Visual electrophysiology device

Abstract

The visual system function can be evaluated using devices and methods that monitor the electrical response to visual stimuli. The improvements in stimulus generation disclosed herein can be used separately or in combination, including improvements in wavelength accuracy, luminance accuracy, and safety. The improvement in wavelength accuracy may be achieved by narrowing the temperature range experienced by the emitter that generates the visual stimulus. The improvement in luminance accuracy may be achieved by narrowing the temperature range experienced by the light emitter, by using a photodetector used to calibrate the light output or to stop the light output after reaching the target value (or by computationally correcting it). The improvement in safety includes having an independent circuit that detects the light output and limits it to a level below the target value.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims priority to U.S. Provisional Patent Application No. 63 / 345,528, filed May 25, 2022, the entire content of which is incorporated herein by reference.

[0002] The embodiments described herein relate to devices and methods improved for evaluating visual system functions.

Background Art

[0003] Electroretinogram (ERG) and visual evoked potential (VEP) are diagnostic tests used to assist in the evaluation of visual system functions. For example, a textbook (Non - Patent Document 1) describes a number of diseases that can be diagnosed with the help of visual electrophysiology. Standards have been developed for the most common of these tests, as described in Robson et al. (2022), Hoffmann et al. (2021), Bach et al. et al. (2012), and Odom et al. (2016). As a specific example, some features of clinical ERG are strongly correlated with diabetic retinopathy (Bresnick and Palta (1987), Han and Ohn (2000), and Satoh et al. (1994)). As another example, Kjeka et al. (2013) showed that in the treatment of central retinal vein occlusion, the treatment strategy was determined based on the results of ERG rather than ophthalmic examination alone, and the results were significantly improved.

[0004] The inventions described in Patent Documents 1 - 3 represent the state - of - the - art in visual electrophysiology devices. Nevertheless, there remains a need for visual electrophysiology devices with improved performance.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] U.S. Patent No. 7,540,613 [Patent Document 2] U.S. Patent No. 9,492,098 [Patent Document 3] U.S. Patent No. 9,931,032 [Patent Document 4] U.S. Patent No. 9,510,762 [Patent Document 5] U.S. Patent No. 10,010,261 [Non-Patent Document]

[0006] [Non-Patent Document 1] Heckenlively and Arden, “Principles and Practice of Clinical Electrophysiology of Vision” 2nd edition (2006) [Summary of the Invention]

[0007] Described herein are embodiments of devices and methods for providing an indicator of visual system function. The improvements in stimulus generation disclosed herein can be used individually or in combination, including improvements in wavelength accuracy, luminance accuracy, and safety.

[0008] According to an embodiment of a device that provides an indicator of a patient's visual system function, the device has an emitter capable of emitting visible light, an optical assembly arranged such that the light emitted from the emitter reaches the patient's eye, and a controller. The controller is configured to modulate the light emission from the emitter to generate a light stimulus, receive and analyze an electrical signal from the patient's visual system, create an analysis, and provide an indicator of the visual system function based on the analysis. The device may also include an active thermal control system configured to reduce temperature fluctuations near the emitter. Alternatively, the device may also include a photodetector configured to detect the light from the emitter and a temperature sensor configured to detect the temperature near the photodetector. Alternatively, when the emitter is capable of generating continuous light emission, the device may also include a circuit that limits the time-averaged light from the emitter in a manner independent of the controller. Alternatively, the device may include a photodetector configured to detect the light from the emitter and a control circuit that modulates the duration of each flash light based on the output from the photodetector obtained during that flash light when the light stimulus includes one or more flash lights.

[0009] In some embodiments, the device may include two or more of the above alternatives. For example, the device may include both an active thermal control system configured to reduce temperature variations near the emitter, a photodetector configured to detect light from the emitter, and a temperature sensor configured to detect the temperature near the photodetector. As another example, the device may include an active thermal control system configured to reduce temperature variations near the emitter, an emitter capable of generating continuous light emission, and a circuit that limits the time-averaged light from the emitter in a manner independent of the controller. As another example, the device may include a photodetector configured to detect light from the emitter, a temperature sensor configured to detect the temperature near the photodetector, an emitter capable of generating continuous light emission, and a circuit that limits the time-averaged light from the emitter in a manner independent of the controller. As another example, the device may include an active thermal control system configured to reduce temperature variations near the emitter, an emitter capable of generating continuous light emission, a circuit that limits the time-averaged light from the emitter in a manner independent of the controller, a photodetector configured to detect light from the emitter, a temperature sensor configured to detect the temperature near the photodetector, and a circuit that limits the time-averaged light from the emitter in a manner independent of the controller. As another example, the light stimulation includes one or more flash lights, and the device may include a photodetector configured to detect light from the emitter, a temperature sensor configured to detect the temperature near the photodetector, and a control circuit that modulates the duration of each flash light based on the output from the photodetector obtained during that flash light.

[0010] According to another embodiment of a device that provides an indicator of a patient's visual system function, the device has an emitter capable of emitting visible light, an optical assembly arranged such that light emitted from the emitter reaches the patient's eye during use, and a controller. The controller, during use, modulates the light emission from the emitter to generate a light stimulus, receives and analyzes an electrical signal from the patient's visual system, creates an analysis, and provides an indicator of the visual system function based on the analysis. The device includes an active thermal control system configured to reduce temperature fluctuations near the emitter.

[0011] According to another embodiment of a device that provides an indicator of a patient's visual system function, the device has an emitter capable of emitting visible light, an optical assembly arranged such that light emitted from the emitter reaches the patient's eye during use, and a controller. The controller, during use, modulates the light emission from the emitter to generate a light stimulus, receives and analyzes an electrical signal from the patient's visual system, creates an analysis, and provides an indicator of the visual system function based on the analysis. The device includes a photodetector configured to detect light from the emitter and a temperature sensor configured to detect the temperature near the photodetector.

[0012] According to another embodiment of a device that provides an indicator of a patient's visual system function, the device has an emitter capable of emitting visible light, an optical assembly arranged such that light emitted from the emitter reaches the patient's eye during use, and a controller. The controller, during use, modulates the light emission from the emitter to generate a light stimulus, receives and analyzes an electrical signal from the patient's visual system, creates an analysis, and provides an indicator of the visual system function based on the analysis. The emitter is capable of generating continuous light emission, and the device includes a circuit that limits the time-averaged light from the emitter in a manner independent of the controller. This circuit may be, for example, non-programmable.

[0013] According to another embodiment of a device for providing an indicator of a patient's visual system function, the device includes an emitter capable of emitting visible light, an optical assembly arranged such that light emitted from the emitter reaches the patient's eye during use, and a controller. The controller, during use, modulates the light emission from the emitter to generate a light stimulus, receives and analyzes electrical signals from the patient's visual system, creates an analysis, and provides an indicator of the visual system function based on the analysis. The light stimulus includes one or more flash lights. The device further includes a photodetector configured to detect light from the emitter and a control circuit that modulates the duration of each flash light based on the output from the photodetector obtained during that flash light.

[0014] According to another embodiment, a method for providing an indicator of a patient's visual system function includes irradiating the patient's eye with a light stimulus from an emitter. Further, the method includes receiving and analyzing electrical signals from the patient and creating an analysis. The method also includes providing an indicator of the visual system function based on the analysis. The method also includes controlling the temperature near the emitter, sensing the light stimulus with a detector and sensing the temperature near the detector, using two or more independent circuits to limit the time-averaged light stimulus from exceeding a threshold, and controlling a light stimulus including one or more flash lights by modulating the duration of each flash light based on the light measurements obtained during that flash light, and performing one or more of the steps.

[0015] In some embodiments, the method includes two or more of the above alternatives. The method may include controlling the temperature near the emitter and detecting the optical stimulus with a detector and sensing the temperature near the detector. The method may include controlling the temperature near the emitter and using an independent circuit to limit the time-averaged optical stimulus. The method may include detecting the optical stimulus with a detector and sensing the temperature near the detector and using two or more independent circuits to limit the time-averaged optical stimulus from exceeding a threshold. The method may include controlling the temperature near the emitter, detecting the optical stimulus with a detector and sensing the temperature near the detector, and controlling an optical stimulus that includes one or more flash lights by modulating the duration of each flash light based on an optical measurement taken during that flash light.

[0016] According to another embodiment, a method for providing an indication of a patient's visual system function includes irradiating the patient's eye with an optical stimulus from an emitter. Further, the method includes receiving and analyzing an electrical signal from the patient and creating an analysis. The method also includes providing an indication of the visual system function based on the analysis. The method also includes controlling the temperature near the emitter.

[0017] According to another embodiment, a method for providing an indication of a patient's visual system function includes irradiating the patient's eye with an optical stimulus from an emitter. Further, the method includes receiving and analyzing an electrical signal from the patient and creating an analysis. The method also includes providing an indication of the visual system function based on the analysis. The method also includes detecting the optical stimulus with a detector and sensing the temperature near the detector.

[0018] According to another embodiment, a method for providing an indicator of a patient's visual system function includes irradiating the patient's eye with a light stimulus from an emitter. Further, the method includes receiving and analyzing an electrical signal from the patient and creating an analysis. The method also includes providing an indicator of the visual system function based on the analysis. The method also includes using two or more independent circuits to limit the time-averaged light stimulus from exceeding a threshold. One of these independent circuits does not have any programmable components.

[0019] According to another embodiment, a method for providing an indicator of a patient's visual system function includes irradiating the patient's eye with a light stimulus from an emitter. Further, the method includes receiving and analyzing an electrical signal from the patient and creating an analysis. The method also includes providing an indicator of the visual system function based on the analysis. The method also includes controlling a light stimulus that includes one or more flash lights by modulating the duration of each flash light based on a light measurement obtained during that flash light.

Brief Description of the Drawings

[0020] The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate several embodiments and, together with the description, serve to explain the novel principles of the embodiments described herein. Different aspects of the invention are shown in different drawings, but this separation is mainly for improving clarity, and all aspects can be used in the same embodiment.

[0021]

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DETAILED DESCRIPTION OF THE INVENTION

[0022] Disclosed herein are embodiments of an improved visual electrophysiology device and an improved method of visual electrophysiology. These devices and methods can be used to provide an indicator of a patient's visual system function. These devices include an electrical circuit that controls light stimulation directed at the eye and measures electrical signals generated by the eye in response to the light. The operation of the device includes stimulating the eye with light and measuring and analyzing the electrical response to the stimulation. By way of example, the analysis can be the time span between a flash of light and the peak of the electrical response, which can indicate the degree of retinal ischemia in the patient. Other analyses include various feature extractions from the electrical response such as the time and amplitude of various features (e.g., a-wave, b-wave, PhNR), or more complex methods such as wavelet analysis, logistic regression, neural networks, machine learning, and methods involving equivalents. These analysis methods are known to those skilled in the art.

[0023] Embodiments of the present invention can improve stimulation generation, for example, by improving the accuracy or consistency of the luminance of the stimulation, by improving the consistency of the spectral characteristics of the stimulation, or by improving the optical safety of the device. The stimulation to the eye can include a flash of light or other modulated light waveform. The stimulation to the eye can include a single flash of light. The stimulation to the eye can include background illumination that is perceptually constant or that changes only slowly.

[0024] Embodiments may provide an emitter capable of emitting visible light, and the emitter may emit, for example, green, red, orange, blue, amber, yellow, or white light. Exemplary types of emitters include LEDs, laser diodes, or xenon flash tubes. Optionally, one or more other (1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more) visible light emitters may be present in separate or the same spectrum. For example, some embodiments may use red, green, blue, and amber LEDs. Some embodiments may use multiple emitters having the same spectrum to increase brightness or increase the dynamic range of brightness. Some embodiments may have an infrared light emitter that emits at a wavelength longer than 710 nm and emits at least 50% of its energy. Other emitters may be provided.

[0025] Embodiments may provide an optical assembly arranged such that the light emitted from the emitter (during use) reaches the patient's eye. In some embodiments, the optical assembly provides diffused light to the eye to stimulate the entire retina. For example, the optical assembly may be part of an integrating sphere or other diffusive reflecting surface. The RETeval device manufactured by LKC Technologies and the UTAS Bigshot ganzfelds are examples of optical assemblies that are part of an integrating sphere. The UTAS Sunburst ganzfeld manufactured by LKC Technologies is an example of an optical assembly having a diffusive reflecting surface. Alternatively, the optical assembly may use lenses to provide diffused light (e.g., using Maxwell optics). Diffused light is useful, for example, in full-field ERG and VEP measurements. In some embodiments, the optical assembly provides patterned or directed light to the eye. Patterned light is useful, for example, in pattern ERG, pattern VEP, multifocal ERG, multifocal VEP, and focal ERG measurements.

[0026] Some embodiments may use a controller to modulate the light emission from the emitter to generate a light stimulus. For example, the light emission may be one or more flash lights (e.g., flashes having a duration of less than 6 ms, 21 ms, or 40 ms). By using pulse width modulation (PWM) or other similar methods known in the art, the apparent brightness of the light stimulus over time can be modulated to create a dimmer, or substantially sinusoidal, triangular, or rectangular stimulus. Individual flashes can have different luminance energies by changing the duration of the flash or by changing the instantaneous luminance of the flash. In embodiments having multiple emitters, the emission duration of each emitter may be different (e.g., the second emitter emits light over a longer period than the first emitter), or the same.

[0027] In visual electrophysiological tests, the light stimulus is routinely changed in color or brightness to accentuate the responses of various aspects of the visual pathway. For example, if the light stimulus inadvertently changes due to inherent fluctuations in the light source or fluctuations in the temperature of the emitter, it can have an adverse effect on the electrical signals measured from the patient's visual system, and thus on the metrics of visual system function based on the measurements.

[0028] Some embodiments may use an active thermal control system configured to reduce temperature variations near the emitter. The light from the emitter may vary in both intensity and color as the temperature of the emitter changes. For example, LEDs generally decrease in light emission as the temperature increases due to an increase in the recombination of electrons and holes that do not contribute to light emission, although the color of the light emission may change due to the temperature dependence of the semiconductor bandgap. Thus, an active thermal control system may be useful for making the light stimulation from the emitter more consistent by narrowing the temperature range experienced by the emitter. Other embodiments for reducing variations in the color of light emission use an optical filter or a light source that is minimally affected by temperature (e.g., laser diodes and xenon flash lamps). As an example, an active thermal control system configured to reduce temperature variations near the emitter may narrow the temperature range experienced by the emitter due to changes in the ambient temperature or due to self-heating of the emitter due to inefficiencies in the light generation process. Narrowing the temperature range experienced by the emitter may allow for more consistent light stimulation.

[0029] Some embodiments may use a photodetector configured to detect light from the emitter and a temperature sensor configured to detect the temperature near the photodetector. As described in Patent Document 2, the photodetector may be used during the calibration phase of the test to compensate for variations in the output of the emitter or the optical efficiency of the optical assembly. However, it has not been disclosed in the prior art that further improvements are possible by understanding that the output of the photodetector may depend on temperature. By having a temperature measurement near the photodetector, the temperature dependence of the photodetector can be reduced. For example, the controller can use knowledge of the temperature dependence (e.g., knowledge obtained from the product datasheet or measurements) to correct the measurements of the photodetector. Alternatively, the temperature near the photodetector can be actively controlled, for example, by using a heating element and a control circuit in addition to the temperature sensor. Having a temperature sensor near the photodetector improves the accuracy of the estimated temperature of the photodetector. The temperature sensor may be arranged such that the shortest distance between the temperature sensor and the photodetector is less than 20 cm, 15 cm, 10 cm, 5 cm, 4 cm, 3 cm, 2 cm, 1 cm, or 0.5 cm from the photodetector.

[0030] In certain cases, the desired light stimulus is a very bright but short flash of light. For example, the ISCEV extended protocol (McCulloch et al. (2019)) for the stimulus-response series for photopic full-field ERG specifies the use of a luminance energy flash. If the flash is exactly 5 ms with a constant luminance, the luminance is (300 cd s / m 2 ) / (5 ms) = 60,000 cd / m 2 ) / (5 ms)=60,000cd / m 2This results in luminance. If this luminance is left unattended indefinitely, it may pose a light hazard to the retina. Some emitter types (e.g., xenon flash tubes) essentially stop emitting light after a short time, while other emitter types, such as LEDs and / or laser diodes, can provide continuous emission. Therefore, devices using emitter types that can provide continuous emission are associated with the optical safety risk of generating potential light hazards. Usually, the controller modulates the light emission from the emitter to generate a light stimulus. However, if an error condition (e.g., software bug) occurs in the controller, the optical safety risk can be reduced by having a circuit that limits the time-averaged light from the emitter in a manner independent of the controller. In addition to reducing the optical safety risk, the circuit can reduce the burden associated with developing high-concern software, especially when neither of the two independent circuits (e.g., the controller and the independent circuit) has any programmable components.

[0031] Potential light hazards are described in detail in the international standard ISO15004-2:2007. One such hazard is the photochemical cataract light hazard to the retina. One limit of this cataract hazard is to keep the weighted retinal radiant luminance L A-R below the limit of 2 mW / (sr cm 2 ) when averaged over any 20-second interval. L A-R is carefully defined in ISO15004-2:2007, but briefly, it is the sum of the retinal radiant luminance from the device at each wavelength after weighting the radiant luminance by the photochemical hazard weighting function A(λ) for the crystalline lens eye, which varies from 6 at wavelengths below 335 nm to 1.43 at 400 nm, 0.1 at 500 nm, and 0.001 above 600 nm. Another such potential light hazard is the retinal visible and infrared radiation heat hazard. One limit of this heat hazard is to keep the weighted retinal visible and infrared heat radiant luminance L VIR-R below the limit of 6 W / (sr cm 2 ) when averaged over any 20-second interval. L VIR-RIt is defined carefully in ISO15004-2:2007. Briefly speaking, it is 1 from 435nm to 700nm, gradually decreases to 0.2 at a wavelength ≧1045nm, and gradually decreases to 0 at a wavelength ≦375nm. Sum up the retinal radiance from the device at each wavelength after weighting the radiance with the thermal hazard weighting function R(λ).

[0032] Some embodiments may have a circuit that can limit the time-averaged output of the emitter so that the device does not generate a potential optical hazard. For example, the circuit can limit the time-averaged output of the emitter, as a result, the device can be classified as a Group 1 device according to ISO15004-2:2007 where no potential optical hazard exists. For example, the circuit can limit the weighted retinal radiance L A-R to a value of 2mW / (sr cm 2 ), for example, values of 0.1, 0.5, 1, or 2mW / (sr cm 2 ). For example, the circuit can limit the weighted retinal visible and infrared thermal radiance L VIR-R to a value of 6W / (sr cm 2 ), for example, values of 0.1, 0.5, 0.6, 1, 2, 3, 4, 5, or 6W / (sr cm 2 ). In the above calculations, ISO15004-2:2007 uses a 20-second interval, but other durations such as 30, 15, 10, 5, 4, 3, 2, 1, 0.5, 0.25, 0.1 seconds, etc. can also be used.

[0033] Some embodiments use a light stimulus that includes one or more flash lights. In these cases, the device can have a photodetector configured to detect light from the emitter and a control circuit that modulates the duration of each flash light based on the output from the photodetector obtained during that flash light. Using one of these embodiments provides real-time luminance correction based on feedback from the photodetector. For example, if there are some luminance variations in the output of the emitter (e.g., arc discharge characteristics or temperature-based variations in a xenon flash lamp), after emitting the desired flash energy, if the control circuit stops the light emission, the luminance variation between flashes can be reduced, thereby potentially improving the results from the device.

[0034] The above description describes both a device that provides an indicator of a patient's visual system function and a method that provides an indicator of a patient's visual system function.

[0035] Combinations of the above descriptions are also contemplated. Configurations and their methods of use are also contemplated. Embodiments improve existing visual electrophysiology devices in other ways that will be apparent from the detailed description herein.

[0036] (Definitions) To provide a clearer description of the embodiments described herein, certain terms are defined as follows. Other terms are defined elsewhere in the present disclosure.

[0037] The term "emitter" refers to anything that emits electromagnetic radiation in the UV, visible, and infrared (IR) ranges. Exemplary emitters include LEDs, display devices, laser diodes, and gas discharge devices such as xenon flash lamps and fluorescent lamps. In some cases herein, the term "infrared" is abbreviated as "IR".

[0038] The term "visible light" refers to electromagnetic radiation that can generate a light stimulus. Visible light typically has a wavelength of 380 nm to 750 nm.

[0039] The term "light stimulation" refers to visible light stimulation.

[0040] The term "LED" refers to a light-emitting diode. LEDs include those containing semiconductors, organic materials, and quantum dots. The term "LED" includes those with phosphors integrated.

[0041] The term "patient" refers to a human or other vertebrate in whom physiological electrical signals are measured. The device is assumed to be placed in proximity to the patient so as to be able to stimulate the patient's visual system and measure the physiological response thereto.

[0042] The phrase "indicator of visual system function" refers to the analysis of electrical signals from the patient's visual system in response to light. It should be distinguished from other metrics of the visual system based only on, for example, imaging of the eye structure by fundus photography, OCT, etc., or psychophysical metrics such as visual acuity using a Snellen chart.

[0043] The term "or" means an inclusive "or" where two or more of the alternatives can be true.

[0044] The term "within" refers to the shortest distance between two objects when the distance describing the relative position of the two objects is described before it. For example, if object A is within 3 cm of object B, the shortest distance between object A and object B is 3 cm or less.

[0045] (Detailed Description) Various embodiments, as well as their additional objectives, features, and advantages, will be more fully understood from the following description.

[0046] Referring to FIG. 1, an exemplary device 100 used to provide an indicator of a patient's visual system function is shown. Emitter 106 illuminates optical assembly 142 with light, and optical assembly 142 directs that light toward the patient's eye 144 during use. In this example, optical assembly 142 acts as an integrating sphere for delivering light emitted from emitter 106 to the patient's eye in a diffused manner. The diffused light source enables examination of most of the retina and makes patient fixation less critical. Optical assembly 142 may have a white inner surface to enhance reflectivity. The white surface may be a coating (e.g., paint), or optical assembly 142 may be made of, for example, white plastic. Other exemplary optical assemblies do not require the light from emitter 106 to be reflected before reaching the patient's eye; for example, the light may be refracted, diffused, scattered, or may have a direct path between the emitter and the patient's eye.

[0047] In some embodiments, emitter 106 may be an LED, a laser diode, or a xenon flash lamp. Multiple emitters may be used to provide, for example, higher brightness, a wider brightness range, different colors.

[0048] The emitter 106 can comprise one, two, three, four, or more emitters. For example, the emitter 106 can comprise a first emitter, which can be an LED or a different type of light emitter. The first emitter has a first emission spectrum. In some embodiments, the first emitter can emit green, red, orange, blue, amber, white, or yellow light. For example, the first emitter can be a green LED. The emitter 106 can also comprise a second emitter. The optional second emitter has, for example, a second visible emission spectrum that is different from the first emission spectrum. The second emitter, if present, can emit green, red, orange, blue, amber, white, or yellow light. The optional second emitter can be an LED or a different type of light emitter, and can be, for example, a red LED. The emitter 106 can also comprise a third emitter. The optional third emitter has, for example, a third visible emission spectrum that is different from the first and second emission spectra. The third emitter, if present, can emit green, red, orange, blue, amber, white, or yellow light. The optional third emitter can be an LED or a different type of light emitter, and can be, for example, a blue LED. The emitter 106 can also comprise a fourth emitter. The optional fourth emitter has, for example, a fourth visible emission spectrum that is different from the first, second, and third emission spectra. The fourth emitter, if present, can emit green, red, orange, blue, amber, white, or yellow light. The optional fourth emitter can be an LED or a different type of light emitter, and can be, for example, an amber LED. The device 100 can have additional (e.g., five, six, seven, eight, or more) visible light emitters. Having four different visible spectrum sources enables independent stimulation of one of the three types of cones or rods in humans (Shapiro et al. (1996)).

[0049] The emitter 106 can be, for example, an RGB (red, green, blue) LED, and can be, for example, a CREE CLV1L-FKB, CREE CLQ6A-FKW, CREE XLamp XML-L, Avago ASMT-MT000-0001, or Osram LRTD-C9TP. The emitter 106 can be, for example, an RGBA (red, green, blue, amber) LED, and for example, individual LEDs such as CREE CLQ6A-YKW or other light sources may be used, which can be obtained from Luxeon C Color line LEDs or CREE Xlamp XQ-E LEDs. The number of components of the emitter 106 can be one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, or more. The larger the number of components included in the emitter 106, the better the uniformity of the light in the integrating sphere, and the brighter the light output can be, but in terms of manufacturing difficulty and cost, it is inconvenient for the number of components to increase.

[0050] As shown in FIG. 1, the camera 101 can image the patient's eye through the hole in the optical assembly 142. The camera 101 may include an infrared light emitter, and at least 50% of its energy is emitted at a wavelength longer than 710 nm. The infrared light emitter can be used to illuminate the patient's eye during the exposure time of the camera 101. In some embodiments, the device 100 has neither the camera 101 nor the infrared light emitter.

[0051] As a further component of the device 100, the device 100 may include a control unit 120, and the control unit 120 can be used to start each test and input customized settings. Further, the device 100 may have a display 118 for assisting the operator in using the device and displaying the test results.

[0052] Device 100 may receive electrical signals from a patient's visual system via electrode 112. Electrode 112 may be a disposable component, for example, as described in Patent Documents 4 and 5. Alternatively, electrode 112 may be a permanent component of device 100. When used, electrode 112 may be near the eye, near the visual cortex at the back of the head, or at other locations selected to provide electrical signals from the patient's visual system. Electrode 112 may be connected to an analog / digital (A / D) converter 150 and communicate with a controller 110 that analyzes the data. Exemplary A / D converters include the ADS1220, ADS1248, ADS1292, ADS1294, ADS1298, or ADS1299 from Texas Instruments, and the AD7195, AD7194, AD7193, AD7799, AD7738 from Analog Devices. In some embodiments, an A / D converter is not used.

[0053] An embodiment of device 100 for providing an indicator of a patient's visual system function includes an emitter 106 capable of emitting visible light, an optical assembly 142 arranged such that light emitted from the emitter reaches the patient's eye 144 during use, and a controller 110. The controller 110 modulates the light emission from the emitter to generate a light stimulus, receives and analyzes electrical signals from the patient's visual system, generates an analysis, and provides an indicator of visual system function based on the analysis. Device 100 may also include an active thermal control system 109 configured to reduce temperature variability near emitter 106, for example within 0.5, 1, 2, 3, 4, or 5 cm from the emitter. The active thermal control system 109 may include a temperature sensor and at least one of a heater and a cooler for affecting the temperature. The temperature sensor may be a separate component (e.g., temperature sensor 107) arranged near emitter 106 (e.g., within 0.5, 1, 2, 3, 4, 5, 10, 15, or 20 cm from the emitter), or measurements from a temperature-dependent aspect of emitter 106 may be utilized. For example, when emitter 106 is an LED, the voltage generated across the component at a certain current is temperature-dependent. When not using an LED, a small probe current can be used to generate the temperature-dependent voltage across the LED used by the active thermal control system 109. The active thermal control system 109 may use a heater to increase the temperature near the emitter. The heater may be a heating element 111. The heating element 111 may be a separate component arranged near emitter 106 (e.g., within 0.5, 1, 2, 3, 4, or 5 cm from the emitter). The heating element 111 may be a resistor or a resistive trace on a printed circuit board. Alternatively, the heater may be emitter 106 as long as unwanted light emission can be avoided (e.g., with a shutter). Optionally, the active thermal control system includes a cooler for lowering the temperature. Having both a heater and a cooler reduces the complexity of the control logic but makes the hardware more complex (e.g., more components may be required). The control logic for the active thermal control system 109 may be part of the controller 110 or may be separate.The control logic may be feedback-type or may include a feedforward element from knowledge of future power dissipation due to the generation of optical stimulation. The active thermal control system may be configured to maintain the temperature near the emitter at 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, or higher. Variations in the power dissipated within the emitter and variations in the ambient temperature may cause variations in the temperature of the emitter, which may lead to changes in the emission wavelength or luminance. This active thermal control system reduces the variations in the temperature of the emitter, thereby improving the stability of the emitted light.

[0054] Referring to FIG. 2, device 200 may include a photodetector 201 and a temperature sensor 207. The temperature sensor 207 may be the same as or different from the optional temperature sensor 107 of FIG. 1. The photodetector 201 may be configured to detect light from emitter 106. The photodetector 201 may be used to monitor optical stimulation so that the controller 110 can compensate for variations in the output of the emitter 106 or the optical efficiency of the optical assembly 142. The controller 110 can adjust the output of the emitter 106 to achieve a desired signal from the photodetector 105, for example, during the calibration phase of a test. If the adjustment is too large, device 200 may be configured to report an error rather than, in some cases, produce incorrect results. The temperature sensor 207 may be disposed within 0.5, 1, 2, 3, 4, 5, 10, 15, or 20 cm of the photodetector 201. Being in the vicinity of the detector reduces any temperature difference between what is being measured and the temperature of the photodetector. The temperature measurement may be used with a model of the temperature dependence of the photodetector to reduce the temperature variations of the measurement. Alternatively, the temperature measurement can be used in a photodetector temperature control circuit to actively maintain the temperature. This photodetector temperature control circuit may be the same as or different from the active thermal control system 109. Even if it is different, it may have the same components (sensors, heaters, optionally coolers, and control logic).

[0055] Referring to FIG. 3, device 300 may include a circuit 302 that limits the time-averaged light from the emitter in a manner independent of controller 110. In this way, circuit 302 prevents the generation of potential optical hazards by device 300 as well. Optional photodetector 301 measures the time-averaged emission (which may be the same as or different from optional photodetector 201). This measured value can be compared to a threshold, and if the threshold is exceeded, further emission is stopped for a first period independently of controller 110.

[0056] Exemplary first periods include a fixed time such as 20 seconds or other durations such as 30, 15, 10, 5, 4, 3, 2, 1, 0.5, 0.25, 0.1 seconds, etc. Other first periods include the difference between the exemplary periods described above and the time it takes to reach the desired time-averaged light limit. As a specific example, if the desired time-averaged light threshold is a weighted retinal radiant luminance L of 2 mW / (sr cm 2 ) averaged over any 20-second interval A-R and the retinal radiant luminance is 20 mW / (sr cm 2 ) during the first 2 seconds, this is the maximum allowable retinal radiant luminance over a 20-second period, and thus the circuit can prevent additional L A-R for at least 18 seconds.

[0057] Methods of stopping further emission include actuating a shutter to block the light from the emitter from reaching the patient's eye and preventing the emitter from generating light. Methods of preventing the emitter from generating light include cutting off its power supply (e.g., through a high-side or low-side driver), or inserting a logic gate into the emitter control circuit that both controller 110 and circuit 302 must agree to turn the emitter on (e.g., if positive logic is used in the emitter control circuit, an AND gate with controller 110 and circuit 302 as inputs can be connected to the emitter control circuit).

[0058] Circuit 302 can also be implemented using a programmable device or alternatively, only using non-programmable components. The instantaneous optical output from photodetector 301 can be digitally time-averaged through a moving window or other low-pass filters known in the art. Alternatively, the instantaneous optical output from photodetector 301 can also be time-averaged using analog electronics via a low-pass filter.

[0059] An exemplary non-programmable implementation of circuit 302 is as follows. Photodetector 301 may be a photodiode connected to a transimpedance amplifier that generates a voltage related to the light within optical assembly 142. This voltage can be filtered through an RC (or other type) low-pass filter and provided as an input to a comparator. When the voltage of the comparator exceeds its setpoint, it can deactivate emitter 106, for example, using the method described above. The deactivation time can be set by a hardware one-shot (i.e., a monostable multivibrator) or a Schmitt trigger feedback loop for the filtered voltage.

[0060] In the absence of an optional photodetector 301, the power consumed by emitter 106, the voltage across emitter 106, or the current through emitter 106 can be used as a measure of the light generated by emitter 106.

[0061] Referring to FIG. 4, the device 400 may include a control circuit 402. The photodetector 401 (which may be the same as or different from the optional photodetectors 201 and 301) measures light emission. As described in Patent Document 2, the photodetector may be used during the calibration phase of the test to compensate for variations in the output of the emitter or the optical efficiency of the optical assembly. However, what is not disclosed in the prior art is using the photodetector 401 to adjust the flash duration (and thus the flash energy) in real time. Since the optical flash is very short (e.g., <100 μs, <10 μs, or <1 μs), measuring the flash energy and stopping the flash output when the desired flash energy is reached requires high-speed electronics. In some embodiments, a high-speed A / D converter (e.g., ≧100,000 samples / second or ≧1,000,000 samples / second) is used with digital logic to determine when the appropriate amount of flash energy has been delivered and the flash should be stopped. In other embodiments, an integrator (or low-pass filter) circuit accumulates a signal related to the flash energy and then sends this signal to a comparator circuit. The comparator compares the signal to a target value set, for example, by a digital-to-analog converter (DAC). The DAC output can be set by the controller 110. When the target value is reached or exceeded, the emitter 106 can be turned off by the controller 110 or by using the circuits described above.

[0062] Controller 110 provides overall control of devices 100, 200, 300, and 400. Controller 110 may be a microcontroller or microcomputer device with a processor, memory, and other connections to other components of device 100. Controller 110 may be a pre-programmed computer programmed to execute the functions and controls described herein. Alternatively, controller 110 may include a wireless or wired connection, which enables remote programming (e.g., for additional features or updates). Those skilled in the art will understand how to program and operate controller 110. The control of emitter 106 is performed by controller 110 (and, optionally, the circuits described above) that can control the timing of the light and camera light sources, as well as their intensity, frequency, and synchronization. As an example, controller 110 can modulate the activity of emitter 106, such as an LED, to provide a series of short flashes of light for a predetermined duration, but other stimulation waveforms or frequencies can also be utilized. Controller 110 can be a single microprocessor, for example, one of the microprocessors sold by Analog Devices, Atmel, Intel, Microchip, Texas Instruments, etc. Alternatively, controller 110 can be distributed among multiple integrated circuits on one or more printed circuit boards within device 100. Controller 110 can be configured to modulate the light output of the emitter and receive and analyze electrical signals from the patient.

[0063] Analysis of the data from the electrical signals sensed by electrode 112 is performed by controller 110. Algorithms for specifically evaluating indicators of visual system function in a patient are publicly available. See, for example, Severns et al. (1991), Severns and Johnson (1991), Kjeka et al. (2013), and Patent Document 3. Other algorithms are described in the references cited in the Background Art section above.

[0064] In some embodiments, the controller 110 can communicate with the camera and measure the pupil size in the image captured by the camera. In some embodiments, the controller 110 can modulate the light output from an additional emitter such as a second emitter, a third emitter, a fourth emitter, or an infrared light emitter. The controller 110 can provide an operator with an indication of the patient's visual system function by using a display and / or by providing means for communicating information to a computer or other electronic device.

[0065] In some embodiments, the device includes two or more of the above alternatives. For example, the device may include both an active thermal control system configured to reduce temperature variations near the emitter, a photodetector configured to detect light from the emitter, and a temperature sensor configured to detect the temperature near the photodetector. As another example, the device may include an active thermal control system configured to reduce temperature variations near the emitter, an emitter capable of generating continuous light emission, and a circuit that limits the time-averaged light from the emitter in a manner independent of the controller. As another example, the device may include a photodetector configured to detect light from the emitter, a temperature sensor configured to detect the temperature near the photodetector, an emitter capable of generating continuous light emission, and a circuit that limits the time-averaged light from the emitter in a manner independent of the controller. As another example, the device may include an active thermal control system configured to reduce temperature variations near the emitter, an emitter capable of generating continuous light emission, a circuit that limits the time-averaged light from the emitter in a manner independent of the controller, a photodetector configured to detect light from the emitter, a temperature sensor configured to detect the temperature near the photodetector, and a circuit that limits the time-averaged light from the emitter in a manner independent of the controller. As another example, the light stimulation includes one or more flash lights, and the device may include a photodetector configured to detect light from the emitter, a temperature sensor configured to detect the temperature near the photodetector, and a control circuit that modulates the duration of the light flash based on the output from the photodetector.

[0066] Referring to FIG. 5, a flowchart diagram is shown that describes a method 500 for providing an indicator of a patient's visual system function. The method includes irradiating the patient's eye with a light stimulus from an emitter (block S501), receiving and analyzing an electrical signal from the patient and creating an analysis (block S502), providing an indicator of the visual system function based on the analysis (block S503), and performing one or more of (a) controlling the temperature near the emitter, (b) sensing the light stimulus using a detector and sensing the temperature near the detector, (c) using two or more independent circuits to limit the time-averaged light stimulus from exceeding a threshold, and (d) controlling a light stimulus that includes one or more flash lights by modulating the duration of each flash light based on a light measurement taken during that flash light (block S504).

[0067] While the foregoing descriptions emphasize the configurations, their use is also contemplated. To provide an indicator of the visual system function, the method includes illuminating the patient's eye with a light stimulus. The method also includes either receiving and analyzing an electrical signal from the patient so as to provide an indicator of the visual system function.

[0068] Some methods include techniques for reducing spurious variations in light stimulation. These techniques include controlling the temperature near the emitter. Since both the color and intensity of the light from the emitter can vary with temperature, narrowing the range of temperatures experienced by the emitter reduces the variation in light stimulation. In some embodiments, the variation in the luminance of the light stimulation can be reduced using a photodetector to monitor the light output. However, the measurements from the photodetector also vary with temperature. Accordingly, some methods include sensing the light stimulation with a detector and sensing the temperature near the detector. Sensing the temperature near the photodetector can be employed to reduce detector error by mathematically adjusting the data that knows the temperature or by actively controlling the temperature near the detector. In some cases, it may be preferable to use an LED or a laser diode to generate short flashes of light rather than using a xenon flash lamp. However, LEDs and laser diodes can be inadvertently left on for extended periods, leading to the patient being inadvertently exposed to light for an extended period. Depending on the luminance of the emitter, this can pose a potential light hazard. Accordingly, some methods include using two or more independent circuits (e.g., controller 110 and circuit 302) to limit the time-averaged light stimulation from exceeding a threshold. Apart from the normal method of controlling the light stimulation, having an independent circuit that limits the time-averaged light stimulation may improve the overall safety of the device by requiring two independent failures to generate a potential light hazard (the threshold is set to prevent potential light hazards). Making at least one of the independent circuits non-programmable can prevent software from affecting optical safety and reduce the complexity of software development. In some embodiments, a photodetector is used to measure and modulate the duration of the light flash to reduce the variation between flashes. Accordingly, some methods include controlling a light stimulation that includes one or more flash lights by modulating the duration of each flash light based on the light measurements obtained during that flash light.

[0069] All references cited in this specification are incorporated by reference in their entirety. If the publications and patents or patent applications incorporated by reference conflict with the disclosure contained herein, this specification is intended to supersede and / or take precedence over any such conflicting material.

[0070] All numbers representing amounts used in this specification and the claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and the appended claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the claims, each numerical parameter should be construed in light of the number of significant figures and ordinary rounding methods.

[0071] The foregoing description of the device includes many novel and advantageous aspects. Combinations of aspects are also envisioned. It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed detection devices, components, and methods without departing from the scope of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The specification and examples are intended to be considered as exemplary only, with the true scope of the invention being indicated by the following claims and their equivalents.

[0072] The terms and descriptions used herein are for illustrative purposes only and are not meant to be limiting. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the invention as defined in the following claims and their equivalents, and that all terms should be understood in the broadest possible sense unless otherwise indicated.

[0073] (Cited References) Bresnick, George, and Mari Palta. (1987) “Temporal Aspects of the Electroretinogram in Diabetic Retinopathy.” Arch Opthalmol, 105:660-4. Han, Young-Keun, and Young-Hoon Ohn. (2000) “Changes of ERG Parameters in Diabetic Retinopathy.” J Korean Ophthalmol Soc, 41: 149-155. Bach, M, et al. (2012) “ISCEV standard for clinical pattern electroretinography - 2012 update.” Doc Ophthalmol, 126:1-7. Hoffman, MB, et al. (2012) “ISCEV standard for clinical multifocal electroretinography (mfERG) (2021 update).” Doc Ophthalmol, 142:5-16. Kjeka, O, RW Jansson, C Bredru, and J Krohn. (2013) “Early panretinal photocoagulation for ERG-verified ischaemic central retinal vein occlusion.” Acta Ophthalmol, 37-41. Odom, Vernon, et al. (2016) “ISCEV standard for clinical visual evoked potentials. (2016 update).” Doc Ophthalmol, 133: 1-9. Satoh, S, H Iijma, M Imai, K Abe, and T Shibuya. (1994) “Photopic electroretinogram implicit time in diabetic retinopathy.” Japanese Journal of Ophthalmology, 38: 178-184. Severns, ML, Johnson, MA and Merritt, SA. (1991) “Automated estimate of implicit time and amplitude of the flicker electroretinogram.” Applied Optics 30:2106-2112. Severns, ML and Johnson, MA (1991) “Automated implicit time and amplitude determination for the 30 Hz flicker electroretinogram: performance prediction of neovascularization central retinal vein occlusion.” Technical Digest Series, Washington, D.C; Optical Society of America, pp. 10-13. Shapiro, AG, Pokorny J, and Smith VC. (1996). “Cone-rod receptor spaces with illustrations that use CRT phosphor and light-emitting-diode spectra.” J. Opt Soc. Am. A., 2319-2323. Robson, AG, et al. (2022) “ISCEV standard for full-field clinical electroretinography (2022 update).” Doc Ophthalmol.

Claims

Claim 1 A device for providing an indicator of a patient's visual system function, comprising: a. An emitter capable of emitting visible light; b. An optical assembly arranged such that light emitted from the emitter reaches the patient's eye; c. A controller configured to: (i) Modulate the light emission from the emitter to generate a light stimulus; (ii) Receive and analyze an electrical signal from the patient's visual system to create an analysis; (iii) Provide an indicator of visual system function based on the analysis; and further comprising an active thermal control system configured to reduce temperature fluctuations near the emitter, a photodetector configured to detect light from the emitter, and a temperature sensor configured to detect the temperature near the photodetector, wherein the emitter is capable of providing continuous light emission, and the device further comprises a circuit for limiting the time-averaged light from the emitter in a manner independent of the controller, or wherein the light stimulus includes one or more flash lights, the device further comprises a photodetector configured to detect light from the emitter, and the device further comprises a control circuit for modulating the duration of each flash light based on the output from the photodetector obtained during that flash light. The device is further configured such that one or more of the above conditions apply. Claim 2 The device according to claim 1, wherein the emitter is selected from an LED, a laser diode, or a xenon flash lamp. Claim 3 The device according to claim 1, comprising an active thermal control system configured to reduce temperature fluctuations near the emitter. Claim 4 The device according to claim 1, further comprising a photodetector configured to detect light from the emitter and a temperature sensor configured to detect the temperature near the photodetector. Claim 5 The device according to claim 1, wherein the emitter is capable of providing continuous light emission, and the device further comprises a circuit for limiting the time-averaged light from the emitter in a manner independent of the controller. Claim 6 ​ ​ The light stimulation includes one or more flash lights, the device further comprises a photodetector configured to detect light from the emitter, and the device further comprises a control circuit configured to modulate the duration of each flash light based on the output from the photodetector obtained during that flash light. The device according to claim 1.

7. The emitter can provide continuous light emission, and the device an active thermal control system configured to reduce temperature fluctuations near the emitter, a photodetector configured to detect light from the emitter, and a temperature sensor configured to detect the temperature near the photodetector, a circuit that limits the time-averaged light from the emitter in a manner independent of the controller The device according to claim 1, further comprising.

8. The active thermal control system estimates the temperature using the electrical characteristics of the emitter. The device according to claim 3 or 7.

9. The emitter is a light-emitting diode (LED), and the electrical characteristic is the voltage across the LED due to the current flowing through the LED. The device according to claim 8.

10. The active thermal control system a temperature sensor, the temperature sensor being arranged such that the shortest distance between the temperature sensor and the emitter is less than 3 cm, a heating element, the heating element being arranged such that the shortest distance between the heating element and the emitter is less than 3 cm The device according to claim 3 or 7, comprising.

11. The active thermal control system is configured to maintain the temperature near the emitter at a value above 25°C. The device according to claim 10.

12. The temperature sensor is arranged such that the shortest distance between the temperature sensor and the photodetector is less than 3 cm. The device according to claim 4 or 7.

13. The controller adjusts the light emission using the measurement from the photodetector. The device according to claim 12.

14. The controller adjusts the light emission using the measurement from the temperature sensor. The device according to claim 13.

15. The device according to claim 13, further comprising a heating element and a control circuit configured to reduce temperature fluctuations near the photodetector.

16. The device according to claim 5 or 7, wherein the circuit restricts the time-averaged light from the emitter so as to prevent generation of potential optical hazards by the device.

17. The potential light hazard, when averaged over any 20-second interval, has a weighted retinal radiant luminance L greater than 2 mW / (sr cm ２ ), as defined in claim 16, of the device according to claim 16. Ａ－Ｒ ​

18. The device according to claim 5 or 7, wherein the circuit does not include any programmable components.

19. (a)The active thermal control system A temperature sensor arranged such that a shortest distance between the temperature sensor and the emitter is less than 3 cm, and A heating element arranged such that a shortest distance between the heating element and the emitter is less than 3 cm, comprising (b)The active thermal control system is configured to maintain a temperature near the emitter at a value exceeding 25 °C, (c)The active thermal control system is further configured to maintain a temperature near the photodetector at a value exceeding 25 °C, (d)The temperature sensor is further arranged such that a shortest distance between the temperature sensor and the photodetector is less than 3 cm, (e)The controller adjusts the light emission using a measurement value from the photodetector. (f)The circuit limits the time-averaged light from the emitter so that the device cannot produce a potential optical hazard, the potential optical hazard being greater than 2 mW / (sr cm ２ 2) weighted retinal radiant exposure L Ａ－Ｒ as defined, of the device according to claim 7.

20. The control circuit includes a digital-to-analog converter, an integrator circuit, and a comparator circuit. (a)The controller is configured to set an analog set value using the digital-to-analog converter. (b)The output from the photodetector is integrated using the integrator circuit to generate a flash energy signal. (c)The comparator circuit is configured to compare the analog set value with the flash energy signal. (d)The output from the comparator circuit is used to stop the light emission, thereby modulating a duration of the light flash. The device according to claim 6.

21. The device according to claim 20, wherein the emitter is a xenon flash lamp.

22. A method for providing an index of a patient's visual system function, comprising: irradiating the patient's eye with a light stimulus from an emitter; receiving and analyzing an electrical signal from the patient to create an analysis; providing an index of visual system function based on the analysis; furthermore, (a)controlling a temperature near the emitter; (b)detecting the light stimulus with a detector and sensing a temperature near the detector. (c) using two or more independent circuits to limit the time-averaged optical stimulation from exceeding a threshold; (d) controlling the optical stimulation including one or more flash lights by modulating the duration of each flash light based on the optical measurement values obtained during that flash light; performing one or more of the above steps; A method comprising the above steps.

23. The method according to claim 22, wherein the temperature near the emitter is controlled.

24. The method according to claim 22, wherein a detector is used to sense the optical stimulation and the temperature near the detector is measured.

25. The method according to claim 22, wherein the time-averaged optical stimulation is limited from exceeding a threshold using two or more independent circuits.

26. The method according to claim 22, wherein the optical stimulation includes one or more flash lights, and the duration of each flash light is modulated based on the optical measurement values obtained during that flash light.

27. The method according to claim 22, wherein the temperature near the emitter is controlled, the time-averaged optical stimulation is limited from exceeding a threshold using two or more independent circuits, a detector is used to sense the optical stimulation, and the temperature near the detector is measured.

28. The method according to claim 23 or 27, wherein the electrical characteristics of the emitter are used to estimate its temperature.

29. The method according to claim 28, wherein the emitter is a light-emitting diode (LED), and the electrical characteristics are the voltage across the LED due to the current flowing through the LED.

30. The temperature is controlled using a temperature sensor disposed within 3 cm of the emitter and a heater disposed within 3 cm of the emitter. The method according to claim 23 or 27.

31. The method according to claim 30, wherein the temperature is controlled to a value greater than 25 °C.

32. The method according to claim 24 or 27, wherein the temperature is measured within 3 cm of the detector.

33. The method according to claim 32, wherein the light emitted from the emitter is adjusted based on the output of the detector.

34. The method according to claim 33, wherein the emitted light is adjusted based on the temperature measurement value.

35. The method according to claim 33, wherein the temperature is controlled near the emitter.

36. The method according to claim 25 or 27, wherein the time-averaged optical stimulation is limited to prevent the generation of potential optical hazards.

37. The potential light hazard, when averaged over any 20 second interval, has a weighted retinal radiant luminance L greater than 2 mW / (sr cm ２ ), as defined in claim 36, of the method according to claim 36. Ａ－Ｒ ​

38. The method according to claim 37, wherein at least one of the independent circuits does not include any programmable components.

39. (a) The temperature is controlled using the temperature measured within 3 cm from the emitter and within 3 cm from the detector, and the heater is disposed within 3 cm from the emitter and within 3 cm from the detector. (b) The temperature is controlled to a value exceeding 25°C. (c) The light emitted from the emitter is adjusted based on the output of the detector. (d) The time-averaged light stimulation is limited such that the device cannot generate a potential light hazard, and the potential light hazard has a weighted retinal radiant exposure L greater than 2 mW / (sr cm ２ ) when averaged over any 20-second interval Ａ－Ｒ as defined The method according to claim 27.

40. The method according to claim 26, wherein the emitter is a xenon flash lamp.

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