Kinetic vs static & automated

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  • 1. Junu Shrestha B. Optom 3rd year MMC, IOM Moderator Sanjeev Bhattarai 5/3/2014 1
  • 2. Contents • Introduction • Kinetic vs. static perimetry • Basis of perimetry • Goldmann Perimetry • Automated perimetry 5/3/2014 2
  • 3. Introduction • The term "visual field" refers to the sum total of visual perception for an eye fixed on a stationary object of regard with the head and body held fixed in position. 5/3/2014 3
  • 4. 5/3/2014 4
  • 5. • Traquair defined visual field as island of vision in the sea of darkness. • Hill of vision is a 3D representation of the retinal light sensitivity • Sea represents the areas of no light perception • Under photopic condition, the shape of hill of vision is closely related to the packing density of the cones and receptive field size. 5/3/2014 5
  • 6. • At 31.5 asb background luminance, fovea - highest sensitivity and is able to detect both the dimmest smallest targets. • Sensitivity drops rapidly between the fovea and 3º decreases gradually out to 30º, and then drops off more rapidly again beyond 50º 5/3/2014 6
  • 7. 5/3/2014 7
  • 8. • Reduction in light sensitivity evenly across the visual field, causes generalised reduction in the height of the hill of vision – DEPRESSION • Reduction in circumference of the island of vision or the peripheral margin of visual field – CONTRACTION • Non uniform reduction in light sensitivity in the visual field – FOCAL LOSS 5/3/2014 8
  • 9. • An area of reduced light sensitivity surrounded by an area of normal sensitivity – RELATIVE SCOTOMA • An area of no light perception surrounded by normal sensitivity – ABSOLUTE SCOTOMA 5/3/2014 9
  • 10. Perimetry • Is a subjective examination method for estimating the extent of visual fields • A decisive diagnostic technique for recognizing disturbance of visual function/ functional loss of vision 5/3/2014 10
  • 11. • Standard unit of measurement differential light sensitivity (DLS). • the threshold of perception of a test object, relative to its background (aka surround). 5/3/2014 11
  • 12. 5/3/2014 12
  • 13. Perimetry are based on: Weber’s law/ Weber-Fencher Fraction I = K I The luminance difference necessary for threshold stimulation increases linearly with the luminance of the surroundings or the adaption. Applied to the area of photopic adaptation in which standard clinical perimetry is based. 5/3/2014 13
  • 14. Bloch’s law: Temporal summation Within sufficiently short intervals (<100msec)the visual system summates brightness information in such a way that stimulus duration and stimulus intensity are reciprocally proportional to each other. T X I = K A target has to be presented for at least msec in order for the measured threshold or sensitivity values to be independent of the duration of target presentation. 5/3/2014 14
  • 15. Ricco’s and Piper’s law: Spatial summation √(A X I) = K The square root of the product of area of target and stimulus intensity is constant. Important when conversion of stimuli of definite area and luminosity into equivalent stimuli of different area or luminosity. An increase of 0.5 log unit intensity produce the same increase in field size as an increase of 0.6 log unit area. 5/3/2014 15
  • 16. Measuring d.l. sensitivity • Decibel is a negative logarithmic unit of attenuation which is used in perimetry for scaling differential light sensitivity. • E(dB)= 10 log Lmax • Apostilb is the unit of light intensity, whereas the dB is the unit of retinal sensitivity. • Apostilb and the dB are inversely proportional to each other. Higher the apostilb value, lower will be the dB value. L 5/3/2014 16
  • 17. • Threshold : the minimum light energy necessary to evoke a visual response with a probability of 0.5, i.e. the observer can detect the stimulus 50% of the time it is presented. • Infrathreshold: a light stimulus presented below the threshold, not detected by the observer. • Suprathreshold: stimulus intensity above threshold which will be detected by the observer. 5/3/2014 17
  • 18. • Threshold is recorded in terms of sensitivity which is reciprocal of threshold. Sensitivity is presented in decibel(dB) • Higher the decibel value, higher the retinal sensitivity. 5/3/2014 18
  • 19. Shows a plot of stimulus intensity against the percentage of “point seen”. Threshold is the intensity with probability of 50% detection5/3/2014 19
  • 20. Visual field testing Visual field screening Confrontation visual field testing Qualitative or diagnostic visual field testing Quantitative field testing Fully quantifies a known or suspected VF defect so that future changes in the defect can be detected. More sensitive to visual field loss Determine the characteristics of a VF defect s/a the location, border, shape, size or whether the field is homonymous 5/3/2014 20
  • 21. When to do perimetry? • To find out the extent of VF • To diagnose and detect diseases as well as extent of damage caused in VF by the disease • To find out the progression of diseases • To locate the possible lesion in neurological disorder5/3/2014 21
  • 22. Kinetic vs. static perimetry 5/3/2014 22
  • 23. Kinetic perimetry • A stimulus of known luminance is placed in an unseen area(outside the border of hill of vision) and moved towards seen area to find the local threshold • Generally performed centripetally • The hill of vision is found by approaching it horizontally 5/3/2014 23
  • 24. • All the locations where the stimulus is first seen have equal sensitivity, these locations can be connected to form a ring shaped locus of points- ISOPTER 5/3/2014 24
  • 25. Static perimetry • A stimulus is presented at a known location for a known duration with varying luminance to find local threshold • The stimulus is not moved as in kinetic perimetry 5/3/2014 25
  • 26. • The threshold is determined exactly by increasing the luminance of an infrathreshold target as well as by decreasing the luminance of a suprathreshold targets, until the threshold has been defined. 5/3/2014 26
  • 27. Static suprathreshold perimetry Static threshold perimetry Suprathreshold stimuli are presented rapidly in a random order at various preselected locations in the visual field. The stimulus are presented twice if missed on the 1st presentation Relative defect and if again missed , the brightest stimulus is presented (if missed) Absolute defect For glaucoma screening, neurological and retinal visual field loss The sensitivity at each test point is determined by a bracketting technique 3 to 5 stimulus presentation for each normal point tested. Indicated when a known or suspected visual field defect must follow with time to detect progression or regression. 5/3/2014 27
  • 28. Comparing kinetic and static perimetry • Principle differences (in the ability to detect VF changes) • The kinetic examination with moving test objects allows us to detect steep gradients or circumscribed scotomas especially well. • The static perimetry where the test target is stationary is a method especially suited to detect field defects with a flat gradient. Eg . Circumscribed flat scotomas or a generalised depression of d. l. sensitivity 5/3/2014 28
  • 29. Eccentricity E d.Lsensitivity d.Lsensitivity Eccentricity 5/3/2014 29
  • 30. • If we find a steep slope in the visual field the kinetic principle with horizontal motion toward the hill of vision or toward the margins of the scotoma will provide a much sharper and well delineated threshold than the vertical approach. • If the slope is flat and if there is only a slightly inclined nearly horizontal gradient, the static method with vertical approach will be superior to the kinetic method. 5/3/2014 30
  • 31. • The physiologic distribution of differential light sensitivity with a relatively flat slope in the paracentral area and in the mid periphery make the static principle for central VF the method of choice. • Similarly, the steep gradients of the peripheral VF make the kinetic principle superior to the static one. 5/3/2014 31
  • 32. Kinetic perimetry Static perimetry Measures the extent of visual field by plotting the isopters Measures the sensitivity of each retinal points Stimulus moves from non seeing to seeing area Stimulus is stationary but increases in luminance until seen Stimulus size can be varied Constant 2D measurement of hill of vision 3D assessment of height of predetermined areas of hill of vision 5/3/2014 32
  • 33. Kinetic perimetry Static perimetry Results depend upon the experience of the operators Though it depends but has very little role of the operator Can rapidly evaluate the peripheral VF, plot deep defects. Can accurately plot steep bordered defects and useful for localization, characterization of neurological defects It has ability to detect scotomas, particularly small, shallow, or fluctuating scotomas but cannot correctly outline the border of the defect Eg. Confrontation perimeter, tangent perimeter, Arc perimeter, Goldmann perimeter Eg. Automated perimeter, Goldmann perimeter 5/3/2014 33
  • 34. • A moving stimulus will be detected more readily in the periphery than a static stimulus because of successive lateral spatial summation. • As the stimulus moves across the visual field, spatial summation of receptive fields adjacent to the receptive field over which the stimulus is placed occurs. 5/3/2014 34
  • 35. • Thus, the detection of the stimulus will be influenced by normal areas of visual field, in addition to any damaged areas, which could lead to shallow focal loss in the visual field being missed. • Also the position of the isopter is dependent upon the patient’s reaction time to the detection of the stimulus and addditionally the reaction time of the examiner in responding to the patient’s response. 5/3/2014 35
  • 36. Indications of perimetry • presence of RAPD • reductions in visual acuity that cannot be improved with a pinhole aperture, stenopaic slit, or refractive correction • visual disturbances of unknown cause including desaturation of color perception, • subjectively reduced brightness perception, disturbances of orientation • selfperception of visual field defects on the part of the patient. 5/3/2014 36
  • 37. Choices of perimetry Manual perimetry 1. Inattentive patients who do not maintain fixation well 2. Defects extending outside the central 30° 3. Residual islands of vision 4. Functional visual loss Automated perimetry 1. Subtle relative defects in central or paracentral vision 2. Sequential monitoring 5/3/2014 37
  • 38. Goldmann perimetry • Is the most common device providing standardised manual exploration of the peripheral field. • Presents targets on a bowl set 33cm away from the cornea of the patient, with a background illumination of 31.5 apostilbs or 10 cd/sq.m. • Both kinetic and static method 5/3/2014 38
  • 39. 5/3/2014 39
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  • 41. Automated perimetry • Is merely a computer assisted examination (and not a fully automatic test) since the results depend on the patient’s collaboration and the accuracy of the answers. • Field testing strategy mainly static field testing • Test target is placed at a preselected field position, and is gradually raised until the patient detects it. • The output is in the form of grayscale with the darkness of shading corresponding to decreased sensitivity in the field. 5/3/2014 41
  • 42. OCTOPUS 300 HUMPHREY 700 BOWL TYPE Direct projection A spherical bowl (1/3m) Background luminance 31.4 asb 31.5 asb Stimulus size Goldmann III and V Goldmann I-V Duration 100ms 200ms Luminance for 0 dB 4800asb 10000asb Measuring range 0 – 40 dB 0-40dB Test strategies 4-2-1dB bracketting Dynamic strategy TOP 4-2dB bracketting SITA Normal SITA Fast Normal values Age correction per yr of age 5/3/2014 42
  • 43. Measurement strategies • The method to determine the differential light sensitivity is called test strategy. Normal testing strategy/4-2 dB bracketting • Dynamic strategy Tendency oriented perimetry • SITA (Swedish Interactive Threshold Algorithm) 5/3/2014 43
  • 44. Normal test strategy/4-2 dB bracketting in HFA • The stimulus luminance is varied up and down in steps. • Testing starts in 4 primary anchor points at NV- 4dB, followed by increase in luminance. 5/3/2014 44
  • 45. • Is capable of detecting shallow pathological depressions in eyes that are supersensitive • Takes 12 to 18 minutes. 5/3/2014 45
  • 46. Dynamic Strategy • The step sizes adapt to the slope of the FOSC (frequency of seeing curve) • With increasing depth of a defect, the stimulus luminance step size increases from 2dB(near normal values) to 10 dB (towards the most depressed levels). • The final measured value is calculated as the mean between the two last stimuli. • About 40-50% reduction in testing time. 5/3/2014 46
  • 47. • Smaller steps near normal sensitivity where FOSC is steep • Larger steps when the FOSC is wider (defective) dBdB 5/3/2014 47
  • 48. Tendency Oriented Perimetry • The threshold values of neighbouring locations are correlated. The anatomical and topographical interdependence of visual field defects establishes a tendency between the thresholds of neighbouring zones. TOP utilises it by bracketting method of d. l. sensitivity detection • Assess the thresholds of neighbouring points by interpolation 5/3/2014 48
  • 49. • The field test location is divided into a network of four evenly intermingled grids. 5/3/2014 49
  • 50. SITA (Swedish Interactive Threshold Algorithm) • Adapts the stimulus presentation speed to the reaction times of the patient, which in most cases reduces test times further. • Uses Bayesian probability which can make predictions about the nature of the threshold. • Estimated threshold + statistical analyses from probability =Maximum Posterior Estimate • SITA Standard • SITA Fast 5/3/2014 50
  • 52. Examination program in OCTOPUS G1/G2 • Central 30 degree, 59 test locations • Glaucoma screening special attention to para- central and nasalstep with resolution of 2.8 deg 5/3/2014 52
  • 53. Program 32 • General threshold examination • Maximum test location is 76 (spaced in an equidistant grid pattern with 6 deg resolution) 5/3/2014 53
  • 54. Macula M1/M2 • Covers central 10 deg VF • M1- 56 test locations in an equidistant grid pattern with a spacing of 2 deg • M2- 45 test locations in central 4 deg area 0.7 deg spacing 5/3/2014 54
  • 55. HUMPHREY ZONE SCREENING THRESHOLD TEST AREA OF FIELD COVERED CENTRAL FIELD ONLY Central 40 pt or Central 80pt Central 76pt or Central 166pt Macula Central 10-2 Central 24-1 Central 24-2 Central 30-1 Central 30-2 0-4° 0-10° 0-24° 0-24° 0-30° 0-30° PERIPHERAL FIELD ONLY Peripheral 68 pt Peripheral 30/60-1 Peripheral 30/60-2 30-60° 30-60° 5/3/2014 55
  • 56. ZONE SCREENING TEST AREA OF FIELD COVERED FULL FIELD Full field 120 pt Full field 246 pt 0-60° 0-60° 5/3/2014 56
  • 57. Special designs ZONE SCREENING TEST THRESHOLD TEST AREA OF FIELD COVERED GLAUCOMA/ OPTIC NEUROPATHY Armaly central Armaly full field Nasal step Nasal step 0-15° plus nasal wedge to 25° 0-15° plus nasal wedge to 60° Nasal field only 30- 50° NEUROLOGIC Temporal crescent Neurologic 20 Neurologic 50 Temporal field only 60-80° Vertical meridian only, 0-20° Vertical meridian only, 0-50° 5/3/2014 57
  • 58. PROGRAM CHOICE: ZONE OF TARGET PRESENTATION Central zone: • common region to test is the central 30° or the central 24°(glaucoma) • Threshold menu offers two versions marked by the suffixes -1 and -2. • Both space their locations 6° apart • -1 versions start their points on the horizontal and vertical meridians • -2 versions place test locations flanking the meridians (better suited for determining nasal and hemianopic steps) 5/3/2014 58
  • 59. Peripheral zone: • Mapping of the field only between 30 and 60° • To supplement central field examination when a more extensive defect is suspected. • It is seldom used, because such defects are better diverted to Goldmann perimetry. 5/3/2014 59
  • 60. Full field: • The full-field 120-point screen is the most commonly used. • Take longer time 5/3/2014 60
  • 61. 5/3/2014 61
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  • 63. Reliability parameters • Fixation losses • False positive error • False negative error 5/3/2014 63
  • 64. Fixation losses • There is a video system to project an image of the eye on monitor. • Perimetrist should detect fixation shifts and faulty head positioning Observation by perimetrist (manual) • Either signals the perimetrist when fixation wanders or repeat the stimulus presentation • Inherent adv. Of excluding unreliable data. However with poor fixation the testing time is increased Automatic fixation monitoring 5/3/2014 64
  • 65. • Humphrey 700 • 5%of total stimuli, on the location of the blind spot. • Fixation losses > 20% are indicative of unreliable field tests 5/3/2014 65
  • 66. 5/3/2014 66
  • 67. False positive error • This is a positive response by the patient even in absence of stimulus or to an audible click by the machine in full threshold tests • Aka positive catch trials • In short programs s/a SITA, anticipatory responses faster than the expected reaction time to stimulus are labeled as false positive • False positive ≤ 15% are acceptable 5/3/2014 67
  • 68. False negative error • Some of the previously threshold “seen” points are again presented with brighter stimuli and absence of response is considered as a false negative • Aka negative catch trials • Acceptable upto 20% 5/3/2014 68
  • 69. Maps • Three maps printed in any single-field analysis, each represented by a number plot and an accompanying pictorial representation. – visual sensitivity – total deviation – pattern deviation. 5/3/2014 69
  • 70. Visual sensitivity 5/3/2014 70
  • 71. Total deviation • The numerical value of threshold is compared with the age matched normative data and the difference in value at each point is printed in numbers. • Lower than normal value is printed with — sign and points with higher than normal value is printed without any sign. 5/3/2014 71
  • 72. • Probability plot of total deviation plot: gives the probability of each deviation being normal or abnormal. • All dot signs are considered as normal, whereas all other symbols denotes the different P-value, • darker the symbol, more chances of it being abnormal. 5/3/2014 72
  • 73. Pattern deviation gives the total deviation plot after correcting it for the generalized field defect. The localized defect will be more prominent in this plot. 5/3/2014 73
  • 74. • Probability plot of pattern deviation plot: depicts the probability of pattern deviation plot being abnormal. • Important for the detection of early glaucomatous field defect. 5/3/2014 74
  • 75. Global indices • Are calculated after the completion of the threshold testing. • Mean sensitivity (MS) • The average sensitivity of all the thresholded points. 5/3/2014 75
  • 76. Mean deviation (MD)/mean defect • is the average deviation from the normative data at all the tested points. • Mean defect in Octopus • negative (-) sign. • A small localized defect will show a small MD, whereas a generalized or an advanced defect will show a high MD. • The value does not differentiate a generalized and a localized field loss. It also does not give the location of the defect. 5/3/2014 76
  • 77. Pattern standard deviation(PSD)/Loss variance(LV) • gives an idea about the resemblance of the patients’ field to the shape of hill of vision. • positive sign • Low PSD indicates a normal shape of the hill, whereas a high value indicates a disturbed shape of the hill. • Localized defect will give a high PSD, whereas a generalized defect will give a low PSD. • Improves with the generalization of the defect in advanced field loss. 5/3/2014 77
  • 78. Short term fluctuation(SF) • Intra-test variability • only with the full threshold printouts. • Ten preselected points are thresholded twice and the variation in the thresholds is represented as a number • SF > 3 indicates unreliable result 5/3/2014 78
  • 79. Long-term fluctuation • inter-test variability • while interpreting the multiple tests over time • however, no machine provides any measure for long-term fluctuation. 5/3/2014 79
  • 80. Corrected pattern standard deviation (CPSD) or corrected loss variance (CLV): • It is the PSD or LV corrected for the SF • Provides a measure of the irregularity of the contour of the hill of vision that is not accounted for by patient variability (SF). • increased when localized defects are present . 5/3/2014 80
  • 81. P-value(probability value) • (P < x%) indicates that less than x% of the normal population has figure like this • in other words there is an x% chance that the index would be seen in normal. • Lower the P value beside the global index the higher chance of it being abnormal. • If no P value is given beside a global index, it can be considered normal. 5/3/2014 81
  • 82. Glaucoma hemifield test • It is based on the fact that the glaucomatous defect occurs on either side of the horizontal midline never crossing it and is unlikely to be symmetrical across the horizontal meridian. • Thresholds derived at the five sets of points, which are mirror image along the horizontal meridian 5/3/2014 82
  • 83. 5/3/2014 83
  • 84. Visual Field Index(VFI) • is a single number that summarizes each patient’s visual field status as a percentage of the normal age- corrected sensitivity. • originally designed to approximately reflect the rate of ganglion cell loss. • It is derived from PD and is centre weighted, considering the high density of the retinal ganglion cells in the central retina. 5/3/2014 84
  • 85. • This index is less affected than the MD by factors that cause a general reduction in sensitivity like cataract, miosis,and refractive error. • Minimum value is 0 for a blind field and 100% for a normal individual. 5/3/2014 85
  • 86. BEBIE CURVE/CUMULATIVE DEFECT CURVE • The Bebié curve is a cumulative distribution of the defect depth at each location and is designed to separate normal visual fields from those with early diffuse loss • X axis- rank of defect from smallest (left) to largest(right) • Y axis- magnitude of defect corresponds to the 5th and 95th percentiles. 5/3/2014 86
  • 87. • A normal visual field yields a curve above or closely following the 95th percentile line. • A curve falling below (i.e. outside) the 95th percentile line indicates visual field loss. 5/3/2014 87
  • 88. BEBIE CURVE 5/3/2014 88
  • 89. PRINTING RESULTS The statistical package that is available with the Humphrey device is called as STATPAC. The analysis of the data acquired is presented in five formats 1. Single field analysis 2. Change analysis 3. Overview printout 4. Glaucoma change probability (GCP, with the full threshold tests) 5. GPA (with the SITA tests) 5/3/2014 89
  • 90. How to read out a printout? G = General information R = reliability A = abnormal or normal field D = defects, after analysis of the field defect should be named/classified E = evaluate. Once the defect has been identified, one should try and correlate clinically and evaluate about the patient’s disease status. S = subsequent evaluation. This is applicable in case repeat fields are done after some time to evaluate the progression (stable, deterioration, or improvement) of the field defect. @ GRADES5/3/2014 90
  • 91. Single field analysis General information Reliability indices → Grayscale→ total deviation → pattern deviation → global indices → hemifield test result → RAW DATA → VFI. 5/3/2014 91
  • 92. ANDERSEN’S CRITERIA for glaucomatous field defect 1. Abnormal GHT 2. Three or more nonedge points of the 30-2 printout, contiguous and with a P < 5%, out of which at least 1 has a P < 1% 3. CPSD should be abnormal and should have a P < 5% 5/3/2014 92
  • 93. 5/3/2014 93
  • 94. R P MILL’S CRITERIA for subtle hemianopic defect(suggestive of neurological disorder) 1. First compare the dB value of adjacent rows on the either side of the vertical meridian. At least three adjacent pairs should show unidirectional difference in sensitivity. 2. The corresponding points pairs on the next column adjacent to the first column should also show difference in sensitivity in the same direction. 3. At least a difference of 2dB is significant and is suggestive of early hemianopic defect. 5/3/2014 94
  • 95. 5/3/2014 95
  • 96. Change Analysis Printout • Includes a maximum of 16 tests and is presented in the form of a box plot analysis of tests, a summary of the global indices and linear regression analysis of MD, all on one page. 5/3/2014 96
  • 97. Box plot • modified histogram that gives a summary of TOTAL DEVIATION test values for each test with reference to the age-related STATPAC database, but without reference to the location on the field • A distribution of all the point thresholds around their mean and how much they deviate from it. 5/3/2014 97
  • 98. Diagnostic outcomes of box plot 5/3/2014 98
  • 99. 5/3/2014 99
  • 100. Overview printout 5/3/2014 100
  • 101. Glaucoma Change Probability (GCP) 5/3/2014 101
  • 102. Glaucoma Progression Analysis 5/3/2014 102
  • 103. Factors influencing perimetry • Background luminance 31.5 asb • Stimulus size • Stimulus duration • Interstimulus Time • Refractive Errors • Pupil Diameter • Age • Facial Structure • Fatigue effect(Troxler fading or Ganzfield blankout) • Psychological Factors 5/3/2014 103
  • 104. 5/3/2014 104
  • 105. Alternatives of standard automated perimetry Short-wavelength automated perimetry (SWAP) • SWAP utilizes the koniocellular pathway and selectively measures the short blue wavelength function by projecting a blue stimulus on a yellow background. • SWAP has been found to identify early glaucomatous damage in ocular hypertensives, glaucoma suspects, and patients with glaucoma. 5/3/2014 105
  • 106. Frequency doubling technology (FDT) • a combination of low spatial frequency and high temporal frequency preferentially targets ganglion cells of the magnocellular pathway. • Due to selective uncovering of functional deficits in the My ganglion cells, FDT has been shown to have high sensitivity and specificity for early detection of glaucoma 5/3/2014 106
  • 107. • Flicker perimetry • Micro perimetry 5/3/2014 107
  • 108. References • OPHTHALMOLOGY PRACTICE Year : 2001;Interpreting automated perimetry Ravi Thomas, Ronnie George • Interpretation of autoperimetry,Barun K. Nayak, Sachin Dharwadkar • Conventional Perimetry, Ophthalmologe 2005 • A field of vision: Manual and atlas of perimetry Jason J. S. Barton, Michael Benatar • Automated perimetry visual field digest 5th edition 2004 • Elsevier Eye essentials visual field, Robert Cubbidge • Borish clinical refraction 5th edition5/3/2014 108
  • 109. 5/3/2014 109