Visual Field Analysis

• Perimetry normally tests the light-difference
sensitivity across the visual field.
• This sensitivity reflects the capability of the
eye to perceive a brightness difference
between a test target and its background.
• Light-difference sensitivity depends upon the
tested location on the retina and upon the
parameters of the measurement technique,
such as intensity of background luminance
and target size.
Perimetry
4/14/2020 Ehab Nafie, perimetric printout 2

Octopus Automated
perimetry
Test Pattern
 General/Glaucoma 30° (G1-Program, 32, 30-2, 24-2)
 General/Glaucoma Periphery (G2-Program: 60°; 07-Program: 75°)
 Macula (M-Program (10°/30°); 10-2)
 Screening (ST)
 Driving (Estermann monocular/binocular; FG: German Driving
Licence)
 Disability (BT – Blepharoptosis; BG: German Blindness)
 Other Pathology (N1: Neurological; D1: Diabetes)
 Custom tests.

Octopus Automated
perimetry

Octopus Automated
perimetry
Test Methods
• Standard white-on-white perimetry SAP
• Blue/yellow perimetry SWAP
• Flicker perimetry for early diagnosis
• Red/white perimetry (custom tests only)
• Goldmann Kinetic Perimetry

Octopus Automated perimetry printout

Humphrey Field Analyzer

Examination Strategies
 SITA, (Swedish Interactive Threshold
Algorithm) (SITA) Standard and SITA Fast
 Full Threshold
 Fast Pac
Humphrey Field Analyzer

Perimetry print out

Reliability
parameters
Gray scale
Pattern
deviation
Global
indices
Probability
symbols
GHT
Patient name
Test
Total deviation
Numeric
sensitivity

An HFA 30-2 dB printout for RT eye
 The tested points
are spaced in an
equidistant grid
pattern, with each
point 6 degrees
apart horizontally
or vertically from
any adjacent
point.
 dB printouts
illustrate the grid
patterns.4/14/2020 Ehab Nafie, perimetric printout 13

30-2 full threshold grid

Glaucoma hemifield test
 The GHT, devised for the Humphrey Field Analyzer,
compares 24-2 visual fields into 10 regions, with 5
inferior regions representing mirror images of 5
corresponding superior regions.
 Differences between corresponding superior and
inferior zones are compared with the differences
present in the population of normal controls.

 Outside normal limits. The GHT is described as
“outside normal limits” when differences between a
matched pair of corresponding zones exceeds the
difference found in 99% of the normal population, or
when both members of a pair of zones are more
abnormal than 99.5% of the individuals with the
normative population.
 Borderline. The GHT is described as borderline when
matched pairs of zones are abnormal at the 97th %
within the normative database,

General reduction of sensitivity. VFs are described to have
generalized reduction of sensitivity when both conditions for
“outside normal limits” are not met, and the best region of
the VF is depressed to a level at the 99.5th percentile within
individuals of the normative database.
Abnormally high sensitivity. The GHT is described as
having abnormally high sensitivity when the overall
sensitivity in the affected region of the VF is better than
99.5% of individuals within the normative population.
Within normal limits. VFs are described as being within
normal limits when none of the above conditions are met.

Message
 A GHT message of "outside normal
limits" on two occasions with
corresponding optic nerve or retinal
nerve fiber layer loss is very strong
evidence that glaucomatous visual
field loss is present.

Patterns of Glaucomatous Visual
Field loss
 Generalized depression
 Paracentral scotoma
 Arcuate or Bjerrum scotoma
 Nasal Step
 Altitudinal Defect
 Temporal Wedge
 Central island
 VF defect must correlate with Optic nerve
damage

An HFA 24-2 dB printout
RT
LT

Reliability tests
 Information
about these
factors is at
the top of the
chart.

Assess reliability
 Diagnostic and management
decisions should not be made on
the basis of unreliable data.
 The three measures of reliability
are
1. fixation losses,
2. false negatives, and
3. false positives.

Reliability tests
 An examination with a false positive
rate of 15% or higher should be
considered unreliable.
 It is important to recognize that it
may take two or three visual field
examinations for the patient to
produce a reliable and valid visual
field test.

Reliability tests
 False negatives occur when a
patient does not respond to a
stimulus that should be visible for
that patient.
 Because false negatives increase
with worsening visual field loss, a
high number of false negatives in a
glaucomatous field do not necessarily
represent unreliable data.

Reliability tests
 False positives, on the other hand, are
always an indicator of an unreliable test.
 They occur when the patient responds when
a response was not expected.
 False positives make the visual field look
better (more sensitive) than it actually is
and may mask shallow depressions.
 Patients with high false positives also may
have a "white" grayscale and/or abnormally
high threshold values, especially in the
peripheral parts of the field.

Test Duration
 A typical 24-2 threshold test
takes about 7-10 minutes.
 A patient with a very disturbed
field will take longer.

LT Eye RT Eye
Grey scale

Grey scale

Glaucomatous defects
 Deviation plots and their corresponding
statistical probability plots demand the
most attention.
 These plots identify areas of the field that
are abnormal compared with an age-
matched normal population for each point
tested.
 The information is given both in decibels
and in statistical probability values.

Glaucomatous defects
 In the probability plots,
increasingly dark squares represent
increasingly significant deviations
from normal.
 The pattern deviation plot gives the
same type of information as the total
deviation plot, after the visual field
has been adjusted for any overall
depression or elevation.

Pattern deviation plot
 This plot is helpful
in patients who may
have a combined
overall depression
(from media
opacity, for
example) as well as
localized loss from
glaucoma.

Global indices
 The two global indices used in SITA
testing are mean deviation (MD) and
pattern standard deviation (PSD).
 The MD is a measure of the average
deviation between the patient's
sensitivity and that of age-matched
normal.

Global indices
 MD is affected by:
 Media opacities,
 Uncorrected refractive error, and
 Small pupils, and it may not reach
statistical significance from a small
or shallow localized glaucomatous
defect.

Global indices
 PSD is a measure that reflects the shape
or "smoothness" of the hill of vision and is
much more reflective of localized loss,
such as that found in glaucoma.
 It is important to realize, that other
disease processes can cause localized loss
and may result in an elevated pattern
standard deviation.

Message
 A PSD that reaches the 5% statistical
significance level on multiple
examinations, in the presence of
other suspicious clinical findings, is
very strong evidence that a
glaucomatous visual field defect is
present.

 When evaluating test reliability, we have
to look at the numbers printed on the
Numeric Results (decibel [dB]) graph.
 A value of 40 dB or higher on this graph
indicates that the patient may be "trigger
happy."
 That is, the patient is anticipating the
presentation of the stimulus and is
responding before the stimulus is seen.

 Readings of 40 dB or higher indicate
an unreliable field that will need to
be repeated.
 It is best to catch these readings
while the test is in progress and
restart the test.
 A typical "normal" dB reading is
around 30.

Refraction
 The appropriate refraction
should be listed to allow
proper vision for the
testing distance of the
perimetry bowl.
 Astigmatism more than
1.25 D should be corrected
in addition to the sphere
adjustments.
 Special attention should be
given to aphakic and
pseudophakic patients,
regardless of age, as well
as those who wear contact
lenses.

Test duration
 A prolonged testing time may
indicate patient fatigue and must be
considered if there is a large
amount of global depression.
 A higher rate of false positives and
negatives may occur at the edges
of scotomas due to glaucoma,
which must be accounted for when
evaluating reliability.

GHT
within normal limits
MD +2.69 dB
PSD 1.35 dB

Single Field Analysis – SITA SWAP

Visual field interpretation
 Look for signs of unreliable fields: Are there
many false positives (> 15% using SITA), or losses
of fixation (> 33%)?
 Is there a lens rim artifact or uncorrected ptosis?
If the fields appear reliable, continue to step 2.
 Look at the sensitivity map to determine whether
the field is within normal limits.
 If the fields are within normal limits, there is no
further analysis.
 If one or both of the eyes exhibit abnormal fields,
continue to step 3.

STEP 2: Look for glaucomatous
defects
 Once the field has been deemed
reliable, it should be evaluated for
glaucomatous defects.
 The grayscale should not be used for
decision-making in glaucoma, but it is
helpful to draw attention to areas that
need further evaluation using number
and probability plots.

STEP 3: Look at the GHT and
global indices.
 The GHT is based on the fact that
glaucoma damages the superior and
inferior fields asymmetrically.
 The GHT compares mirror-image
clusters of points in the superior and
inferior fields, and it alerts the clinician
when significant differences are
found between the two hemifields.

 Is the visual field damage present in one or both
eyes?
 If only one eye is affected, the damage is located
in front of the optic chiasm (i.e. the cornea,
vitreous, retina, or optic nerve of only one eye).
 Damage in the visual fields of both eyes could be
due to damage at the level of the optic chiasm
and beyond, or due to separate damage in the
visual pathways of each eye anterior to the
chiasm.

 Locate the region of the visual field deficit.
 Refer to the patterns of visual field defects chart
to determine the likely region of damage to the
visual pathway.
 Identify the shape of the visual field defect.
 Refer to the chart to determine the likely region
of damage to the visual pathway.

 Compare these visual fields with each of the
patient's previous visual field tests to identify
progression of visual field loss.
 Do not take a shortcut by comparing these fields
to only the most recent visual field, as this may
be misleading.
 Generally three or more visual field tests are
necessary to evaluate disease progression.
 Consider the findings in the context of the
physical exam findings and the results of other
tests and imaging.

Not every VF defect is
glaucoma

Visual Field Analysis

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