3 Tests for Binocular Single Vision
- 3. Tests for BSV Contents Worth Four dot/light test Bagolini glasses 4 Prsim diopter test Lang two pencil test Titmus Fly test TNO test After image test
- 4. Worth Four Lights This is a dissociation test which can be used with both distance & near fixation to differentiate b/w BSV, ARC & suppression. Results can only be interpreted if the presence or absence of a manifest squint is known at time of testing.
- 6. Worth Four Lights Apparatus:It consist of four circular lights two green one red and one white which are viewed through complementary red and green goggles. The red light is seen through the red filter and the green lights through the green filter, the white light is common to both eyes.
- 7. Worth Four Lights Procedure: A patient wears a red green goggles with the red lens in front of the right eye , which filters out all colors except red ,and a green lens in front of the left eye, which filter out all colors except green . The patient then views a box with four lights, one red, two green and one white.
- 8. Worth Four Lights Results If BSV is present all four lights are seen If all four lights are seen in the presence of a manifest strabismus, ARC If two red lights are seen , left suppression is present If three green lights are seen, right suppression is present If two red and three green lights are seen, diplopia is present
- 9. Worth Four Lights If the red and green lights are seen alternatively, alternating suppression is present If the patient sees 2 or 3 lights at 6m & 4 lights at 0.33m- the diagnosis is microtropia.
- 11. Bagolini Striated Glasses This is the test for detecting BSV, ARC 0r suppression. The test can be used at 6m, 33cm or in any desired gaze position,e.g. in up & down gaze in A-& V- patterns. The apparatus consists of a pair of Plano glasses, marked with fine parallel striations at 45° on one glass & 135° on the other. When a spot light is viewed through the glasses each produces a line image at 90°to the axis of the striation.
- 13. Bagolini Striated Glasses Procedure : The two lenses are placed at 45°& 135°in front of each eye & patient fixates a small light source Each eye perceives an oblique line of light, perpendicular to that perceived by the fellow eye Dissimilar images are thus presented to each eye under binocular viewing conditions.
- 14. Bagolini Striated Glasses Results: If the two streaks intersects at their centers in the form of an oblique cross the patient has straight eyes with BSV or squint with ARC If the lines do not cross in center ,the patient has squint with NRC and diplopia If only one streak is seen ,there is no simultaneous perception and suppression is present
- 15. Bagolini Striated Glasses If a small gap is seen in one of the streaks, a central suppression scotoma (as found in microtropia) is present but in practice this is often difficult to demonstrate & the patient describes a cross. This scotoma can be confirmed with the 4Δtest If only one line is seen, large regional suppression is present.
- 17. 4Δ prism test This test differentiates bifoveal fixation (normal BSV) from a central suppression scotoma Method of use: Place a prism base –out in front of one eye whilst the patient fixate a near target, observe the movements. Now repeat the test with the base-out prism in front of the other eye & observe the movement, in order to confirm the findings.
- 19. 4Δ prism test Results : 1. In the presence of bifoveal fixation: the eye behind the prism make an inward movement to regain foveal fixation The other eye will make a conjugate outward movement (Herings’law) resulting in diplopia,which stimulates convergence to regain fusion.
- 20. 4Δ prism test 2. In left microtropia with CSS: The patient fixates a distance target with eyes open and a 4Δ prism is placed base out in front of the left eye with suspected central suppression scotoma scotoma. The image is moved temporally in the left eye but falls within the CSS & no movement of either eye observed.
- 21. 4Δ prism test The prism is then moved to the right eye which adducts to maintain fixation : the left eye similarly moves to the left (Herring's), but the second image falls within the CSS and no refixation movement is seen.
- 23. Tests for stereopsis Qualitative test: Lang two pencil test; This is a rudimentary test for the presence of stereopsis which compares the patient’s responses with both eyes open & with one eye covered, both in manifest strabismus to assess if abnormal BSV is present & in apparently straight eyes when it can confirm the presence of BSV. It is a very simple test requiring only two pencils & a cover.
- 25. Lang two pencil test Method of use: The patient is given a pencil to hold vertically & is asked to place this on top of the examiner’s vertically held pencil, thus using horizontal disparity detectors to locate the correct position. The test is then repeated with one eye occluded (the deviating or amblyopic eye if present).
- 26. Lang two pencil test The subject is not given too long to perform the test so that he does not use any monocular or motion clues to depth. The test is repeated several times & the responses compared.
- 27. Lang two pencil test Results : If accuracy in locating the examiner’s pencil is repeatedly better with both eyes open then stereopsis is present thus confirming normal or abnormal BSV If the response is comparable with both eyes open & with the squinting eye covered, the squinting eye is suppressed & BSV is absent.
- 28. Lang two pencil test A person with suppression may perform this test in both monocular & binocular conditions. A person with ARC passes this test only under binocular condition.
- 29. Tests for stereopsis Quantitative tests: TNO test: The TNO random dot test consists of seven plates of randomly distributed paired red & green dots which are viewed with complementary red & green goggles.
- 31. TNO test Within each plate the dots of one color forming the target shape are displaced horizontally in relation to their paired dots of other color so that they have a different retinal disparity from those outside the target.
- 32. TNO test 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. The first plate contains two butterflies,the second plate contains four circles,& the third five different shapes; each plate has at least one image which can be appreciated monocularly. There is a suppression test plate with three circles.
- 33. TNO test The first three plates are used to establish the presence of stereoscopic vision & subsequent plates to quantify it. Because there is no monocular clues , the TNO test provides a true positive measurement of stereopsis than the Titmus test, but can give the false negative errors when fusion is poor.
- 34. TNO test The disparities measured range from 480 to 15 seconds of arc tested at 40cm. Most children are able to do this test from the age of about 4 years. Method of use: The red-green spectacles are worn & the apparatus is held at 40cm perpendicular to the patient.
- 35. TNO test The screening plates subtending 980 seconds of arc are shown first, & if these are successfully completed the graded plates from 480 to 15 seconds of arc are presented until the patient is unable to locate the three-dimensional shape correctly. If the screening plates are not appreciated the response can be checked with the suppression plate, which consists of three circles, the middle one being common to both eyes.
- 36. Frisby The Frisby stereo test consists of three transparent plastic plates of varying thickness. On the surface of each plate are printed four squares of small randomly distributed shapes. One of the squares contains a hidden circle,in which the random shapes are printed on the reverse of the plate. The patient is required to identify this hidden circle.
- 38. Frisby The test does not require special spectacles because the disparity is created by the thickness of the plate & can be varied by increasing or decreasing the working distance ,which needs to be accurately measured. The disparities measured range from 600 to 15 seconds of arc. Is is important not to allow the subject to tilt the plate or move their head during testing as this gives monocular clues.
- 39. Lang stereo test This test combines panography with random dots. The targets are fine vertical section that are seen alternatively by each eye as they are viewed through the built in cylindrical lens elements,& does not require special spectacles. Displacement of the random dots creates the disparity.
- 40. Lang stereo test The test comes in two versions: Lang I,with a disparity range of 12oo-550 seconds of arc;& Lang II, with a disparity range of 600-200 seconds of arc. Method of use: The card is held at normal reading distance & the child is asked to name or point to the pictures.on the Lang II test a star can be seen monocularly.
- 42. Lang stereo test The examiner can also observe the child’s eye movements from picture to picture on the card. However ,the card must be held exactly parallel to the plane of the face for the effect to be seen.
- 43. Wirt or Titmus test Three dimensional Polaroid vectograph consisting of two plates in the form of a booklet viewed through Polaroid spectacles. On the right is a large fly & on the left is a set of circles & animals, one of which is disparate in each set. The image seen by one eye is polarized at 90° to that seen by the other eye when viewed through the polarized spectacles.
- 44. Wirt or Titmus fly test
- 45. Wirt or Titmus test The test gives monocular clues, especially when viewing the first three sets of circles, when it is easy to see monocularly that one circle is displaced & therefore different from the others. The test is performed at a distance of 40cm.
- 46. Wirt or Titmus test If only gross stereopsis is demonstrated the apparatus should be turned through 90°, when there is no depth effect, or one eye occluded & the response compared.
- 47. Wirt or Titmus test 1. Fly is test of gross stereopsis (3000 seconds of arc), & is especially useful for young children. The fly should appear to stand out from the page & the child is encouraged to pick up the tip of one of its wings b/w finger & thumb. In the absence of gross stereopsis the fly will appear as an ordinary flat photograph.
- 48. Wirt or Titmus test If the book is inverted,the targets will appear to be behind the plane of the page. If the patient states that the fly’s wings are still ‘popping out’,then they are not appreciating true stereoscopic vision.
- 49. Wirt or Titmus test 2. Circles comprise of 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 & will appear forward of the plane of reference in the presence of normal stereopsis.
- 50. Wirt or Titmus test The disparity measured range from 800 to 40 seconds of arc. If the patient perceives the circle to be shifted to the side , then they are not appreciating stereoscopic vision, but are using monocular clues instead. The animals are similar to the circles test but consist of three rows of five animals each, one of which will appear forward of the plane of reference. The degree of disparity ranges from 400 to 100 seconds of arc.
- 51. After-image test Hand held apparatus: The apparatus consists of a linear light with a central black band within a circular background mounted on a flash apparatus. The line can be presented horizontally or vertically.
- 52. After-image test Method of use: The patient must have steady foveal fixation. The deviating eye is covered & the line is presented horizontally at a distance of approximately 50cm. The apparatus is flashed while the patient fixates the black band.
- 53. After-image test The fixating eye is then covered & the process is then repeated with the line presented vertically. A vertical line is more likely to fall outside the suppression scotoma. The patient looks at a blank wall in normal illumination and should see two negative linear after images each with a central gap corresponding to the fixation and therefore representing the visual direction of the fovea.
- 54. After-image test He is asked to draw or describe the position of the lines. blinking may aid appreciation of the images. Alternatively the position of positive after- images can be assessed in a dark room.
- 55. After-image test Results A symmetrical cross with coincident gaps indicates normal retinal correspondence Displacement of the lines indicates abnormal retinal correspondence the separation between the gaps is determined by the size of the angle of anomaly there will be crossed projection in esotropia If eccentric fixation is present the results will need to be assessed accordingly a symmetrical cross would then indicate ARC.
- 56. After-image test
- 57. References Diagnosis & management of ocular motility disorders Strabismus & pediatric ophthalmology by American academy of ophthalmology