Haag-Streit Octopus perimetry User manual
Below you will find brief information for perimetry Octopus. This manual describes fixed examination parameters in perimetry testing, which include background intensity, color and stimulus duration. The chapter also discusses patient-specific parameters like type of perimetry, stimulus type and test pattern. It helps you understand the functionality of the device and how to use it effectively.
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47
CHAPTER 4
KEY EXAMINATION PARAMETERS
FIXED EXAMINATION PARAMETERS
Perimetric testing must be as standardized as possible, in order to allow comparisons over time and across different eye care providing of ices. Therefore, many examination parameters are ixed by the perimeter used and are not specifically selected by the user of the perimeter. These ixed parameters typically include background color and luminance, maximum stimulus luminance and stimulus duration.
Different perimeter models use different ixed settings.
Therefore, when switching from one device to another, it is important to consider their in luence on the perimetric results. Chapter 12 provides an overview of the most common differences between devices and provides practical advice on how to successfully master the transition.
For the sake of completeness, a summary of the most essential ixed examination parameters of current Octopus perimeters and the rationales behind them is provided in
BOX 4A
. Note that the settings presented below apply to Standard Automated Perimetry. In special situations, other ixed examination parameters are chosen. They are discussed in the respective chapters.
FIXED EXAMINATION PARAMETERS
BACKGROUND INTENSITY AND COLOR
Background luminance (i.e., the re lected light intensity of the background) determines the contrast between the stimulus presented and the background, and thus has a considerable in luence on stimulus perception. To achieve comparable test results, it must be kept constant.
The ideal background luminance of a perimeter should not be too bright, in order to allow display of very dim stimuli for a large dynamic testing range. Neither should it be too dark, to avoid time-consuming dark adaptation of the eye. It should stimulate selected cell types.
The standard background luminance of current Octopus models consists of white light with a luminance of 31.4 asb, which equals 10 cd/m . This luminance level is at the low end of photopic vision (i.e., the visual system used in normal daylight conditions) and does not require time for dark adaptation, but still provides a high dynamic testing range. White light is used because it is detected by all cell types in the retina and is therefore non-selective.
MAXIMUM STIMULUS LUMINANCE
As seen in Chapter 2, the maximum stimulus luminance (i.e., the maximum stimulus intensity) of a perimeter de ines the luminance associated with 0 dB on the decibel scale. It is also part of the formula to calculate a decibel value from the stimulus luminance. If the maximum stimulus luminance were to change, then the whole decibel scale would shift, so it must be kept constant for comparable results to be achieved.
In order to offer a large dynamic testing range from normal to impaired vision, the maximum stimulus intensity value should be as high as possible. However, when the maximum stimulus intensity is
BOX 4A
48 Chapter 4 | Key examination parameters
too high, a part of it will be re lected from the back of the eye (stray light) and will then be detected by neighboring cells, which will produce inaccurate test results. Empirically, a maximum stimulus luminance of 4,000 asb has been shown to offer a large dynamic range, while minimizing stray light effects.
,
STIMULUS DURATION
In order to reduce ixation losses, the perimetric stimulus duration (i.e., exposure time) is kept below the reaction time of the human re lex of quick eye movements towards rapidly appearing stimulus
(i.e., saccadic eye movement). As the reaction time of the saccadic eye movement is around 200 ms, the stimulus duration should be shorter, but still suf iciently long to be seen. For that reason, Octopus perimeters use a standard stimulus duration of 100 ms.
PATIENT-SPECIFIC EXAMINATION
PARAMETERS
As described in Chapter 2, there is always a trade-off between testing time and accuracy in perimetric examinations. In this respect, it is very important to maximize the clinically relevant information, while at the same time minimizing test duration. As perimetry has a wide range of applications, there is no “one parameter its all” approach for all situations. Each Octopus perimeter thus contains a library of standardized examination parameters from which the optimum set can be chosen for each patient. These patient-speci ic examination parameters thus have to be selected for every patient.
In essence, there are four essential questions each clinician must answer, in the order shown below, prior to ordering a perimetric test:
1. Which type of perimetry should be used: static or kinetic perimetry?
2. Which type of stimulus should be used: standard white-on-white, function-speci ic or low-vision?
3. Which test pattern should be used?
4. Which test strategy should be used?
The irst two questions are typically easy to answer.
Indeed, static and standard perimetry are indicated for the needs of patients in most clinical practices and are by far the most commonly used types of perimetry.
With regard to test strategy and test pattern, various selections are commonly employed, and these decisions must be made individually.
TYPE OF PERIMETRY: STATIC OR KINETIC PERIMETRY
STATIC PERIMETRY
For reasons of simpli ication, so far this book has concentrated on static perimetry. In static perimetry, stimuli of varying luminance levels are used to determine visual sensitivity thresholds at a speci ied number of ixed locations
(
FIG 4-1A
). With this type of perimetry, it is possible to detect small changes in sensitivity thresholds with relatively high accuracy. For this reason, static perimetry is the standard for slowly progressing diseases such as
Patient-specifi c examination parameters 49
glaucoma. Since it is fully automated, it is also easy to use in clinical practice.
As the majority of visual ield tests are performed for glaucoma, static perimetry is the most commonly used type of perimetry today.
KINETIC PERIMETRY
Kinetic perimetry was the irst quantitative method of performing visual ield testing and is an alternative to static perimetry. In kinetic perimetry, moving stimuli of pre-determined light intensities are moved from non-seeing to seeing areas. The patient response then de ines the visual ield location of the speci ic light sensitivity threshold (
FIG 4-1B
).
STATIC AND KINETIC PERIMETRY TESTING METHODS
A) STATIC PERIMETRY
Dim
Stimulus
= Seen
= Not seen
Do you see the stimulus?
No
No
No
Fixation
Yes
Yes
Yes
Yes
Stimulus
Bright
Stimulus
B) KINETIC PERIMETRY
Patient response
Do you see the stimulus?
135
165
150
= Seen
= Not seen
Fixation
180 Yes
Yes
No
195
Yes
Vector
(Stimulus trajectory)
210
No
225
FIGURE 4-1 Both static and kinetic perimetry are designed to provide visual sensitivity thresholds that allow mapping the hill of vision of a patient. In static perimetry (A), stimuli of differing light intensity are shown at given locations, to determine the sensitivity threshold at those positions. In kinetic perimetry (B), a stimulus of a given light intensity is moved along the visual fi eld (non-seeing to seeing), to determine the location of that sensitivity threshold.
50 Chapter 4 | Key examination parameters
After repeating this process for a speci ic stimulus size and intensity across the entire visual ield, the visual sensitivity thresholds can be connected to form an isopter
(line of equal sensitivity). An isopter marks the boundary between seeing and non-seeing around the hill of vision for a given stimulus size and intensity and is similar to an altitude line on a geographical map. Local regions of reduced sensitivity inside the isopter are identi ied in the same way and are called scotomas.
FIG 4-2
shows how static and kinetic perimetry results are displayed.
DISPLAY OF STATIC AND KINETIC VISUAL FIELDS
STATIC
Scotoma
(here blind spot)
SEEING
KINETIC
Isopter
NON-SEEING
SEEING NON-SEEING
10 20 30 40 50 60 70 80 90
Scotoma
(here blind spot)
FIGURE 4-2 In static perimetry, each sensitivity threshold is displayed independently, either as a color or as a numerical map
(not shown here). In kinetic perimetry, areas of equal sensitivity thresholds form an isopter that provides similar information to static perimetry about the shape of defects. Local areas of depression inside an isopter are called scotomas.
Since the patient can report seeing the stimulus at any location along the trajectory of the stimuli, kinetic perimetry provides high spatial resolution and fast testing over a large area. It is therefore bene icial for diseases affecting the periphery and sharp-edged defects and is frequently used to evaluate neurological diseases and peripheral retinal diseases. As moving stimuli are easier to see than non-moving ones in the periphery, kinetic perimetry is also often used for children and for patients with cognitive impairment or severe visual ield loss. However, kinetic perimetry is currently not fully automated, making it more challenging in everyday use.
As the majority of visual ield tests are performed to assess glaucoma and due to the ease of use of automation, static perimetry is by far the most commonly used type of perimetry today. For that reason, all of the following paragraphs and chapters focus on static perimetry, while kinetic perimetry will be discussed in depth in Chapter 11.
The key differences between static and kinetic perimetry are summarized in
TABLE 4-1
.
Patient-specifi c examination parameters 51
COMPARISON BETWEEN STATIC AND KINETIC PERIMETRY
ADVANTAGES
WHAT IT IS BEST
AT DETECTING
COMMON USES
STATIC
Clinical gold standard
High precision sensitivity thresholds
Fully automated
Small changes in sensitivity thresholds
Changes in the central area
Glaucoma
Macular diseases
Visual ability testing
TABLE 4-1
KINETIC
High spatial resolution
Fast peripheral testing
Provides information about other visual functions
Highly interactive, lexible and adaptable
Small changes in spatial extent of a defect
Peripheral changes
Remaining vision in advanced diseases
Neuro-ophthalmological conditions
Peripheral retina diseases
Low vision
Children
Patient with cognitive impairment
STIMULUS TYPE: STANDARD OR NON-CONVENTIONAL
STANDARD WHITE-ON-WHITE PERIMETRY
The standard perimetric stimulus is white on a white background, and this type of perimetry is commonly referred to as white-on-white perimetry, or Standard Automated Perimetry (SAP).
The white color stimulus offers the advantage of stimulating all different retinal cell types. As a result, white light allows visual ield testing from early to advanced disease (i.e., it offers a large dynamic testing range). By convention, the standard stimulus used is round, with a diameter of 0.43°, which is also the Goldmann stimulus size III, based on the de inition of Professor Hans Goldmann. For more information on Goldmann stimulus sizes, refer to
BOX 4B
.
52 Chapter 4 | Key examination parameters
BOX 4B
GOLDMANN SIZES I TO V
The size conventions used today to describe a perimetric stimulus are derived from the work of Professor Hans Goldmann, who developed the
Goldmann perimeter in 1946. He de ined standard sizes for perimetric stimuli, and the Goldmann sizes
I to V are still widely used. Each step corresponds to a change in diameter by a factor of 2 and in area by a factor of 4. Size III is several times smaller than the physiological blind spot and was considered to be an accurate measurement size.
The Goldmann stimulus sizes I to V are presented in relation to the size of the physiological blind spot.
BLIND SPOT
V 1.7°
20
IV 0.8°
III 0.43°
II 0.2°
I 0.1°
FUNCTION-SPECIFIC PERIMETRY
Function-speci ic perimetry uses different stimulus types to stimulate different visual functions (e.g., motion, or color vision), but they all have the same purpose: measuring a subset of the visual system individually, to get more sensitive responses for early disease detection.
Different Octopus perimeter models offer different function-speci ic stimuli (
FIG 4-3
): a blue stimulus on a yellow background (Short-Wavelength Automated Perimetry, or SWAP); a white lickering stimulus on a white background (Flicker Perimetry); or a pulsating stimulus with concentric rings changing in both spatial resolution and contrast (Pulsar Perimetry). They are described in more detail in Chapter 10.
FUNCTION-SPECIFIC PERIMETRY
Time 1
ON
Flicker
Time 2
OFF
SWAP Pulsar
FIGURE 4-3 Stimuli used in function-specifi c perimetry from left to right: Short Wavelength Automated Perimetry (SWAP),
Flicker Perimetry and Pulsar Perimetry.
Patient-specifi c examination parameters 53
PERIMETRY FOR LOW VISION
There is a limit to the visibility of the standard size III white perimetric stimulus in patients with signi icantly impaired visual sensitivity. In order to increase the dynamic range into the low vision region and to make the stimulus more visible to these patients, the Goldmann stimulus size V is typically used, instead of the standard size III. It is 16 times larger in area and is therefore more detectable. Chapter 10 provides more information about stimulus size V.
OVERVIEW OF DIFFERENT STIMULUS TYPES
ADVANTAGES
STANDARD
White-on-white, stimulus III
Clinical standard
WHAT IT IS BEST
AT DETECTING
COMMON USES
Follow-up of a disease from early to late stage
Glaucoma
Macular diseases
TABLE 4-2
FUNCTION-SPECIFIC
Pulsar, Flicker, SWAP
Earlier detection in some patients
Provides information about other visual functions
Early loss in some patients
LOW VISION
White-on-white, stimulus V
Better visibility for patients with signi icant visual ield loss
Advanced visual ield loss
Con irm defects observed on standard perimetry
Identify defects in glaucoma suspects who do not show defects on standard perimetry
Advanced glaucoma or other ocular or neurological diseases
54 Chapter 4 | Key examination parameters
TEST PATTERN
In clinical practice, patients can sometimes become tired quickly during perimetric testing, which signi icantly limits the number of test locations that can be reliably tested.
-
A reasonably dense grid of test locations, covering the entire visual ield with 2° degree spacing, would require around 4,800 size III stimuli, and a grid with 6° degree spacing would require approximately 550 test locations. A very rough grid with 10° degree spacing between the stimuli would require approximately 190 test locations, but would be highly inaccurate, as there would be only 5 test points in the central 10° of vision, which is an important area for visual functions such as reading and identifying objects (
FIG 4-4
).
ILLUSTRATION OF THE LOW SPATIAL RESOLUTION OF PERIMETRIC TESTING
10º SPACING
~190 size III targets
90
6º SPACING
~550 size III targets
90
2º SPACING
~4800 size III targets
90
180 0 180 0 180 0
270 270 270
FIGURE 4-4 Covering the entire visual fi eld with high resolution within a reasonable test duration is not possible. Either the fi eld is only roughly covered, or the test duration is unacceptable, as shown in this example with three different test patterns.
In order to maximize perimetric information and minimize test duration, a test pattern should be chosen with a high density of test locations in the area of high interest and a low density of test locations in areas of low interest (
FIG 4-5
). For that reason, Octopus perimeters offer a large library of testing patterns for common perimetric applications.
The most commonly used test patterns available on the
Octopus perimeter and the rationale for which to select are described in depth in Chapter 5.
Patient-specifi c examination parameters
EXAMPLES OF DIFFERENT TEST PATTERNS
A) G-PATTERN
(Glaucoma)
90
B) M-PATTERN
(Macula)
90
180 10 30 40 50 60 70 80 90 0 180 10 30 40 50 60 70 80 90 0
C)
270
ESTERMAN
(Visual driving ability)
90
D)
270
PTOSIS
90
180 10 30 40 50 60 70 80 90 0 180 10 30 40 50 60 70 80 90 0
270 270
FIGURE 4-5 Examples of test patterns for various clinical perimetric applications are presented. Each pattern maximizes the relevant information for that clinical situation, while minimizing the test duration by only evaluating the most relevant areas. (A)
The G-pattern for glaucoma tests within 30° at locations that follow the retinal nerve fi bre bundle patterns. (B) The M-pattern for the macula tests within the central 10°. (C) The Esterman tests binocularly for visual fi tness to drive (120° horizontally and 60° vertically). (D) The Ptosis test pattern only evaluates the upper hemifi eld along common eyelid locations.
55
56 Chapter 4 | Key examination parameters
TEST STRATEGY
For the detection and follow-up of a disease, the sensitivity thresholds should be determined with high accuracy. However, in clinical practice, even very cooperative and reliable patients experience fatigue, which limits the number of stimulus luminance levels that can be presented during a perimetric test. If we were to sample the entire range in steps of 1 dB, from 0 dB (maximum stimulus luminance) to 32 dB (approximate foveal sensitivity threshold of a 20-year-old on the Octopus 900), 32 stimuli would have to be presented at one test location.
Performing the same procedure in 2 dB steps would require 16 stimuli, while 4 dB steps would still require the presentation of 8 stimuli
(
FIG 4-6
).
ILLUSTRATION OF THE LOW RESOLUTION OF SENSITIVITY THRESHOLDS IN PERIMETRIC TESTING
4 dB PRECISION
Up to 8 stimuli/location
2 dB PRECISION
Up to 16 stimuli/location
1 dB PRECISION
Up to 32 stimuli/location
32 dB 32 dB 32 dB
0 dB 0 dB 0 dB
FIGURE 4-6 Determining a sensitivity threshold with high precision with a sequence of stimuli of increasing intensity is not possible. Either too many stimuli are required, or the step sizes are too large, as the example with three different step sizes demonstrates.
Instead of using the strategy of increasing stimulus intensity step by step until the sensitivity threshold is reached, an ef icient strategy is therefore needed that maximizes precision but minimizes test duration. they only assess whether stimuli are seen or unseen (
FIG
4-8
). Qualitative strategies are commonly used in legal visual ability evaluations, such as in the tests used to assess visual itness to drive. Examples of a quantitative and a qualitative test strategy are given in
FIG 4-7
and
FIG 4-8
, for the sake of illustration. Octopus perimeters offer several test strategies with different trade-offs between test duration and accuracy for different clinical situations. Some strategies are quantitative, which means that they are used to determine a sensitivity threshold (
FIG 4-7
). Qualitative strategies are also offered in which the testing time is reduced, because
The most commonly used strategies available on the
Octopus perimeter and the rationale for which strategy to select are described in depth in Chapter 6.
Patient-specifi c examination parameters
EXAMPLE OF A QUANTITATIVE STRATEGY
QUANTITATIVE STRATEGY
Do you see?
30 dB
Threshold Zone
3
4
1
2
5
Sensitivity
Threshold
= Seen
= Not seen
0 dB
1.
Sampling in large steps
2.
Detailing within threshold zone
FIGURE 4-7 Example of a quantitative thresholding strategy: The visual fi eld is fi rst scanned with stimuli with large steps in light intensity, in order to identify a suspected threshold zone. Once that zone has been identifi ed, further testing inside that zone will allow for determination of an accurate threshold with minimal test duration.
EXAMPLE OF A QUALITATIVE STRATEGY
QUALITATIVE STRATEGY
Do you see?
30 dB
Do you see?
30 dB
= Seen
= Not seen
Sufficient vision to drive
Sufficient vision to drive
Insufficient vision to drive
Patient is not fit to drive
Insufficient vision to drive
Patient is fit to drive
0 dB 0 dB
FIGURE 4-8 Example of a qualitative strategy: For visual driving ability, one stimulus is shown at the fi xed stimulus intensity which is the minimum needed to drive safely. If a person sees that stimulus at a required number of test locations, this means that the person fulfi lls the visual fi eld criteria to be able to drive.
57
58 Chapter 4 | Key examination parameters
REFERENCES
1. Fankhauser F, Haeberlin H. Dynamic range and stray light. An estimate of the falsifying effects of stray light in perimetry.
Doc Ophthalmol. 1980;50:143-167.
2. Anderson RS, Redmond T, McDowell DR, Breslin KM, Zlatkova MB. The robustness of various forms of perimetry to different levels of induced intraocular stray light. Invest Ophthalmol Vis Sci. 2009;50:4022-4028.
3. Johnson CA, Adams CW, Lewis RA. Fatigue effects in automated perimetry. Appl Opt. 1988;27:1030-1037.
4. Wild JM, Searle AE, Dengler-Harles M, O’Neill EC. Long-term follow-up of baseline learning and fatigue effects in the automated perimetry of glaucoma and ocular hypertensive patients. Acta Ophthalmol (Copenh). 1991;69:210-216.
5. Hudson C, Wild JM, O’Neill EC. Fatigue effects during a single session of automated static threshold perimetry.
Invest Ophthalmol Vis Sci. 1994;35:268-280.
6. Gonzalez de la Rosa M, Pareja A. In luence of the “fatigue effect” on the mean deviation measurement in perimetry.
Eur J Ophthalmol. 1997;7:29-34.

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Key features
- Standardized testing parameters
- Adjustable patient-specific parameters
- Various test patterns for different applications
- Large dynamic testing range
- Automated testing