Visual Fields in Glaucoma

1
???????????????

• Visual Fields

• Sultan F. AL-Mutairi MD, FRCS-C
• Department of ophthalmology,
• AL-Bahar Eye Center

2

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

3

• Traquair, an island of vision in the sea of
  darkness
• Depicts the visual field as a three-dimensional
  spatial model
• The shoreline of the island represents the
  peripheral limits of the visual field (least
  sensitive), and the peak correspond to the fovea
  (greatest sensitivity)

4
NORMAL VISUAL FIELD LIMITS
60?
60?
60?
100?
100?
X
X
Fixation
75?
75?
X
Physiological Blind spot
Diameter of Optic Disc Relation of Disc to Fovea
Horizontal 1.1mm, 5.5? Nasal 3.0mm, 15.0?
Vertical 1.5mm, 7.5? Inferior 0.3mm, 1.5?
5
Papillomacular bundle
Horizontal raphe

• The contour of the island of vision relates to
  both the anatomy of the visual system and the
  level of retinal adaptation
• The highest concentration of cones is in the
  fovea, which project to their own ganglion cell.
  This one-to-one ratio between foveal cone and
  ganglion cell results in maximal resolution in
  the fovea

6
Normal Visual Field

• Visual field measurement can be affected by
• Patient's age
• Size and position of the nose
• Orbital structures
• Location of eye within the orbit
• Color of stimuli
• Refractive error
• Fixation
• Eye movement
• Patient cooperation
• Ease of operation of the instrument

7
History of Perimetry

• In 1856 Dr. Von Graefe is the first to draw the
  field using white piece of paper
• In 1889 Dr. Bjerrum was using a tangent screen on
  the back of his clinic door and he described the
  arcuate scotoma
• In 1909 Dr. Ronne developed kinetic isopter
  perimetry and described the nasal step in
  glaucoma
• In 1945 Dr. Goldmann designed the first cupola
  perimeter for manual kinetic perimetry
• In 1973 the era of automation began with Dr.
  Fankhuser and his coworkers in Bern, Switzerland
• The first standard automated perimeter OCTOPUS
  201 - In 1976 OCTOPUS 2000 - In
  1980 OCTOPUS 500 - In 1983
  OCTOPUS 1-2-3 - In 1989 OCTOPUS
  101 - In 1993

8
Knee of Wilbrands
Meyers loop
9
(No Transcript)
10
KINETIC PERIMETRY

• In kinetic perimetry, a stimulus is moved from a
  non seeing area of the visual field to a
  seeing area
• Procedure is repeated with use of the same
  stimulus along a set of meridians, usually spaced
  every 15
• Aim is to find points in the visual field of
  equal retinal sensitivity. By joining these
  points an isopter is defined
• Then luminance and the size of the target is
  changed to plot other isopters

11
KINETIC PERIMETRY

• In kinetic perimetry, the island of vision is
  approached horizontally. Isopters can be
  considered as the outline of horizontal slices of
  the island of vision
• Disadvantages of this technique include the
  subjectivity, highly dependant on the operator
  efficiency, time consuming, difficulties with
  randomising targets and patient cooperation

12
STATIC PERIMETRY

• In static perimetry, the size and location of the
  test target remain constant
• Retinal sensitivity at a specific location is
  determined by varying only the brightness
  of the test target
• The shape of the island is then defined by
  repeating the threshold measurement at various
  locations in the field of vision
• This strategy allows for a quantitative measure
  of the relative density of a defect, more
  easily than in kinetic perimetry

13
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.

14
SENSITIVITY VERSUS THRESHOLD

• As one ascends the hill of vision toward the
  fovea, the sensitivity of the retina increases,
  dimmer targets will become visible.
• Therefore, as retinal sensitivity increases, the
  differential light threshold measured in
  apostilbs decreases.
• In automated perimetry, however, threshold is
  recorded in the inverted decibel scale, and
  dimmer targets have higher decibel values.
• Therefore, threshold in decibels is directly
  proportional to retinal sensitivity.

15
MANUAL PERIMETRY

• Goldmann perimeter is the most widely used
  instrument for manual perimetry.
• It is a calibrated bowl projection instrument
  with a background intensity of 31.5 apostilbs.
• Size and intensity of targets can be varied to
  plot different isopters kinetically and determine
  local static thresholds.

16
GOLDMANN VISUAL FIELD

• The stimuli used to plot an isopter are
  identified by Roman numeral, number, and a letter
• Roman numeral represents the size of the target,
  from Goldmann size 0 to Goldmann size V
• Each size increment equals a fourfold increase in
  area
• Number and letter represent the intensity of the
  stimulus
• change of one number represents 5-dB change in
  intensity
• change each letter represents 1-dB change in
  intensity

17
GOLDMANN VISUAL FIELD

• Isopters in which the sum of the Roman numeral
  (size) and number (intensity) are equal can be
  considered equivalent
• The equivalent isopter combination with the
  smallest target size usually is preferred because
  detection of isopter edges is more accurate with
  smaller targets
• One usually starts by plotting small targets with
  dim intensity (I1e) and then increasing the
  intensity of the target until it is maximal
  before increasing the size of the target

The usual progression
18
GOLDMANN VISUAL FIELD

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

19
AUTOMATED PERIMETRY

• The introduction of computers and automation
  heralded a new era in perimetric testing.
• Static testing can be performed in an objective
  and standardized fashion with minimal perimetrist
  bias.
• A quantitative representation of the visual field
  can be obtained more rapidly than with manual
  testing.
• The computer presents the stimuli in a random
  fashion. Patients do not know where the next
  stimulus will appear, so fixation is improved.
  Also increase the speed of the test by bypassing
  the problem of local retinal adaptation.

20
AUTOMATED PERIMETRY

• Humphrey Field Analyzer uses a constant target
  size equal to a Goldmann "III" (4 mm²) and varies
  the target brightness only. unless otherwise
  instructed.
• The stimulus intensity can reach up to 10,000 asb
  in 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

21
Comparison of static and kinetic perimetry to
detect shallow scotomas

• Kinetic evaluation can clearly outline the normal
  visual field
• Kinetic perimetry may miss shallow scotomas and
  poorly define the flat slope seen nasally
• The edge of steeply sloped scotomas may be
  identified easily with kinetic perimetry, but the
  steepness of the slope may not be appreciated
• D. E. Static perimetry readily detects shallow
  scotomas and can define the slope of both shallow
  and steep scotomas

22

• 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
23
GLAUCOMATOUS VISUAL FIELD DEFECTS

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

24
DIFFUSE DEPRESSION

• Diffuse depression of the visual field results
  from widespread diffuse loss of nerve fibers of
  the retina.
• It is common in glaucoma but it is non specific
  sign that can be caused by many etiologies.
• By far the most common reason for a diffuse
  depression is lens opacity.
• Other factors include other media opacities,
  miosis, improper refraction, patient fatigue,
  inattentiveness or inexperience with the
  examination, ocular anomalies, and age.

25
DIFFUSE DEPRESSION

• In manual perimetry, is manifested by contraction
  of the isopters. The isopters retain their normal
  contour. The most central isopters may disappear
  entirely as the peak of the island of vision
  sinks.
• In automated perimetry, diffuse depression
  results in relative defects across the entire
  visual field.

26
LOCALIZED NERVE FIBER BUNDLE DEFECTS

• Localized visual field defects in glaucoma result
  from damage to the retinal nerve fiber bundles.
• Because of the unique anatomy of the retinal
  nerve fiber layer, axonal damage causes
  characteristic patterns of visual field changes.
• The most common location of visual field defects
  occurs within an arcuate area (Bjerrums area)
  extending from blind spot nasally 10-20 around
  fixation and terminate at the median raphe.

27
Nerve Fiber Bundle Defects

• The superior and inferior poles of the optic
  nerve head are most vulnerable to glaucomatous
  damage.
• It has been postulated that these areas may be
  watershed areas at the junction of the vascular
  supply from adjacent ciliary vessels.
• Ultrastructural examination of the lamina
  cribrosa shows that the pores in the
  superotemporal and inferotemporal areas are
  larger. The large pores may make these regions
  more vulnerable to compression.

28
PARACENTRAL DEFECTS

• Circumscribed paracentral defects are an early
  sign of localized glaucomatous damage.
• The defects may be relative or absolute and
  frequently found in Bjerrums area along the
  course of the nerve fiber bundle.
• With progression paracentral scotomas become
  deeper and longer and may gradually coalesce
  forming an arcuate or Bjerrums scotoma.

29
ARCUATE SCOTOMAS

• More advanced loss of nerve fiber bundle leads to
  a scotoma that starts at or near the blind spot,
  arches around fixation, and terminates abruptly
  at the nasal horizontal meridian .
• In the temporal portion of the field, it is
  narrow because all of the nerve fiber bundles
  converge onto the optic nerve.
• The scotoma spreads out on the nasal side and may
  be very wide along the horizontal meridian.

Differential Diagnosis of Arcuate Scotomas
Glaucoma Branch Vein Occlusion Branch Artery Occlusion Optic Neuritis Ischemic Optic Neuropathy Optic Nerve Drusen Optic Nerve Pit Optic Nerve Cloboma Myelinated NFL
30
NASAL STEP DEFECTS

• A steplike defect along the horizontal meridian
  results from asymmetric loss of nerve fiber
  bundles in the superior and inferior hemifields.
• Nasal steps frequently occur in association with
  arcuate or paracentral scotomas, but a nasal step
  also may occur in isolation.
• Nasal step defects may be evident in some
  isopters but not in others, depending on which
  nerve fiber bundles are damaged.
• Approximately 7 of initial visual field defects
  are peripheral nasal step defects.

31
TEMPORAL WEDGE DEFECTS

• Damage to nerve fibers on the nasal side of the
  optic disc may result in temporal wedge-shaped
  defects.
• These defects are much less common than defects
  in the arcuate distribution.
• Occasionally, they are seen as the sole visual
  field defect.
• Temporal wedge defects do not respect the
  horizontal meridian.

32
EARLY VISUAL FIELD DEFECTS

• Werner and Drance found in 35 eyes with
  previously normal visual fields that the earliest
  defects were paracentral scotomas with a nasal
  step (51), isolated paracentral defects (26),
  isolated nasal steps (20), and sector defects
  (3).
• Hart and Becker found the following initial
  visual field defects in 98 eyes nasal steps
  (54), paracentral or arcuate scotomas (41),
  arcuate blind spot enlargement (30), isolated
  arcuate scotomas separated from the blind spot
  (20), and temporal defects (3).

33
BLIND SPOT CHANGES

1. Enlargement or vertical elongation of the blind
   spot may occur with early arcuate defect that
   connects with the blind spot or peripapillary
   atrophy, which frequently accompanies
   glaucomatous damage.
2. Baring of the blind spot may be physiologic or
   pathologic. Physiologic 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 inferior retina is
   less sensitive than the superior retina.

34
End-stage defects

• Only a small central island and a temporal island
  of vision remain.
• The temporal island is more resistant than the
  central island

35
Visual field changes in Normal-Tension Glaucoma

1. Greater depth
2. Steeper slops
3. Closer to fixation

36
Important Points

• Both central visual acuity and field of vision
  may improve if the IOP is reduced in early stages
  of the disease
• In most patients with glaucoma, clinically
  recognizable disc changes precede detectable
  field loss
• With standard manual perimetric techniques as
  many as 35 of fibers may gone in an eye with
  normal field
• 20 loss of cells, especially large gangelion
  cells in the central 30? of the retina,
  correlates with a 5-dB sensitivity loss

37
(No Transcript)
38
The following table indicates the threshold tests and the points tested The following table indicates the threshold tests and the points 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
The following table indicates screening tests and the points tested The following table indicates screening tests and the points tested
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
39
Commonly used programs for glaucoma.

• The Octopus program 32 and the Humphrey program
  30-2 are tests of the central 30 with 6 of
  separation between locations.
• The Humphrey program 24-2 eliminates the most
  peripheral ring of test locations from program
  30-2 because it provides the least reliable data,
  except in the nasal step region, so
  testing time can be shortened.

40
DIFFERENTIAL LIGHT THRESHOLD

• Static computerized perimetry measures retinal
  sensitivity at predetermined locations in the
  visual field.
• These perimeters measure the ability of the eye
  to detect a difference in contrast between a test
  target and the background luminance.
• Threshold is defined as the dimmest target
  perceived by the patient at a given discrete
  point psychophysicists define the term as the
  ability to perceive a stimulus 50 of the time.

frequency-of-seeing curve
41
THRESHOLD PROGRAMS

• Strategy
• Full thresholdA staircase, or bracketing,
  strategy is used to estimate threshold at each
  test point. Most commonly, a 4-2 algorithm is
  employed.
• Testing starts with a suprathreshold stimulus.
  The intensity of the stimulus is decreased in
  4-db steps until the stimulus is no longer seen (
  threshold is crossed ). Threshold is crossed a
  second time by increasing the stimulus intensity
  in 2-db steps until it is seen again.

42
The 4-2 bracketing strategy

• Octopus perimeter estimates threshold as the
  average of the last seen and unseen stimulus
  intensities.
• Humphrey perimeter uses the intensity of the last
  seen stimulus as threshold.
• Full threshold is rarely indicated, since newer
  thresholding algorithms are equally as valid and
  much faster.

43
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.

44
OTHER THRESHOLD PROGRAMS

• FASTPAC
• Was most commonly used strategy
• Use 3dB step and only cross threshold once
• Save 25 of test time (Humphreys).
• Measurement are statistically identical to the
  standard strategy
• Trade off ST fluctuation over estimated

45

• 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.

46
SCREENING PROGRAMS

• First the four primary points in each quadrant
  are thresholded to calculate 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 result in different strategies as the
  following Two Zone 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 display circles for seen
  stimuli and solid squares for unseen stimuli.
  Three-zone Points that are not detected after
  being presented twice 6dB 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, "x on the printout for a
  relative defect or a solid block if the target is
  not seen. Quantify defects The points missed
  twice at the 6dB brighter than 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
  numbers for defects.

47
READING FIELD PRINTOUT

• Name, ID and AgeEnsure that this data is
  accurate. The correct age is essential as the
  patient is compared to age matched normals.
• 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.
• Pupil Diameter
• 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.
• Automated pupil size measurement (Humphry)

48

• Glasses Used
• The proper near add refraction, as determined by
  the patient's age and the diameter of the
  perimeter's cupola, must be used.
• This lens must be positioned properly to prevent
  artifactual defects caused by the rim of the
  lens.
• Use Trial lenses only for central tests (within
  30?), or the central part of a full field test.
  For Peripheral test gt 30 degrees, remove the
  lenses.
• Uncorrected refractive errors cause defocusing of
  the test target and apparent depression of
  retinal sensitivity. Each diopter of uncorrected
  refraction causes a 1.26-db depression of retinal
  sensitivity

49
ASSESSING RELIABILITY (Reliability Indices)

• Fixation losses
• Fixation is central to the validity of a visual
  field.
• The following strategies are employed to ensure
  adequate fixation
• Video monitoring of the eye or Gaze tracking
  (Octopus)
• The manual method which requires constant
  supervision of the patient during the test
  (Goldmann)
• Heijl-Krakau Technique in which fixation during
  the examination is periodically monitored by
  presenting stimuli in blind spot (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

50
ASSESSING RELIABILITY (Reliability Indices)

• False positives Catch 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 Catch 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

51

• The 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 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.

52
Deviations

• Humphery Field Analyzer's statistical package
  (STATPAC) uses a model based on test results of
  patients with normal fields, retinal sensitivity,
  and pupil size for each different age group. It
  compares the patient's test results against this
  model to determine how their threshold results,
  for each tested point, compares or falls outside
  the normal population model.
• Total deviation (Comparisons in Octopus)
• Upper numerical display shows difference (dB)
  between patients results and age-matched normal
• These negative values become diagnostic when they
  reach (-5) or greater and more so if there are
  several grouped together.
• Lower graphic display shows these differences as
  grey scale ie. the defect depth

53
Deviations

• Pattern deviation (Corrected Comparisons in
  Octopus)
• Similar to total deviation except the STATPAC
  correct total it for diffuse effects eg.
  cataract, miotic pupils or incorrect testing lens
  
• Display any superimposed pattern of localized
  loss (eg. subtle glaucoma changes) that is hidden
  under a generalized depression
• Probability plot

• Indicate the degree of abnormality
• The darker the symbol in the probability plot
  the more significant the deviation from normal
• Plt1 means that this deviation happens in
  less than 1 of the normal population

54

• Glaucoma Hemifield Test
• GHT is based on the fact that glaucoma usually
  causes asymmetric field loss and not a
  generalised global depression.
• GHT evaluates five zones in the superior field
  and compares these zones to their mirror image
  zones in the inferior field. Then prints one of
  three messages below the graytone format
• GHT within normal limits Outside Normal
  limits Borderline
• The test is not available with tests using
  Fastpac
• Defect (Bebie) Curve in Octopus

55
GLOBAL INDICES

• Mean deviation (Mean defect in Octopus)
• Reflects deviation of patients overall field
  from normal
• It is simply the average (Octopus) or the
  weighted average (HFA) of the deviation values
  for all locations tested.
• p values are lt 5, lt 2, lt 1 and lt 0.5
• The lower the p value the greater the
  significance
• The mean deviation is most sensitive to diffuse
  changes and is less sensitive to small localized
  scotomas.
• Pattern standard deviation (Loss variance in
  Octopus)
• measurement of the degree to which the shape of
  the patient's field departs from the age-matched
  normals reference field.
• Represent the local non-uniformity of the visual
  field
• low PSD indicates a smooth hill of vision or if
  the damage is more or less even
• high PSD indicates an irregular hill or presence
  of scotoma

56
GLOBAL INDICES

• Short-term fluctuation
• Represent intra test variability and measure the
  consistency of responses
• 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 second readings.
• 2 dB or less indicates reliable field
• gt 3 dB indicates either poor patient compliance
  or a sign of glaucomatous field loss and flagged
  with p values, eg. Plt 0.01
• Corrected pattern standard deviation CPSD
  (Corrected Lloss variance
  in Octopus)
• 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, after being corrected for intra-test
  variability (short-term fluctuation)
• It is increased when localized defects are present

57
PSD SF CPSD
58
MD 11.9
CPSD .7
MD 1.9
CPSD .7
CATARACT
NORMAL
MD 11.9
CPSD 2.6
MD 1.9
CPSD 2.6
GLAUCOMA
GLAUCOMA CATARACT
59
INTEREYE COMPARISONS

• The difference in the mean sensitivity between a
  patient's two eyes is less than 1 db 95 of the
  time and less than 1.4 db 99 of the time.
• Intereye differences greater than these values
  are suspicious if they are unexplained by non
  glaucomatous factors, such as unilateral cataract
  or miosis.

60
(No Transcript)
61
(No Transcript)
62
(No Transcript)
63
(No Transcript)
64
Clover leafe field
65
(No Transcript)
66
Glaucoma (1)
Humphrey Central 24-2 Threshold Test
67
Glaucoma (2)
68
Glaucoma (3)
69
Glaucoma
70
Incomplete Left Superior Quadrantonopia (Temporal
lobe Syx)
71
Neuro (1)
72
Neuro (2)
73
Neuro (3)
Bilateral Optic Neuropathy
74
Pseudotumour cerebri
75
Retinal Toxicity secondary to Plaquenil
76
Post portum CVA
2nd VF largely resolved
77
(No Transcript)
78
(No Transcript)
79
Conclusion

• Visual field measurement is a critical component
  in the armament against potentially blinding
  diseases.
• Visual field measurement has undergone an
  evolution from the mechanical to the automated
  measurement process, resulting in greater
  accuracy, ease of use and greater depth of
  analysis.
• Other psychophysical methods for testing the
  visual field for damage are now being explored.
  These methods include contrast sensitivity,
  acuity perimetry, and color perimetry.

80
References

• Cavallerano A. A. When When not to Do
  Perimetry. Guide for Interpretation of Visual
  Fields. 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.