Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
  • A61B3/02—Subjective types, i.e. testing apparatus requiring the active assistance of the patient
  • A61B3/024—Subjective types, i.e. testing apparatus requiring the active assistance of the patient for determining the visual field, e.g. perimeter types
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
  • A61B3/0016—Operational features thereof
  • A61B3/0025—Operational features thereof characterised by electronic signal processing, e.g. eye models
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
  • A61B3/0091—Fixation targets for viewing direction
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/16—Devices for psychotechnics; Testing reaction times ; Devices for evaluating the psychological state
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/16—Devices for psychotechnics; Testing reaction times ; Devices for evaluating the psychological state
  • A61B5/163—Devices for psychotechnics; Testing reaction times ; Devices for evaluating the psychological state by tracking eye movement, gaze, or pupil change

Definitions

• This invention relates to methods and apparatus for assessing and practising function of the visual system, especially visual field, visual search ability, visual decision making, saccadic eye movement and smooth pursuit of the eye. More specifically this invention relates to method of accurately determining the orientation of the eye or eyes. With this invention it is possible to verify without active monitoring of the eye or eyes that the visual axis or the fovea centralis of the retina of the eye or eyes is aimed at, or fixates to a given fixation object at a defined time point by designing the features of the fixation object to be detectable only by foveal vision.
• This monitoring of the fixation of the eye can be done visually by the examiner, which is rather unreliable and depends on the alertness of the examiner, or with electronic camera image processing system, or with automatic electronic video camera based eye-tracker, which requires complex and therefore expensive electronic systems and also requires prior calibration procedure.
• the existing devices for examination of the visual field are usually large and technically complex, and therefore expensive, requiring a separate instrument table which occupies plenty of floor space in small examination rooms when not in use.
• the orientation of the eye i.e. where the line of sight (visual axis) or the fovea centralis of the retina of the eye is aimed at, or fixates, is monitored usually by automatic electronic video based eye-tracker, which requires complex and therefore expensive electronic systems.
• a calibration procedure must be conducted so that the device can match a detected specific position of the eye to eye's foveal fixation to known fixation target.
• a further object of the present invention is to provide a system for providing markers for evaluating and/or practising the visual field recognizable by an eye, and/or eyes, and/or visual system of a person.
• a still further object of the present invention is to provide a software product for a system for carrying out a method for providing markers for evaluating, and/or practising the visual field recognizable by the eye, and/or eyes, and/or visual system of a person.
• the present invention provides a method for providing markers for evaluating and/or practising the visual field recognizable by an eye, and/or eyes, and/or visual system of a person wherein said method comprises evaluating
• the present invention also provides a use of a system for providing markers for evaluating and/or practising the visual field recognizable by an eye, and/or eyes, and/or visual system of a person, which system comprises a) a display or displays capable of providing at least a saccade triggering stimulus STS or a smooth pursuit triggering stimulus SPTS, and a fixation object FO at specified locations; b) a reporting means with which a person identifying said FO can report to said data processing unit his or her identification of said FO; c) a data processing unit with software for at least i) providing, on said display or displays, at least said STS and/or SPTS, and said FO at said specified locations; ii) recording correctness of reported identification of said FO; iii) recording time points of providing said STS and/or SPTS, and a FO at said specified locations; and reporting of said identification; and iv) calculating at least time period between providing said STS or FO, and said reporting of identification of FO, if said STS is employed; and/
• the present invention further provides a system for providing markers for evaluating and/or practising the visual field recognizable by an eye, and/or eyes, and/or visual system of a person by carrying out any of the methods of the present invention, which system comprises a) a display or displays capable of providing at least a saccade triggering stimulus STS or a smooth pursuit triggering stimulus SPTS, and a fixation object FO at specified locations; b) a reporting means with which a person identifying said FO can report to said data processing unit his or her identification of said FO; c) a data processing unit with software for at least i) providing, on said display or displays, at least said STS and/or SPTS, and said FO at said specified locations; ii) recording correctness of reporting of identification of said FO; iii) recording time points of providing said STS and/or SPTS, and said FO at said specified locations; and reporting of said identification; and iv) calculating at least time period between providing said STS and reporting of said identification of FO, if said STS is
• the present invention still further provides a software product for a system for carrying out any of the methods for providing markers for evaluating, and/or practising the visual field recognizable by the eye, and/or eyes, and/or visual system of a person according to any of the present invention
• said software product comprises means for at least i) providing, on a display or displays, at least a saccade triggering stimulus STS and/or smooth pursuit triggering stimulus SPTS, and a fixation object FO at specified locations; ii) recording correctness of reported identification of FO by said eye or eyes of said person; iii) recording time points of providing said STS and/or SPTS, and said FO at said specified locations; and reporting of said identification; and iv) calculating at least time period between providing said STS or FO, and reporting of said identification of FO; and/or time period between providing said FO and reporting of said identification of FO, if said SPTS is employed.
• Figures 1 illustrates the visual acuity of the eye along the horizontal meridian of the visual field. Visual acuity at the fovea centralis of the retina is good and drops abruptly peripherally.
• Figure 2 illustrates an embodiment of the device with display units 1 - 6 in a one- dimensional array for simplicity and an example of a sequence of the method of the present invention..
• Figure 3 illustrates several phases and time points of a sequence for evaluating the eye of a person.
• Figure 4 illustrates the use of visual search distractor objects.
• Figure 5 illustrates the phases and time points of the sequence of providing several consecutive further fixation objects FFO to the same display.
• Figure 6 illustrates a sequence of an examination wherein a further fixation object has been provided to the same display unit as a preceding fixation object.
• Figure 7 illustrates a sequence of an examination of one location of visual field.
• Figure 8 illustrates a sequence of an examination where a person has a defective visual field location.
• Figure 9 illustrates a situation where a person has a normal visual field but defective saccades to the left but normal saccades to the right.
• Figures 10 and 1 1 illustrate the benefit of adjusting the length of the delay before FO is provided when assessing the motor functions required of the eye and/or head to shift his or her gaze direction from one location to another.
• Figure 12 illustrates assessing function of the visual system, especially reading ability, of a person employing paragraphs of text.
• This invention relates to methods and apparatus for assessing function of the visual system.
• This invention is useful inter alia in the diagnosis of glaucoma and other visual disorders which affect the visual field of the eye, in Alzheimer disease and other brain disorders which affect ocular motor functions or neural connections or functions of various brain areas responsible for visual search and visual decision making, in assessing a person's fatigue, wakefulness and alertness and in assessment of visual fitness for driving a power-driven vehicle or operating machinery.
• This invention can be used also to assess and practice visual search ability, visual decision making, saccadic eye movements and smooth pursuit of the eye
• the object of the present invention is to substantially reduce or eliminate the disadvantages mentioned above.
• the invention makes it possible to know with certainty that the visual axis or the fovea centralis of the retina of the eye is aimed at, or fixates to a given fixation object (FO) at a defined time point.
• a fixation object F
• the gist of the invention is in that the person himself reports, by correct identification of a fixation object (FO), whereto the eye of the person has been fixated at any time point of identification. This is accomplished by choosing identification objects identifiable only when the eye is accurately fixated at the fixation object (FO), i.e.
• fixation object the fovea centralis of the retina of the eye is aimed at the fixation object.
• fixations to fixation objects FOs
• no need for external monitoring of e.g. saccade or smooth pursuit or fixation of the eye is needed. Accordingly means for external monitoring involving complicated and costly devices and awkward in use, are redundant when employing the present invention.
• Another alternative could be to compare reaction times calculated using the time points of the fixations, to reaction times regarded normal or to reaction times of the same person obtained earlier in his or her life. In this way one could detect an effect of a brain disease, fatigue or use of alcohol or drugs to the reaction times.
• the present invention uses anatomy of the human eye and visual psychophysics for monitoring the fixation of the eye.
• fovea or fovea centralis
• Foveal vision has many special features which are unique in the visual field of a man. It allows for maximum acuity of vision (figure 1 ). In daylight conditions (i.e. not in dim light) the fovea is also the most sensitive area of visual field for detecting light differences between visual target and the background (differential light sensitivity). Also colour vision is most sensitive in foveal vision.
• the fixation object (FO) for a person to fixate at is designed so that it uses these special features of foveal vision and is recognizable only if the fovea is aimed at the object.
• the FO can contain a small character, symbol or pattern which a person must identify and report.
• the FO can be so dim or it can have so faint colour tint that it is only detectable with foveal vision.
• This time point offers a possibility to provide a further stimulus or stimuli at precisely known peripheral locations of the visual field.
• a person can detect this new peripheral stimulus, he can, according to the invention, make a rapid eye movement to shift his or her line of sight or redirect the fovea from fixation object FO and make a saccade to this peripheral saccade triggering stimulus (STS).
• STS peripheral saccade triggering stimulus
• Alternatively so called anti-saccade task paradigm can also be used: the person is instructed to make a saccade to the opposite direction of the STS.
• a second fixation object (FO2) which has the same design properties as the first fixation object (FO1) and thus is only recognizable by foveal vision can be provided at this symmetrical location of the STS in relation to FO1 or origo of the visual field.
• the STS can also be selected to resemble the FO, or any other character or object.
• a normal person's saccades to an unexpected peripheral stimulus normally take about 200 milliseconds (ms) to initiate, and then last from about 20-200 ms, depending on their amplitude. Therefore it takes in total about 200 ms-400 ms before the person has executed his or her saccade and redirected his or her fovea to the location of the peripheral STS.
• the STS can be replaced by a second fixation object (FO2), which has the same design properties as the first fixation object (FO1) and thus is only recognizable by foveal vision.
• FO2 the first fixation object
• FO1 the first fixation object
• FO2 the second fixation object
• the time period i.e. reaction time (RT), or verified visual search reaction time (WS-RT), for conducting the sequence from providing the STS (corresponding approximately to the time point of correctly reporting of the identification of the fixation object FO1) to correctly reporting of the identification of FO2 is rather constant for a person if the angular size and the other properties of the stimuli are kept constant. If, however, one location of the visual field has impaired vision (reduced sensitivity), the visibility (luminance) of the STS doesn't reach the threshold of detection and the initiation of the saccade fails. The saccade triggering stimulus is replaced after predetermined interval by second fixation object FO2, which the person must then search using several saccades before he can correctly identify it.
• RT reaction time
• WS-RT verified visual search reaction time
• VVT-RT prolongation of the time period VVT-RT is an indication for impaired vision in that location of the visual field.
• this invention is used in visual field examination and the duration of the saccade triggering stimulus STS is 100 ms according to International Standard for Perimeters (ISO 12866), it is beneficial to have a brief interval of 100 - 200 ms before FO2 is provided at the same location where the STS was provided in order to make it easier for the visual system to distinguish between the STS and the FO when the intensity of STS is very low.
• Adjusting the length of the delay before FO2 is provided can also be used to probe the time that is needed for the motor actions of the eye and/or head to shift his or her gaze direction from the location of FO1 to STS. If a person has abnormally slow saccades or otherwise difficulties with shifting his gaze direction, the time period between providing FO1 and correctly reporting of the identification of it becomes shorter if the length of the delay before the FO2 is provided is increased. This is discussed in more detail in the example 8.
• one way of checking if the person is steadily fixating the immovable fixation mark is to provide a test stimulus to the location of the visual field where the blind spot of the normal eye exists. If the alignment of the eye is correct, i.e. the eye is fixating the fixation mark, the person cannot see the test stimulus. If however the alignment is incorrect, the test stimulus is not any more inside the area of the blind spot and the person can see the flash and report seeing it by pressing the button.
• the human visual system is very efficient in conducting visual search. Therefore when performing examination according to this invention, the person sometimes finds and reports the FO with surprisingly short reaction time even if he has not detected the saccade triggering stimulus STS, which precedes the FO at the same location. If, as normally is the case, we want to examine the visibility of the STS with different luminance values, we might want to make finding of the FO more difficult for a person who has not detected the preceding STS. This can be done, according to this invention, by inserting visual search distractor fixation objects (FOvsS) nearby the location of the STS.
• FOvsS visual search distractor fixation objects
• Another means for making finding of the correct FO at the location where STS is provided more difficult is to provide one or several fixation objects with a misleading pattern (FO m ) that causes the person, if he finds it with visual search in the case when STS was undetectable for him, to report an incorrect identification of the true fixation object FO which triggers a saccade towards FO.
• FO m a misleading pattern
• the sensitivity of a given location of the visual field can be measured by repeating the sequence directed to a particular location of peripheral vision and by providing saccade triggering stimuli (STSs), which have different luminance values.
• STSs saccade triggering stimuli
• the time period for the detection of the stimulus increases compared to stimuli that have luminance values that are clearly above the threshold.
• the STS is not visible to the person and gives no advance cue about the location of the fixation object (FO). This increases the reaction time for finding and identification of a FO and gives indication for the threshold for detection of STS of specified luminance. Adjusting brightness of fixation objects
• the contrast sensitivity of the fovea can be measured by diminishing the brightness of the FO pattern.
• the threshold for visibility of the FO pattern can be detected when reaction time for correctly reporting the identification FO increases.
• the time period from providing STS to correctly reporting the identification of FO2 by e.g. pressing a correct button can be divided to several phases which are controlled by various areas of the visual system and the brain and have differences in variation between individual persons: (1 )
• the time period for the detection of the STS in specific location of the visual field is dependable upon the sensitivity of the corresponding retinal location for that specific STS (e.g. depends on the size, duration, wavelength composition) and the adaptational state of the retina for the ambient illuminance.
• the influence of temporal integration and Pullfrich effect has been discussed above.
• the STS is brighter than the threshold of the retina, a nerve stimulus travels through nerve paths to visual areas of the brain. This time period does not have much variation between persons, if the parameters mentioned above are kept constant.
• the WS-RT is longer for STS which are displayed to the left compared to STS which are displayed to the right of the fixation of the eye even if the visual field of this person is normal and symmetrical.
• the initiation of the movement of the hand towards the STS can be monitored e.g. by a sensor that measures acceleration of the hand. This sensor can be an integral part of the response buttons of the person.
• the threshold luminance for different background luminances by measuring the ambient luminance of the background where the stimulus is displayed with a suitable sensor or sensors mounted in the device. The measured and calculated ambient brightness in different areas of the display or displays can be compensated by adjusting the brightness of STS and FO stimuli accordingly.
• Smooth pursuit eye movements allow the eyes to closely follow a moving object so that the movements stabilize the projection of the moving target onto the fovea and corrects for any velocity error between eye and target. It is one of two ways that a person can voluntarily shift gaze, the other being saccadic eye movements. Smooth pursuit eye movement requires a moving visual stimulus, smooth pursuit triggering stimulus (SPTS). Pursuit is modified by ongoing visual feedback, which detects if the fovea is not aimed at the SPTS and initiates catch-up saccades to correct the aiming of the eye. The oculomotor system of the brain adjusts the angular velocity of smooth pursuit of the eye to match the velocity of moving stimulus SPTS to compensate for retinal slip of the SPTS.
• SPTS smooth pursuit triggering stimulus
• the eye is accurately pursuing the SPTS and it is, according to the invention, replaced by a fixation object (FO), which is identifiable by the person only when the eye is accurately fixated on the FO, the person can quickly identify the fixation object FO and report the identification of it by e.g. pressing a correct button. If, however, the eye is not accurately aimed at the SPTS, the person cannot quickly recognize the FO but must make first a catch-up saccade or saccades or adjusts the velocity of smooth pursuit to aim the fovea accurately to FO for correct identification. Thus, the time period, from providing the FO to correctly reporting the identification of the FO, increases, if the smooth pursuit of the eye is not accurate.
• FO fixation object
• human oculomotor system is capable also performing saccades towards a memorized location in the visual field.
• the present invention in which the sequence of using the new fixation object location of FO2 as a centre of the visual field and providing a further peripheral STS which in turn is replaced by further fixation object FO3 in the same location as STS was, can be used to assess the ability to perform memory guided saccades as follows:
• the person identifies the FOs by performing a sequence of saccades which are guided only by memory.
• the fovea fixates accurately the fixation object in the sequence and it can be identified and reported by the person without any delay.
• the invention can also be used as visual ignition interlock device installed in a motor driven vehicle when assessing if a person's fatigue, wakefulness or alertness, or use of alcohol or drugs makes him unfit for driving a power-driven vehicle. If the performance in conducting a visual search and visual decision making procedure utilizing this invention is inferior to normal values or inferior to person's own values obtained at earlier time point, the motor vehicle can not be started or the device will log the event, warn the driver and then start up an alarm.
• the invention can also be used in sports related applications, e.g. in team games like soccer or ice hockey.
• a good player has the ability to observe other team members and to evaluate which of the team members are situated in good strategic locations on the playing field for passing the ball or puck.
• a novice player on the other hand easily concentrates too much on handling the ball or puck and accordingly observes the playing field and team members insufficiently.
• the invention can be used by the coach of the team when coaching a novice player to shift his attention to other team members.
• a display described in this invention can be attached to the player's head or hockey stick so that the coach of the team can light up a saccade triggering stimulus STS on the display of a player who is in a good strategic position in the playing field.
• the task of the novice player is to notice the STS and to report the identification of the fixation object FO, which is shown on the display unit of the team member, with a wireless response unit.
• the time points and the time periods of each of the players are recorded according to the invention.
• the coach can afterwards review the summary of the results of each individual player and track the development of the player's ability to make observations of his team members.
• an electronic sensor for monitoring the acceleration e.g. a motion sensing device, is installed in the response unit which the person holds with his or her hand. Monitoring movement of head
• the person cannot report the identification of the FO or detecting of the STS by pressing a button.
• the sensor can detect the movement of the head when the person detects the STS and tries to turn his eyes and head toward the STS.
• a sensor or sensors for measuring the inclination angle of the device is preferably installed in the device, e.g. a display set, which is used for displaying the stimuli.
• a system for monitoring the distance to the eye of the person is preferably included. In a preferred embodiment of the device, distance monitoring can be done by the person who is assessing the function of the visual system by using electronic distance or proximity sensors, using optical distance meter based on double images produced by mirrors or in a simpler way by a neck strap which holds the device at fixed distance from the person.
• a smooth pursuit triggering stimulus SPTS can be provided at one of the display units, e.g. at unit 1 .
• the device or display unit is moved at desired velocity either manually or automatically.
• a smooth pursuit triggering stimulus SPTS is replaced by a FO at the same display unit. If a person is accurately pursuing the moving SPTS, he can quickly identify the FO and report the identification by pressing a button.
• Visual system refers to the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world.
• the visual system accomplishes a number of complex tasks, including the reception of light and the formation of monocular representations; the construction of a binocular perception from a pair of two dimensional projections; the identification and categorization of visual objects; assessing distances to and between objects; and guiding body movements in relation to visual objects.
• Visual system consists of: the eye, especially the retina, the optic nerve, the optic chiasma, the optic tract, the lateral geniculate body, the optic radiation, the visual cortex and the visual association cortex
• the term "person” refers to the individual whose function of the visual system is assessed or practised. Likewise “eye”, “visual field”, “oculomotor functions”, “saccade” and “smooth pursue” refers to the person.
• focala is the region with the highest visual acuity of the retina of the eye.
• fixation object is a visible target where the line of sight (visual axis) or the fovea centralis of the retina of the eye is aimed at, or fixates and it typically consists of a small character, symbol or pattern.
• visual field refers to the physical objects and light sources in the external world that impinge the retina of the eye of the person.
• standard visual field coordinate system refers to reference system for designating locations in the visual field, and which is in wide use in the field of visual field examination and is also referenced in the International Standard for Perimeters (ISO 12866).
• ISO 12866 International Standard for Perimeters
• the pupil of the eye is located in the origo of the spherical coordinate system.
• the location of any visual field locus is specified by the half-meridian O and the eccentricity ⁇ of the centre of the test stimulus, both expressed in degrees (O, ⁇ ).
• the zero-degree half-meridian is defined to the right of the patient (as seen by the patient).
• the specified half-meridian then proceeds anticlockwise through 360° about the fixation stimulus (as seen by the patient).
• the fixation point is defined as having 0° eccentricity.
• meridian refers to two half-meridians constituting one straight line in the visual field coordinate system through the origo. It's direction in the visual field coordinate system is specified by either of the half-meridians.
• blind spot or "physiological blind spot” is the area in the visual field that corresponds to the lack of light-detecting photoreceptor cells on the optic disc of the retina where the optic nerve passes through it. Since there are no cells to detect light on the optic disc, a part of the field of vision is not perceived.
• the blind spot is located about 12-15° temporal and 1 .5° below the horizontal and is roughly 7.5° high and 5.5° wide.
• contrast is the difference in luminance and/or colour of the foreground and background of the object that makes an object (or its representation in an image or display) distinguishable.
• contrast sensitivity is a measure of the ability of the visual system to detect contrast.
• saccade is a fast movement of the eye from one fixation object to a target which is located somewhere within the visual field of the eye in order to correct for a position error between eye and target.
• STS saccade triggering stimulus
• STS is a visible target within the visual field which elicits a saccade which redirects the fovea or line of sight from fixation object FO to the STS. If anti-saccade paradigm is used the target for a saccade is at the symmetrical location of the STS in relation to FO or origo of the visual field.
• smooth pursuit refers to a slow eye movement that stabilizes the projection of the moving target onto the fovea and corrects for any velocity error between eye and target.
• FBS feedback stimulus
• FFO fixation object
• IFS interrupting fixation stimulus
• FBS feedback stimulus
• WS-RT verified visual search reaction time
• Many preferred embodiments of the method of the invention further comprise g) providing a further fixation object FFO, identifiable by the person only when the eye or eyes is accurately fixated on said FFO,, i.e. when said FFO, is positioned at the fovea of said eye or eyes of said person, provided at the same location as that of an immediately preceding further fixation object FFO p , preferably with a short interrupting fixation stimulus IFS at said same location between provided sequential further fixation objects FFOs, h) having said person identify said FFO,, said identification referred to as an identification of said FFO,, i) having said person report said identification of FFO,, j) recording correctness of reported identification of said FFO, and time point of providing said FFO, and time point of reporting of identification of FFO,, and k) calculating time periods between providing FFO, and said reporting of identification of said FFO,; wherein said time period is subtracted from the time periods calculated in step f) of claim 1 to estimate the time period between
• a feedback stimulus FBS giving visible feedback about the correctness of the report by the person of the identification of a fixation object FO
• FBS a feedback stimulus
• a feedback stimulus FBS giving visible feedback about the correctness of the report by the person of the identification of a fixation object FO
• a multitude of cycles comprising the following sequential steps: i) having the eye or eyes of the person fixate on a first fixation object FOi identifiable by the person only when said eye or eyes is accurately fixated on FOi, i.e.
• the second fixation object FO 2 is provided after a delay, preferably a delay of 50-1000 ms, after termination of the first saccade triggering stimulus STSi .
• the delay of providing the second fixation object FO 2 after termination of the first saccade triggering stimulus STS 1 differs between the cycles, being preferably between 50-1000 ms.
• the duration of the saccade and fixation can be obtained by defining the minimum delay in providing the second fixation object FO 2 after termination of the first saccade triggering stimulus STSi, resulting in the shortest calculated time period between providing said FO 2 and correctly reporting the identification of said FO 2 when providing a STSi, with a defined intensity and duration at a defined location of the visual field of the eye or eyes of the person.
• the intensities of the saccade triggering stimuli STSs differ between the cycles, being between intensities that are not visible to the eye or eyes of the person at any location of the visual field, preferably zero, and intensities high enough for said person to respond to said saccade triggering stimulus STS independent of the intensity of the STS.
• reporting an incorrect result when identifying the fixation object FO results in providing a new fixation object FO n , preferably preceded by a new saccade triggering stimulus STS n , at the same physical location as the erroneously identified fixation object FO e i before providing a saccade triggering stimulus STS at a different physical location.
• a blind spot saccade triggering stimulus STSbs is provided essentially simultaneously, preferably between 0 ms and 300 ms after reporting of an identification of a preceding FO p , with the saccade triggering stimulus STS intended to trigger execution of a saccade of the eye or eyes of the person, wherein said STSbs is provided at the location at which the blind spot of the visual field of the eye or eyes of the person is when said eye or eyes is fixated at the preceding fixation object FO p .
• a blind spot distractor fixation object FObsd is typically provided at the location of the blind spot saccade triggering stimulus STSbs-
• one or more visual search distractor fixation objects FOvs and/or misleading fixation objects FO m are provided at selected locations of the visual field of the eye or eyes of the person essentially simultaneously with, preferably not earlier than 500 ms before and not later than 1000 ms after, the fixation object FO at the location of the saccade triggering stimulus STS, wherein the FO vs s are distinguishable from the FO provided at the location of the STS.
• the method of the invention comprises evaluating the accuracy of smooth pursuit of the eye and/or eyes of a person, said smooth pursuit being triggered by a smooth pursuit triggering stimulus SPTS; by i) having said eye or eyes of said person smoothly pursue in response to said SPTS, ii) providing a fixation object FO which object is identifiable by the person only when said eye or eyes is accurately fixated on said FO, i.e.
• the method of the invention does not comprise active monitoring of saccades, if saccade triggering stimuli STSs are employed; and/or smooth pursuit, if smooth pursuit triggering stimuli SPTSs are employed, of the eye or eyes of said person.
• Preferred embodiments of the use according to the invention include use wherein the software of the data processing unit is also for recording the locations of the saccade triggering stimuli STSs provided, preferably for different tilt angles of the device, in a standard visual field coordinate system with its origo located at the centre of the visual field.
• Some preferred embodiments of the system of the invention comprise a display set with a multitude of displays, preferably from 3 to 100 displays, more preferably from 4 to 30 displays, even more preferably from 20 to 30 displays and most preferably 24 displays.
• a small system is preferred a multitude of small displays, typically in a set, are employed.
• the displays typically in a display with a multitude of displays, are very small, the size preferably being from 0.2" to 5", more preferably 0.5" to 2" and most preferably about 1 ".
• Some preferred embodiments of the system comprise one display, displays or a display set wherein the size of the display or displays are from 12" to 168", preferably from 20" to 1 12", more preferably 32" to 84", and most preferably from 40" to 55".
• the display or displays are each capable of displaying at least the saccade triggering stimuli STS and the fixation object FO, and preferably also smooth pursuit triggering stimulus SPTS, further fixation object FFO and feedback stimulus FBS.
• the displays are in a row being parallel with the longitudinal axis of the display set.
• the displays are positioned in the parallel row so that, when the display unit is placed at the distance, intended to be employed when evaluating an eye of a person, from said eye to be evaluated, the display units, when facing said eye and perpendicular to the optical axis of said eye fixated at said display unit, are at different eccentricity angles of the optical axis of the eye, when fixated to said display units, applicable for intended evaluation.
• the different display units are at eccentricity angles of 0, 5, 15, 25, 35, 75 and 90 degrees relative to the display unit furthest at one end of the display set, and preferably an additional display unit at an eccentricity angle of 23 degrees relative to said display unit furthest at one end is included.
• Another typical set of eccentricity angles for display units is 0, 10,15, 40, 70 and 90 degrees.
• the display or displays are positioned so that, when the display unit is placed at the distance, intended to be employed when evaluating an eye or eyes of a person, from said eye or eyes to be evaluated, the display units, when facing said eye or eyes fixated at said display unit can display saccade triggering stimuli STSs and/or fixation objects FOs at different eccentricity angles of the visual axis of the eye or eyes, when fixated to any of said FOs of said display or displays, applicable for intended evaluation.
• the display, displays or display set comprise a position sensor or sensors enabling confirmation of the display, displays or display set being perpendicular to the optical axis of the eye, and/or eyes, to be evaluated and/or the angle with which the longitudinal axis of the display, displays or display set deviates, either to the left or right, from the upright position.
• Some preferred embodiments of the system comprise displays as mentioned above but arranged in two dimensions in order to cover the whole visual field, in which case the number of displays may be large, preferable more than 50.
• the system may consist of one or more large displays, which are capable of displaying at minimum the STS and FO in many different physical locations in either one or two dimensions.
• Some preferred embodiments of the system comprise at least one, preferably 2 or more, sensors for monitoring the distance between said display, displays or display set and the eye or eyes of said person.
• at least one sensor, preferably 2 or more sensors, for monitoring the ambient illumination of the room where the measurements are being conducted is comprised in the system, preferably in the display, displays or display set of the system.
• Preferred embodiments of the system comprise means for adjusting the brightness of the STS and/or FO.
• Preferred embodiments of the system comprise a sensor or sensors to be attached to the head of the person, wherein said sensor or sensors can detect the speed, timing or/and the angle of rotation of the head when displaying saccade triggering stimuli in the visual field of the person.
• Preferred embodiments of the system do not comprise means for active monitoring of saccades, if saccade triggering stimuli STSs are employed; and/or smooth pursuit, if smooth pursuit triggering stimuli SPTSs are employed, of the eye or eyes of said person.
• Preferred embodiments of the software product of the invention further comprise means for recording the locations of the saccade triggering stimuli STSs provided in standard visual field coordinate system of the eye or eyes of the person.
• Preferred software products of the invention comprise means for determining for each intensity of saccade triggering stimuli STSs and/or fixation objects FOs the margin of error of the results provided employing the software product.
• a preferred embodiment of a device for utilizing the method of the invention consists of a display unit, which is capable of providing both fixation object FO, which is designed so that it is only detectable by foveal vision, and saccade triggering or smooth pursuit triggering stimuli (STS or SPTS) which are designed to the needs of the function of the visual system which are being assessed or practised.
• several display units can be used (figure 2) They can be located at various angular distances in relation to the eye of a person. In figure 2, consecutive angular distances 10, 5, 25, 30, and 20 degrees are used.
• the eye makes saccadic eye movements between display units 1 - 6.
• Table 1 summarizes all the possible saccades which the eye can make between the six display units. In Table 2 all possible angular distances are arranged in order.
• Figure 2 illustrates a sequence of an examination according to the invention: At time point to a fixation object FO is provided at display unit 4. When the person correctly identifies and reports the FO at time point ti, a saccade triggering stimulus STS is provided at display unit 3, which is located 25 degrees from display unit 4. At time point t 2 a second fixation object FO2 is provided at display unit 3. At time point t 3 , when the person correctly identifies and reports the FO2, a saccade triggering stimulus STS is provided at display unit 5, which is located 55 degrees from display unit 3. Table 1 Angular distances in degrees between the different displays (1-6; figure 2) when device is placed perpendicular to the axis of vision at the recommended distance for the particular device.
• Evaluation of visual field Evaluation of the visual field of an eye of a person can be carried out e.g. as follows (see figure 3):
• FIG 3 starts with providing a saccade triggering stimulus STSi and ends in correctly reporting the identification of FO2. Only display units 3 and 4 (see figure 2) are visible in this illustration. The responses of the person are also illustrated: the movement of the hand towards the display unit is recorded by a hand movement sensor and choice of the button the person has pressed reports the identification of the fixation object FO.
• Fixation object FO1 is provided at display unit 4 at time point t 0 .
• a person identifies it (an arrow to the left) and reports by pressing a correct button (left button) at time point ti, the fixation object FOi is extinguished and a saccade triggering stimulus STSi is provided at display unit 3 which is located 25 degrees apart from display unit 4.
• STSi saccade triggering stimulus
• the size, shape, duration and luminance of the STS can be chosen to conform to the standards for visual field examinations (ISO 12866: International standard for Perimeters).
• the duration of STS is 100 ms after which it is extinguished at time point t and a brief delay interval of 100 - 200 ms can be used before a second fixation object FO2 is provided at the same display unit 3 at time point t 5 .
• a person identifies it (an arrow to the right) and reports by pressing a correct button (right button) at time point t 8 , the fixation object FO2 is extinguished and a saccade triggering stimulus STS2 is provided again at display unit 4.
• This cycle can be repeated using different display units as required to collect time points for all the visual field locations needed and varying the parameters of STS and FO as needed to measure e.g. the threshold value for detection of STS in specified visual field location.
• the orientation of the device is vertical and therefore only visual field locations in this vertical meridian can be measured. Visual field locations in different meridians can be measured by tilting the orientation of the device to desired inclination.
• the time period for identification and reporting the fixation object (see figure 3, the time period between time points t 8 and t 7 ) can be measured separately without any eye movements e.g. as follows (see figure 5):
• a further fixation object FFO p is provided which the person correctly identifies by pressing the correct button at time point ti .
• Interrupting fixation stimulus IFS optionally replaces the FFO p and optionally gives the person a visible feedback about the correctness of the reporting the identification of FFO p .
• a further fixation stimulus FFO replaces the IFS and the person correctly identifies it by pressing the correct button at time point t 3 .
• the time period between providing FFO, (t 2 ) and identification and reporting of FFO, (t 3 ) reflects nearly the same visual and motor processes as the time period between t 8 and t 7 in figure 3 (identification and reporting of FO2).
• time period between providing STS and accurate fixation on fixation object FO2 For estimating the time period between providing STS and accurate fixation on fixation object FO2 (see figure 3, time period between t 7 and ti) the time period between t 3 and t 2 in figure 5 can be subtracted from the time period between t 8 and ti in figure 3 (time period between providing STS and identification and reporting of FO2).
• the accuracy of the time periods can be increased by repeating the sequences several times so that mean of several measurements can be calculated.
• Figure 4 illustrates the use of visual search distractor fixation objects (named 'distractor object' in figure 4).
• one or many optional distractor objects are provided to the display unit(s) n in addition to FO2 provided to the display unit 3.
• the person has detected saccade triggering stimulus STS1 and has made a saccade toward display 3, he or she finds easily and without delay the FO2 and reports the identification of it.
• the distractor objects resemble FO but are distinguishable from it by careful inspection, finding the FO among many distractor objects solely by visual search without detecting first the STS becomes difficult and makes the reaction time for reporting the correct identification of FO longer compared to the situation where FO is found with the help of detecting the STS which triggers a saccade towards FO.
• Table 3 Results from measuring the time period for identification and reporting the fixation object (see Fig. 4):
• Figure 6 illustrates an embodiment according to claim 2.
• the results of an examination are presented where a further fixation object FFO has been provided to the same display unit (display unit 3, LineNo 3) as the preceding fixation object (LineNo 1 ).
• duration 100 ms, interrupting fixation stimulus IFS (LineNo 2) has been provided between the two fixation objects.
• IFS interrupting fixation stimulus
• the time period between providing FFO and identification of FFO is 525 ms.
• This kind of stimulus presentation does not need any ocular movement because further fixation objects are located at visual axis (foveal). See figure 5 for presentation of this type of examination as a schematic timeline and table 3 for more complete data set of the examination.
• FIG. 7 illustrates a sequence of an embodiment according to claim 1 .
• an example of an examination of one location of visual field 25° peripherally to the right from the fixation or the centre of the visual field
• STS saccade triggering stimulus
• This stimulus is detected by corresponding peripheral visual field location and triggers a saccade towards display unit 4.
• Figure 8 illustrates a sequence of an embodiment where a person has a defective visual field location at 25° to the left from the fixation or the centre of the visual field.
• the time period for providing STS (LineNo 3) at visual field location 25° to the right from the fixation and identification of FO by pressing the button (LineNo 5) is 992 ms compared to 1403 ms when the STS is provided 25° to the left from the fixation (LineNo 7). This prolongation of the reaction time is an indication of decreased retinal sensitivity at this specific location which delays the saccade towards the STS.
• Figure 9 illustrates a sequence of an embodiment of the invention where a person has a normal visual field, defective saccades to the left, but normal saccades to the right.
• the reaction time measured from the button press is prolonged when the STS is provided in the visual field to the left from the fixation compared to the situation where the STS is provided to the right from the fixation (1733 ms vs. 951 ms).
• reaction time is measured from hand movement (the task for the person was to point to the flashing light with his or her hand and report the direction of the arrow with the response buttons), there is not much difference (1048 ms vs 1030 ms). This is an indication of normal peripheral visual field at the locations specified but defective saccade to the left.
• Figures 10 and 1 1 illustrate the benefit of adjusting the length of the delay, the time period between time points t 3 and t , before FOi is provided at location where the STSi was provided.
• the person reports the identification of FOi by pressing a correct button and thus confirnning that he or she is fixating to the FOi at display unit 4.
• STSi is provided which triggers a saccade towards the location of display unit 3.
• figure 1 1 the same display units, and thus the same saccade length and direction, are used as in figure 10. Also the intensities of STS and FO stimuli are the same.
• delay 2 is used compared to delay in figure 10 (“delayi") before FO 2 is provided at time point t resulting shorter time period between providing FO (time point t ) and reporting of identification of FO (time point t 5 ).
• delayi delay in figure 10
• the time period between t 2 and t corresponds the time needed for motor functions of the eye and/or head to shift his or her gaze direction from the location of FOi (display unit 4) to STS (display unit 3).
• Figure 12 illustrates a sequence of an embodiment of the invention assessing function of the visual system, especially reading ability, of a person with paragraphs of text.
• the task for a person is to read the midmost word of the paragraph, i.e. the middle word of the second line and press a button marked with '1 ' if the word is numeral (e.g. One', 'two', 'three') and a button marked with 'A' in case of other words.
• this midmost word of the text paragraph at display unit 3 is 'herself and serves as a fixation object FO which the person recognizes and reports it by pressing the button marked with 'A' at time point 5694 ms (LineNo 1 ).
• LineNo 2 which serves as peripheral saccade triggering stimulus STS.
• the person can report the recognition of the word by pressing the button marked with ⁇ at time point 6747 ms (LineNo 2).
• Other preferred embodiments
• the methods of the present invention can be incorporated in the form of a variety of embodiments, only a few of which are disclosed herein.
• the system can be built so that the stimuli can be displayed in two dimensions, and therefore the measurements can cover a two- dimensional visual field.
• the display units can be separate, unattached to each other so that they can be placed to desired locations e.g. in the examination room so that the examiner can direct the gaze of the person to desired direction when conducting e.g. fundus examination of the eye of the person.
• desired locations e.g. in the examination room so that the examiner can direct the gaze of the person to desired direction when conducting e.g. fundus examination of the eye of the person.

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