Testing of Field of Vision

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How to test the Field of Vision - fully explained


<ul><li> 1. TESTING OF FIELD OFVISIONBySRIDEVI RAJEEVE2008 BATCH</li></ul> <p> 2. VISUAL FIELDVisual field3 dimensional area of a subjects surrounding that can be seen at anyone time around an object of fixationExtent of normal fieldSuperiorly 50*Nasally 60*Inferiorly 70*temporally 90* 3. VISUAL FIELD1.Central field includes an area from fixation pointto a circle 30* away.Contains the Physiological Blind Spot on itstemporal side.2. Peripheral field refers to rest of the area beyond30* to outer extent of field of vision 4. Methods of estimating Visual fields(1) Perimetry .It is the procedure for estimating extent of the visual fields.It can be classified as below:a. Kinetic perimetry: In this the stimulus of known luminance ismoved from periphery towards the centre to establishisopters.Various methods of kinetic perimetry are; ConfrontationmethodListers perimeteryTangent screen scotometryGoldmanns perimetry 5. .b. Static perimetry. .This involves presenting astimulus at a predetermined position for presetduration with varying luminance.Various methods of static perimetryadopted are;Goldmann perimetryFriedmann perimetryAutomated perimetry. 6. Extent of normal visual field 7. Peripheral versus central field charting Peripheral field charting Central field chartingConfrontation methodPerimetry: Listers, Goldmanns &amp;AutomatedCampimetry or scotometryGoldmanns perimetryAutomated field analysis 8. Manual perimetry &amp; Automated perimetryA. Manual perimetry1. Confrontation method (central field): Assuming the examiners fieldto be within the normal range, they are compared with patients visualfieldsRough, rapid &amp; extremely simple methodMoE: The patient is seated facing the examiner at a distance of 1 metre. Whiletesting the left eye, thepatient covers his right eye and looks into the examinersright eye. The examiner occludes his left eye and moves his hands in from theperiphery keeping it midway between the patient and himself. The patient and theexaminer ought to see the hand simultaneously, for the patients field to beconsidered normal. The hand is moved similarly from above, below and from rightand left. 9. Listers perimeter 10. 2. Listers Perimeter Extent of peripheral field Metallic semicircular arc, graded with degrees&amp; white dot in centre for fixation. Arc can be rotated in different meridians MoE: Patient seated facing arc. One eyeoccluded, fixates on the central white dot.Test object (white, 3-5mm) moved along thearc from periphery towards centre. Point which is 1st seen is registered on chart Arc moved 30* each time &amp; 12 readingsnoted. Perimeter extent of Peripheral field is noted 11. 3. Campimetry (Scotometry)To evaluate the central and paracentral area (30*) of thevisual field. .The Bjerrums screen is used and can be of size 1 metre or 2metres square.MoE: Pt seated at 1m or 2m. Screen has white object forfixation in centre around which concentric circles from 5* to30* are marked. Pt fixates on the central dot with one eyeoccluded. A White target (1-10mm) moved from peripherytowards centre in various meridians 12. .Initially physiological blind spot (15* temporalto fixation pt) is charted which correspondsto optic nerve head. Blind spot dimensions: Horizontally 7-8*Vertically 10-11* Central &amp; paracentral scotoma -Found in - Optic neuritisOpen angle glaucoma 13. BJERRUMS SCREEN. 14. 4. Goldmanns perimeter 15. Goldmanns perimeter Hemispherical dome Test condition &amp; intensity of target are always same Permits greater reproducibility 16. .B. AUTOMATED PERIMETRYAutomated perimeters are computer assisted and testvisual fields by a static method.The automated perimeters automatically test supra-thresholdand threshold stimuli and quantify depth offield defect.Commonly used automated perimeters are;OctopusField MasterHumphrey field analyser 17. .Advantages over manual perimetryAutomated computerized perimetry offers an unprecedented flexibility, alevel of precision and consistency of test method that are not generallypossible with manual perimetry.Other advantages;Data storage capabilityEase of operationWell controlled fixationMenu driven softwareOnline assistance making them easy to learn and use.Facility to compare results statistically with normal individuals ofthe same age group and with previous tests of the same individual. 18. Humphrey field analyser 19. INTERPRETATION OF AUTOMATED PERIMETRY PRINTOUT FIELD CHARTS Automated perimeter variables Testing strategies and programmeFollowing discussion is based on the HFA. 20. A. AUTOMATED PERIMETER VARIABLES1. Background illumination2. Stimulus intensity3. Stimulus size4. Stimulus duration 21. . 1. BACKGROUND ILLUMINATIONHFA Uses 31.5 apostilb[asb] background illumination.Apostilb [asb] = Unit of brightness per unit area (1/35 candela/sq.m) 2. STIMULUS INTENSITYHFA uses projected stimuli Intensity varied more than 5%log units (51 decibel) b/w 0.08 &amp;10,000 asb. In db notation, value refers to retinal sensitivity. Higher no. Indicate logarithmic reduction in test objectbrightness &amp; greater sensitivity of vision 22. 3.STIMULUS SIZE HFA offers 5 sizes of stimuli corresponding to Goldmannsperimeter stimuli 1 through v Standard target size equivalent to Goldmann size III (4sq.mm)4. STIMULUS DURATIONShorter than latency time for voluntary eye movements(about 0.25 sec)HFA - 0.2secOCTOPUS - 0.1sec 23. Stimulus intensity scales comparison 24. Testing strategies and programmes Visual threshold - physiological ability to detect a stimulus underdefined testing conditions. Normal threshold = Mean threshold in normal peoplein a given agegoup at a given location in the visual field. Machine compares patient sensitivity against these values. Threshold: 0-50 db 50 db dimmest target 0 db - brightest illumination perimeter can project 50 db - high sensitivity 0 db low sensitivity 25. TESTING STRATEGIES&amp;PROGRAMMESBasic strategies Supra threshold testing Threshold testing1. Full threshold testing2. Fast Pac3. SITA (Swedish Interactive ThresholdAlgorithm) 26. .SUPRA THRESHOLD TESTINGTarget obove brightness a patient should be able to seeScreening procedure for gross defectsTHRESHOLD TESTINGPreciseClinician preferredMore time consumingExpensive 27. 1. FULL THRESHOLD TESTING Determines threshold value at each pt. By bracketing tech 4-2 on HFA 4-2-1 on OCTOPUS Stimulus test pt. 0.2 sec Machine wait y/n If stimulus not seen-intensity of stimulus increased 4dbsteps Once threshold crosses stimulus intensity is decreased2db steps till stimulus not seen 28. 2. FAST PAC More rapid Threshold once cross strategy not applicable3. SITA Swedish interactive threshold algorithm Reduces test time Fast SITA Standard SITA 29. TEST PROGRAMMESA. Central field testscentral 30-2 testcentral 24-2 testcentral 10-2 testmacular grid testB. Peripheral field testsperipheral 30/60-1peripheral 30/60-2nasal steptemporal cresentC. Speciality testsNeurological-20Neurological-50Central 10-12Macular testD. Custom tests 30. Central 30-2 test Most comprehensive form of visual field assessment of central 30degrees Consists of 76 points, 6 degrees apart on either sides of vertical &amp;horizontal axis Inner most points are 3* from fixation point. 31. Central 24-2test 54 points examined Near similar to 30-2 test except -2 peripheral nasal points at 30* on either side ofhorizontal axis are not included (while testingcentral 24*) 32. Central 10-2 test Most pt.s in arcuate region b/w 10* &amp; 30* -marked depression Assess and follow 68 pt.s 2 degrees apartin central 10 degrees 33. Macular grid test Used when field is limited to central 5 degrees Test examines 10 points spaced on 29 degreesquare grid centered on point of fixation 34. Arbitraty division of Humphry Single Field printout(Statpacprintout) with central 30-2 test in sparts (zones) 35. EVALUATION OF HFA SINGLE FIELDPRINT OUTSoftware used - Statpac printout. Divided into 8 zones viz;I. Patient data &amp; test parameters1. Patient data: NameDate of birthEye (right/left)Pupil sizeVisual acuity2. Test parameters: Test nameStrategyStimulus usedBackground 36. .II. Reliability Indices (RI)Shows Reliability indices &amp; Test durationVisual field examination = Unreliable - if three or more ofthe following reliability indices have below mentionedvalues; Fixation losses &gt;= 20% False positive error &gt;= 33% False negative error &gt;= 33% Short term fluctuations &gt;= 4.0dB Total questions &gt;= 400 37. .III. Gray scale stimulation Depicted in Zone 3. The darker the print out the worse is the field. Provides field defects at a glance. We do not make a diagnosis based on this.Nb: Main emphasis on statistical help shows inzone IV to VIII of the printout. 38. . IV. Total deviation plots Provides deviation of patients threshold values from that ofage corrected normal data.1.Numerical value plot2.Probablity plot (grey scale symbol plot)Numerical value plot Represents the differences in decibels . Zero value-expected threshold for that age. Positive numbers points that are more sensitive thanaverage for that age. Negative numbers-reflect points that are depressedcompared with the average. 39. .Probability plot In the lower part of zone IV of the printout, the totaldeviation plot is represented graphically. Darker the representation,the more significant it is.V.Pattern deviation plots 1. Numeric PDP 2. Probability PDP Shown in zone V Similar to the total deviation plots except that here Statpacsoftware has corrected the results for the changes caused bycataract, small pupil etc. 40. .VI. Global indices Depicted in zone VI of printout. Are calculations made by Statpac to provide overallguidelines to help the practitioner assess the fieldresults as a whole. Used to monitor progression of glaucomatousdamage than initial diagnosis.1. Mean deviation - Mean difference betweenthe normative data for that age compared with thatof collected data. Indicator of general depression of field. Worse than normal value is indicated by a negativevalue. 41. .2. Pattern std deviation (PSD) -Measureof variability within the field. It measures the diffbetween a given point &amp; adjacent points. Points out localized field loss &amp; is most useful inidentifying early defects.3. Short term fluctuation (SF) - Measureof the variability between two differentevaluations of the same 10 points in the field. Not available with SITA strategy. High SF means either decreased reliability or anearly finding indicative of Glaucoma. 42. .. 4.Corrected pattern std deviation (CPSD)- PSDcorrected for SF. Indicates the variability between adjacent points that may be due todisease than intra-test variability.VII. Glaucoma hemifield test (GHT) Compares the 5 clusters of points in the upper field with the5 mirror images in the lower field. Clusters developed based on anatomical distribution of nervefibres Specific for detection of Glaucoma. Depending on differences between upper and lower clustersof points, five inferences can be made; 43. .1. Outside normal limitsDenotes that either the values in upper &amp; lower clusters differ toan extent found in less than 1% of population or any one air ofclusters is depressed to the extent that would be expected in lessthan 0.5% of population.2. Borderline Difference between any one of the upper &amp; lower mirror clusters iswhat might be expected in less than 3% of population.3. General reduction in sensitivity Best part of visual field is depressed to an extent expected in lessthan 0.5% of the population.4. Abnormally high sensitivity Best part of visual field is such as would be found in less than 0.5%of population .5. Within normal limits When none of above criteria is met. 44. .VIII. Actual threshold values Inspected for any pattern or Scotoma whenclinical features are suspeciant and even if all theseven other parts of printout are normal. A Scotoma is the depressed part of field ascompared to surroundings (not w.r.t normal). When actual test threshold values are below15dB sensitivity of the test is lost. 45. .THANK YOU! </p>