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Perimetry

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• Perimetry normally tests the light-differencesensitivity across the visual field.

• This sensitivity reflects the capability of the eyeto perceive a brightness difference between atest target and its background.

• Light-difference sensitivity depends upon thetested location on the retina and upon theparameters of the measurement technique,such as intensity of background luminance andtarget size.

Perimetry

Perimetry

• The normal visual field extends further awayfrom fixation temporally and inferiorly thansuperiorly and nasally.

• From the center of the retina this sensitivitydecreases towards the periphery, evoking theclassically defined ‘hill of vision:’ a three-dimensional representation of retinal lightsensitivity.

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Perimetry

Differential light sensitivity

Hill of vision

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Perimetry

• The physiological blind spot corresponds to thelocation where the optic nerve enters the eye andits center is located about 15° temporal fromfixation.

Physiological blind spot

Corresponding to the optic n head,

15 ⁰ temporal to the point of fixation,

2/3 below the horizontal meridian,

Size 5⁰ horizontal, 7⁰ vertical

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Importance of visual field testing

It reflects topographic sensitivity of various foci on the retina

Resolution – acuity

Differential light sensitivity.

Contrast.

Colour,

Motion,

flickers

Physiological basics

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Factors affecting the visual field

Apparent size of the spot (actual size, distance),

Duration of the stimulus,

Background illumination,

Intensity of the stimulus,

Contrast,

Colour of the stimulus,

Patient factors:

➢ Light dark adaptation,

➢ Refraction,

➢ Education, attentiveness.

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Monocular visual field

Binocular visual field

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Stereoscopic visual field

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Enlarged Blind Spot

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Confrontation test

Tangent screen

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Tangent screen

Tangent screen

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Arc perimeter

Goldmann Manual kinetic visual field testing

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Manual visual field testing

Amsler grid

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Octopus perimetry

Humphrey Field Analyzer

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Threshold Static Automated Perimetry

The most commonly used visual field test is Threshold Static Automated perimetry.

A specific point is chosen for examination and the stimulus is increased until its threshold is determined.

Threshold Static Automated Perimetry

▪ With Threshold Static Automated perimetry, acomputer program is selected.

▪ The most commonly used one is the central30°, 24° of the visual field using a six degreespaced grid.

▪ This is accomplished by keeping the size andlocation of a target constant and varying thebrightness until the dimmest target thepatient can see at each of the test locations isfound.

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Testing stratgies

▪ Full threshold. ▪ Threshold.

▪ Suprathreshold.▪ Fastpac.

▪ Sita standard.▪ Sita fast.

Perimetry print out

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Reliability parameters

Gray scale

Pattern deviation

Global indices

Probability symbols

GHT

Patient nameTest

Total deviation

Numeric sensitivity

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◼ The tested pointsare spaced in anequidistant gridpattern, with eachpoint 6 degreesapart horizontallyor vertically fromany adjacentpoint.

◼ dB printoutsillustrate the gridpatterns.

Numeric threshold values

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30-2 full threshold grid

30-2 full threshold

▪ Number of test points is 76 ▪ Density is 6 degrees.

▪ Only 3 degrees bare area is left surrounding the

fixation points.

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24-2 full threshold

▪ Number of test points is 54. ▪ Density is 6 degrees.

▪ Only 3 degrees bare area is left surrounding the fixation

points.

Glaucoma hemifield test

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Glaucoma hemifield test

The GHT, devised for the Humphrey Field Analyzer,compares 24-2 visual fields into 10 regions, with 5inferior regions representing mirror images of 5corresponding superior regions.

Differences between corresponding superior andinferior zones are compared with the differencespresent in the population of normal controls.

Glaucoma hemifield test

❑Outside normal limits,

❑Borderline,❑ General reduction of sensitivity, ❑Abnormally high sensitivity, ❑Within normal limits,

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Physiological blind spot

❑Corresponding to optic nerve head,

❑ 15⁰ temporal to the fixation point,❑ size 5⁰ horizontal, 7⁰ vertical ❑2/3 below horizontal meridian,

Reliability tests

◼ Informationabout thesefactors is atthe top of thechart.

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Assess reliability

◼ Diagnostic and managementdecisions should not be made onthe basis of unreliable data.

◼ The three measures of reliabilityare

1. fixation losses,

2. false negatives, and

3. false positives.

LT Eye RT Eye

Grey scale

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Pattern deviation plot

◼ This plot is helpfulin patients who mayhave a combinedoverall depression(from mediaopacity, forexample) as well aslocalized loss fromglaucoma.

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Guided progression

analysis (GPA)

GPA software identifies statistically significant changes in visual field threshold sensitivity

automatically.

• Never rely on first field report

• Always correlate clinically.• Correct any significant

refractive errors before testing.

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Not every VF defect is glaucoma

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