Perimetry

PERIMETRY slides for PG

1. PERIMETRY Presented by : Dr.Ritika Kishore Sahay Moderator: Dr.Yogesh Arora

2. VISUAL FIELDS The visual field is defined as that part of the environment that is visible to the steadily fixing eye. The extension of visual field is as follows.

3. Traquair defined visual field as “ island or hill of vision surrounded by the sea of darkness”. It has a shape of a hill which correlates to density of photoreceptors and their receptive field sizes. Peak representing fovea 2 slopes representing nasal and temporal field of vision

4. PERIMETRY Perimetry is the systematic measurement of visual field function. It is the measurement of Hill of Vision in terms of establishing the patient’s differential light sensitivity across the visual field.

5. HISTORY 1970 - The original octopus perimeter was first introduced. Because of its room size and high expensive nature it became unpopular 1982 - Humphrey field analyzer was first displayed at American Academy of Ophthalmology. 1983 - Michael Patella showed its first clinical trail 1984 – started production and became very popular because of its small size and affordable price.

6. INDICATIONS OF PERIMETRY Detection of glaucoma, progression Chorioretinal lesions Optic disc and optic nerve lesions Neuro-ophthalmological diseases

7. TYPES KINETIC PERIMETRY Confrontation Tangent screen Lister perimetry Campimetry Goldmann STATIC PERIMETRY Humphrey Octopus Oculus

8. KINETIC PERIMETRY Manual AIM : To find points in the visual field of equal retinal sensitivity METHOD : Stimulus is moved from a non seeing area to a seeing area of visual field. Procedure is repeated with the use of same stimulus along a set of meridians , usually spaced every 15 The speed ,size , color and brightness of target are the different variables

9. When the island hill-of-vision is kinetically explored along the X-Y axes i.e. a plane parallel to the surface of the sea, the locations of points with the same threshold are identified; these are isopters

10. ADVANTAGES Moving targets can define isopter contours and scotomas rapidly Mapping the extent of scotoma is more precise with kinetic Relatively inexpensive and durable Patients are comfortable with human contact of examination

11. DISADVANTAGES Technical skill, training and retraining personnel are difficult Early or subtle changes can be overlooked Statistical analysis are difficult

12. LISTER’s PERIMETER Peripheral charting

13. BJERRUM’s SCREEN ( CAMPIMETRY) Patient sits at 1 or 2 m from flat screen For central 30 deg only Done under subdued lighting

14. GOLDMANN’s PERIMETER Bowl type Standardization Peripheral as well as central Background intensity of 31.5 apostilbs (asb) The size and intensity of targets may be varied to plot different isopters kinetically and determine local static thresholds .

15. The stimuli used to plot an isopter are identified by a roman numeral, a number, and a letter. The roman numeral represents the size of the object.

16. The number and letter represent the intensity of the stimulus. A change of one number represents a 5-dB (0.5 log unit) change in intensity, and each letter represents a 1-dB (0.1 log unit) change in intensity

17. STATIC PERIMETRY Computerized Aim : To find out the threshold of retina at various fixed points. METHOD : Patient looks into a white hemispherical bowl at a small fixation point at the center. Visual field stimuli are briefly presented at fixed stationary locations Duration of presentation is about 200 milliseconds Patient presses a response button when the stimulus is detected.

18. Stimulus size and location is maintained constant Brightness varied at various predetermined constant locations in order to find out the threshold at these locations In other words contrast sensitivity is tested thru out the extent of area perceived This type is concerned with altitude or vertical Z axis of island of vision

19. When island hill of vision is explored along Z axis: plane perpendicular to the surface of sea, varying points of sensitivity is identified. These are thresholds displayed as meridional cuts

20. ADVANTAGES The data are quantifiable, reproducable , amenable to statistical manipulation Threshold detection is more sensitive The standardized technology reduces the need for highly trained technicians Depth of scotoma is more accurate with static perimetry

21. DISADVANTAGES Large amounts of unfamiliar data are generated making interpretation difficult Tedious and time consuming The equipment is expensive.

22. HUMPHREY FIELD ANALYSER THE MACHINE HAS 2 PARTS- -perimetric unit- bowl type screen - control unit- computer Use static stimuli Viewing distance of 33 cms. Background luminance- 31.5 asb Stimulus size-( Goldmann stimulus size 1-V ) Stimulus duration- 0.2 sec

23. Stimulus Size and Intensity Most commonly Goldmann size III is used The stimulus intensity can be made upto 10,000 asb in humphrey As intensity increases stimulus size decreases.

24. TERMINOLOGY RELATED TO PERIMETRY APOSTILBS Absolute unit Unit of light intensity DECIBEL Relative unit Unit of light intensity and retinal sensitivity Inverted logarithmic scale

25. Decibel value increase Brigtness of light decreases Retinal sensitivity increases

26. 40 decibel stimulus 1 asb unit LEAST projected stimulus intensity ‘0 ’ decibel stimulus 10,000 asb units MAXIMUM intensity of stimulus

27. THRESHOLD If a particular intensity of light is shown 100 times and if it is appreciated 50 times and that particular intensity of light is termed as THRESHOLD . If the stimulus intensity is seen 90% of times it is termed as SUPRATHRESHOLD. If it is seen 15% of times, it is termed as INFRATHRESHOLD

28. FREQUENCY OF SEEING CURVE NOTE: As the dB value is decreasing, the light intensity is increasing

29. SENSITIVITY VERSUS THRESHOLD

30. HUMPHREY VISUAL FIELD TEST THRESHOLD TEST (Threshold stimulus ) CENTRAL TEST 30-2 24-2 10-2 Macular program PERIPHERAL TEST 60-4 Nasal step Temporal crescent SPECIALITY TEST Neurological 20 Neurological 30 SCREENING TEST (Suprathreshold stimulus)

31. THRESHOLD TEST POINT PATTERN The point pattern where the threshold has to be determined is usually designed according to the disease pattern. Points to be noted: 1.Extension of visual field testing. 2.Number of test points. 3.Point density (the distance between two points in degrees). 4.The degree of bare area around the fixation spot. 5.The relation of the points to the horizontal and vertical axes.

32. 30-2 Number of test points: 76 Density : 6 degree Bare area : 3 degree Area of testing from the fixation point is 30° Indication: suspicious cases of glaucoma

33. 24-2 Number of test points: 54 Density: 6 degree Bare area : 3 degree Area of testing from the fixation point is 24° Indication : established case of glaucoma

34. 10-2 Number of test points: 68 Density: 2 degree Bare area : 1 degree Area of testing from the fixation point is 10° Indication : advanced cases of glaucoma

35. MACULAR PROGRAMME Number of test points: 16 Density: 2 degree Bare area : 1 degree Area of testing from the fixation point is 5° Indication : advanced cases of glaucoma

36. NASAL STEP THRESHOLD PATTERN It is the peripheral test pattern it explores from 30° to 50° . Number of points : 14 The nasal step test points provide 2 points above and below the horizontal axes at 30°, 40°, 50° as well as 2 accentric central points Indication: advanced glaucoma

37. SELECTION OF THE POINT PATTERNS IN PATIENTS OF GLAUCOMA ACCORDING TO THE STAGE OF GLAUCOMA

38. TEST STRATEGY The test “strategy” refers to the method of presenting stimuli to the patient to attain the desired information. THRESHOLD TEST QUANTITATIVE CONSUMES MORE TIME SUPRATHRESHOLD SCREENING TEST QUALITATIVE CONSUMES LESS TIME

39. THRESHOLD TEST STRATEGY Old standard threshold strategies Full Threshold strategy Newer Threshold strategies FASTPAC SITA Standard SITA Fast

40. FULL THRESHOLD STRATEGY Determination of threshold bracketing or staircase method ( 4-2 algorithm)

41. FASTPAC Less time consuming It changes the stimulus intensity in 3 db steps either increasing it or decreasing it depending on patients initial response High intratest variability i.e., Short-term fluctuation

42. SITA ( Swedish Interactive Threshold Algorithm) More efficient estimation of threshold 2 strategies- SITA standard Sita fast Short test time without compromising on the sensitivity It creates prior probability models for normal and glaucomatous populations The pace of the test is dependent on patient’s response It uses informative index derived from visual field model for each point that determines when to stop.

43. SELECTION OF TESTING STRATEGY Does not depend on the cup/disc ratio of glaucomatous optic atrophy Usually SITA Standard or Full Threshold testing strategy will be selected If the patient is old and not able to concentrate for a longer time SITA Fast or FAST PAC can be selected.

44. PROFORMA OF ORDER FORM FOR VISUAL FIELD TESTING

45. SINGLE FIELD ANALYSIS PRINTOUTS WITH STATPAC ANALYSIS

46. ZONE 1 PATIENTS DATA Name of the patient : Date of birth and age : Pupil diameter : Visual acuity : Refractive error correction for N.V. THE TEST DATA Fixation monitor - blind spot Colour of the stimulus - white Back ground illumination - 31.5 asb Fixation target - central Stimulus size - goldmann size III Threshold test pattern Testing strategy

47. AGE OF THE PATIENT : Since the interpretation of raw data by STATPAC is age dependent , it it is the very important to enter the age of patient accurately. SIZE OF THE PUPIL : Normally the size of the pupil should be between 3-4 mm. Constricted pupil give rise to diffuse visual field depression or edge scotomas. REFRACTIVE ERROR : The patient’s near vision refractive error must be properly corrected. Otherwise the visual field will show generalized depression

48. FIXATION TARGET Central —Yellow light in the center of the bowl Small diamond —It is located below the central target . Used in macular degeneration Large diamond — used for patient with central scotoma Bottom LED —tests that require a lower fixation light than the central target.

49. STIMULUS SIZE The standard size of the stimulus is size III for all routine tests. But in situations like advanced glaucoma, the test will be conducted with size V to know the status of macular split.

50. ZONE 2 Reliability Indices Fixation loss >20% is unreliable False positive >33% is unreliable False negative >33% is unreliable Short- term fluctuations.

51. ZONE 3 – RAW DATA Retinal sensitivity in db units of the selected points calculated by field analyzer ‘0’ indicates absolute scotoma 40 indicates response to 1 asb unit, highest retinal sensitivity

52. ZONE 4 GREY SCALE Shows thresholds for each spot tested in db Areas of high sensitivity are denoted by lighter shades and areas of low sensitivity are denoted by darker shades. Quickly identifies overall depressions Not used for diagnosis Good for patient education No comparison for age related normals No adjustment for media opacities

53. ZONE 5 - TOTAL DEVIATION NUMERICAL PATTERN

54. NORMAL RETINAL SENSITIVITY PATIENTS RETINAL SENSITIVITY DIFFERENCE TOTAL DEVIATION NUMERICAL PATTERN

55. Words indicates retinal sensitivity is equal to mean normal values of the same age group. Value without sign (positive ) indicates the measured retinal sensitivity is better than mean normal values of the same age group. The numerical value with negative sign indicates the measured retinal sensitivity is worse than the mean normal values of the same age group.

56. The TDNP becomes the platform for the calculations of global indices TDNP values in the range of 0 to -2db – no field loss

57. ZONE 6 - TOTAL DEVIATION PROBABILITY PLOT Aim of the field chart is to show the field loss in scotomatous form.

58. P VALUE Probability values (P) :Indicates the significance of the defects . The lower the P value, the greater is its clinical significance clinical significance : : if there are abnormal points in total deviation plot that persist in the pattern deviation plot, we are looking at scotomas .

59. ZONE 7- PATTERN DEVIATION NUMERICAL PLOT It is a modified form of TDNP to bringout deep scotomas

60. 7th best retinal sensitivity of TDNP is converted to zero. Addition of the threshold value that converts the 7th best retinal sensitivity of TDNP to 0 to all points in TDNP The pattern deviation numerical plot is also the basis for glaucoma hemi field test analysis.

61. ZONE 8 - PATTERN DEVIATION PROBABILITY PLOT It is the symbolic representation of P value of each numerical threshold deviation values of pattern deviation numerical plot .

62. It bring out deep scotomas in a generalized depression. It differentiates uniform generalized depression from the irregular generalized depression. It is almost normal in uniform generalized depression and in irregular generalized depression the pattern deviation probability plot shows localized field defects

63. ZONE 9 – GLOBAL INDICES Mean deviations (MD) 2. Short term fluctuation (SF) 3. Pattern standard deviation (PSD) 4. Corrected pattern standard deviation (CPSD)

64. Hill of vision The hill of vision has two components: Height of hill of vision (represented by mean deviation index), 2) The contour of hill of vision (represented by PSD value).

65. Mean deviation Signifies average overall severity of field loss. It is the average of all the numbers shown in the total deviation plot except the two points nearer to the blind spot. Expressed in db units with p value. The positive value indicates that the patient’s overall sensitivity is better than normal observer Negative value indicates that the patient’s overall sensitivity is worse than the average normal individual.

66. SIGNIFICANCE In glaucoma suspect on the basis of assymmetry of intra ocular pressure or of disc cupping, the difference of mean deviation index between both the eyes of 2db should be taken as a clue in conforming the diagnosis of glaucoma. In the follow-up tests : normally mean deviation index will be changed by 0.08 db to 0.1 db Printed along with a solid triangle to indicate degradation or an open triangle to indicate improvement.

67. PATTERN STANDARD DEVIATION Index of irregular loss of retinal sensitivity. It is the standared deviation around the mean that constitutes the MD index The contour of hill of vision will be represented by PSD value. PSD zero indicates no departure from the average Positive number indicates depature from the normal slope of hill of vision.

68. SHORT TERM FLUCTUATION Index of intra test variation Indicator of reliability It measures the variation at each point on repeated thresholding in the same test. Value is almost always less than 3 dB used to correct PSD to produce CPSD.

69. CORRECTED PATTERN STANDARD DEVIATION (CPSD) Intra testing variability (SF) is removed from PSD for produce CPSD. CPSD is not calculated if SF is not estimated during the test.

70. ZONE 10- GLAUCOMA HEMI FIELD TEST Compares mirror image locations of superior and inferior retina and gives five comments GHT— OUTSIDE NORMAL LIMIT ,if difference found in 1% population GHT— BORDERLINE , if difference found in up to 3% population GHT— ABNORMALLY LOW SENSITIVE , best sensitive part is seen in less than 5% of the population GHT— ABNORMALLY HIGH SENSITIVE , best sensitive part seen is more than that found in 99.5% population GHT— WITHIN NORMAL LIMIT , when none of the above 4 conditions are seen

71. GAZE MONITORING Heijl-Krakau method of fixation monitoring- It provides index of quality of patient fixation during examination by periodically exposing stimuli in blind spot Eye Monitoring by perimetrist Infra red Gaze Monitors

72. Upward spike indicate that patient has lost fixation Spike reaching the top horizontal means 10degree off fixation Spike reaching half way to top line indicate 5 degree off fixation Downward spike indicate Short spike indicates that gaze at the time cannot be determined by software Long spike indicate patient blinked at the time of fixation check

73. SCREENING TEST PATTERN Glaucoma test point pattern Central test point pattern Full field test point pattern Peripheral field test point pattern STRATEGY Two-zone strategy(threshold-related strategy) Three-zone strategy Quantify defects screening strategy Single intensity strategy

74. TWO-ZONE STRATEGY.

75. THREE-ZONE STRATEGY.

76. QUANTIFY DEFECT SCREENING STRATEGY

77. CUSTOM TEST Feature of automated static field analyzers It focuses an area where the first test indicated defects. We can design a custom point pattern where we want to concentrate more We can create points separated by 1° in an area where we are expecting the progress of the disease Used for the follow-up tests No progrssion in disease is concluded only after it is proved by custom tests.

78. ARTEFACTS OBSTRUCTION .Rim Artefact .Ptosis .Media Opacities .Angioscotoma MIOSIS REFRACTIVE ARTEFACTS

79. OCTOPUS PERIMETRY Projection system perimeters which can perform full threshold programme Stimulus is Goldmann target size III Stimulus intensity can reach upto 1000 asb Background luminance is 4 asb Testing distance is 42.5 cm

80. ZONES IN OCTOPUS VISUAL FIELD ANANLYSIS Reproducibility (Zone-1) Reliability factors (Zone-2) Gray scale (Zone-3) Comparison (Zone-4) Corrected comparison (Zone-5) Numeric data/raw data(Zone-6) Visual field indices (Zone-7) Bebie.’s curve (Zone-8)

81. ADVANCED TECHNIQUES FOR VISUAL FIELD EXAMINATION SWAP[Short Wave Automated Perimetry] FDP[Frequency Doubling Perimetry] HPRP[High Pass Resolution Perimetry] Flicker Perimetry Multifocal Electroretinography ACCUMAP [Multifocal Visual Evoked Potential] Motion Perimetry

82. SWAP Short Wave Automated Perimetry Helps to diagnose damage due to glaucoma at an early stage Yellow background is used to highlight isolated blue cone response PRINCIPLE:Green and red cone pigments are bleached by the intense yellow background where as the blue cones are much less affected. INDICATION: Significant signs and risk factors of glaucoma but normal fields on white on white perimetry Goldmann target V stimulus is used to enhance spatial summation

83. DISADVANTAGE OF SWAP It is influenced by nuclear sclerosis as lens acts a blue filter Time consuming The mean normal SWAP threshold values are lower than for white stimuli and the SWAP gray scale is darker in its appearance and may mislead clinicians accustomed to the gray scale for white on white perimetry.

84. FDP (FREQUENCY DOUBLING PERIMETRY)

85. RETINAL GANGLION CELLS PARVOCELLULAR P Cells Small axon diameter Slow conduction velocity High spatial frequency( fine details) Low temporal frequency ( constant stimuli) MAGNOCELLULAR M Cells Large axon diameter Fast conduction velocity Low spatial frequency ( broad pattern) High temporal frequency( flickering stimuli)

86. FDP is based on detecting damage to M ‘y’cells which are a subset of Magnocellular cells Test stimulus- series of white and black bands flickering at 25 Hz Uses target of 10 deg square The non linear response to stimuli produces frequency doubling appearance.

87. It is cheap, desk mounted and sensitive Not reliable for progression analysis.

88. FLICKER PERIMETRY It detects light and dark stimulus alternations (flicker) at various locations in the field It targets magnocellular pathway (responsible for flicker perception) Not influenced by media opacities and refractive error Two types- 1) Critical Fusion Frequency 2) Temporal Modulation Perimetry

89. HPRP [High Pass Resolution Perimetry] Ring perimetry It tests the parvocellular system selectively Based on resolution method rather than differential light sensitivity Series of ring of different sizes and having a light centre and dark annular surround are presented These targets are spatially high pass filtered vanishing targets for determination of resolution of central 30 deg

90. VISUAL FIELD INTERPRITATION

91. FIELD DEFECT PATHOLOGY Nerve fibre bundle damage at the disc Area of loss of visual sensitivity supplied by the bundle Scotoma or localised depression

92. CHARACTERISTICS OF GLAUCOMATOUS VISUAL FIELD DEFECTS Almost always localized Respect horizontal meridian Begin nasal to the blind spot Upper pole affected more than lower pole Almost always detectable within the central 30°

93. STAGES OF GLAUCOMATOUS DAMAGE Based on Number of axons damaged indicated by MD location of the defect EARLY DEFECT MODERATE DEFECT SEVERE DEFECT

94. ANDERSON CRITERIA SIGNIFICANCE: To detect early glaucoma. CRITERIAS Abnormal glaucoma hemifield test. Pattern standard deviation abnormal at P < 5% level Three non-edge adjacent points in total or pattern deviation probability plot. The points must be in a cluster in an expected locations. Two points P < 5% One point P < 1% Must be demonstrated on 2 field tests

95. EARLY PARACENTRAL SCOTOMA

96. EARLY NASAL STEP

97. MODERATE INFERIOR ARCUATE SCOTOMA

98. MODERATE SUPERIOR ARCUATE SCOTOMA

99. ADVANCED SUPERIOR ARCUATE SCOTOMA

100. SEVERE DOUBLE ARCUATE SCOTOMA WITH TEMPORAL SPARING

101. CLOVER LEAF PATTERN

102. PTOSIS

103. LENS ARTIFACT

104. OCCLUSION OF UPPER BRANCH OF CRA

105. CATARACT

106. BITEMPORAL HEMIANOPIA DUE TO LESION IN CHIASMA

107. LEFT HOMONYMOUS HEMIANOPIA IN POSTERIOR CEREBRAL ARTERY OCCLUSION

108. REFERENCES A visual field evaluation with automated devices by GR Reddy Diagnosis and therapy of glaucoma by Becker and Shaffers Ophthalmology – Yanoff and Duker Visual fields examination and interpretation- Thomas J. Walsh Automated Perimetry - Anderson DR, Vincent Michael Patella.

109. THANK YOU