Perimetry by dr.ricky


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Perimetry by dr.ricky

  1. 1. Seminar on Assessment of Visual field. Automated Perimetry. Moderator - Prof. H.Ashraf. Presenter - Dr. Ricky Mittal. 25/08/09 Saifi Hall .
  2. 2. <ul><li>What is the normal visual field? </li></ul><ul><li>Traquair-“island of vision surrounded by the sea of darkness.” </li></ul><ul><li>3 dimensional- strategies that are the foundation of all perimetric examinations. </li></ul><ul><li>X-Y axis, Z axis. </li></ul><ul><li>Kinetic perimetry: </li></ul><ul><li>extent along X-Y axis. </li></ul><ul><li>Static perimetry: differential light sensitivity ,altitude of the hill of vision along vertical z axis. </li></ul>
  3. 3. <ul><li>Extent of visual field, XY axis: </li></ul>
  4. 4. Basic terminologies : <ul><li>Threshold : </li></ul><ul><li>Physiological capacity to detect a stimulus at a given location, that stimulus intensity that has a 50%probability of being seen. </li></ul><ul><li>Apostilbs : </li></ul><ul><li>Absolute units of light intensity. </li></ul><ul><li>Luminance of test target. </li></ul><ul><li>1 asb=.3183 candela/m 2 </li></ul><ul><li>Decibels : </li></ul><ul><li>Relative scale, created by manufacturers. </li></ul><ul><li>Attenuation of light by neutral density filters. </li></ul><ul><li>1dB=1/10 log units of attenuation of max. stimulus. </li></ul><ul><li>Measures sensitivity at each point.0to40dB. </li></ul>
  5. 5. Sensitivity Vs threshold: <ul><li>Inverse relationship. </li></ul><ul><li>In automated perimetry, threshold is recorded in the inverted decibel scale, and dimmer targets have higher decibel values. </li></ul><ul><li>Therefore, threshold in decibels is directly proprotional to retinal sensitivity . </li></ul>
  6. 6. Apostilbs Vs decibels : <ul><li>Lumininance of test targets is measured in an absolute unit, apostilbs. </li></ul><ul><li>Decibel is a relative scale created by manufacturers of automated perimeters to measure sensitivity. </li></ul><ul><li>Inverted logarithmic scale with 0dB=brightest stimulus. Not standardized. </li></ul>
  7. 7. <ul><li>Total deviation :difference between patient’s threshold measured and value expected in age matched normals. </li></ul>
  8. 8. Global indices : <ul><li>Mean deviation : mean difference between sensitivities of age matched normals and subject. </li></ul><ul><li>Highlights overall depression, dB, STATPAC, p value. </li></ul><ul><li>Indicated as: </li></ul><ul><li>-ve in Humphrey. </li></ul><ul><li>+ve in Octopus. </li></ul><ul><li>Pattern standard deviation : this is a measure of degree to which the shape of patients field differ from normal, extent of focal loss as a single value. </li></ul><ul><li>PSD can be normal when there is a diffuse loss. </li></ul>
  9. 9. <ul><li>primarily reflects retinal condition. </li></ul><ul><li>excludes conditions affecting the overall field. </li></ul><ul><li>PSD: </li></ul><ul><li>small value-normal field or diffuse loss. </li></ul><ul><li>scotoma -clearly abnormal. </li></ul><ul><li>advanced -PSD starts decreasing if many threshold values near 0dB. </li></ul>
  10. 10. <ul><li>SF : Intratest test variability, threshold at 10 predetermined points, twice. </li></ul><ul><li>SD – SF </li></ul><ul><li>indicator of patient’s consistency, pathology. </li></ul><ul><li>1-2.5dB. </li></ul><ul><li>CPSD : extent of focal loss in the visual field, taking short term fluctuations in account i.e. which is not caused by SF. </li></ul><ul><li>Probability analyses : </li></ul><ul><li>symbolic represenation. </li></ul><ul><li>Statistical probability of a threshold value measured at a point that exists in age-matched normals. </li></ul><ul><li>Darker the symbol lower the probability. </li></ul><ul><li>Comparison on a point by point basis. </li></ul><ul><li>Cataract, ref.error excluded. </li></ul><ul><li>Retinal condition. </li></ul>
  11. 11. Glaucoma hemifield test: <ul><li>Compares five zones (along the nerve fibre bundles) in the upper field with their mirror images in the lower field. </li></ul><ul><li>A very good determinant of the presence of glaucomatous damage on a single field. </li></ul><ul><li>Does not analyze temporal nerve fibre bundle defects. </li></ul>
  12. 12. <ul><li>Inference: </li></ul><ul><li>Outside normal limits. </li></ul><ul><li><1%,0.5%. </li></ul><ul><li>Borderline. </li></ul><ul><li>3% </li></ul><ul><li>Abnormally low sensitivity. </li></ul><ul><li>5% </li></ul><ul><li>Abnormal high sensitivity. </li></ul><ul><li>higher than 99.5% </li></ul><ul><li>Within normal limits. </li></ul>
  13. 13. Basics of the Humphrey field analyser: <ul><li>Projection type automated static perimeter. </li></ul><ul><li>Most popular, consistency of basic hardware, </li></ul><ul><li>constant upgradation of the software on the basis of clinical feedback from the ophthalmologists. </li></ul><ul><li>The machine: </li></ul><ul><li>Viewing distance-33cms. </li></ul><ul><li>Background illumination-31.5asb. </li></ul><ul><li>Static mode, newer models - kinetic. </li></ul>
  14. 14. <ul><li>Stimulus size: Goldman stimulus size(1to5) </li></ul><ul><li>Stimulus duration:0.2 second. </li></ul><ul><li>Fixation monitor : Heijl Krakau blind spot technique, gaze monitoring. </li></ul>
  15. 15. <ul><li>Data storage. </li></ul><ul><li>STATPAC: computerised statistical package </li></ul><ul><li>Comparison of patients results with age matched normal data. </li></ul><ul><li>Patients own baseline with follow up data. </li></ul><ul><li>Newer HFA series: database of stable glaucoma patients for glaucoma change probability analysis. </li></ul>
  16. 16. Interpretation of visual field: <ul><li>Recognise artifacts: </li></ul><ul><li>Reliability. </li></ul><ul><li>Assessment of damage . </li></ul>
  17. 17. <ul><li>Baseline visual field exam : </li></ul><ul><li>2 fields – min. baseline. </li></ul><ul><li>1 st field-Central 30-2 threshold </li></ul><ul><li>2 nd -central 30-2 threshold within 1 to 2 months. </li></ul><ul><li>Provided: </li></ul><ul><li>Consistent ,no learning effect. </li></ul><ul><li><2dB (MD). </li></ul><ul><li>If 1 st field constricted or depressed: </li></ul><ul><li>Obtain 10-2 threshold test. </li></ul><ul><li>Retest with size5 stimulus(64mm 2 ). </li></ul><ul><li>Or combine. </li></ul>
  18. 19. Artifacts <ul><li>Lid. </li></ul><ul><li>Lens rim-too far or the eye is not centered. </li></ul><ul><li>Refractive error. </li></ul><ul><li>Learning effect. </li></ul><ul><li>Pupillary size. </li></ul><ul><li>Rapid fatigue. </li></ul>
  19. 23. Reliability: <ul><li>False positives-tendency of the patient to press the trigger not in response to seeing a stimulus but at random, either as a response to an audible cue or due to the expectation of the stimulus. </li></ul><ul><li>Ratio of such responses to the number of FP catch trials done. </li></ul><ul><li>>33%FP rate is flagged with a double XX. </li></ul><ul><li>Low reliability. </li></ul>
  20. 26. False negative : <ul><li>False negative responses are failure of the patient to respond to stimulus 9 dB more intense than the previously determined threshold at that point due to patient inattention or fatigue. </li></ul><ul><li>Reason may be a tired patient. </li></ul><ul><li>A high FN rate may or may not be reliable. </li></ul><ul><li>Cloverleaf defect due to high FN. </li></ul>
  21. 29. Fixation losses: <ul><li>Not all fixation losses represent true loss of fixation. </li></ul><ul><li>High fixation loss may indicate, centre of blind spot was slightly mislocated. </li></ul><ul><li>If FP, FN rates and STF are low, then the high FL can be discounted. </li></ul><ul><li>If two baseline fields are similar it can again be discounted. </li></ul><ul><li>Mislocation of the blind spot. </li></ul><ul><li>Macular disease. </li></ul>
  22. 30. Short term fluctuations: <ul><li>Testing option, shows variability of patients response over a single test period. </li></ul><ul><li>low ( ≤2dB) SF- good reproducibilty </li></ul><ul><li>high (≥ 3dB) SF-poor reproducibility </li></ul>
  23. 31. Minimum Criteria for Diagnosing Acquired Glaucoma : <ul><li>A Glaucoma Hemifield Test outside normal limits on at least two fields. </li></ul><ul><li>or </li></ul><ul><li>A cluster of three or more non edge points in a location typical for glaucoma, all of which are depressed on the PD plot at p <5% level and one of which is depressed at p <1%level on two consecutive fields. </li></ul><ul><li>or </li></ul><ul><li>A CPSD that occurs in less than <5% of normal fields on two consecutive fields. </li></ul>
  24. 33. <ul><li>Early defect : </li></ul><ul><li>Neither extensive nor near fixation. </li></ul><ul><li>Mean deviation index (MD) –better than -6dB. </li></ul><ul><li>On PD plot: </li></ul><ul><li>1.<25%(18) points are below 5% level. </li></ul><ul><li>2.< 10 points below 1% level. </li></ul><ul><li>Central 5°-no points having less than 15dB sensitivity. </li></ul>
  25. 37. <ul><li>Moderate defect : </li></ul><ul><li>MD<-12dB. </li></ul><ul><li>1.PD-<50%( 37) points < 5% and < 20 points <1%. </li></ul><ul><li>Central 5°-no points with 0dB. </li></ul><ul><li>Only one hemifield may have a point in central 5° with <15dB sensitivity. </li></ul>
  26. 41. <ul><li>Severe defect : </li></ul><ul><li>Any of the following: </li></ul><ul><li>1.MD plot >-12dB </li></ul><ul><li>2.PDplot: </li></ul><ul><li>>37 points depressed below<5%. </li></ul><ul><li>>20 points depressed below 1%. </li></ul><ul><li>Any point in central 5°has sensitivity of 0dB. </li></ul><ul><li>Central 5°-points <15dB in both hemispheres . </li></ul>
  27. 45. Recognition of progressive damage : <ul><li> defect. </li></ul><ul><li>2.deepening of pre exisiting defect. </li></ul><ul><li>3.expansion of pre existing defect. </li></ul><ul><li>4.entire field develops decreased sensitivity. </li></ul>
  28. 46. How would u approach ? <ul><li>Compare baseline field to each individual field </li></ul><ul><li>Study the entire series. </li></ul>
  29. 47. Compare with baseline field : <ul><li>1.For a new defect in previously normal area . </li></ul><ul><li>Cluster of 3 or or more non edge points each </li></ul><ul><li>of which declines by 5 or >5dB. </li></ul><ul><li>2.For deepening of pre existing defect . </li></ul><ul><li>A cluster of 3 or more non edge points, each of which declines by 10 or>10dB. </li></ul><ul><li>3.Generalized depression : </li></ul><ul><li>Decline of all points by 3dB. </li></ul>
  30. 48. Glaucoma change probability programme: <ul><li>Point by point probability of any change in baseline field and new field. </li></ul><ul><li> defect : 3 or more non-edge points each of which, p<5%,on two consecutive fields. </li></ul><ul><li>2.deepening of pre existing defect : part of a scotoma, cluster, p<5%. </li></ul><ul><li>3. expansion : </li></ul><ul><li>Within 15 ° of field-2 previous normal points. </li></ul><ul><li>Outside 15° of field-3 previously normal points depressed with p,5%. </li></ul>
  31. 49. <ul><li>Generalized depression : </li></ul><ul><li>Decline in MD, p<1%. </li></ul>
  32. 50. References : <ul><li>Illustrated Automated Static Perimetry G.R.Reddy. </li></ul><ul><li>Testing of the Field of Vision-Douglas R.Anderson. </li></ul><ul><li>Clinical Decisions in Glaucoma-Elizabeth Hodapp,Richard K.Parrish,Doughlas R.Anderson. </li></ul><ul><li>Visual Field Examination-A.K.Gupta ,Reena M.Chaudhary,Charu Tandon. </li></ul>
  33. 51. <ul><li>. Thank you . </li></ul>