Fundamentals of hfa perimetry

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Humphrey Field Analyzer II/IIi
Fundamentals of Perimetry
Measurement

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Measurement
There are three International Standards of measurement for
Perimetry:
ASBASB
dBdB
FT/LFT/L

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Measurement
ASBASB
AApopoSStiltilBB
0 (Dimmest) – 10,000 (Brightest)
A measurement of light, dealing
with the brightness of the
surface of the bowl
International StandardInternational Standard

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Measurement
FT/LFT/L
Foot LambertFoot Lambert
HFA Range
0 (dimmest) – 929 (Brightest)
FT/L
Higher number = Brighter light

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Measurement
dBdB
DecibelDecibel
HFA Range
0.1 dB (Brightest) – 51dB (Dimmest)
Higher number = Dimmer Spot

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Measurement
International Standards Comparison
Dimmest Brightest
0 ASB 10,000 ASB
0 FT/L 929 FT/L
51 dB 0.1 dB

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Measurement
All Perimeters use the same standards
These standards are based on the
Goldmann Perimeter
ASB
ASB
ASB
ASB
ASBASB
ASB
ASB
ASB
ASB
FT/LFT/L
FT/LFT/L
FT/LFT/L
FT/L
FT/L
FT/L
FT/L
FT/L
FT/L
dBdB
dBdB
dBdB
dBdB
dBdB
dBdB

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Measurement
The Goldmann Perimeter, which defined
the Standards of Perimetry. These
standards are still in use today.

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Measurement
The standards of Perimetry are:
 Spot IntensitySpot Intensity
 Background IlluminationBackground Illumination
 Spot DurationSpot Duration
 Spot SizeSpot Size
 Spot SpeedSpot Speed

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Measurement
Background Illumination
 The standard value is 31.5 ASB.The standard value is 31.5 ASB.
 The illumination in the bowl must remainThe illumination in the bowl must remain
constant throughout the test.constant throughout the test.

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Measurement
Why 31.5 ASB?
 Originally used by Goldmann Perimeter
 Adopted as standard by International Peremetric Society
(International Council of Ophthalmology 1979)
 Approximates minimum level for photopic or daylight vision
 Photopic vision relies on retinal cone function instead of rods
 Cones – Object Contrast Rods – Absolute Brightness
 Small changes in pupil size or clarity of media do not have an
effect on Contrast, so have little effect on test results.

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Measurement
Spot IntensitySpot Intensity
 Glass Wedge/Film WedgeGlass Wedge/Film Wedge
 The Spot intensity is controlled by filter wheelsThe Spot intensity is controlled by filter wheels
 The spot intensity is directly related to theThe spot intensity is directly related to the
bowl intensity.bowl intensity.

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Measurement
Spot Size
 Size V spot is the largestSize V spot is the largest
 The size of the spot can be size I,II,III,IV,or VThe size of the spot can be size I,II,III,IV,or V
 The default spot size is size IIIThe default spot size is size III
Mr. DefaultMr. Default
to you!to you!

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Measurement
Spot size 3 is .43 degrees
Spot Size is smaller in the HFA II bowl
than in the HFA I, because the bowl
radius is smaller.

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Measurement
Spot Duration
 The default time duration is 200mSThe default time duration is 200mS
(milliseconds) + or – 10mS(milliseconds) + or – 10mS
 How long the spot is displayedHow long the spot is displayed
 Duration can be changed to 500 mS for olderDuration can be changed to 500 mS for older
patients.patients.

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Measurement
The principle of temporal summation holds that for
very short durations, the visibility of a stimulus
increases with duration; when a stimulus lasts more
than about 0.5 seconds, on the other hand, its
visibility is basically independent of duration.
200 ms – long enough for visibility to not be affected
by small variations in duration. But less than …
250 ms – latency for voluntary eye movement

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Measurement
Spot Speed
 This only applies toThis only applies to KineticKinetic testing.testing.
 How fast the spot movesHow fast the spot moves
 Default speed for the HFA is 4 degrees per second.Default speed for the HFA is 4 degrees per second.

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Measurement
Goldmann vs. Humphrey Parameters
Goldmann HumphreyGoldmann Humphrey
Spot Size I,II,III,IV, V I,II,III,IV,VSpot Size I,II,III,IV, V I,II,III,IV,V
(V is the largest) (V is the largest)(V is the largest) (V is the largest)
Filters 1,2,3,4 Glass WedgeFilters 1,2,3,4 Glass Wedge
(4 is the brightest) Film Wedge(4 is the brightest) Film Wedge
a,b,c,d,ea,b,c,d,e
(e is the brightest)(e is the brightest)

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Measurement
Kinetic Testing
Single intensity; Moving Target
A light spot (Stimulus) is introduced along a particular meridian, following a
straight line until a patient response (sees the light spot) is indicated.
MeridianMeridian
Patient ResponsePatient Response

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Measurement
Static Testing
Varies the intensity of the spot
over the entire Hill of Vision.
Patient does not see the spot
move. The spots are projected at
different positions on the bowl,
but the instrument will return to
the spots at different intensities.
Variable Intensity; Stationary Target

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Measurement
The “Island” of Vision
AA StaticStatic test on atest on a
normal eye willnormal eye will
produce a patternproduce a pattern
similar to the one atsimilar to the one at
right.right.
DimDim
BrightBright
Blind SpotBlind Spot
FoveaFovea
NasalNasal TemporalTemporal

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Measurement
Scotomas
There are two types ofThere are two types of ScotomasScotomas::
Definition: A defect on the Retina. An area or spot onDefinition: A defect on the Retina. An area or spot on
the Retina that is not as sensitive to light as it shouldthe Retina that is not as sensitive to light as it should
be.be.
1.1. RelativeRelative – An area or spot on the Retina that– An area or spot on the Retina that can detect light,detect light,
but not as good as when compared to a normal eye at that samebut not as good as when compared to a normal eye at that same
spot.spot.
2. Absolute – An area or spot on the Retina that cannot detect
light, no matter how bright it is.

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Measurement
Scotoma
Is this Scotoma RelativeIs this Scotoma Relative
or Absolute?or Absolute?
Relative!!Relative!!
BlindspotBlindspot

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Measurement
Hey man, like, ALL myHey man, like, ALL my
relatives are Scotomas!relatives are Scotomas!
Absolutely!!!Absolutely!!!
Can you dig it??!!Can you dig it??!!
Cool!!Cool!!

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Measurement
The Blind spot exhibits the same characteristics as an
________ ________?
AbsoluteAbsolute
Scotoma!Scotoma!

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Measurement
Thresholding and Bracketing
What is thresholding?
Threshold (or Threshold Level) is the minimum amount
of light that the eye can detect at a particular point on
the retina.
Bracketing is the process of determining the
Threshold value.

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Measurement
Thresholding by Bracketing
For our purposes, we will assume that the instrument begins the
threshold test with a spot of 36db. The spot or stimulus is
presented at a particular spot on the bowl to see if there is a
patient response.
0 dB36 dB55 dB
Indicates a negative (did not see) responseIndicates a negative (did not see) response
Indicates a positive (did see) responseIndicates a positive (did see) response
DimmerDimmer BrighterBrighter

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Measurement
The patient did not respond, indicating that he/she did NOT see the
spot. The instrument will now introduce a spot of 32dB (a 4dB change)
at the exact same location.
0 dB0 dB36 dB36 dB55 dB55 dB
Indicates a negative (did not see) responseIndicates a negative (did not see) response
Indicates a positive (did see) responseIndicates a positive (did see) response
32 dB32 dB

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Measurement
The patient responded positively, indicating that he/she DID see
the spot. The instrument will now introduce a spot at the same
exact position, at a brightness of 34dB. (A 2dB change)
00 dBdB
36 dB
55 dB
Indicates a negative (did not see) response
Indicates a positive (did see) response
32 dB
34 dB

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Measurement
Once again, the patient did not see the spot. The instrument has
determined by BRACKETING that the threshold for this spot is 32dB.
(NOTE: Some tests may closer define the threshold by testing at 1 dB
steps.)
0 dB
36 dB
55 dB
Indicates a negative (did not see) response
Indicates a positive (did see) response
32 dB
34 dB34 dB

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Measurement
What happens when you start a test?
1. One spot in each1. One spot in each
quadrant will bequadrant will be
bracketed to determinebracketed to determine
the Threshold level.the Threshold level.
At the same time, theAt the same time, the
location of the Blindlocation of the Blind
Spot will be determined.Spot will be determined.
Bracketing begins at 24dBBracketing begins at 24dB
Blindspot

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Measurement
What happens when you start a
test?
2. Once the threshold
value for a spot in each
quadrant has been
found, an Expected Hill
of Vision is determined.
DimmerDimmer
Expected “Hill of Vision”
36dB (CEN)36dB (CEN)

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Measurement
The “CEN” is defined asThe “CEN” is defined as
the Central ReferenceCentral Reference
LevelLevel, or the, or the ExpectedExpected
Foveal SensitivityFoveal Sensitivity, or the, or the
Expected FovealExpected Foveal
Threshold.Threshold.
Expected “Hill of Vision”
DimmerDimmer
36dB (CEN))

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Measurement
3. As the test is run, the
patients “Actual”
readings are plotted.
Expected “Hill of Vision”Expected “Hill of Vision”
DimmerDimmer
36dB36dB
Actual Patient plotsActual Patient plots
Blind Spot

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Measurement
Types of Tests
1. Screening Tests – A QUICK overview of the patient’s field of
vision. Most screening tests tell only if the patient did or did not
see the spot. In general, screening tests do not quantify. That is,
they do not determine how bad a scotoma is.
Now you see it……..Now you see it…….. Now you don’t!!!!!!!!!Now you don’t!!!!!!!!!

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Measurement
Types of Tests
2.2. Threshold TestsThreshold Tests –– QuantifiesQuantifies each spot. That is, it finds the thresholdeach spot. That is, it finds the threshold
level. Determines how bad the scotoma is by calculating thelevel. Determines how bad the scotoma is by calculating the exactexact lightlight
level the patient can see at a particular spot on the Retina.level the patient can see at a particular spot on the Retina.
I don’t see it…
I don’t see it…
Now I see it!!!!!
Now I see it!!!!!

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Measurement
 Short Wavelength Automated Perimetry (SWAP)
 Blue Goldmann Size 5 Stimulus on bright Yellow background
 Yellow Background reduces responsiveness of the red and
green cone system
 Blue Stimuli are seen primarily by the Blue Cone System
 SWAP can detect progression of field loss earlier in patients
than standard White on White perimetry
 SWAP eliminates the redundancy in the visual system by
reducing responsiveness from non blue cones and the rod
system

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Measurement
Reliability Factors
After a Field Test has been completed, aAfter a Field Test has been completed, a
determination must be made if the test is accuratedetermination must be made if the test is accurate
and therefore reliable. Several Reliabilityand therefore reliable. Several Reliability
Indicators appear on the test printout:Indicators appear on the test printout:
 Fixation LossesFixation Losses
 False Negative ErrorsFalse Negative Errors
 False Positive ErrorsFalse Positive Errors
 Gaze TrackingGaze Tracking

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Measurement
Fixation Losses
During the test, the patient is told to
Fixate (Stare) at a central LED. The
instrument records the number of
times that the patient lost this
fixation and reports it on the
printout.
Excessive fixation losses can
render a test invalid.

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Measurement
Fixation Monitoring
The HFA uses two systems for measuring
patient fixation: the standard Heijl-Krakau blind-
spot monitoring and the IR Gaze Tracking
System. Both methods can be used, either
together or alone, or they can both be turned off,
as required.

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Measurement
Heijl-Krakau Blind Spot
Monitoring

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Measurement
Gaze Tracking
Location of Corneal Reflex Marker
Corneal Reflex marker Location Digitized and
Stored in Memory

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Measurement
The direction of a patient's gaze is
determined in two steps:
1. A reflex marker is established
on the corneal surface.
2. The location of the pupil center
is determined.
Gaze Tracking

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Measurement
Gaze Tracking
Gaze tracking is initialized in the following manner
when a selected test is first started:
The patient is asked to fixate on the central
illumination LED. Gaze tracking turns on the reflex
gaze IR LED located just under the diamond fixation
pattern and turns off eye illumination briefly . Light
from the LED is reflected off the cornea, and back to
the IR sensitive camera.

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Measurement
Gaze Tracking
The majority of the cornea appears black except for the
reflected spot. This image is digitized and stored in
memory. The reflected spot is referred to as the reflex
marker. Because the corneal surface is rounded, the
reflex marker will move very little even if the patient's
eye rotates, and thus the marker becomes a (relatively)
stationary reference point.

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Measurement
Gaze Tracking
Next, the system locates the pupil center by
illuminating the entire eye with the two IR LEDs
located either in the bottom of the bowl, or in the trial
lens holder (when in the raised position). The iris
appears bright with a dark pupil. This image is also
digitized and stored in memory. It is the relationship
between the location of the reflex marker on the
cornea and the location of the pupil center that
determines fixation.

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Measurement
Gaze Tracking
During a test, each time a spot is projected into the bowl,
the locations of the reflex marker and the center of the
pupil are compared to the initial images stored in
memory. If the patient is fixating correctly, the positional
relationship between the reflex marker and the pupil
center will be the same as that of the stored images. If
the patient is off fixation, the positional relationship
between the reflex marker and the pupil center will be
different. The greater the misalignment, the higher the
mark on the Gaze Graph.

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Measurement
Gaze Tracking
Determining the Pupil Center
Patient Fixating – Corneal
Reflex Marker and Pupil in
Proper
Relationship
Patient Not Fixating –
Corneal Reflex Marker and Pupil
Not in Proper Relationship

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Measurement
Gaze Tracking
Gaze Graph
Upward spikes indicate that the patient has lost fixation;
• a spike that reaches the top horizontal line (or higher) indicates 10 degrees (or
more) off fixation;
• a spike that extends halfway to the top line indicates 5 degrees off fixation.
P Downward spikes indicate as follows:
• a short spike downward indicates that the gaze at that time cannot be
determined by the software.
• a long spike downward indicates that the patient blinked at the time fixation
was checked.
The absence of marks on the graph indicates proper fixation.

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Measurement
Gaze Tracking

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Measurement
Gaze Tracking

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Measurement
Gaze Tracking

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Measurement
False Negative Errors
Let us say that aLet us say that a StimulusStimulus (Spot) is presented at(Spot) is presented at 26dB26dB,,
and the patient responds that the spot was seen.and the patient responds that the spot was seen.
Later in the same test, at the same location, a brighterLater in the same test, at the same location, a brighter
spot, sayspot, say 22dB22dB, is presented, and the patient does not, is presented, and the patient does not
respond, that is, the patient does not see the spot.respond, that is, the patient does not see the spot.
““Yessir, I see it!”Yessir, I see it!”
““Nosir, I didn’t see that one!”Nosir, I didn’t see that one!”

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Measurement
False Positive Errors
The patient responds that a spot of light was seenThe patient responds that a spot of light was seen
when none was presented. This sometimes canwhen none was presented. This sometimes can
occur when the motors move on the Humphreyoccur when the motors move on the Humphrey
Field Analyzer, or a patient gets into a rhythm andField Analyzer, or a patient gets into a rhythm and
anticipates spots.anticipates spots.
SpotsSpots

Fundamentals of hfa perimetry

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