Sensory evaluation of strabismus


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Sensory evaluation of strabismus

  1. 1. Review of BSV SENSORY EVALUATION OF STRABISMUS Gauri S. Shrestha, M.optom, Lecturer Deepa Dhungel, B.Optom II year
  2. 2. Normal Binocular Vision
  3. 3. • Monocular: 160°(w)X175°(h) • Binocular: 200° (w)X175°(h) • Region of binocular overlap: 120° (w)X135°(h)
  4. 4. visual field Prerequisite for BSV • Separate fields of vision must overlap in all direction of gazes. • Separate fields of fixation must overlap with coordinated movements of the two eyes. • Neural transmission from the two eyes must reach the same area of brain. • Perceptual co-ordination must take place.
  5. 5. Corresponding retinal points • Every retinal point or area has a partner in the fellow retina with which it shares relative subjective visual direction
  6. 6. Horopter • “Locus of all the object points that are imaged in corresponding retinal elements at a given fixation point”
  7. 7. 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.
  8. 8. Physiological diplopia • The diplopia elicited by an object off the Panum’s fusional area • Types – Crossed (heteronymous) diplopia – Uncrossed (homonymous) diplopia
  9. 9. Grades of BSV • 1 – simultaneous perception • 2 - superimposition • 3 – flat fusion • 4 - Stereopsis
  10. 10. Simultaneous perception • Is the most elementary type of binocularity • Occurs when the visual cortex perceives separate stimuli to the two eyes at the same time and concerns itself essentially with the absence of suppression.
  11. 11. • The two different pictures are seen simultaneously in the same direction • Differing targets are the superimposed into one 2 - superimposition
  12. 12. • Cortical unification of visual stimuli into a single percept after simultaneous stimulation of corresponding retinal areas. • The objects must be similar in shape and size 3 – flat fusion
  13. 13. 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
  14. 14. Abnormal binocular vision • Sensory adaptation – Confusion – Diplopia – Supression – Ecccentric fixation – Anomalous retinal correspondence (ARC) – Amblyopia
  15. 15. Diplopia /Confusion
  16. 16. Introduction - 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 axes • Physiologic suppression occur in eyes with BSV
  17. 17. Patient without suppression
  18. 18. Classification of suppression • Physiologic v/s Pathologic • Central v/s peripheral • Monocular v/s alternating • Facultative v/s obligatory
  19. 19. 3. ARC • Sensory anomaly where the fovea of the fixating eye and a non-foveal site of the deviating eye have a common visual direction • Objective angle(<H)– • Subjective angle(<S)– • Angle of anomaly (<A)
  20. 20. Types A= H-S • No anomaly • Harmonic ARC • Unharmonic ARC • Paradoxical ARC I & II
  21. 21. 4/6/2007 27 Types of ARC • Harmonious ARC; – Angle of anomaly(A)= objective angle (D) – (S)=0
  22. 22. 4/6/2007 28 • Unharmonious ARC – Subjective angle(S) is less than Obj angle but greater than zero. – Angle of anomaly not equal to the obj angle
  23. 23. Eccentric fixation • The fovea has lost its principal visual direction • Px reports that they are looking straight at an object stimulating 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
  24. 24. Tests for Sensory Anomalies
  25. 25. Worth Four-Dot Test • a gross test which provides information only about the status of peripheral binocular cooperation • Harmonious ARC= 4 lights (Deviation) • 2 lights (Left suppression) • 3 lights (right suppression • 5 lights (Diplopia)
  26. 26. 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
  27. 27. 4/6/2007 33 Bagolini striated glasses test NRC/ HAC UAC, Esotrope , UAC, Exotrope Vertical ARC
  28. 28. 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.
  29. 29. Vectographic tests • Polarised charts seen with polarising lenses • One eye sees half of the chart and the other sees the other half • Polamirror • Looking into the mirror while wearing polarising glasses • No suppression both eyes seen • With suppression only one eye seen
  30. 30. • an instrument for the assessment of strabismus and the grade of binocular vision Synoptophore
  31. 31. 4/6/2007 39 Vectographic slide • Subjective angle calculated and compared with objective angle
  32. 32. Binocular Perimetry and Haploscopy • use of one form of color differentiation, such as red-green spectacles • If left eye, provided with a green filter, fixates a green spot and right eye is provided with a red filter, a projected red light will be seen every where by the right eye except in the region of the scotomas.
  33. 33. Filter Bar Method • Patient fixates a spot of light • A filter bar (palest filter) is placed before the non- suppressing eye • the density of the filter is increased until two lights are seen • This filter is a measure of depth Fig: Red filter bar
  34. 34. 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
  35. 35. 4/6/2007 43 Hering-Beilschowsky After Image Test
  36. 36. • 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
  37. 37. • 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
  38. 38. 4. Red Filter/Diplopia Method • A spotlight is taken into account with both eyes open • A red filter before the strabismic eye and a vertical prism (6-15∆) before one eye to move the image out of the suppression area
  39. 39. • The patient should see one red and one white light • If vertically aligned but a strabismus is present = HRC • If separated, either NRC or UNRC
  40. 40. 5. Foveo-Foveal Test of Cu¨ppers • An asterisk is placed on the fovea of the deviated eye while the other eye fixates the light on a Maddox cross or tangent screen • If the fixation target appears to be superimposed on the central fixation light of the Maddox cross → normal retinal correspondence
  41. 41. • In the presence of anomalous correspondence foveae have different visual directions – The asterisk will be superimposed on one of the numbers on the horizontal bar of the Maddox scale – This number indicates the angle of anomaly in degrees
  42. 42. A,Schematic representation of the testing arrangement. B,Patient sees the asterisk superimposed on the central fixation light of the Maddox scale(NRC, normal retinal correspondence). C, The asterisk appears over the number 4 on the horizontal bar of the Madd scale
  43. 43. 4/6/2007 53 Visuoscopy Test of eccentric fixation Available in ophthalmoscope
  44. 44. 4/6/2007 54
  45. 45. Tests for stereopsis 1. Titmus stereotest • is a vectograph and uses Polaroid dissociation glasses
  46. 46. 2. TNO random dots stereotest • An anaglyph, dissociation is by color instead of Polaroid filters
  47. 47. • TNO Random Dot Test: – consists of seven plates, each of which contains various shapes Tests For Stereopsis:…
  48. 48. 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
  49. 49.  Lang test