مركزالبحرللعيون

The field of vision is defined as the area that is The field of vision is defined as the area that is perceived simultaneously by a fixating eyeperceived simultaneously by a fixating eye

• Traquair, “an island of vision in the sea of darkness”Traquair, “an island of vision in the sea of darkness”

• Depicts the visual field as a three-dimensional spatial modelDepicts the visual field as a three-dimensional spatial model

• The shoreline of the island represents the peripheral limits of the visual The shoreline of the island represents the peripheral limits of the visual field (least sensitive), and the peak correspond to the fovea (greatest field (least sensitive), and the peak correspond to the fovea (greatest sensitivity)sensitivity)

NORMAL VISUAL FIELD LIMITSNORMAL VISUAL FIELD LIMITS

6060

6060 6060

100100 100100

7575 7575

FixationFixation

XX XX

= Physiological Blind spot= Physiological Blind spot

Diameter of Optic DiscDiameter of Optic Disc Relation of Disc to FoveaRelation of Disc to Fovea

Horizontal: 1.1mm, 5.5Horizontal: 1.1mm, 5.5 Nasal: 3.0mm, 15.0Nasal: 3.0mm, 15.0

Vertical: 1.5mm, 7.5Vertical: 1.5mm, 7.5 Inferior: 0.3mm, 1.5Inferior: 0.3mm, 1.5

XX

• The contour of the island of vision relates to both the anatomy of The contour of the island of vision relates to both the anatomy of the visual system and the level of retinal adaptationthe visual system and the level of retinal adaptation

• The highest concentration of cones is in the fovea, which project The highest concentration of cones is in the fovea, which project to their own ganglion cell. This one-to-one ratio between foveal to their own ganglion cell. This one-to-one ratio between foveal cone and ganglion cell results in maximal resolution in the foveacone and ganglion cell results in maximal resolution in the fovea

Horizontal

raphe

Papillomacular

bundle

Normal Visual FieldNormal Visual Field

Visual field measurement can Visual field measurement can be affected by:be affected by: – Patient's age Patient's age

– Size and position of the noseSize and position of the nose

– Orbital structuresOrbital structures

– Location of eye within the orbitLocation of eye within the orbit

– Color of stimuliColor of stimuli

– Refractive errorRefractive error

– Fixation Fixation

– Eye movementEye movement

– Patient cooperationPatient cooperation

– Ease of operation of the instrumentEase of operation of the instrument

History of PerimetryHistory of Perimetry• In 1856 Dr. Von Graefe is the first to draw the field using white piece of In 1856 Dr. Von Graefe is the first to draw the field using white piece of

paperpaper

• In 1889 Dr. Bjerrum was using a tangent screen on the back of his clinic In 1889 Dr. Bjerrum was using a tangent screen on the back of his clinic door and he described the arcuate scotomadoor and he described the arcuate scotoma

• In 1909 Dr. Ronne developed kinetic isopter perimetry and described the In 1909 Dr. Ronne developed kinetic isopter perimetry and described the nasal step in glaucomanasal step in glaucoma

• In 1945 Dr. Goldmann designed the first cupola perimeter for manual kinetic In 1945 Dr. Goldmann designed the first cupola perimeter for manual kinetic perimetryperimetry

• In 1973 the era of automation began with Dr. Fankhuser and his coworkers In 1973 the era of automation began with Dr. Fankhuser and his coworkers in Bern, Switzerlandin Bern, Switzerland

• The first standard automated perimeter The first standard automated perimeter OCTOPUS 201 - In 1976OCTOPUS 201 - In 1976 OCTOPUS 2000 - In 1980OCTOPUS 2000 - In 1980 OCTOPUS 500 - In 1983 OCTOPUS 500 - In 1983 OCTOPUS 1-2-3 - In 1989 OCTOPUS 1-2-3 - In 1989 OCTOPUS 101 - In 1993 OCTOPUS 101 - In 1993

Knee of Wilbrand`s

Meyer`s loop

KINETIC PERIMETRYKINETIC PERIMETRY

• In kinetic perimetry, a stimulus is In kinetic perimetry, a stimulus is moved from a non seeing area of moved from a non seeing area of the visual field to a seeing areathe visual field to a seeing area

• Procedure is repeated with use of the Procedure is repeated with use of the same stimulus along a set of same stimulus along a set of meridians, usually spaced every meridians, usually spaced every 15°15°

• Aim is to find points in the visual field Aim is to find points in the visual field of equal retinal sensitivity. By joining of equal retinal sensitivity. By joining these points an isopter is definedthese points an isopter is defined

• Then luminance and the size of the Then luminance and the size of the target is changed to plot other isopterstarget is changed to plot other isopters

KINETIC PERIMETRYKINETIC PERIMETRY

• In kinetic perimetry, the island of vision is approached horizontally. In kinetic perimetry, the island of vision is approached horizontally. Isopters can be considered as the outline of horizontal slices of the Isopters can be considered as the outline of horizontal slices of the island of visionisland of vision

• Disadvantages of this technique include the subjectivity, highly Disadvantages of this technique include the subjectivity, highly dependant on the operator efficiency, time consuming, difficulties with dependant on the operator efficiency, time consuming, difficulties with randomising targets and patient cooperationrandomising targets and patient cooperation

STATIC PERIMETRYSTATIC PERIMETRY

• In static perimetry, the size and location of the test target remain constant In static perimetry, the size and location of the test target remain constant

• Retinal sensitivity at a specific location is determined by varying only Retinal sensitivity at a specific location is determined by varying only the brightness of the test targetthe brightness of the test target

• The shape of the island is then defined by repeating the threshold The shape of the island is then defined by repeating the threshold measurement at various locations in the field of visionmeasurement at various locations in the field of vision

• This strategy allows for a quantitative measure of the relative density This strategy allows for a quantitative measure of the relative density of a defect, more easily than in kinetic perimetryof a defect, more easily than in kinetic perimetry

Terminology Related to Perimetry Terminology Related to Perimetry

• Isopter is a line within the visual field which connects points of equal sensitivity or threshold.

• Apostilb (asb) is the unit of measurement of luminance (brightness). One apostilb equals to 0.3183 candela/m², or 0.1 mililambert. – A healthy patient can perceive a stimulus of 1 abs in the macular area.

• Decibels (dB) is the unit of measurement of neutral density filters. Each decibel equals 1/10 log unit. Thus 10 dB equals 1 log unit or 10 fold change in intensity.– The decibel scale is not standardized because the

maximal luminance varies between instruments.– Data needs to be captured on the same instrument

for comparisons.40

30

20

10

0

50

40

30

20

10

0

0.1

1

10

100

1000

10,000

OctopusOctopus

DecibelsDecibels

HumphreyHumphrey

DecibelsDecibels

AbostilbsAbostilbs

40

30

20

10

0

50

40

30

20

10

0

0.1

1

10

100

1000

10,000

OctopusOctopus

DecibelsDecibels

HumphreyHumphrey

DecibelsDecibels

AbostilbsAbostilbs

SENSITIVITY SENSITIVITY VERSUSVERSUS THRESHOLD THRESHOLD

• As one ascends the hill of vision toward the As one ascends the hill of vision toward the fovea, the sensitivity of the retina increases, fovea, the sensitivity of the retina increases, dimmer targets will become visible. dimmer targets will become visible.

• Therefore, as retinal sensitivity increases, Therefore, as retinal sensitivity increases, the differential light threshold measured in the differential light threshold measured in apostilbs decreases. apostilbs decreases.

• In automated perimetry, however, threshold In automated perimetry, however, threshold is recorded in the inverted decibel scale, and is recorded in the inverted decibel scale, and dimmer targets have higher decibel values. dimmer targets have higher decibel values.

• Therefore, threshold in decibels is directly Therefore, threshold in decibels is directly proportional to retinal sensitivity.proportional to retinal sensitivity.

0 10,000

1000

100

10

1

0.1

One Log Unit 10

Two Log Unit 20

Three Log Unit 30

Four Log Unit 40

Five Log Unit 50

DECIBELS APOSTILBS

Least SensitiveLeast Sensitive

Most SensitiveMost Sensitive

GOLDMANN COMPARISON

III 4e

III 3e

III 2e

III 1e

III 1a

MANUAL PERIMETRYMANUAL PERIMETRY

• Goldmann perimeter is the most widely used Goldmann perimeter is the most widely used instrument for manual perimetry. instrument for manual perimetry.

• It is a calibrated bowl projection instrument It is a calibrated bowl projection instrument with a background intensity of 31.5 apostilbs. with a background intensity of 31.5 apostilbs.

• Size and intensity of targets can be varied to Size and intensity of targets can be varied to plot different isopters kinetically and plot different isopters kinetically and determine local static thresholds.determine local static thresholds.

GOLDMANN VISUAL FIELDGOLDMANN VISUAL FIELD

The stimuli used to plot an isopter are The stimuli used to plot an isopter are identified by Roman numeral, number, and identified by Roman numeral, number, and a lettera letter

Roman numeral represents the size of the Roman numeral represents the size of the target, from target, from Goldmann size 0 to Goldmann size V Goldmann size 0 to Goldmann size V

– Each size increment equals a fourfold increase in areaEach size increment equals a fourfold increase in area

Number and letter represent the intensity of Number and letter represent the intensity of the stimulusthe stimulus– change of one number represents 5-dB change in intensitychange of one number represents 5-dB change in intensity

– change each letter represents 1-dB change in intensitychange each letter represents 1-dB change in intensity

Size of Goldmann Targets

1/16

¼

1

4

16

64

0

I

I I

I I I

IV

V

Area (mm²)Target1/16

¼

1

4

16

64

0

I

I I

I I I

IV

V

Area (mm²)Target

Intensity of Goldmann Targets

31.5

100

315

1000

1e

2e

3e

4e

Intensity (asb)Filter31.5

100

315

1000

1e

2e

3e

4e

Intensity (asb)Filter

GOLDMANN VISUAL FIELDGOLDMANN VISUAL FIELD

Isopters in which the sum of the Roman Isopters in which the sum of the Roman numeral (size) and number (intensity) are numeral (size) and number (intensity) are equal can be considered equivalentequal can be considered equivalent

The equivalent isopter combination with the The equivalent isopter combination with the smallest target size usually is preferred smallest target size usually is preferred because detection of isopter edges is more because detection of isopter edges is more accurate with smaller targetsaccurate with smaller targets

One usually starts by plotting small targets One usually starts by plotting small targets with dim intensity (I1e) and then increasing with dim intensity (I1e) and then increasing the intensity of the target until it is maximal the intensity of the target until it is maximal before increasing the size of the targetbefore increasing the size of the target

VV

IVIV

IIIIII

IIII

II

00

11223344NONO

VV

IVIV

IIIIII

IIII

II

00

11223344NONO

TheThe usual progressionusual progression

GOLDMANN VISUAL FIELDGOLDMANN VISUAL FIELD

Once an isopter is plotted, the stimulus used to plot the isopter Once an isopter is plotted, the stimulus used to plot the isopter is used to statically test within the isopter to look for localized is used to statically test within the isopter to look for localized defects. In this way, it acts as a suprathreshold stimulus. defects. In this way, it acts as a suprathreshold stimulus.

AUTOMATED PERIMETRYAUTOMATED PERIMETRY

The introduction of computers and automation The introduction of computers and automation heralded a new era in perimetric testing. heralded a new era in perimetric testing.

Static testing can be performed in an objective and Static testing can be performed in an objective and standardized fashion with minimal perimetrist bias. standardized fashion with minimal perimetrist bias.

A quantitative representation of the visual field can A quantitative representation of the visual field can be obtained more rapidly than with manual testing.be obtained more rapidly than with manual testing.

The computer presents the stimuli in a random The computer presents the stimuli in a random fashion. Patients do not know where the next fashion. Patients do not know where the next stimulus will appear, so fixation is improved. Also stimulus will appear, so fixation is improved. Also increase the speed of the test by bypassing the increase the speed of the test by bypassing the problem of local retinal adaptation.problem of local retinal adaptation.

AUTOMATED PERIMETRYAUTOMATED PERIMETRY

• Humphrey Field Analyzer uses a constant target size Humphrey Field Analyzer uses a constant target size equal to a Goldmann "III" (4 mmequal to a Goldmann "III" (4 mm²²) and varies the target ) and varies the target brightness only. unless otherwise instructed. brightness only. unless otherwise instructed.

• The stimulus intensity can reach up to 10,000 asb in The stimulus intensity can reach up to 10,000 asb in Humphrey and 1000asb in Octopus.Humphrey and 1000asb in Octopus.

• The background luminance in Humphery is 31.5 asb and the testing distance 33 cm. while Octopus model uses 4 asb and the testing distance 42.5 cm

Comparison of static and kinetic Comparison of static and kinetic perimetry to detect shallow scotomasperimetry to detect shallow scotomas

A.A. Kinetic evaluation can clearly outline the normal visual fieldKinetic evaluation can clearly outline the normal visual field

B.B. Kinetic perimetry may miss shallow scotomas and poorly define the flat Kinetic perimetry may miss shallow scotomas and poorly define the flat slope seen nasallyslope seen nasally

C.C. The edge of steeply sloped scotomas may be identified easily with kinetic The edge of steeply sloped scotomas may be identified easily with kinetic perimetry, but the steepness of the slope may not be appreciatedperimetry, but the steepness of the slope may not be appreciated

D. & E.D. & E. Static perimetry readily detects shallow scotomas and can define the Static perimetry readily detects shallow scotomas and can define the slope of both shallow and steep scotomasslope of both shallow and steep scotomas

In a study of patients with open angle glaucoma, Dr. Ourgaud reported that a defect was found in one third of cases with static perimetry that was

missed by kinetic perimetry

J Fr Ophthalmol,1982

GLAUCOMATOUS VISUAL FIELD GLAUCOMATOUS VISUAL FIELD DEFECTSDEFECTS

Any clinically or statistically significant deviation from Any clinically or statistically significant deviation from the normal shape of the hill of vision can be considered the normal shape of the hill of vision can be considered a visual field defect. In glaucoma, these defects are a visual field defect. In glaucoma, these defects are either diffuse depressions of the visual field or localized either diffuse depressions of the visual field or localized defects that conform to nerve fiber bundle patterns.defects that conform to nerve fiber bundle patterns.

DIFFUSE DEPRESSIONDIFFUSE DEPRESSION

• Diffuse depression of the visual field results from widespread diffuse Diffuse depression of the visual field results from widespread diffuse loss of nerve fibers of the retina. loss of nerve fibers of the retina.

• It is common in glaucoma but it is non specific sign that can be caused It is common in glaucoma but it is non specific sign that can be caused by many etiologies. by many etiologies.

• By far the most common reason for a diffuse depression is lens opacity. By far the most common reason for a diffuse depression is lens opacity.

• Other factors include other media opacities, miosis, improper refraction, Other factors include other media opacities, miosis, improper refraction, patient fatigue, inattentiveness or inexperience with the examination, patient fatigue, inattentiveness or inexperience with the examination, ocular anomalies, and age. ocular anomalies, and age.

DIFFUSE DEPRESSIONDIFFUSE DEPRESSION

• In manual perimetry, is manifested by In manual perimetry, is manifested by contraction of the isopters. The isopters contraction of the isopters. The isopters retain their normal contour. The most retain their normal contour. The most central isopters may disappear entirely central isopters may disappear entirely as the peak of the island of vision sinks.as the peak of the island of vision sinks.

• In automated perimetry, diffuse In automated perimetry, diffuse depression results in relative defects depression results in relative defects across the entire visual field. across the entire visual field.

LOCALIZED NERVE FIBER LOCALIZED NERVE FIBER BUNDLE DEFECTSBUNDLE DEFECTS

• Localized visual field defects in glaucoma Localized visual field defects in glaucoma result from damage to the retinal nerve result from damage to the retinal nerve fiber bundles. fiber bundles.

• Because of the unique anatomy of the Because of the unique anatomy of the retinal nerve fiber layer, axonal damage retinal nerve fiber layer, axonal damage causes characteristic patterns of visual causes characteristic patterns of visual field changes.field changes.

• The most common location of visual field The most common location of visual field defects occurs within an arcuate area defects occurs within an arcuate area (Bjerrum’s area) extending from blind spot (Bjerrum’s area) extending from blind spot nasally 10-20 around fixation and nasally 10-20 around fixation and terminate at the median raphe.terminate at the median raphe.

Nerve Fiber Bundle DefectsNerve Fiber Bundle Defects

The superior and inferior poles of the optic nerve The superior and inferior poles of the optic nerve head are most vulnerable to glaucomatous damage.head are most vulnerable to glaucomatous damage.

It has been postulated that these areas may be It has been postulated that these areas may be watershed areas at the junction of the vascular supply watershed areas at the junction of the vascular supply from adjacent ciliary vessels.from adjacent ciliary vessels.

Ultrastructural examination of the lamina cribrosa Ultrastructural examination of the lamina cribrosa shows that the pores in the superotemporal and shows that the pores in the superotemporal and inferotemporal areas are larger. The large pores may inferotemporal areas are larger. The large pores may make these regions more vulnerable to compression.make these regions more vulnerable to compression.

PARACENTRAL DEFECTSPARACENTRAL DEFECTS

• Circumscribed paracentral defects are an early sign of localized Circumscribed paracentral defects are an early sign of localized glaucomatous damage. glaucomatous damage.

• The defects may be relative or absolute and frequently found in The defects may be relative or absolute and frequently found in Bjerrum’s area along the course of the nerve fiber bundle.Bjerrum’s area along the course of the nerve fiber bundle.

• With progression paracentral scotomas become deeper and longer and With progression paracentral scotomas become deeper and longer and may gradually coalesce forming an arcuate or Bjerrum’s scotoma.may gradually coalesce forming an arcuate or Bjerrum’s scotoma.

ARCUATE SCOTOMASARCUATE SCOTOMAS• More advanced loss of nerve fiber bundle leads to a scotoma that More advanced loss of nerve fiber bundle leads to a scotoma that

starts at or near the blind spot, arches around fixation, and terminates starts at or near the blind spot, arches around fixation, and terminates abruptly at the nasal horizontal meridian . abruptly at the nasal horizontal meridian .

• In the temporal portion of the field, it is narrow because all of the nerve In the temporal portion of the field, it is narrow because all of the nerve fiber bundles converge onto the optic nerve. fiber bundles converge onto the optic nerve.

• The scotoma spreads out on the nasal side and may be very wide The scotoma spreads out on the nasal side and may be very wide along the horizontal meridian.along the horizontal meridian.

Differential Diagnosis of Differential Diagnosis of Arcuate ScotomasArcuate Scotomas

Glaucoma

Branch Vein OcclusionBranch Vein Occlusion

Branch Artery OcclusionBranch Artery Occlusion

Optic Neuritis Optic Neuritis

Ischemic Optic NeuropathyIschemic Optic Neuropathy

Optic NerveOptic Nerve Drusen

Optic NerveOptic Nerve Pit

Optic Nerve ClobomaOptic Nerve Cloboma

Myelinated NFLMyelinated NFL

NASAL STEP DEFECTSNASAL STEP DEFECTS

• A steplike defect along the horizontal meridian results from asymmetric A steplike defect along the horizontal meridian results from asymmetric loss of nerve fiber bundles in the superior and inferior hemifields.loss of nerve fiber bundles in the superior and inferior hemifields.

• Nasal steps frequently occur in association with arcuate or paracentral Nasal steps frequently occur in association with arcuate or paracentral scotomas, but a nasal step also may occur in isolation. scotomas, but a nasal step also may occur in isolation.

• Nasal step defects may be evident in some isopters but not in others, Nasal step defects may be evident in some isopters but not in others, depending on which nerve fiber bundles are damaged. depending on which nerve fiber bundles are damaged.

• Approximately 7% of initial visual field defects are peripheral nasal step Approximately 7% of initial visual field defects are peripheral nasal step defects.defects.

TEMPORAL WEDGE DEFECTSTEMPORAL WEDGE DEFECTS

• Damage to nerve fibers on the nasal side of the optic disc may result Damage to nerve fibers on the nasal side of the optic disc may result in temporal wedge-shaped defects. in temporal wedge-shaped defects.

• These defects are much less common than defects in the arcuate These defects are much less common than defects in the arcuate distribution. distribution.

• Occasionally, they are seen as the sole visual field defect. Occasionally, they are seen as the sole visual field defect.

• Temporal wedge defects do not respect the horizontal meridian.Temporal wedge defects do not respect the horizontal meridian.

EARLY VISUAL FIELD DEFECTSEARLY VISUAL FIELD DEFECTS

Werner and DranceWerner and Drance found in 35 eyes with previously found in 35 eyes with previously normal visual fields that the earliest defects were normal visual fields that the earliest defects were paracentral scotomas with a nasal step (51%), isolated paracentral scotomas with a nasal step (51%), isolated paracentral defects (26%), isolated nasal steps (20%), paracentral defects (26%), isolated nasal steps (20%), and sector defects (3%). and sector defects (3%).

Hart and Becker Hart and Becker found the following initial visual field found the following initial visual field defects in 98 eyes: nasal steps (54%), paracentral or defects in 98 eyes: nasal steps (54%), paracentral or arcuate scotomas (41%), arcuate blind spot enlargement arcuate scotomas (41%), arcuate blind spot enlargement (30%), isolated arcuate scotomas separated from the blind (30%), isolated arcuate scotomas separated from the blind spot (20%), and temporal defects (3%).spot (20%), and temporal defects (3%).

BLIND SPOT CHANGESBLIND SPOT CHANGES

1.1. Enlargement Enlargement oror vertical elongation of the blind spot may occur with early vertical elongation of the blind spot may occur with early arcuate defect that connects with the blind spot or peripapillary atrophy, arcuate defect that connects with the blind spot or peripapillary atrophy, which frequently accompanies glaucomatous damage.which frequently accompanies glaucomatous damage.

2.2. BaringBaring of the blind spot may be physiologic or pathologic. Physiologic of the blind spot may be physiologic or pathologic. Physiologic baring of the blind spot is an artifact of kinetic perimetry usually is baring of the blind spot is an artifact of kinetic perimetry usually is confined to a single central isopter in the superior visual field. Because confined to a single central isopter in the superior visual field. Because inferior retina is less sensitive than the superior retina. inferior retina is less sensitive than the superior retina.

End-stage defectsEnd-stage defects

• Only a small central island and a Only a small central island and a temporal island of vision remain.temporal island of vision remain.

• The temporal island is more The temporal island is more resistant than the central island resistant than the central island

Visual field changes in Normal-Visual field changes in Normal-Tension GlaucomaTension Glaucoma

1.1. Greater depthGreater depth

2.2. Steeper slopsSteeper slops

3.3. Closer to fixationCloser to fixation

Important PointsImportant Points

Both central visual acuity and field of vision may improve if the Both central visual acuity and field of vision may improve if the IOP is reduced in early stages of the diseaseIOP is reduced in early stages of the disease

In most patients with glaucoma, clinically recognizable disc In most patients with glaucoma, clinically recognizable disc changes precede detectable field losschanges precede detectable field loss

With standard manual perimetric techniques as many as 35% With standard manual perimetric techniques as many as 35% of fibers may gone in an eye with normal fieldof fibers may gone in an eye with normal field

20% loss of cells, especially large gangelion cells in the central 20% loss of cells, especially large gangelion cells in the central 3030 of the retina, correlates with a 5-dB sensitivity loss of the retina, correlates with a 5-dB sensitivity loss

++== ++

Etc.Etc.Etc.Etc.Etc.Etc.

SITA or TOPSITA or TOPNasal StepNasal Step

Blue/YellowBlue/YellowSupra thresholdSupra thresholdMacula Macula 1010--22

White/WhiteWhite/WhiteFull ThresholdFull ThresholdProgram 30Program 30--22

PerimetryPerimetryTechniqueTechnique

Test StrategyTest StrategyTest ProgramTest Program

++== ++

Etc.Etc.Etc.Etc.Etc.Etc.

SITA or TOPSITA or TOPNasal StepNasal Step

Blue/YellowBlue/YellowSupra thresholdSupra thresholdMacula Macula 1010--22

White/WhiteWhite/WhiteFull ThresholdFull ThresholdProgram 30Program 30--22

PerimetryPerimetryTechniqueTechnique

Test StrategyTest StrategyTest ProgramTest Program

Exa

min

atio

nE

xam

inat

ion

pro

ced

ure

pro

ced

ure

The following table indicates screening tests and the points The following table indicates screening tests and the points testedtested

Screening Test Extent of Visual Field/Number of Points

Central 40 30 degrees/40 points

Central 76 30 degrees/76 points

Central Armaly 30 degrees/84 points

Peripheral 60 30 to 60 degrees/60 points

Nasal step 50 degrees/14 points

Armaly full field 50 degrees/98 points

Full Field 81 55 degrees/81 points

Full Field 120 55 degrees/120 points

The following table indicates the threshold tests and the The following table indicates the threshold tests and the points testedpoints tested

Threshold Test Extent of Visual Field/Number of Points

10-2 10 degrees/68 point grid

24-2 24 degrees/54 point grid

30-2 30 degrees/76 point grid

60-4 30 to 60 degrees/60 points

Nasal Step 50 degrees/14 points

Commonly used programs Commonly used programs for glaucoma.for glaucoma.

The Octopus program 32 and the Humphrey program 30-2 The Octopus program 32 and the Humphrey program 30-2 are tests of the central 30° with 6° of separation between are tests of the central 30° with 6° of separation between locations. locations.

The Humphrey program 24-2 eliminates the most The Humphrey program 24-2 eliminates the most peripheral ring of test locations from program 30-2 peripheral ring of test locations from program 30-2 because it provides the least reliable data, except in because it provides the least reliable data, except in the nasal step region, so testing time can be shortened.the nasal step region, so testing time can be shortened.

DIFFERENTIAL LIGHT THRESHOLDDIFFERENTIAL LIGHT THRESHOLD

• Static computerized perimetry measures retinal sensitivity at Static computerized perimetry measures retinal sensitivity at predetermined locations in the visual field. predetermined locations in the visual field.

• These perimeters measure the ability of the eye to detect a difference These perimeters measure the ability of the eye to detect a difference in contrast between a test target and the background luminance. in contrast between a test target and the background luminance.

• Threshold is defined as the dimmest target perceived by the patient at Threshold is defined as the dimmest target perceived by the patient at a given discrete point; psychophysicists define the term as the ability a given discrete point; psychophysicists define the term as the ability to perceive a stimulus 50% of the time.to perceive a stimulus 50% of the time.

frequency-of-seeing curvefrequency-of-seeing curve

3.3. StrategyStrategy

Full thresholdFull thresholdA staircase, or bracketing, strategy is used to estimate A staircase, or bracketing, strategy is used to estimate threshold at threshold at each test pointeach test point. Most commonly, a 4-2 . Most commonly, a 4-2 algorithm is employed. algorithm is employed.

• Testing starts with a suprathreshold stimulus. The intensity Testing starts with a suprathreshold stimulus. The intensity of the stimulus is decreased in 4-db steps until the stimulus of the stimulus is decreased in 4-db steps until the stimulus is no longer seen ( threshold is crossed ). Threshold is is no longer seen ( threshold is crossed ). Threshold is crossed a second time by increasing the stimulus intensity crossed a second time by increasing the stimulus intensity in 2-db steps until it is seen again.in 2-db steps until it is seen again.

THRESHOLD THRESHOLD PROGRAMSPROGRAMS

The 4-2 bracketing strategyThe 4-2 bracketing strategy

2211

ThresholdThreshold

0.1 40

1

10

100

1000 0

10

20

30asbasb dBdB

PhasePhase

• Octopus perimeterOctopus perimeter estimates threshold as the average of the last estimates threshold as the average of the last seen and unseen stimulus intensities.seen and unseen stimulus intensities.

• Humphrey perimeterHumphrey perimeter uses the intensity of the last seen stimulus uses the intensity of the last seen stimulus as threshold.as threshold.

• Full threshold is rarely indicated, since newer thresholding Full threshold is rarely indicated, since newer thresholding algorithms are equally as valid and much faster.algorithms are equally as valid and much faster.

How can test time be minimized? How can test time be minimized? • The closer the initial stimulus is to the actual threshold, the faster the test

will be. Humphrey and Octopus use a "region growing" technique to determine the starting level for each point.

• The test begins with measuring the threshold at one spot in each quadrant of the central field. This then determines their reference hill of vision after correcting for age and general responsiveness of the patient. Adjacent locations are tested with appropriate starting thresholds.

OTHER THRESHOLD OTHER THRESHOLD PROGRAMSPROGRAMS

FASTPACFASTPAC

– Was most commonly used strategyWas most commonly used strategy

– Use 3dB step and only cross threshold onceUse 3dB step and only cross threshold once

– Save 25% of test time (Humphreys). Save 25% of test time (Humphreys).

– Measurement are statistically identical to the Measurement are statistically identical to the standard strategystandard strategy

– Trade off ST fluctuation over estimatedTrade off ST fluctuation over estimated

Swedish Interactive Thresholding Algorithm (SITA)Swedish Interactive Thresholding Algorithm (SITA)

– SITA utilises an alternative strategy to the bracketing method.

– Fast with similar accuracy and reproduciblity

– It is available as either SITA standard or SITA fast.

– Use computer intelligence by calculating expected thresholds and begin testing close to the actual threshold value.

– Two likelihood functions are calculated for each test location, one based on the assumption that the test location is glaucomatous and the other based on the assumption that the location is normal. The likelihood functions are updated as the examination progresses. The updating is informed by a combination of patient responses and internal models of normality and glaucoma.

SCREENING PROGRAMSSCREENING PROGRAMS• First the four primary points in each quadrant are thresholded to calculate First the four primary points in each quadrant are thresholded to calculate

the theoretical hill of vision. the theoretical hill of vision.

• Targets are then presented 6dB brighter than the theoretical hill of vision. Targets are then presented 6dB brighter than the theoretical hill of vision. Failure to detect the stimulus after it is presented for the second time will Failure to detect the stimulus after it is presented for the second time will result in different strategies as the following: result in different strategies as the following:

Two ZoneTwo Zone Points are presented the 6dB above the theoretical hill of Points are presented the 6dB above the theoretical hill of vision level. If the point is not seen it is tested for a second time Printouts vision level. If the point is not seen it is tested for a second time Printouts display circles for seen stimuli and solid squares for unseen stimuli. display circles for seen stimuli and solid squares for unseen stimuli.

Three-zoneThree-zone Points that are not detected after being presented twice 6dB Points that are not detected after being presented twice 6dB above theoretical hill of vision level, are retested at the brightest level above theoretical hill of vision level, are retested at the brightest level which is 10 000 asb. If target is seen a circle is displayed, "which is 10 000 asb. If target is seen a circle is displayed, "xx‘ on the ‘ on the printout for a relative defect or a solid block if the target is not seen. printout for a relative defect or a solid block if the target is not seen.

Quantify defectsQuantify defects The points missed twice at the 6dB brighter than the The points missed twice at the 6dB brighter than the theoretical hill of vision level, are thresholded to quantify the depth of the theoretical hill of vision level, are thresholded to quantify the depth of the defect at that location. Printouts display circles for seen stimuli, and defect at that location. Printouts display circles for seen stimuli, and numbers for defects.numbers for defects.

READING FIELD PRINTOUTREADING FIELD PRINTOUT

1. Name, ID and AgeEnsure that this data is accurate. The correct age is essential as the patient is compared to age matched normals.

2. Type of TestThis indicates whether the test was a threshold or screening test.

• Screening tests are a fast effective method to detect suspect areas in the visual field and indicate the need for further evaluation

• Threshold tests determine the sensitivity at various points in the visual field and detect early changes in retinal sensitivity.

4.4. Pupil DiameterPupil Diameter– While large pupils do not affect the results significantly, miotic pupils can induce a While large pupils do not affect the results significantly, miotic pupils can induce a

defect. The pupil should be at least 3mm to avoid false defects. defect. The pupil should be at least 3mm to avoid false defects. – Automated pupil size measurement (Humphry)Automated pupil size measurement (Humphry)

5.5. Glasses UsedGlasses Used

– The proper near add refraction, as determined by the patient's age The proper near add refraction, as determined by the patient's age and the diameter of the perimeter's cupola, must be used. and the diameter of the perimeter's cupola, must be used.

– This lens must be positioned properly to prevent artifactual defects This lens must be positioned properly to prevent artifactual defects caused by the rim of the lens. caused by the rim of the lens.

– Use Trial lenses only for central tests (within 30Use Trial lenses only for central tests (within 30), or the central ), or the central part of a full field test. For Peripheral test > 30 degrees, remove part of a full field test. For Peripheral test > 30 degrees, remove the lenses.the lenses.

– Uncorrected refractive errors cause defocusing of the test target Uncorrected refractive errors cause defocusing of the test target and apparent depression of retinal sensitivity. Each diopter of and apparent depression of retinal sensitivity. Each diopter of uncorrected refraction causes a 1.26-db depression of retinal uncorrected refraction causes a 1.26-db depression of retinal sensitivitysensitivity

ASSESSING RELIABILITY ASSESSING RELIABILITY ((Reliability Indices)Reliability Indices)

Fixation lossesFixation losses

• Fixation is central to the validity of a visual field. Fixation is central to the validity of a visual field.

• The following strategies are employed to ensure adequate The following strategies are employed to ensure adequate fixation: fixation:

– Video monitoring of the eye or Video monitoring of the eye or Gaze tracking Gaze tracking (Octopus)(Octopus)

– The manual method which requires constant supervision of the The manual method which requires constant supervision of the patient during the test patient during the test (Goldmann)(Goldmann)

– Heijl-Krakau Technique in which fixation during the examination is in which fixation during the examination is periodically monitored periodically monitored by presenting stimuli in blind spot (Humphry)(Humphry)

• If fixation losses exceed 20% indicative of poor fixation or that the blind spot was not correctly mapped out then XX will be printed next to the numbers

ASSESSING RELIABILITY ASSESSING RELIABILITY ((Reliability Indices)Reliability Indices)

False positives False positives Catch TrialsCatch Trials

• By withholding of a stimulus projection (only sound is presented) and patient is still responding. The patient responds to the sound clue alone

• The scores are flagged with XX if errors exceed 33% of the trials

• High score suggests a ‘trigger happy’ patient

False negatives False negatives Catch TrialsCatch Trials

• Failure to respond to a stimulus 9 dB brighter than previously seen at same location

• The scores are flagged with XX if errors exceed 33% of the trials

• High score indicates inattention, or advanced field loss

The numeric dataThe numeric dataExpresses the patient's test responses in decibels. The STATPAC software analyses this info and gives it age adjusted significance and it is then that this information is really relevant and worth drawing conclusions from.

The GrayscaleThe GrayscaleThe grayscale is a colour scheme of the visual loss. It is useful to provide an overview of the visual field loss but cannot be relied on by the clinician to make a definitive diagnosis of the extent of the visual field loss. It is useful for the patients to understand the extent of the visual field loss and the risks that they face.

DeviationsDeviations HumpheryHumphery Field Analyzer'sField Analyzer's statistical package statistical package (STATPAC) (STATPAC)

uses a model based on test results of patients with normal uses a model based on test results of patients with normal fields, retinal sensitivity, and pupil size for each different age fields, retinal sensitivity, and pupil size for each different age group. It compares the patient's test results against this model group. It compares the patient's test results against this model to determine how their threshold results, for each tested point, to determine how their threshold results, for each tested point, compares or falls outside the normal population model.compares or falls outside the normal population model.

1.1. Total deviation Total deviation (Comparisons in Octopus)(Comparisons in Octopus)

– Upper numerical display shows difference (dB) between patient’s Upper numerical display shows difference (dB) between patient’s results and age-matched normalresults and age-matched normal

– These negative values become diagnostic when they reach (-5) or These negative values become diagnostic when they reach (-5) or greater and more so if there are several grouped together. greater and more so if there are several grouped together.

– Lower graphic display shows these differences as grey scale ie. Lower graphic display shows these differences as grey scale ie. the defect depththe defect depth

DeviationsDeviations2.2. Pattern deviation Pattern deviation (Corrected Comparisons in Octopus)(Corrected Comparisons in Octopus)

– Similar to total deviation except the STATPAC correct total it for Similar to total deviation except the STATPAC correct total it for diffuse effects eg. cataract, miotic pupils or incorrect testing lens diffuse effects eg. cataract, miotic pupils or incorrect testing lens

– Display any superimposed pattern of localized loss (eg. subtle Display any superimposed pattern of localized loss (eg. subtle glaucoma changes) that is hidden under a generalized depression glaucoma changes) that is hidden under a generalized depression

3.3. Probability plotProbability plot– Indicate the degree of abnormalityIndicate the degree of abnormality

– The darker the symbol in the probability The darker the symbol in the probability plot the more significant the deviation from plot the more significant the deviation from normal normal

– P<1% means that this deviation happens P<1% means that this deviation happens in less than 1% of the normal populationin less than 1% of the normal population

Glaucoma Hemifield TestGlaucoma Hemifield Test– GHT is based on the fact that glaucoma usually GHT is based on the fact that glaucoma usually

causes asymmetric field loss and not a causes asymmetric field loss and not a generalised global depression.generalised global depression.

– GHT evaluates five zones in the superior field GHT evaluates five zones in the superior field and compares these zones to their mirror image and compares these zones to their mirror image zones in the inferior field. Then prints one of zones in the inferior field. Then prints one of three messages below the graytone format:three messages below the graytone format:

» GHT GHT within normal within normal limitslimits

Outside Normal Outside Normal limitslimits

BorderlineBorderline

– The test is not available with tests using FastpacThe test is not available with tests using Fastpac

Defect (Bebie) Curve in OctopusDefect (Bebie) Curve in Octopus

GLOBAL INDICESGLOBAL INDICES1.1. Mean deviation Mean deviation (M(Mean defect in Octopus)ean defect in Octopus)

– Reflects dReflects deviation of patient’s overall field from normaleviation of patient’s overall field from normal• It is simply the average (Octopus) or the weighted average (HFA) of It is simply the average (Octopus) or the weighted average (HFA) of

the deviation values for all locations tested. the deviation values for all locations tested. • pp values are < 5%, < 2%, < 1% and < 0.5% values are < 5%, < 2%, < 1% and < 0.5%• The lower theThe lower the p p value the greater the significance value the greater the significance• The mean deviation is most sensitive to diffuse changes and is less The mean deviation is most sensitive to diffuse changes and is less

sensitive to small localized scotomas.sensitive to small localized scotomas.

2.2. Pattern standard deviation Pattern standard deviation (Loss variance in (Loss variance in Octopus) Octopus)

– measurement of the degree to which the shape of the patient's field measurement of the degree to which the shape of the patient's field departs from the age-matched normals reference field. departs from the age-matched normals reference field. • Represent the local non-uniformity of the visual fieldRepresent the local non-uniformity of the visual field• low PSD indicates a smooth hill of visionlow PSD indicates a smooth hill of vision or if the damage is more or or if the damage is more or

less evenless even• high PSD indicates an irregular hill orhigh PSD indicates an irregular hill or presence of scotoma presence of scotoma

GLOBAL INDICESGLOBAL INDICES3.3. Short-term fluctuationShort-term fluctuation

– Represent intra test variability and measure the consistency of responsesRepresent intra test variability and measure the consistency of responses

– The threshold is measured twice at 10 pre-selected points. A fluctuation The threshold is measured twice at 10 pre-selected points. A fluctuation value is then determined by using the difference between the first and the value is then determined by using the difference between the first and the second readings. second readings.

– 2 dB or less indicates reliable field2 dB or less indicates reliable field

– > 3 dB indicates either poor patient compliance or a sign of > 3 dB indicates either poor patient compliance or a sign of glaucomatous glaucomatous field loss and flagged with p values, eg. P< 0.01field loss and flagged with p values, eg. P< 0.01

4.4. Corrected pattern standard deviation CPSD Corrected pattern standard deviation CPSD (C(Corrected Lloss variance in Octopus) orrected Lloss variance in Octopus)

– Measurement of how much the total shape of the patient's hill of vision Measurement of how much the total shape of the patient's hill of vision deviates from the shape of the "NORMAL" hill of vision for the patient's age, deviates from the shape of the "NORMAL" hill of vision for the patient's age, after being corrected for intra-test variability after being corrected for intra-test variability (short-term fluctuation)(short-term fluctuation)

– It is increased when localized defects are presentIt is increased when localized defects are present

40 dB40 dB 40 dB40 dB

PSD – SF = CPSDPSD – SF = CPSD

40 dB40 dB 40 dB40 dB

40 dB40 dB 40 dB40 dB

MD = 1.9MD = 1.9

MD = 1.9MD = 1.9

MD = 11.9MD = 11.9

MD = 11.9MD = 11.9

CPSD = .7CPSD = .7

CPSD = 2.6CPSD = 2.6 CPSD = 2.6CPSD = 2.6

CPSD = .7CPSD = .7

NORMALNORMAL CATARACTCATARACT

GLAUCOMAGLAUCOMA GLAUCOMA + CATARACTGLAUCOMA + CATARACT

INTEREYE COMPARISONSINTEREYE COMPARISONS

• The difference in the mean sensitivity between a patient's The difference in the mean sensitivity between a patient's two eyes is less than 1 db 95% of the time and less than two eyes is less than 1 db 95% of the time and less than 1.4 db 99% of the time.1.4 db 99% of the time.

• Intereye differences greater than these values are Intereye differences greater than these values are suspicious if they are unexplained by non glaucomatous suspicious if they are unexplained by non glaucomatous factors, such as unilateral cataract or miosis.factors, such as unilateral cataract or miosis.

Clover leafe fieldClover leafe field

Glaucoma (1)

Humphrey Central 24-2 Threshold Test

Glaucoma (2)

Glaucoma (3)

Glaucoma

Incomplete Left Superior Quadrantonopia (Temporal lobe Syx)

Neuro (1)

Neuro (2)

Bilateral Optic Neuropathy

Neuro (3)

Pseudotumour cerebri

Retinal Toxicity secondary to Plaquenil

Post portum CVA

2nd VF largely resolved

Conclusion

• Visual field measurement is a critical component in the Visual field measurement is a critical component in the armament against potentially blinding diseases. armament against potentially blinding diseases.

• Visual field measurement has undergone an evolution from the Visual field measurement has undergone an evolution from the mechanical to the automated measurement process, resulting mechanical to the automated measurement process, resulting in greater accuracy, ease of use and greater depth of analysis.in greater accuracy, ease of use and greater depth of analysis.

•

• Other psychophysical methods for testing the visual field for Other psychophysical methods for testing the visual field for damage are now being explored. These methods include damage are now being explored. These methods include contrast sensitivity, acuity perimetry, and color perimetry.contrast sensitivity, acuity perimetry, and color perimetry.

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Dicon 1995.

• Harrington D. O. The Visual Fields. Saint Louis: C.V. Mosby Company, 1976 pp 1-4.

• Haley MR. (ed). The Field Analyser Primer. San Leandro, California: Allergan Humphrey, 1987.

• Townsend JC, Selvin GJ, Griffin JR, Comer GW. Visual Fields. Clinical Case Presentations. Boston: Butterworth-Heinemann, 1991 pp 3-37.

• Lalle P. A. Visual Fields. In Fingeret M & Lewis TL, eds. Primary Care of the Glaucomas. Norwalk, Connecticut: Appleton and Lange; 1993: 159-196.

• Humphrey Field Analyser: Users Guide. Allergan Humphrey,1994.

• William TD. Quantitative Perimetry. In Eskeridge BJ, Amos JF & Bartlett JD, eds. Clinical Procedures in Optometry. Philadelphia: JB Lippincott, 1991 pp 447-461.

• Melton R & Randall T. How to Interpret the Visual Field Printout. A Supplement to Review of Optometry. June 1998 pp 12A-13A.

• Viswanathan AC. Visual Field analysis in Glaucoma. In www.city.ac.uk/optometry.

• Melton R & Randall T. Interpreting a Visual Field Printout. In 4th Annual Guide to Therapeutic Drugs (supplement). Optometric Management May 1995 pp 52-56.

• Flammer J. The concept of visual field indices. Graefes Arch Clin Exp Ophthalmology 1986 224 389-395.