IPS PERIMETRIC STANDARDS, 1978
1. Definitions of Perimetry and of the Visual Field
Perimetry is the measurement of visual functions of the eye at topographically defined loci in the visual field. The visual field is that portion of the external environment of the observer wherein the steadily fixating eye(s) can detect visual stimuli.
2. Need for Specifications and Tolerances
The fundamental purpose of standardization is to provide a common framework for measurement. This allows exchange and comparison of information obtained at different times and in different places. If a common measurement scheme can be achieved, then development upon that base can proceed in an orderly manner.
In perimetry few standards exist and certain of these are imperfectly specified. This situation needs to be rectified.
Specification also implies consideration of tolerances. Tolerances include instrument setting accuracy as well as measurement accuracy. Because tolerances in a clinical office are not comparable with those achievable in a research laboratory, an effort will be made to set standards which define conditions where small errors do not significantly alter results or interpretations of data.
3. Applicability of this Standard
This standard is written for all individuals engaged in perimetry and especially for clinicians for use in their offices, departments and clinics. It is directed also towards the manufacturer who provides visual field test equipment. These standards also set minimum criteria for reporting research results. The goal is to set a reasonable minimum set of standards for testing of the visual field. Note that different requirements or strategies may be needed for different tasks.
4. Specifications of Magnitudes and Units
This committee makes use of the International System of Units published by the International Bureau of Weights and Measures (Le Systeme International d'Unites, 1970, OFFILIB, 48 Rue Gay-Lussac, F-75005, Paris, France, Revised edition 1977). See also: The International System of Units, NBS Special Publication 330, 1977, US Department of Commerce, National Bureau of Standards, US Government Printing Office, Washington DC 20402 (SD Catalogue No. C13.10:330/4). Supplemental use is made of the Vocabulary of the Commission Internationale de l'Eclairage (International Lighting Vocabulary of the Commission Internationale de l'Eclairage, 3rd ed;, 1970, Bureau Central de la CIE, 4 Avenue du Recteur Poincare, F-75016, Paris, France).
In the Proceedings (Acta) of the XXIInd International Ophthalmological Congress, Paris, 1974, p78 and 93, the Concilium Ophthalmologicum Universale published recommendations regarding the use of the International System of Units in ophthalmological practice.
There is on record an earlier international standard on perimetry which was published by the XIII Concilium Ophthalmologicum 1929, Hollandia, NV Boek- en Steendrukkerij, Edward Ijdo, Leiden, 9 pages. The present document is meant to supercede this earlier standard.
Recently the Committee on Vision, the National Research Council, National Academy of Sciences of the United States of America published the "First Interprofessional Standard for Visual Field Testing," National Academy of Sciences, Washington, DC, 1975. Certain aspects of the present document are based upon this publication.
5. Photometric Specification
For proper control of visual stimuli in perimetry, provision of one or more light sources is necessary. That is, the background, test stimuli, and all supplementary targets or display fields need to be specified photometrically.
The specification of visual stimuli is complex. Properly, radiant energy determinations should be made, followed by suitable luminous conversions for different field areas and stimulus conditions. For most practical clinical situations the IPS recommends that the visual stimulus in perimetry be specified in luminance units measured at the center of the entrance pupil of the eye. The visual stimulus is essentially defined by this luminance, the direction of the stimulus in the field of view and the area of the entrance pupil of the eye. Since we often cannot control pupil size in the clinical environment, the least we can achieve is to specify luminance at the center of the entrance pupil of the eye, and to request the examiner to record this luminance and the entrance pupil size at the time of the measurement. In certain conditions special additional calibration requirements exist, e.g. for short duration or coloured stimuli.
We ask the manufacturer to specify the operating conditions of his instrument. ideally this would include the complete specifications of lamps, filters (including transmission curves), and desired operating conditions. Luminance at the center of the entrance pupil of the eye should be specified for defined operating conditions of properly centred light sources and associated optics. Similarly, the spectral distribution at the entrance pupil of the eye should be defined. In addition, definition of desired operating colour temperature and CIE co-ordinates is highly desirable. A simple scheme for assuring that the instrument is functioning within reasonable tolerances of these specified values should be provided. Included would be some test of luminance and/or indication for replacement of light sources.
The international unit of luminance is the candela per meter squared, cd/m2 or cd.m-2. Other units are now regarded as obsolete. Although strictly speaking not the same units2, conversion to apostilb and millilambert values can be made using the following relationships:
10/p candela/m2 = 1 millilambert = 10 apostilbs,
where 10/p = 3.183 (approximate)
While this group would prefer luminance measurement of perimetric devices by objective small field test instruments, an acceptable alternative would be to provide a measure convertible into luminance at the center of the entrance pupil of the eye.
6. Background or Adapting Luminance
A. Specification of luminance
For routine perimetric instruments used in clinical offices it is recommended that a value of background luminance be chosen such that it is photopic and it falls within that range of background luminances over which the Weber fraction remains constant, ie, DL/LB = constant.3 DL is defined as the just detectable luminance difference between test target and background,4 and LB is background luminance (also see section on contrast). The proposed background level is generally higher than that found in perimeters in use today. This setting criterion is recommended because (a) it requires less sensitive calibration equipment, (b) it is less sensitive to modest fluctuations (or changes) in light source output, (c) the result is less dependent upon modest variations in eye pupil size, (d) visual functions are tested at clearly defined photopic levels, and (e) fixation control is easier than at low luminance adaptation levels.
If this background luminance cannot be achieved, it is recommended that for routine office purposes no less than 10 candelas/m2 be used. A background luminance of 10 candelas/m2 is below, but near the level where DL/LB = constant over an extended range of values.
Other light or adaptation levels offer advantages. Lower levels may provide an extended range of contrast values for testing, cataract patients may be better evaluated, and rod anomalies may be more effectively studied, etc. Thus, where adequate calibration capability exists and careful studies are conducted to rule out loss of confidence due to increased measurement variance, lower photopic or mesopic background luminance levels can serve a useful purpose. Similarly, higher background luminance values can be useful in test of the visual fatigue factor or for the development of colour perimetric tests.
Thus the IPS recommends that instruments be constructed to be capable of calibration over a range of values. The IPS suggests that the standard be a minimum test condition rather than a limiting condition. We encourage careful research on this rather complex and crucial set of questions. We recognise that stability of determinations in special disease conditions, e.g., glaucoma, cataract, chorioretinal degenerations, optic neuropathies, etc., may require use of special or specific background luminance levels and special purpose instruments suitable for advanced diagnostic laboratories.
2 See discussion in the recently published US Standard relative to this point.
3 For example, see E Aulhorn, H Harms, and M Raabe, Documenta Ophthal. 20, 538-556, 1966; and J Enoch, Physiology (Chapter 3, pp 202-289) in A Sorsby, Modern Ophthalmology, Vol I, First Ed, 1963; and the recent USA Standard referenced above.
4 The specification of DL is somewhat arbitrary, because the probability of detecting the test target varies between 0 and 1 over a small range of luminances. DL is commonly specified as the luminance increment or difference corresponding to a detection probability of 0.5 (50% frequency-of-seeing).
B. Preadaptation conditions
It is highly desirable that the patient be adapted to the luminance of the background field before commencement of the perimetric test. A longer time period of preadaptation to this field is necessary for lower background luminance levels. It should also be longer if the patient enters the examination chamber from an intensely luminous environment. It is desirable that the manufacturer and examiner determine the light adaptation period which provides relatively stable response for the instrument and conditions used. Preadaptation conditions can also be important when testing individuals manifesting certain types of pathology.
C. Diffusely reflecting surface
It is desirable that the background field be a diffusely reflecting surface, ie, a non-glossy surface which at least approximates Lambert's Law.
7. Specification of the location of an Object in the Visual Field
A polar co-ordinate system should be used when defining (a) the half-meridian and (b) the eccentricity of the center of the test target, both expressed in degrees. The zero degree half-meridian is defined to the right of the patient (as seen by the patient). The specified half-meridian then proceeds counterclockwise through 360 degrees about the fixation target (as seen by the patient). The fixation point is defined at having zero degree eccentricity. This assumes the patient has normal fixation.
This system does not allow fine specification of the area of a scotoma or of an isopter because of non-linearity of representation,5 except in the case of a hemisphere where proportional solid angles are present. This requires the center of the entrance pupil of the eye to lie at the center of curvature of the hemisphere. In this special case, two equal solid angles located at different loci in the visual field subtend equal areas on the surface of the hemisphere. This condition does not exist if a flat test surface is used for examination of the visual field, e.g., when a tangent screen is employed. The same statement may be applied to the cartographic deformation of the field as expressed on a flat sheet of paper. There exist cartographic projections which attempt to represent areas proportionately.
It is highly desirable to keep the tolerances for location, registration, and replication of test object position within narrow limits. If this cannot be achieved, the reliability of subsequent determinations is limited, especially for static (target not moving) perimetry. Accuracy is limited by the size and nature of the fixation target, the stability of patient fixation, and the mechanical capabilities of the perimetric device.6 In turn, these factors influence the selection of the smallest useful target size.
Optimal fixation targets have not yet been defined. This is an important question which needs clarification through research. Obviously, it is desirable to monitor patient fixation directly. When central vision is impaired, special fixation targets or displays are often needed.
It is desirable that measured test points should be indicated on the test record in an obvious manner. Clearly the more points tested, the better the characterisation of the visual field. The more repetitions of evaluations made at a single point, the greater the reliability of the determination. It is desirable that one or more points be evaluated more than once in order to define the approximate reliability of the test. It is desirable that interpolation or analysis techniques employed be clearly defined
5 Distinguish between ability to specify a location and an area.
6 Lens factors also influence accuracy of location and re-location of a target in the visual field. Apparent location of a target is influenced by power and centration of the lens correction, vertex distance, base curve and lens thickness. It is desirable that the lens(es) used and the vertex distance be noted. There is an advantage in keeping vertex distance small.
8. Target Specification (non-photometric)
A. Size, distance, and form
Ideally target dimensions should be specified in terms of the solid angle subtended at the centre of the entrance pupil of the eye and measured in steradians. Practically, this is not done, nor do we recommend such designation as essential at this time.
A conceptually simpler scheme is the specification of the diameter of the target in terms of visual angle subtended at the center of the entrance pupil of the eye. This assumes that a round target is located at the point of fixation. If the target is not round, the diameter of the equivalent round target subtending the same area at the point of fixation may be used. Target diameters should be expressed in degrees, minutes, and seconds of arc. It is highly desirable to specify test target distance from the eye, because luminance is dependent on test distance for perimetric test targets of small dimension. (The same is not true for extended background fields.) Thus, for proper specification, it is highly desirable that both angular subtense and target distance be specified. Other factors, such as image blur resulting from several causes, also make specification of target distance desirable (see below, Image sharpness). As an example of proper specification, a target may subtend 6' of arc (angular diameter) at a 330 millimeter test distance.
Alternatively, specification of the tangent of the angle subtended at the center of the entrance pupil of the eye for a target located at the fixation point has been widely used.
DIAGRAM
Fig. 1. d/D = 2 tan ( /2)
This measure is expressed as a fraction, the diameter (d) of the target in millimeters divided by the distance of the fixation point from the eye (D) in millimeters (e.g. 2 mm white/1000mm). Of the two schemes (the angle subtended plus the test distance versus the tangent fraction ) the angle subtended and test distance is the preferred form of representation because it is conceptually simpler to compare angular subtense of targets on two different test instruments. Thus the IPS recommends the specification of equivalent7 test target diameter and distance as follows:
(a) minutes of arc diameter at (b) millimeters test distance. In publications this form is preferred. Other systems may be used if a logical scheme is formulated and if conversion to the above preferred form is provided.
When a tangent screen is used, and targets are displayed from the point of fixation, the angular subtenses, the solid angle subtended by the target, and the effective test distance are all altered. If a projector is used with a tangent screen, its center of projection must effectively be placed as near as possible to the location of the test eye in order to minimize distorting effects and blur. When tangent screens are used (or other perimetric devices) every effort should be made to make background luminance as uniform as possible.
It is desirable that a number of different size targets be available for testing, and that the visual angles subtended by these targets extend from an effective point source to large targets in an orderly series.
It is desirable that the target shape or form used be described. For targets that depart meaningfully from round or near round, it is desirable that orientation be indicated as well as its shape or form.
6 Lens factors also influence accuracy of location and re-location of a target in the visual field. Apparent location of a target is influenced by power and centration of the lens correction, vertex distance, base curve and lens thickness. It is desirable that the len(es) used and the vertex distance be noted. There is an advantage in keeping vertex distance small.
7 The use of equivalence is only valid for targets which approximate round shapes.
B. Contrast
The contrast of the test target against the background field may be represented in various ways, depending upon usage. Let LT = luminance of the test target, and LB = luminance of the background or adapting field,8 then DL is the just detectable change in target luminance, and would be defined as DL = LT - LB at threshold. A contrast may be positive or negative, that is, the target may have a higher luminance than the background (positive contrast) or the darker than the background (negative contrast). All of the following formats have been used to describe contrast = C:
(a1) C = LT - LB (Recommended)
______
LB
(a2) C = LT - LB 9
__________
LB
(a3) CT = DL CT = contrast at threshold (Recommended)
__
LB
(b) C = LT
_____
LB
(c) C = LT - LB = LT - LB where (LT + LB) / 2 = mean luminance
___________ _________
LT + LB 2 {(LT + LB) / 2}
NOTE: In a projection perimeter, DL is the projected incremental field and the luminance at the pointed tested LT = DL + LB. Negative contrast, ie, a darker target against a brighter background, is rarely used in perimetry, but is commonly used in conjunction with visual acuity charts.
DIAGRAM
Fig. 2.
In routine perimetry form a1 or a3 is the recommended usage. For simplicity of design most tests performed use positive contrast. Form c is often used as a description of modulation in contrast sensitivity functions. Form a3 is also known as the Weber fraction. As the increment or contrast threshold, form a1 is equivalent to a3. Since many forms exist for expression of contrast, it is desirable that the form employed be indicated.
C. Duration of Presentation
1. Non-moving or static target(s) (here we only consider a single presentation of the test target). The response of the visual system changes with duration of exposure of a visual stimulus. The exposure time at which this transition occurs is known as the critical duration. The critical duration is about 100 milliseconds, and varies with several factors, including test target locus in the field, target size, background field luminance and pathology.
8 That which follows assumes that LB is greater than zero.
9 |c| symbol denotes absolute value, ie, a value without sign.
For exposures shorter than the critical duration,
DL x Duration of exposure = Constant
while for durations of exposure longer than the critical duration,
DL = Constant
Obviously the latter is a less demanding test situation for calibration as one less parameter needs to be specified in the test instrument. Shorter durations may be advantaged, but adequate calibration capability is advisable.
If the duration of exposure exceeds the latency for a saccadic eye movement (approximately 250 milliseconds), there is a tendency for some patients to avert their eyes from the fixation point to look at the target.
It is desirable that duration of exposure provided by the manufacturer be specified and that some scheme be available to determine whether a mechanical shutter or test flash device is operating properly if the duration of exposure is less than the critical duration.
One must use care when presenting serial stimuli at the same test locus. It is desirable that the prior presentation shall not affect response to the later ones.
2. Moving or kinetic targets. If the target or stimulus is moved, as in kinetic perimetry, the most important point is the stability of rate of movement, ie, a fixed angular velocity, initially and at the time of re-examination. Some perimetrists use a different strategy, e.g., a somewhat slower rate of movement, in the central field. In most instances the target is moved from non-seeing to seeing. Other strategies may be used to fit specific needs. In recording and/or reporting results it is desirable (to the extent possible) that test conditions employed be described. Detectability of a moving target is dependent upon test target luminance and/or contrast, area, direction, and rate of movement. The measured results are subject to meaningful variation if such factors are not properly controlled. The specification of optimal test conditions is a complex question requiring further research. Thus, at this time, the IPS does not recommend any single desired rate of movement or test strategy. In so stating, the IPS in no way means to under-estimate the importance of kinetic perimetry.
D. Image sharpness
One of the least appreciated variables in visual field testing is the blur of the retinal image of the test target. Many factors affect image blur. Appropriate optical correction to the test distance is needed especially for small test targets. This correction will vary with presbyopia, the use of miotics, cycloplegics, and in the presence of many forms of pathology, etc.
9. Color Perimetry
When reporting data, it is highly desirable to specify the observer's task, whether it be just detection or a judgement of hue and saturation of the target.
In colour perimetry we recommend that both target and background field radiance and luminance be specified at the center of the entrance pupil of the eye. In anticipation of the development of new colour perimetric tests, the IPS recommends a general increase in background and target luminance levels; spectral specification in the plane of the entrance pupil of light sources and stimuli (including the properties of filters); and, if possible, designation of CIE co-ordinates of the same elements.10 Further, definition of colour temperature of the source and a logical scheme for replacement of aged light sources has been recommended above. For colour testing it is preferable to use nearly monochromatic stimuli as this greatly simplifies calibration requirements. Similarly (and particularly when non-monochromatic light stimuli are used) the use of light sources which emit continuous spectra simplifies analysis of stimuli.
10. Other Factors
A. Attention signal and shutter noise
In many applications of perimetry it is useful to provide a signal or cue to indicate that a stimulus is about to be presented. Such cues are often auditory. This clearly influences the probability of response and in certain situations may be more effective. Similarly, for long duration stimuli, the noise of an activated shutter can serve the same purpose.
B. Distractions to be avoided
It is recommended that the perimeter be placed in a quiet room where light conditions can be completely controlled, and distractions can be avoided.
C. Relative and absolute scotomas
It is important to differentiate between relative and absolute scotomas. A relative scotomas is defined as a partial visual deficit in a given area of visual field. An absolute scotoma implies total loss of vision in a given field area. Practically, absolute scotomas are usually defined in terms of the largest, most intense target available to the perimetrist. In fact, some response may yet remain and may have been revealed if still larger or more intense targets had been used (assuming stray light effects have been considered). Thus, it is desirable, in discussions of absolute scotomas, to specify the largest and most intense stimulus employed.
11. Acceptance and Revision of these Standards
a. The proposed standards have been approved by the R.G. on Standards and the Board of the IPS.
b. These Standards, once approved, will remain in force until revised by the R.G. on Standards of the IPS. These Standards must be reviewed every four years and either reaffirmed, modified, or replaced.
c. The R.G. on Standards stands ready to provide reasonable advice, and to offer clarification relative to matters contained in this set of standards. All correspondence relative to such matters and suggested improvements should be directed to the Secretary of the IPS.
10 It should be recognized that CIE coordinates as specified for central vision may not be valid for peripheral field test points.
IPS English
A0 Stimulation
A1 Inadequate stimulus
A2 Adequate stimulus
A3 Distal stimulus
A4 Proximal stimulus
A5 Threshold stimulus
A6 Subthreshold stimulus
A7 Suprathreshold stimulus
A8 Radiation
A9 Complex radiation
A10 Monochromatic radiation
A11 Wavelength - l
A12 Nanometer - nm
A13 Spectral distribution
A14 Colour (or)
A15 Colour (or) temperature
A16 Kelvin - K
A17 Dominant wavelength - ld
A18 Excitation purity pe
A19 Chromaticity coordinates - x, y; x10, y10
A20 Standard illuminant - A, B, C, D65
A21 Complementary colour (or)s
A22 Radiance - Le
A23 Watt per steradian per square metre (er) - W.sr-1 .m-2
A24 Luminance - L
A25 Candela per square metre (er) - cd.m-2
A26 Irradiance - Ee
A27 Watt per square metre (er) - W.m-2
A28 Illuminance - E
A29 Lux - lx
A30 Reflection
A31 Specular reflection
A32 Diffuse reflection
A33 Uniform diffuse reflection
A34 Mixed reflection
A35 Regular reflectance - pr
A36 Diffuse reflectance - pd
A37 Gloss
A38 Transmission
A39 Regular transmission
A40 Diffuse transmission
A41 Uniform diffuse transmission
A42 Mixed transmission
A43 Regular transmittance - tr
A44 Diffuse transmittance - tr
A45 Absorption
A46 Absorptance - a
A47 Optical density - D
A48 Diffusion
A49 Refraction
A50 Dispersion
A51 Diffraction
A52 Polarized light
A53 Unpolarized light
A54 Coherent light
A55 Incoherent light
A56 Temporal modulation
A57 Intermittent stimulation
A58 Pulsed stimulation
A59 Periodic pulsed stimulation
A60 Period
A61 Frequency - v
A62 Hertz - Hz
A63 Duty cycle, light dark ratio
A64 Sinusoidally varying stimulation
A65 Modulation depth
A66 Spatial modulation
A67 Modulation transfer function - MTF
A68 Interferometric resolution
A69 Object, target (=O)
A70 Background (=Bd)
A71 Surround (=Sd)
A72 (O, Bd, Sd) shape
A73 round
A74 elliptical
A75 square
A76 (O, Bd, Sd) contour
A77 Edge gradient
A78 (O, Bd, Sd) distance -l
A79 (O, Bd, Sd) diameter -d
A80 Millimetre (er) - mm
A81 (O, Bd, Sd) visual angle - q
A82 Minute of arc - '
A83 Second of arc - "
A84 (O, Bd,Sd) area -S
A85 Square millimetre (er) -mm2
A86 (O, Bd, Sd) solid angle - w
A87 Steradian -sr
A88 (O, Bd, Sd) luminance - L
A89 Decibel - dB
A90 (O) intensity - I
A91 Candela - cd
A92 (O, Bd, Sd) colour (or)
A93 red
A94 orange
A95 yellow
A96 green
A97 blue
A98 violet
A100 white
A101 grey
A102 black
A103 (O, Bd, Sd) Munsell notation
A104 (O, Bd, Sd) exposure duration - t
A105 Second of time -s
A106 (O) angular velocity
A107 Degree per second
A108 Rate of increase of (O, Bd, Sd) luminance
A109 (Photometric) luminance contrast - C = DL/L
A110 Corneal illuminance -Ecor
A111 Luminance measured from the position of the centre (er) of the entrance pupil - Lpup
A112 Pupil diameter -d pup
A113 Pupil area - S pup
A114 Retinal illuminance - Eret
A115 Troland - td
A116 Reduced troland - tdr
A117 Blur of the retinal image
A118 Intraocular stray light
A119 Equivalent veiling luminance
B0 Perception
B1 Brightness
B2 Lightness
B3 Hue
B4 Saturation
B5 Chromaticity
B6 Bezold-Brucke phenomenon
B7 Flicker
B8 Stroboscopic effect
B9 Speed of perception
B10 Subjective colour (or)s
B11 Fusion frequency - FF
B12 Local adaptation
B13 Discomfort glare
B14 Disability glare
B15 Adaptation
B16 Photopic vision
B17 Mesopic vision
B18 Scotopic vision
B19 Adaptation curve
B20 Break (in adaptation curve)
B21 Chromatic adaptation
B22 Threshold
B23 Sensitivity
B24 Absolute threshold
B25 Absolute sensitivity
B26 Difference (or increment) threshold - DL
B27 Difference (or increment) sensitivity - 1/DL
B28 Perceived contrast
B29 Luminosity contrast
B30 Colour (or) contrast
B31 Simultaneous contrast
B32 Successive contrast
B33 Contrast threshold (=Weber fraction) - DL/L
B34 Contrast sensitivity L/DL
B35 Modulation threshold - DL/S(L1 + L2)
B36 Liminal brightness increment (UK) - Just noticeable difference (US)- j.n.d.
B37 Visual resolution
B38 Visual acuity
B39 Stereoscopic visual acuity
B40 Kinetic (=dynamic) visual acuity
B41 Achromatic threshold
B42 Chromatic threshold
B43 Photochromatic interval
B44 Spatial summation
B45 Successive lateral spatial summation
B46 Receptive field
B47 Temporal summation
B48 Summation exponent
B49 Summation number
B50 Critical duration
B51 Inhibition
B52 Sensitization
B53 Sustained-type visual response
B54 Westheimer function
B55 Transient-type visual response
B56 Rivalry in the visual field
B57 Binocular rivalry
B58 Spectral relative luminous efficiency function - V(l)
B59 Purkinje phenomenon
B60 Stiles' p function
B61 Directional sensitivity function (= Stiles-Crawford effect)
B62 Entoptic phenomenon
B63 Maxwell's spot
B64 Haidinger's brushes
B65 Directional selectivity
B66 Reaction time
B67 Optokinetic nystagmus
B68 Attention
B69 Breadth of attention
B70 Expectancy
B71 Conspicuousness
B72 Distraction
B73 Fatigue
B74 Mental processing block
B75 Visual performance
C0 Technique
C1 Psycho-physical method
C2 Perimetry
C3 Campimetry
C4 Screening method
C5 Confrontation test
C6 Scotometer
C7 Plate for evaluating scotomas
C8 Tangent screen
C9 Angioscotometer
C10 Perimetric arc
C11 Portable hand perimeter
C12 Hemispheric (=cupola, = bowl) perimeter
C13 Projection perimeter
C14 Monocular perimetry
C15 Binocular perimetry with fusional stimulus
C16 Participation binocular perimetry
C17 Phase difference haploscopy
C18 Measurement of peripheral visual acuity
C19 Werblin's rotating windmill pattern
C20 Colour (or) perimetry
C21 Flicker perimetry
C22 Photopic perimetry
C23 Mesopic perimetry
C24 Scotopic perimetry
C25 Adaptoperimetry
C26 Temporal adaptoperimetry
C27 Steady-state adaptoperimetry
C28 Fundus image-controlled perimetry
C29 Combined method (=check-up)
C30 Subjective method
C31 Entoptic method
C32 Objective method
C33 Pupillomotor perimetry
C34 Optokinetic perimetry
C35 ERG (=electroretinographic) perimetry
C36 VER (= visual evoked response) perimetry
C37 EEG (= electroencephalographic) perimetry
C38 Light source
C39 Daylight#
C40 Incandescent lamp
C41 Projector lamp
C42 Halogen lamp
C43 Fluorescent lamp
C44 Electronic flash tube
C45 Light emitting diode
C46 Arc lamp
C47 Xenon arc
C48 Laser
C49 Point-source
C50 prefocussed
C51 clear
C52 frosted
C53 Filament
C54 Vacillation
C55 Ageing
C56 Life of a lamp
C57 Light housing
C58 Reflector
C59 Cut-off
C60 Projector
C61 Dimmer
C62 Shutter
C63 Screen
C64 Diaphragm
C65 Ground glass
C66 Opal glass
C67 Mirror
C68 Semitransparent mirror
C69 Neutral density filter
C70 Neutral density wedge
C71 Neutral step density filter
C72 Luminance scale
C73 Luminance step
C74 Colour(or) filter
C75 Complementary filter
C76 Interference filter
C77 Heat absorbing filter
C78 Polarizing filter
C79 Nicol prism
C80 Polaroid
C81 transparent
C82 translucent
C83 opaque
C84 Projection obliquity
C85 Zoom magnification system
C86 Calibration
C87 Photometric control
C88 Radiometer
C89 Spectroradiometer
C90 Photometer
C91 Spectrophotometer
C92 Photocell
C93 Photomultiplier
C94 Luminance meter
C95 Luxmeter
C96 Standard of light
C97 Comparison surface
C98 Discolouration (UK), discoloration (US)
C99 Yellowing
C100 Smudging
C101 Ametropia
C102 Empty field myopia
C103 Night myopia
C104 Instrument myopia
C105 Presbyopia
C106 Cycloplegia
C107 Resting point of accommodation
C108 Optical correction
C109 Spectacles
C110 Correction lens
C111 Correction lens holder
C112 Tinted lens
C113 Contact lens (hard, soft, flexible, corneal, scleral)
C114 Eikonic lens
C115 Achromatizing lens
C116 Blinking
C117 Natural pupil
C118 Pupillometer
C119 Artificial pupil
C120 Maxwellian view
C121 Stabilized retinal image
C122 Chin rest
C123 Forehead rest
C124 Dental bite bar
C125 Occluder
C126 Fixation device
C127 Fixation control
C128 Infrared image converter
C129 Visual fixation control
C130 Electronic fixed monitor
C131 Isopter perimetry
C132 Profile perimetry
C133 Meridional perimetry
C134 Circular perimetry
C135 Kinetic perimetry
C136 centripetal
C137 centrifugal
C138 clockwise
C139 anticlockwise (UK), counter-clockwise (US)
C140 Rate of movement
C141 Automatic object translation
C142 Static perimetry
C143 Single stimulus
C144 Multiple stimuli
C145 Multiple pattern
C146 Frequency of presentation
C147 Flash
C148 Tachistoscopic presentation
C149 Kinetic-static perimetry
C150 Perimetrist
C151 Subject (=observer, =patient)
C152 experienced
C153 inexperienced
C154 Ascending method of limits
C155 Descending method of limits
C156 Frequency-of-seeing curve
C157 Forced binary choice
C158 Forced multiple choice
C159 Subject's response criterion
C160 Judgement time
C161 (Degree of) Coopration of the subject
C162 Motivation
C163 Reaction time
C164 Chronometer
C165 Test period
C166 Rest period
C167 Accommodation
C168 Relaxation of accommodation
C169 Spiral shaped pattern
C170 Star shaped pattern
C171 Repeat static test
C172 Extinction phenomenon
C173 False positive response
C174 False negative response
C175 Delayed response
C176 Signal device
C177 Verbal response
C178 Manual response
C179 Push-button
C180 Buzzer
C181 Manual recording
C182 Semi-automatic recording
C183 Computerised perimetry
C184 Automation
C185 Programme (UK), Program (US)
C186 Computerised perimetry
C187 Chart
C188 Chart scale
C189 Polygonal connection (of isopter)
C190 Fluent fitting (of isopter) by eye
C191 Cartographic deformation
C192 Polar azimuthal equidistant projection
C193 Central tangential projection
C194 Parabolic projection
C195 Equivalent projections
C196 Conformal projections
C197 To hatch
C198 Interpretation of a visual field chart
C199 Area of a field defect
C200 Density of a field defect
C201 Protocol
C202 Control examination
C203 Follow-up
C204 Data bank
D0 Normal Visual Field
D1 Ergoramic occupational visual field
D2 Panoramic occupational visual field
D3 Total dynamic field
D4 Fixation point
D5 Meridian
D6 Parallel circle
D7 Central field
D8 Midzone
D9 Periphery
D10 Hemifield
D11 Quadrant
D12 temporal
D13 nasal
D14 superior
D15 inferior
D16 supero-temporal, etc
D17 Eccentricity
D18 Absolute limits
D19 Profile
D20 Isopter
D21 Central peak
D22 Peripheral limits
D23 Blind spot
D24 Angioscotoma
D25 Vertical symmetry of the isopters
D26 Central scotoma at low light levels
D27 Hemiopic border
D28 Horizontal raphe
D29 Refractive scotoma
D30 Rotation of the blind spot
E0 Pathology
E1 Defect
E2 Absolute defect
E3 Relative defect
E4 Chromatic defect
E5 Gradient
E6 Steep slope
E7 Gradual (=gentle) slope
E8 Notch
E9 Peripheral defect
E10 Contraction
E11 Concentric contraction
E12 Generalized concentric contraction
E13 Scotoma
E14 Positive scotoma
E15 Negative scotoma
E16 Depression of the sensitivity curve
E17 Central scotoma
E18 Eccentric fixation
E19 Eccentric viewing
E20 Displacement of the blind spot
E21 Macular scotoma
E22 Scotoma caused by inhibition
E23 Paracentral scotoma
E24 Pericentral scotoma
E25 Paracaecal scotoma
E26 Pericaecal scotoma (=enlargement of the blind spot)
E27 Baring of the blind spot
E28 Centrocaecal scotoma
E29 Ring scotoma
E30 Zonular scotoma
E31 Nerve fibre(er)s bundle defect (=NFBD)
E32 Central NFBD
E33 Juxta-papillary NFBD
E34 Arcuate NFBD (=Bjerrum scotoma)
E35 A NFBD in a nasal quadrant
E36 A NFBD in a temporal quadrant
E37 Cuneate NFBD
E38 NFBD proceeding away from the blind spot
E39 NFBD proceeding towards the blind spot
E40 Break through
E41 Swiss cheese defect, Sieve-like defect
E42 Defect of vascular origin
E43 Neuroscotoma
E44 Hemianopia
E45 hemianopic
E46 Hemidysopia (=relative hemianopia)
E47 Hemiachromatopsia
E48 Quadrantanopia
E49 quadrantic
E50 Quadrant dysopia (=relative quadrantanopia)
E51 heteronymous
E52 bitemporal
E53 binasal
E54 homonymous
E55 left
E56 right
E57 vertical
E58 horizontal
E59 crossed
E60 Step (nasal etc)
E61 hemianopic central scotoma (heteronymous-, etc)
E62 Quadrantanopic central scotoma (id)
E63 Symmetrical defect
E64 Asymmetrical defect
E65 Congruent defect
E66 Incongruent defect
E67 Temporal crescent
E68 Overshot
E69 Sparing of the macula
E70 Splitting of the macula
E71 Agnosia
E72 Cortical blindness
E73 Handicap
E74 Degree of disability
E75 one-eyed
E76 Esterman grid
E77 Enlargement of a field defect
E78 Diminution of a field defect
E79 Disappearance of a field defect
E80 Malingering (or simulation) of a field defect
E81 Hysterical field defect
E82 Concealment of a field defect