1. 1. Abnormal retinal correspondence and eccentric fixation Rajeshwori Ngakhushi
2. 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. 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. 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. 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. 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. 7. Retinal Correspondence can be of two types: 1. Normal Retinal Correspondence 2. Abnormal Retinal Correspondence
8. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 20. Retinal Rivalry / Binocular Rivalry When dissimilar contours are presented to corresponding retinal areas fusion becomes impossible and retinal rivalry may be observed.
21. 21. Simultaneous excitation of corresponding retinal areas by dissimilar objects does not permit fusion and leads to confusion
22. 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. 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. 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. 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. 26. fixation light is seen as an elongated streak
27. 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. 28. In esotropia the images appear in homonymous (uncrossed) diplopia,
29. 29. In exotropia the images appear in heteronymous (crossed) diplopia This represents NRC.
30. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 41. Displacement between the centres of the two after images is proportional to the angle of anomaly Tan = dispalcement / distance of testing
42. 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. 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. 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. 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. 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.
47. 47. Variety of descriptive terms Anomalous correspondence Anomalous projection False associated fixation Positive secondary retinal correspondence False projection Retinal incongruity False macula Anomalous binocular junction
48. 48. Requirements for ARC Early onset squint Constant angle of deviation Small esodeviations
49. 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. 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. 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. 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. 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. 54. Disadvantages Prevents the development of normal retinal correspondence, true fusion and normal stereopsis Represents an abnormal reflex development
55. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 65. 9. Past pointing test 10. Angle kappa 11. Neutral density filter 12. Speed of accommodation
66. 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. 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. 68. Visuoscopy Targets A. Propper ophthalmoscope B. Welch-Allyn ophthalmoscope C. Keeler ophthalmoscope D. Determining location & magnitude of EF using Welch-Allyn ophthalmoscope
69. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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