignment in which non- corresponding retinal
points are linked in the visual cortex to provide binocular
fusion.
48. Requirements for ARC Early onset squint Constant angle of
deviation Small esodeviations
49. Classification (1) Harmonious ARC angle of anomaly is equal
to the objective angle of deviation ( subjective angle = o) This
indicates that the ARC fully corresponds to the strabismus.
provides a compensation for the angle of squint Eliminate the
awareness of diplopia and confusion
50. (2) Unharmonious ARC angle of anomaly is less than the
objective angle of deviation subjective angle 0 (3)Paradoxical,
when the angle of anomaly is greater than the objective angle of
deviation
51. Theory of ARC Linksz returned to the original rigid theory
(Muller and von Graefe) that normal correspondence is a strictly
anatomical fact based on an immutable connection between distinct
retinal and cortical areas ARC has been put forward as cause of
strabismus
52. Morgan proposed that some ocular movements are registered
in coordinating centers and some are not registered, depending on
whether they affect egocentric localization. He used this concept
to explain not only anomalous correspondence but also monocular
diplopia.
53. Advantages Avoids the necessity for dense amblyopia ( HRC )
Permits anomalous fusion range and some degree of stereopsis
Prevents consecutive divergence Allows a form of binocular
convergence to take place
54. Disadvantages Prevents the development of normal retinal
correspondence, true fusion and normal stereopsis Represents an
abnormal reflex development
55. Treatment Occlusion Preventive as well as curative measure
Prolonged alternating occlusion is not recommended - prevent
further development of ARC as well as normal correspondence
Exercises with major amblyoscope
56. Eccentric fixation A uniocular condition in which some part
of retina other than fovea is used for fixation, but in which the
fovea retains its normal straight ahead projection It may be
associated with a defect of central vision caused by a stuctural
lesion of fovea.
57. Eccentric fixation can be present during both monocular and
binocular viewing conditions, but it is best diagnosed under
monocular viewing conditions. This is important to keep in mind to
avoid confusion with anomalous correspondence. Anomalous
correspondence is relevant only during binocular fusion
58. Four Theories as to the cause of Eccentric 1. Fixation
Suppression Theory (Worth, 1906, Bangerter,1953) 2. Anomalous
correspondence theory (Chavasse, 1939, Cuppers, 1956) 3. Motor
theory (Schor, 1978) 4. Pickwell (1981)
59. Suppression Theory: occurs when central acuity has dropped
to a level below that of the surrounding area, so that better
acuity results now thought to be unlikely as foveal VA still seems
to be better than in the rest of the retina Strabismic patients
suppress to get rid of double vision
60. Anomalous correspondence theory a change in the central
area of localisation resulting from a central scotoma in the
amblyopic eye EF secondary to the development of ARC Major problem
with this theory is that the angle of anomaly is usually much
greater than angle of EF
61. Motor theory failure of the EOM to relax from the deviation
(in strabismus) . This is a likely cause as habitual strabismic
deviation causes an adaptive after-effect which modifies the
subsequent monocular localisation
62. Pickwell (1981) a sequel to an enlargement of Panums
fusional area following decompensated heterophoria at an early age
eventually leads to microtropia a loss of accurate
correspondence
63. In amblyopia reduced VA by one Snellen line per 0.5 degree
of eccentricity (very rough guide) EF = 100x displacement / testing
distance MAR = EF + 1 Total deviation = measured deviation + EF (
correction for the effects of EF)
64. Diagnostic testing methods 1. Corneal reflex test 2.
Ophthalmoscopic methods/Visuscope 3. Bjerrum Screen Method 4.
After-image Transfer Test 5. Haidingers Brushes 6. Maxwells spots
7. Projectoscope 8. Euthyscope
65. 9. Past pointing test 10. Angle kappa 11. Neutral density
filter 12. Speed of accommodation
66. 1. Corneal Reflex Test: comparing the position of corneal
reflection of pentorch in amblyopic eye with that of the fellow
eye. Relative displacement of reflex by 1mm would indicate the
eccentric fixation of 11(or20prism) approximately
67. 2. Ophthalmoscopic methods/Visuscope: Project the
ophthalmoscopic target onto the patients retina Dilated pupil may
be necessary With the fixating eye occluded the examiner observes
the amblyopic eye noting the point or area of retina upon which the
star is projected when the patient is attempting to look at the
star straight at it.
68. Visuoscopy Targets A. Propper ophthalmoscope B. Welch-Allyn
ophthalmoscope C. Keeler ophthalmoscope D. Determining location
& magnitude of EF using Welch-Allyn ophthalmoscope
69. 3. Bjerrum Screen Method In normal subjects the blind spot
is the same angular distance from fixation in both eyes. Plot the
blind spot carefully in both eyes and compare positions Degree of
eccentricity can be measured by the difference in angular distance
of blind spot from fixation in each eye Requires good
co-operation
70. 4. After-image Transfer Test After images are transferred
to normally corresponding points in the other eye. photography
flashgun that is masked to provide a very bright strip of light
occlude amblyopic eye and Pt fixates the centre of the strip flash
then produces a central after- image
71. occluder is then changed to the good eye and Pt looks at a
small fixation target the after image then appears after a few
seconds (transferred at cortical level) Pt is then asked to locate
position of after-image in relation to the fixation point. If it
appears at one side of the letter = EF
72. 5. Haidingers Brushes an entoptic phenomenon due to
characteristics of the central fovea area seen with a brightly
illuminated blue polarised field when the direction of the
polarisation is rotated looks like two darkened and opposing
sections rotating in the central field
73. The direction and magnitude of EF can be assessed by asking
the px to report the location of Propeller in relation to fixation
point Practitioner can measure distance between these two points
and convert mm dispalcement to PD.eg at 1 meter,10 mm=1 PD,at 40
cm,4mm=1 PD.
74. 6. Maxwells spot Entopic phenomenon caused by the radial
orientation of the yellow pigment xanthophyll in the macula
Orientation of the macular pigment acts like a polarizing filter It
absorbs blue light & transmits red & yellow light
75. When the pt. looks at a rotating disc which is white on one
half & purple on the other, a red spot is seen This corresponds
to the macula with fovea in the center. In patients with EF, Red
spot will not be at the center of the disc
76. 7. Projectoscope Modified keeler opthalmoscope which may be
used for diagnosis and treatment. The Nut Auto-disc is provided
with three graticules. Stage 1: Localisation of the fovea With the
Auto-disc position 1 The linksz star in green light may be focused
on the retina and accurately placed on the patients fovea.
77. Stage 2: Dazziling the extra macular retina With the
Auto-disc position 2 By pressing the trigger on the projectoscope
the second graticule consisting of a 3 or 5 black spot
78. Stage 3: Foveal stimulation by flashing light With the
Auto-disc position 3 The 3 black spot is automatically replaced by
a disc of white light, whilst the extra macular retina is projected
by a green filtered light
79. 8. Euthyscope: modified opthalmoscope by cuppers beam of
light illuminates an area of approximately 30 at the posterior pole
of the eye. green filter is incorporated and also two black discs
of 5 and 3 diameter which can be placed in the centre of the beam
of the light.
80. light allowed to stimulate the circular paramacular zone
for 20 to 30 seconds. instructed to look through one of the
instrument incorporating haidingers brushes encouraged to find the
brushes within the clear centre of the after image.
81. 9. Past Pointing Test Related to localisation Occlude
amblyopic eye, hold pen 25cm in front and ask patient to touch pen
with the tip of their finger If finger goes a few cm to the side
then past pointing has been demonstrated This result indicates that
fixation does not coincide with the centre of localisation
82. 10. Angle kappa Angle Kappa- Worth Test Compare angle
lambda of each eye under monocular conditions Any difference
associated with reduced acuity indicate EF 1 mm of displacement =
22 pd
83. 11. Neutral density Filters If a ND filter is added and no
reduction in VA occurs then EF is likely to be present 12. Speed of
Accommodation Much slower in EF (?also in other amblyopes)
84. Treatment The principles of treatment were those used to
restore the normal sensory relationship of the two retinae.
encourage foveal fixation Refractive Error Correction, especially
in high anisometropia.
85. Inverse occlusion Infants with eccentric fixation who are
too young for treatment with Haidingers brushes Continued as long
as improvement is made Rarely suitable in adult eccentric fixation
is too firmly established
86. Red filter 600 640 nm Only stimulate cones Patient will
attempt to fix with area of the retina which contains maximum no of
cones
87. Pleoptics Therapy Pleos=full,optikos=sight Aim is to
actively stimulate macula in dense amblyopia with eccentric
fixation Two methods,either Bangerter or Cupper
88. Bangerters method Bangerter dazzled the extramacular retina
including the eccentric point by bright light protecting the macula
by a disc projected onto it. It was followed by intermittent
stimulation of macula with flashes of light Performed by modified
Gullstrands Ophthalmoscope,called as Pleoptophore.
89. Cuppers method Cupper used Euthyscope which had discs of
varying sizes to create a central after image apart from dazzling
the eccentric point He used the alternate flashing of room
illumination(Alternascope) to perpetuate the after images(forming
negative after image in light and positive after image in dark)
patient perceives an afterimage resembling the white doughnut
90. Treat underlying amblyopia by occlusion of non-squinting
eye (if patient 6 years correct refractive error, otherwise do not
treat the microtropia. Surgery is not appropriate
91. Refrences Lyle and Jacksons Practical orthoptics in the
treatment of squint Strabismus simplified, Pradip Sharma Binocular
single vision and ocular motility, Von Noorden Previous
presentations internet