Perimetry by dr.ricky

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  • 1. Seminar on Assessment of Visual field. Automated Perimetry. Moderator - Prof. H.Ashraf. Presenter - Dr. Ricky Mittal. 25/08/09 Saifi Hall .
  • 2.
    • What is the normal visual field?
    • Traquair-“island of vision surrounded by the sea of darkness.”
    • 3 dimensional- strategies that are the foundation of all perimetric examinations.
    • X-Y axis, Z axis.
    • Kinetic perimetry:
    • extent along X-Y axis.
    • Static perimetry: differential light sensitivity ,altitude of the hill of vision along vertical z axis.
  • 3.
    • Extent of visual field, XY axis:
  • 4. Basic terminologies :
    • Threshold :
    • Physiological capacity to detect a stimulus at a given location, that stimulus intensity that has a 50%probability of being seen.
    • Apostilbs :
    • Absolute units of light intensity.
    • Luminance of test target.
    • 1 asb=.3183 candela/m 2
    • Decibels :
    • Relative scale, created by manufacturers.
    • Attenuation of light by neutral density filters.
    • 1dB=1/10 log units of attenuation of max. stimulus.
    • Measures sensitivity at each point.0to40dB.
  • 5. Sensitivity Vs threshold:
    • Inverse relationship.
    • In automated perimetry, threshold is recorded in the inverted decibel scale, and dimmer targets have higher decibel values.
    • Therefore, threshold in decibels is directly proprotional to retinal sensitivity .
  • 6. Apostilbs Vs decibels :
    • Lumininance of test targets is measured in an absolute unit, apostilbs.
    • Decibel is a relative scale created by manufacturers of automated perimeters to measure sensitivity.
    • Inverted logarithmic scale with 0dB=brightest stimulus. Not standardized.
  • 7.
    • Total deviation :difference between patient’s threshold measured and value expected in age matched normals.
  • 8. Global indices :
    • Mean deviation : mean difference between sensitivities of age matched normals and subject.
    • Highlights overall depression, dB, STATPAC, p value.
    • Indicated as:
    • -ve in Humphrey.
    • +ve in Octopus.
    • 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.
    • PSD can be normal when there is a diffuse loss.
  • 9.
    • primarily reflects retinal condition.
    • excludes conditions affecting the overall field.
    • PSD:
    • small value-normal field or diffuse loss.
    • scotoma -clearly abnormal.
    • advanced -PSD starts decreasing if many threshold values near 0dB.
  • 10.
    • SF : Intratest test variability, threshold at 10 predetermined points, twice.
    • SD – SF
    • indicator of patient’s consistency, pathology.
    • 1-2.5dB.
    • CPSD : extent of focal loss in the visual field, taking short term fluctuations in account i.e. which is not caused by SF.
    • Probability analyses :
    • symbolic represenation.
    • Statistical probability of a threshold value measured at a point that exists in age-matched normals.
    • Darker the symbol lower the probability.
    • Comparison on a point by point basis.
    • Cataract, ref.error excluded.
    • Retinal condition.
  • 11. Glaucoma hemifield test:
    • Compares five zones (along the nerve fibre bundles) in the upper field with their mirror images in the lower field.
    • A very good determinant of the presence of glaucomatous damage on a single field.
    • Does not analyze temporal nerve fibre bundle defects.
  • 12.
    • Inference:
    • Outside normal limits.
    • <1%,0.5%.
    • Borderline.
    • 3%
    • Abnormally low sensitivity.
    • 5%
    • Abnormal high sensitivity.
    • higher than 99.5%
    • Within normal limits.
  • 13. Basics of the Humphrey field analyser:
    • Projection type automated static perimeter.
    • Most popular, consistency of basic hardware,
    • constant upgradation of the software on the basis of clinical feedback from the ophthalmologists.
    • The machine:
    • Viewing distance-33cms.
    • Background illumination-31.5asb.
    • Static mode, newer models - kinetic.
  • 14.
    • Stimulus size: Goldman stimulus size(1to5)
    • Stimulus duration:0.2 second.
    • Fixation monitor : Heijl Krakau blind spot technique, gaze monitoring.
  • 15.
    • Data storage.
    • STATPAC: computerised statistical package
    • Comparison of patients results with age matched normal data.
    • Patients own baseline with follow up data.
    • Newer HFA series: database of stable glaucoma patients for glaucoma change probability analysis.
  • 16. Interpretation of visual field:
    • Recognise artifacts:
    • Reliability.
    • Assessment of damage .
  • 17.
    • Baseline visual field exam :
    • 2 fields – min. baseline.
    • 1 st field-Central 30-2 threshold
    • 2 nd -central 30-2 threshold within 1 to 2 months.
    • Provided:
    • Consistent ,no learning effect.
    • <2dB (MD).
    • If 1 st field constricted or depressed:
    • Obtain 10-2 threshold test.
    • Retest with size5 stimulus(64mm 2 ).
    • Or combine.
  • 18.  
  • 19. Artifacts
    • Lid.
    • Lens rim-too far or the eye is not centered.
    • Refractive error.
    • Learning effect.
    • Pupillary size.
    • Rapid fatigue.
  • 20.  
  • 21.  
  • 22.  
  • 23. Reliability:
    • 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.
    • Ratio of such responses to the number of FP catch trials done.
    • >33%FP rate is flagged with a double XX.
    • Low reliability.
  • 24.  
  • 25.  
  • 26. False negative :
    • 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.
    • Reason may be a tired patient.
    • A high FN rate may or may not be reliable.
    • Cloverleaf defect due to high FN.
  • 27.  
  • 28.  
  • 29. Fixation losses:
    • Not all fixation losses represent true loss of fixation.
    • High fixation loss may indicate, centre of blind spot was slightly mislocated.
    • If FP, FN rates and STF are low, then the high FL can be discounted.
    • If two baseline fields are similar it can again be discounted.
    • Mislocation of the blind spot.
    • Macular disease.
  • 30. Short term fluctuations:
    • Testing option, shows variability of patients response over a single test period.
    • low ( ≤2dB) SF- good reproducibilty
    • high (≥ 3dB) SF-poor reproducibility
  • 31. Minimum Criteria for Diagnosing Acquired Glaucoma :
    • A Glaucoma Hemifield Test outside normal limits on at least two fields.
    • or
    • 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.
    • or
    • A CPSD that occurs in less than <5% of normal fields on two consecutive fields.
  • 32.  
  • 33.
    • Early defect :
    • Neither extensive nor near fixation.
    • Mean deviation index (MD) –better than -6dB.
    • On PD plot:
    • 1.<25%(18) points are below 5% level.
    • 2.< 10 points below 1% level.
    • Central 5°-no points having less than 15dB sensitivity.
  • 34.  
  • 35.  
  • 36.  
  • 37.
    • Moderate defect :
    • MD<-12dB.
    • 1.PD-<50%( 37) points < 5% and < 20 points <1%.
    • Central 5°-no points with 0dB.
    • Only one hemifield may have a point in central 5° with <15dB sensitivity.
  • 38.  
  • 39.  
  • 40.  
  • 41.
    • Severe defect :
    • Any of the following:
    • 1.MD plot >-12dB
    • 2.PDplot:
    • >37 points depressed below<5%.
    • >20 points depressed below 1%.
    • Any point in central 5°has sensitivity of 0dB.
    • Central 5°-points <15dB in both hemispheres .
  • 42.  
  • 43.  
  • 44.  
  • 45. Recognition of progressive damage :
    • 1.new defect.
    • 2.deepening of pre exisiting defect.
    • 3.expansion of pre existing defect.
    • 4.entire field develops decreased sensitivity.
  • 46. How would u approach ?
    • Compare baseline field to each individual field
    • Study the entire series.
  • 47. Compare with baseline field :
    • 1.For a new defect in previously normal area .
    • Cluster of 3 or or more non edge points each
    • of which declines by 5 or >5dB.
    • 2.For deepening of pre existing defect .
    • A cluster of 3 or more non edge points, each of which declines by 10 or>10dB.
    • 3.Generalized depression :
    • Decline of all points by 3dB.
  • 48. Glaucoma change probability programme:
    • Point by point probability of any change in baseline field and new field.
    • 1.new defect : 3 or more non-edge points each of which, p<5%,on two consecutive fields.
    • 2.deepening of pre existing defect : part of a scotoma, cluster, p<5%.
    • 3. expansion :
    • Within 15 ° of field-2 previous normal points.
    • Outside 15° of field-3 previously normal points depressed with p,5%.
  • 49.
    • Generalized depression :
    • Decline in MD, p<1%.
  • 50. References :
    • Illustrated Automated Static Perimetry G.R.Reddy.
    • Testing of the Field of Vision-Douglas R.Anderson.
    • Clinical Decisions in Glaucoma-Elizabeth Hodapp,Richard K.Parrish,Doughlas R.Anderson.
    • Visual Field Examination-A.K.Gupta ,Reena M.Chaudhary,Charu Tandon.
  • 51.
    • . Thank you .