Automated perimetry
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AUTOMATED PERIMETRY. DR.JYOTI SHETTY MEDICAL DIRECTOR BANGALORE WEST LIONS EYE HOSPITAL, BANGALORE. BASIC CONCEPTS.

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AUTOMATED PERIMETRY

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Automated perimetry

AUTOMATED PERIMETRY

DR.JYOTI SHETTY

MEDICAL DIRECTOR

BANGALORE WEST LIONS EYE HOSPITAL, BANGALORE


Basic concepts

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


Basic concepts contd

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.


Basic machine design

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).


Fixation control

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


Basic software design

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


Information display

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.


Parameters recommended for testing

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


Threshold tests

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.


Automated perimetry

30 – 2 24 – 2 Macular threshold


Interpretation

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 <3dB.


Interpretation contd

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%.


Statistical global indices

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.


Glaucoma defect with automated perimetry anderson s criteria

Glaucoma defect with automated perimetry- Anderson's Criteria

  • 3 or more cont.non edge points with >= 5 dB loss

  • 2 or more cont. non edge points with >=10 dB loss

  • Diff. of 10 dB across nasal hor. meridian at 2 or more adj. points ( nasal step.)

  • GHT - ONL

  • PSD plot - >= 3 pts , p< 5% of which one < 1%

  • CPSD ( p <5% ) GHT ONL


Interpretation contd1

INTERPRETATION ----contd.

  • Progression of defect

  • Test parameters comparable

  • Defect - increased in size / depth

  • >= 7 dB increase in depth of existing defect

  • >= 9 dB depression adj. to abnormal point

  • >= 11 dB depression of a normal point ( New Defect )

  • Box plot change analysis

  • Overview

  • Glaucoma change probability analysis


Automated perimetry

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


Swap contd

SWAP -- contd

  • Field defect precedes SAP by >= 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


Automated perimetry

THANK YOU


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