ISCEV and IPS guideline for the full-field stimulus test (FST)

The full-field stimulus test (FST) is a psychophysical technique designed for the measurement of visual function in low vision. The method involves the use of a ganzfeld stimulator, as used in routine full-field electroretinography, to deliver full-field flashes of light. This guideline was developed jointly by the International Society for Clinical Electrophysiology of Vision (ISCEV) and Imaging and Perimetry Society (IPS) in order to provide technical information, promote consistency of testing and reporting, and encourage convergence of methods for FST. It is intended to aid practitioners and guide the formulation of FST protocols, with a view to future standardisation. Supplementary Information The online version contains supplementary material available at 10.1007/s10633-023-09962-7.

Full Field Stimulus Test (FST) aims to measure lowest luminance flash which elicits a visual sensation perceived by the subject.The FST evolved from dark adapted perimetry.In conventional perimetry, the standard unit of measurement for the visual field is the differential light sensitivity (DLS).This is defined as the threshold of perception of a test object, relative to its background.The subjectively perceived brightness of an object such as the FST stimulus are related to their luminance.
To understand the quantification of the test object various photometry terms are required.
Luminous flux (ϕ): is the power of visible light emitted by an object and is measured in the International System of Units (SI) unit Lumens (lm).Luminous flux takes into account the entire range of wavelengths that are visible to the human eye.The term describes the brightness of a light source.Luminous intensity (I): is the luminous flux emitted in a particular direction.I= ϕ/ Ω where Ω is the solid angle expressed in steradians Luminous intensity is measured in candela (cd).Illuminance (E): is the luminous intensity per unit of area of an object.E=I/A where A is the reflective area.Unit is the lux (lm•m -2 ).Illuminance is a measure of the amount of light falling on a surface from a light source.It is measured with a luxmeter.Luminance: the amount of light emitted or reflected from a surface in a particular direction.It is defined as the amount of luminous flux per unit area, per unit solid angle, in a specific direction.Luminance is measured in candelas per square meter (cd•m -2 ).Luminance refers to the brightness of a surface e.g., of long duration or background light.Stimulus flash strength: is measured in luminance*time (cd•m -2 .s).This is equivalent to candelaseconds per square meter (cd•s•m -²).This is a measurement of luminous power (flux) per unit solid angle (steradian) per unit surface area.

SI Units Defined and compared to older or non-metric terms
Nits: are a measure of luminance.1 nit = 1 candela per square meter.Lux (lx): is a unit of measurement for illuminance.It is defined as the amount of light that falls on a surface that is one square meter in size, and that is located at a distance of one meter from a light source with a luminous intensity of one candela.Steradian (sr) is a unit of measurement for solid angles in three-dimensional space.It is defined as the solid angle that subtends a surface area of one square meter at the centre of a sphere with a radius of one meter.Troland (Td) is a unit of measurement of retinal illuminance, the amount of light reaching the retina of the eye.Specifically, a troland is defined as the retinal illuminance produced by a luminance of one candela per square meter (cd•m -²) viewed through a pupil with an area of one square millimetre (mm²).An example of such an explanation is given below for a 2-button FST, although not intended to be prescriptive or suitable for all patients.

Appendix 2B: Amended Newcastle scoring tool for quality grading of the papers
"We are now going to test the sensitivity of your vision.You will hear a number of beeps and each time there may or may not be a light presented that is visible to you.Many of the lights will be extremely dim, much more so than you are used to seeing in your typical day or during visual field tests you have done in the past, so even if you think you have seen it, please press yes.We are trying to find out the limits of your vision so you are not expected to see all the lights.If you see a light with a beep please press the button on the right, if you don't see a light with a beep please press the button on the left.Please do not be concerned about "right" or "wrong" responses, or about where the light is coming from or what colour it is.You do not need to respond too quickly, but it is equally important not to be too hesitant, and to act on your first impressions, and to press the button on the right if you think you see any light." , consider what criterion is met.Each section can be scored with a maximum of one star.If the study meets at least one of the starred criteria, then place a 1 in the next column.If the study does not meet any starred criteria, then leave the next column blank.Scoring Equipment used a) Study identifies equipment used plus the button box * b) Study identifies equipment but not full information about the set up * c) No information given about equipment used Staircase Paradigm a) Details of the staircase and psychometric function are given * b) Only partial details given, so calculations could not be replicated c) No information given about the staircase paradigm Stimulus colour a) Wavelengths of all test stimuli are provided, along with details of generating sources * b) Only colour names are given c) No information given about stimulus colour Interstimulus interval a) ISI details are given and remain stable for all recordings, unless specified.If ISI intervals varied at all, this was adjusted for in the analysis * b) Not enough information about ISI given Inter-trial duration a) Details given about rest periods between repeat testing of same stimuli, and of different stimuli * b) Limited details given c) No information given Eye and test order a) Information given about the order in which the eyes were tested, and the order in which colours were tested, with full details about dark adaptation periods in between testing * b) Limited details given c) No information given Dilation status a) Details given about dilation status before testing, and pupil diameter is recorded * b) Details given about dilation status before testing, but pupil diameter not recorded * c) No information given Length of dark adaptation a) Information is given about length of dark adaptation prior to testing, AND re-adaptation at any points during testing * b) Information is given about length of dark adaptation prior to testing, but no information given about re-adaptation periods during testing * c) No information given about dark adaptation prior to testing Definition of 0dB point a) Units are reported in log cd•m -2 or in log cd•s•m -2 * b) Units are reported in decibels with a defined 0dB point in the above units * c) Units are reported in decibels with no defined 0dB point d) Units are not defined Number of repeats a) Information is given on number and order of repeats, with full details of breaks and adaptation periods between repetitions given * b) Information is given on number and order of repeats, but no information given on breaks and adaptation periods between repetitions * c) Information given on the number of repeats only d) No information given If audible cues used a) Information is given about whether audible cues were used on stimulus presentation was carried out and full description was given of procedure; QA results were accounted for in the analysis * b) QA carried out but not accounted for in analysis, or QA not done c) No mention of whether QA was done Whether binocular/monocul ar a) Information is given about whether they tested one or two eyes * b) No information given If the case definition or cohort inclusion criteria are adequate a) The study population is well defined and verifiable through validated records or healthcare records * b) Cases are based on participant self-reporting only c

Table 2 : Key parameters reported used in all the high quality papers and studies.
Effective communication between the practitioner and observer will optimise psychophysical performance and compliance, and is pivotal to accurate and reliable FST measurements.It is essential to explain to observers or patients what they should expect and what is required before testing, and to offer reassurance and/or encouragement during testing.Instructions may be tailored to be appropriate for individuals or patient groups, but explanations about key features and task are usually included and presented in a similar way for each patient.