Perimetry is the procedure for estimating extent of the visual fields
It is the measurement of visual functions of the eye at topographically defined loci in the visual field.
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HISTORY
1970- Octopus perimeter was first introduced
1982 – Humphrey field analyser first displayed at AAO
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1983 – Michael Patella showed first clinical trial
1984 – Became popular
Visual field
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Visual field is a three-dimensional area of a subject's surroundings that can be seen at any one time around an object of fixation.
Traquair described it as an "island of vision surrounded by a sea of darkness"
Island of vision
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visual field division
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- central
- peripheral
central
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an area from the fixation point to a circle 30° away.
The central zone contains physiologic blind spot on the temporal side.
Peripheral field
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The rest of the area beyond 30° to outer extent of the field of vision
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Isopter
a contour line in a representation of the visual field around the points representing the macula that passes through the points of equal visual acuity.
each isopter can be defined as a threshold line forming points of equal sensitivity on a visual field chart
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Scotoma
an area of loss of vision totally (absolute scotoma) or partially (relative scotoma) in the visual field.
It is the depressed part of the field as compared to the surrounding and not as compared to normals.
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Perimetry
Kinetic versus static perimetry
Peripheral versus central field charting
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Manual versus automated perimetry
Kinetic
In this the stimulus of known luminance is moved from a peripheral non seeing point towards the centre till it is perceived to establish the isopters.
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confrontation method
Lister's perimetry,
tangent screen scotometry
Goldmann's perimetry.
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confrontation method
Lister's perimetry
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Goldmann's perimetry
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Goldmann's perimetry
Goldmann Perimeter
Static perimetry
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This involves presenting a stimulus at a predetermined position for a preset duration with varying luminance in the field of vision
Goldmann perimetry
Friedmann perimetry
Automated perimetry.
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Friedmann perimetry
Automated perimetry- Humphrey field analyser
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Automated perimetry- octopus field analyser
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Peripheral field charting
Confrontation method
Perimetry: Lister's, Goldmann's and automated
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Central field charting
Campimetry or scotometry
Goldmann's perimetry
Automated field analysis.
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MANUAL PERIMETRY
Confrontation method
Lister's perimeter
Campimetry (scotometry)
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Goldmann's perimeter
Confrontation method
This is a rough but rapid and extremely simple method of estimating the peripheral visual field.
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Assuming the examiner's fields to be within the normal range
Confrontation method
The patient is seated facing the examiner at a distance of 1 metre. While testing the left eye, the patient covers his right eye and looks into the examiner's right eye. The examiner occludes his left eye and moves his hands in from the periphery keeping it midway between the patient and himself.
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The patient and the examiner ought to see the hand simultaneously, for the patient's field to be considered normal. The hand is moved similarly from above, below and from right and left.
Lister's perimeter
It has a metallic semicircular arc, graded in degrees, with a white dot for fixation in the centre.
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Campimetry (scotometry)
Bjerrum's screen of either I metre or 2 metres square is used
not used now-a-days
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Goldmann's perimeter
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The test conditions and the intensity of the target are always the same.
It permits greater reproducibility.
AUTOMATED PERIMETRY
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The automated perimeters automatically test suprathreshold and threshold stimuli and quantify depth of field defect
The problem of subjectivity of perimetrist was eliminated by automation which began in the 1970s
Automated perimetry improved the uniformity and reproducibility of visual fields
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Lister's perimeter
Octopus Field Master
Humphrey field analyser
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Octopus Field Master
Humphrey field analyser
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Advantages of automated perimetry
flexibility, precision and consistency of test method
data storage capability, ease of operation, well controlled fixation, menu driven software and on line assistance
compare results statistically
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compare with previous tests of the same individual
Automated perimeter variables
Background illumination
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Stimulus intensity
Stimulus size
Stimulus duration
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Testing strategies and programmes
The normal threshold is defined as the mean threshold in normal people in a given age group at a given location in the visual field.
range of 0–50. 50(db) -dimmest
0 db is the brightest illumination.
the higher the decibel value, the higher is the sensitivity
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Suprathreshold testing
Threshold testing.
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Suprathreshold testing
targets that are well above the brightness
screening procedure to detect gross defects
It should not be used to monitor glaucoma.
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Screening central > 6 points
Full field 120 points
Threshold testing.
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Full threshold testing.
Fast Pac
SITA
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Test programmes -HFA
Central field tests
Peripheral field tests
Speciality tests
Custom tests
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Evaluation of Humphrey single-field Statpac printout
I. Patient data and test parameters.
II. Reliability indices.
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III. Gray scale simulation
IV. Total deviation plots
V. Pattern deviation plots.
VI. Global indices
VII. Glaucoma hemifield test (GHT)
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VIII. Actual threshold values
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This download link is referred from the post: MBBS Lecture Notes for all subjects (updated for 2021 syllabus) - All universities