AUTOMATED PERIMETRY

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AUTOMATED PERIMETRY

• DR.JYOTI SHETTY
• MEDICAL DIRECTOR
• BANGALORE WEST LIONS EYE HOSPITAL, BANGALORE

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BASIC CONCEPTS

• Traquair's has defined the visual field as been a
  hill island of vision in a sea of darkness
  testing along X-Y axes of this 3 dimensional
  area determines the location in the visual field
  and along the Z axis identifies the visibility
  threshold.
• X - Y axis - kinetic perimetry
• Z axis - static perimetry
• Automated Perimetry - " Differential light
  threshold Ability to differentiate an
  illuminated target against an illuminated
  background."
• Threshold Perimetry - Modality of choice

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BASIC CONCEPTS --- contd

• THRESHOLD
• Luminance of stimuli that is seen 50 of times it
  is presented
• Logarithmic unit dB ( dB prop. 1 / brightness )
• Bracketing strategy ( 4 - 2 - 2 algorithm )
• Supra threshold - 95 chance a stimulus is seen.
• Infra threshold - 5 chance a stimulus is seen.

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BASIC MACHINE DESIGN

• Illuminated hemispherical bowl 33 cm away with
  target of fixation
• Stimuli - spot of light - LED / Projection system
  / Comp. Video monitor
• HFA - II ( 700 Series ) Aspherical bowl 30 cms
  away ,smaller ,more ergonomic stimuli in
  periphery more closer,
• programmed to decrease stimuli brightness
  (4dB).

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FIXATION CONTROL

• CC TV monitor
• Heijl - Krakau Blind spot method
• Gaze tracker
• Full time two variable Gaze monitor
• Image analysis
• Errors - upward / downward
• Fixation checked 100 of stim. Time
• No testing time for fixation check

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Basic software design

• Strategies for threshold detection
• Intensity of the stimulus presented at a given
  point is related to the normal threshold at that
  stimulus site.
• Bracketing strategies to define threshold at any
  point.
• 4-2-2 algorithm
• SITA

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INFORMATION DISPLAY

• Numeric data display actual dB
  value at each point
• Gray scale range of decibels and their
  corresponding luminance
• Difference / Depth defect actual value is
  arithmetically subtracted from a presumed
  expected field.

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Parameters recommended for testing

• Foveal fixation target small and large diamond
  with yellow lights.
• Goldmann size III target for stimuli blind
  spot check. If excessive fixation loss it can be
  decreased to II or I or if vision less than 6/36
  than it can be increased to V.
• White stimulus colour
• Normal testing speed. can be slow down if patient
  is slow to response.
• Foveal threshold - ON / OFF

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Threshold tests

• Central 30-2 76 points are tested . Each point
  6 deg apart. Straddling the horizontal and
  vertical axis so that the 2 inner most test
  points are 3 deg from fixation point.
• Central 24-2 56 points are tested . Avoids rim
  artifacts.
• Central 10-2 68 points space 2 deg apart.
  Useful in advance disease with spilt fixation.
• Macular threshold test square grid of 16 points
  each 2 deg apart , with each point thresholded 3
  times.

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30 2 24 2
Macular threshold
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INTERPRETATION

• Factors for consistency in testing
• Best Refractive correction used. Contact lens to
  avoid rim artifacts.
• Pupil Diameter at least 3.5 mm in size.
• Visual Acuity
• Date Time of testing
• Age-For comparison with normative data
• Short term fluctuation-Fluctuation occurring
  within the test. Should be lt3dB.

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INTERPRETATION ----contd.

• Reliability of patient
• Fatigue, anxiety and learning effect
• Fixation loss should be less than 20
• False positive and negative response should be
  less than 33.

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Statistical global indices

• MD mean deviation sensitive to total loss
• PSD pattern standard deviation sensitive to
  localized loss.
• CPSD corrected pattern standard deviation PSD
  corrected for short term fluctuation. Very
  sensitive index.

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Glaucoma defect with automated perimetry-
Anderson's Criteria

• 3 or more cont.non edge points with gt 5 dB loss
• 2 or more cont. non edge points with gt10 dB loss
• Diff. of 10 dB across nasal hor. meridian at 2 or
  more adj. points ( nasal step.)
• GHT - ONL
• PSD plot - gt 3 pts , plt 5 of which one lt 1
• CPSD ( p lt5 ) GHT ONL

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INTERPRETATION ----contd.

• Progression of defect
• Test parameters comparable
• Defect - increased in size / depth
• gt 7 dB increase in depth of existing defect
• gt 9 dB depression adj. to abnormal point
• gt 11 dB depression of a normal point ( New
  Defect )
• Box plot change analysis
• Overview
• Glaucoma change probability analysis

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SWAP

• Tests subset of Ganglions affected earlier
  selectively -- Blue / Yellow
• Reduces the redundancy of responsiveness to
  stimuli
• Intense yellow background - bleaches green / red
  cones
• Blue stim. ( 440nm ) - isolates blue cones
• Adaptation - 3 mts. Room illumination - minimal
• Stimulus size BS check size V
• Mean threshold values lower than SAP - Gray scale
  darker
• Stat Pac probability plots more reliable

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SWAP -- contd

• Field defect precedes SAP by gt 3 yrs
• Once abnormal - remain abnormal ( no recovery of
  damaged blue cones )
• No role in advanced POAG / advanced lenticular
  changes / colour vision abnormalities
• Most useful in younger Glaucoma suspects, OHT ,
  POAG with mild to mod.damage
• Time consuming - SITA optimised for SWAP / Fast
  Pac can be used

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THANK YOU