Determining information about corneal moisture content

Abstract

According to an exemplary aspect of the present disclosure, there is provided a measurement system (1) for determining information about corneal moisture content wherein the system (1) is configured to illuminate a cornea (40) with a plurality of terahertz beams and to receive a backscattered beam of the plurality of terahertz beams, a joint statistics of backscattered beams of the plurality of terahertz beams is determined, and information about the water content of the cornea (40) is determined based on the joint statistics.

Description

Technical Field

[0001] This disclosure relates to the determination of corneal water content, and more specifically, to a system and method for determining information about corneal water content gradients. Background Technology

[0002] The cornea is the transparent part at the front of the eyeball, covering the iris, pupil, and anterior chamber. The optical properties of the cornea depend on its water content, which is approximately 79% by mass. Water content is distributed in a gradient along the thickness of the cornea, with the upper (anterior surface) having a lower water content than the lower (posterior surface). The basal layer (endothelial cell layer and Descemet's membrane) is responsible for maintaining corneal tissue water content (CTWC) by actively pumping out water that diffuses naturally from the aqueous humor. Determining corneal water content is helpful for the management and care of at least a variety of diseases and can also be applied to many other applications. Summary of the Invention

[0003] The subject matter defined in the independent claims is provided in several respects. Some embodiments are defined in the dependent claims.

[0004] According to a first aspect of this disclosure, a measurement system for determining information about corneal water content is provided, wherein the system is configured to: irradiate the cornea with multiple terahertz beams and receive backscattered beams from the multiple terahertz beams, determine joint statistics of the backscattered beams from the multiple terahertz beams, and determine information about corneal water content based on the joint statistics.

[0005] An exemplary embodiment of the first aspect may include at least one feature from the following bulleted list, or any combination of the following features:

[0006] • The information regarding corneal water content includes at least one of corneal tissue water content gradient or corneal thickness;

[0007] The measurement system also includes a terahertz transmitter configured to irradiate the cornea using the multiple terahertz beams.

[0008] The measurement system also includes a terahertz receiver configured to receive the backscattered beams of the multiple terahertz beams.

[0009] • The measurement system is also configured to use the multiple terahertz beams with a frequency band between 100 GHz and 600 GHz to irradiate the cornea, preferably with a frequency band between 140 GHz and 220 GHz, between 220 GHz and 330 GHz, or between 330 GHz and 500 GHz.

[0010] The number of the multiple terahertz beams is between 20 and 30, preferably about 30;

[0011] • The number of the multiple terahertz beams is sufficient for processing material properties and for deconvolution of target positions and interference factors in the beam path;

[0012] • The measurement system is also configured to determine joint statistics by calculating the average value of the backscattered beams of the multi-beam terahertz beams;

[0013] • The measurement system is also configured to determine joint statistics by using particle swarm optimization on the backscattered beams of the multiple terahertz beams.

[0014] According to a second aspect of this disclosure, a method for determining information about corneal water content is provided, comprising: irradiating the cornea with a multi-beam terahertz wave and receiving backscattered beams of the multi-beam terahertz wave, determining joint statistics based at least on the backscattered beams of the multi-beam terahertz wave, and determining information about corneal water content based on the joint statistics. Attached Figure Description

[0015] Figure 1 A measurement system according to at least some embodiments of the present disclosure is shown;

[0016] Figure 2 The total water content is shown according to at least some embodiments of this disclosure;

[0017] Figure 3 The bound water content according to at least some embodiments of this disclosure is shown;

[0018] Figure 4 An electromagnetic model of a corneal phantom according to at least some embodiments of the present disclosure is shown;

[0019] Figure 5 Simulation results for a first frequency range according to at least some embodiments of the present disclosure are shown;

[0020] Figure 6 Simulation results for a second frequency range according to at least some embodiments of the present disclosure are shown;

[0021] Figure 7 Sensitivity analysis of three WR waveguides according to at least some embodiments of the present disclosure is shown;

[0022] Figure 8 A flowchart is shown according to at least some embodiments of the present disclosure. Detailed Implementation

[0023] Embodiments of this disclosure relate to the determination of corneal water content. More specifically, embodiments of this disclosure provide a measurement system for determining information about corneal water content based on joint statistics, which are at least further based on the backscattering beams of multiple terahertz beams. Furthermore, by using submillimeter-wave reflectance measurements, simultaneous joint extraction of posterior corneal surface water content and corneal thickness can be achieved, wherein rapid, continuous, and repeated measurements enable the definition and description of the joint statistics. The joint statistical features can be used to provide an estimate of the corneal tissue water content gradient, thereby providing an estimate of posterior corneal water content even when the penetration capability of terahertz radiation into the posterior segment is negligible.

[0024] In some embodiments, the transceiver of the measurement system can irradiate the cornea using only a single frequency at any given time. However, the scanning speed of this frequency is extremely fast, making it appear as if all frequencies are generated simultaneously on a human-perceptible timescale. Furthermore, the shape of the beam, its source location, its focal point, etc., do not actually change as the frequencies are scanned. Therefore, the irradiation can be viewed as a single beam whose "color" changes rapidly, or as multiple beams, where each frequency represents a different beam.

[0025] Conditions such as Fuchs endothelial dystrophy can impair the cornea's water retention function, leading to increased corneal tissue water content (CTWC). Furthermore, some immune responses, such as corneal transplant rejection, often present as a precursor or accompanying symptom of corneal edema. Late-stage edema can be detected visually because the overhydrated cornea appears "milky white" due to the scattering of wavelengths by the congested collagen fibers. However, relying solely on visual inspection to determine the timing of treatment often has limited effectiveness. Early and accurate quantification of corneal edema is crucial for the management and care of these ophthalmic conditions and harmful immune responses.

[0026] Current diagnostic methods limit the quantification of in vivo CTWC to corneal thickness measurement, an ophthalmic examination that measures corneal thickness and infers tissue hydration from the quantified corneal thickness measured by ultrasound or optical backscattering. However, the mapping from central corneal thickness (CCT) measured by corneal thickness measurement to corneal tissue hydration does not account for physiological variations and returns erroneous hydration values ​​for corneal thicknesses deviating from the nominal value of 580 μm. Therefore, there is a need for non-contact, in vivo CTWC quantification.

[0027] Therefore, embodiments of this disclosure can use a terahertz system to determine information about corneal water content, applicable, for example, to mapping human corneal water content via a lossy longitudinal mode coupled to the cornea. With reference to the terahertz wavelength (λ, approximately 3–0.3 mm), the cornea presents an optically smooth spherical structure whose dielectric properties vary radially due to the axial water content gradient. Furthermore, with reference to the terahertz wavelength, the natural physiological variation in the corneal radius of curvature (RoC, approximately 7.8 mm ± 0.5 mm) is negligible; therefore, the cornea can be considered a perfect sphere with an approximately fixed radius of curvature.

[0028] In the case of terahertz irradiation of the cornea, the incident field can be modeled or assumed to be a Gaussian beam whose wavefront radius of curvature matches the spherical radius of curvature at the optical axis. Since the focused spot size of the incident field is smaller than the planar radius of the cornea, the electromagnetic properties of the cornea can be modeled using effective medium theory (EMT) to calculate the effective dielectric constant at a given depth; and layered medium theory (SMT) can be used to capture the dielectric gradient and describe the aggregated, frequency-dependent complex reflection coefficients. An optimization procedure can then be applied to estimate the corneal water content and thickness based on backscattered terahertz irradiation.

[0029] The embodiments of this disclosure address at least two challenges more specifically. First, when the signal-to-noise ratio decreases and is not improved, the fitting results will be affected by non-negligible uncertainty. This uncertainty can lead to multiple combinations of corneal thickness, posterior corneal water content, and anterior corneal water content, all of which will produce the same goodness of fit. Second, the water content gradient and posterior corneal water content can be too high, preventing a significant amount of terahertz irradiation energy from reaching the posterior cornea. In this case, the capacity of the longitudinal mode is negligible, and spectral fluctuations are suppressed, which, without improvement, will introduce even greater uncertainty to the measurement.

[0030] Figure 1 A measurement system according to at least some embodiments of the present disclosure is shown. Figure 1 The measurement system (1) shown includes a terahertz transmitter (10) and a terahertz receiver (20). In some embodiments, Figure 1 The measurement system (1) shown may include a Gaussian beam irradiation device (30). The cornea is indicated by 40.

[0031] Custom optics designed to match specific antenna patterns can be used to generate near-ideal, laser-like beams, matching the curvature of the terahertz beam to the curvature of the cornea. For example, a dual-reflector antenna can be used, with its two generatrices configured to share a common annular focal point. The primary reflector can be designed with a parabolic generatrix, and the electric field distribution at the focal point can approximate a Bessel beam.

[0032] A terahertz transmitter (10) is configured to irradiate the cornea (40) with multiple terahertz beams, and a terahertz receiver (20) is configured to receive the backscattered beams of the multiple terahertz beams. Therefore, the beams interact with the cornea (40) and the aqueous humor (water) beneath it, with the interactions varying at different frequencies. These frequency-varying interactions manifest as fluctuations and variations in the amplitude and phase of reflection in the irradiation spectrum, as shown in Figure 1 (boxes next to the Gaussian beam irradiation scheme). Corneal thickness and corneal tissue water content gradients are encoded in these fluctuating spectra, and the water content gradient and thickness can be extracted by fitting the spectra.

[0033] Therefore, the system (1) is configured to irradiate the cornea (40) with the multi-beam terahertz wave and receive the backscattered beam of the multi-beam terahertz wave. The system (1) is also configured to determine joint statistics based at least on the backscattered beam of the multi-beam terahertz wave and to determine information about corneal water content based on the joint statistics. In some embodiments, the information about the water content of the cornea (40) may include a gradient of corneal (40) water content. The terahertz wave may be a Gaussian wave.

[0034] In some embodiments, the system (1) may also be configured to irradiate the cornea (40) such that the curvature of the terahertz beam matches the curvature of the cornea (40). For example, when a Gaussian beam irradiation device (30) is integrated into the system (1), the Gaussian beam irradiation device (30) may be configured to irradiate the cornea (40) such that the curvature of the terahertz beam matches the curvature of the cornea (40).

[0035] The system (1) can also be configured to irradiate the cornea with the multiple terahertz beams, the frequency band of which is between 100 GHz and 600 GHz, preferably between 140 GHz and 220 GHz, 220 GHz and 330 GHz, or 330 GHz and 500 GHz. The number of the multiple terahertz beams is between 20 and 30, preferably about 30.

[0036] Figure 2 The total water content is shown according to at least some embodiments of the present disclosure. Figure 3 The bound water content according to at least some embodiments of this disclosure is shown. Figure 2 and Figure 3 The data obtained from the eyes of isolated animals are shown. Figure 2 The report shows the total water content as a function of depth, while Figure 3This is further defined to limit the percentage of bound water in the total water content. Some sample gradients produce very strong contrast. Other samples produce near-perfect impedance matching between the cornea (40) and aqueous humor, thereby minimizing spectral fluctuations and maximizing measurement uncertainty. Therefore, embodiments of this disclosure turn the weakness of measurement uncertainty into an advantage.

[0037] Figure 4 An electromagnetic model of a corneal phantom according to at least some embodiments of the present disclosure is shown. Figure 5 Simulation results for a first frequency range according to at least some embodiments of the present disclosure are shown. Figure 6 Simulation results for a second frequency range according to at least some embodiments of the present disclosure are shown.

[0038] Figures 4 to 6 The Monte Carlo simulation experiment is shown. Figure 4 A forward model of the cornea employing layered media and effective media theory is shown. This forward model is computed over a given illumination band, with complex white Gaussian noise added, and then particle swarm optimization (PSO) is used to solve the inverse problem. Thus, the system (1) can also be configured to determine joint statistics by using PSO on the backscattered beams of the multi-beam terahertz beams.

[0039] Noise addition and inverse solving can be repeated approximately 30 times for 6 different candidate combinations of posterior surface water content and corneal thickness. The extracted posterior surface water content is plotted on [the graph / plotting table]. Figure 5 (140–220 GHz) and Figure 6 (330–500 GHz). For simplicity, the anterior surface water content was fixed. The x-axis represents central corneal thickness (CCT), and the y-axis represents corneal posterior surface water content (CPWC). Six pairs of noise-free CCT and CPWC are represented by small white circles, while the noisy Monte Carlo iteration results are distributed around each noise-free point using color markers.

[0040] It is worth noting that a very clear distribution pattern emerges in the 140-220 GHz band. The distribution in the lower CPWC rows is vertical. The middle rows are diagonally distributed, with similar spans but different slopes. The upper rows show significant differences in span length, but more similar slopes.

[0041] These characteristics can still be observed in the 330-500 GHz band, but the results appear noisier. This is not due to increased measurement noise, but rather to increased path loss of the cornea at higher frequencies, leading to reduced reflections from the back segment. Although a particular noisy point can be assigned to multiple different noise-free points, CPWC and CCT can be determined more accurately by considering the span of the point distribution and the primary and secondary distribution axes.

[0042] Uncertainty in a single measurement can lead to unacceptable errors in water content estimation. By characterizing the statistical properties of the uncertainty in multiple measurements, water content estimation errors can be significantly reduced. Therefore, according to embodiments of this disclosure, measurements are not performed only once. Instead, measurements are performed multiple times, for example, by averaging the results of multiple measurements. In this case, the system (1) can also be configured to determine joint statistics by calculating the average of the backscattered beams of the multiple terahertz beams. In some embodiments, multiple measurements can be performed, and the statistics of the measurement uncertainty can be quantified.

[0043] If we assume either of the following: (1) the CTWC gradient does not exist, or (2) the water content gradient exists and is very important, and for measurement, reflection from the rear section is required by retaining significant irradiation energy in the rear section. Assumption (1) is incorrect. Assumption (2) is risky because it is highly likely that the interaction between the irradiation field and the rear section will not be observable, and therefore, parameter extraction cannot rely on the lossy longitudinal mode.

[0044] The embodiments disclosed herein significantly reduce the risks of terahertz corneal sensing technology because they provide alternative strategies for dealing with excessive corneal path loss and / or unexpectedly high impedance matching between the anterior segment and the aqueous humor.

[0045] Figure 7 Sensitivity analysis of three WR waveguides according to at least some embodiments of this disclosure is shown. More specifically, Figure 7 The noise sensitivity analysis is shown in three WR waveguide bands (WR 5.1, WR 3.4, WR 2.2) with a signal-to-noise ratio of 40 dB. Figure 7 The diagram shows the constituent parameters extracted for six different configurations: anterior water content (AWC), posterior water content (PWC), and central corneal thickness (CCT). Each configuration has a different grayscale shade. Each column represents the same set of data, but the first row focuses on the relationship between AWC and thickness, while the second row focuses on the relationship between PWC and thickness.

[0046] exist Figure 7 In the diagram, a scatter plot illustrates an example of the joint distribution of the estimated parameters. The top row shows the joint distribution describing the relationship between the estimated pre-water content and thickness. The bottom row shows the joint distribution describing the relationship between the estimated post-water content and thickness. The distributions depend on both water content and thickness. Different correlations can be observed. The joint statistics calculated from these joint distributions can be used to form the basis of measurements.

[0047] For a given irradiation frequency band, we simulated 18 different combinations of three corneal parameters:

[0048] · → Front (front surface) moisture content → (x1) value, enter the triplet;

[0049] · → Back (back surface) moisture content → (x3) value, enter the triple;

[0050] · → Central corneal thickness → (x2) value, enter the triplet;

[0051] · → Illumination band → (x3) band, input band.

[0052] These parameters are input into a model that predicts the measurement results when a cornea described by a specific parameter triplet and a given operating frequency band is measured. The output is equivalent to a noise-free measurement. We calculated noise-free measurements for all six parameter combinations across three frequency bands, performing a total of 18 measurements. Measurement noise was then added to the noise-free results, and the resulting noisy measurement signal was input into an optimization algorithm that predicts the input triplets. For clarity, the algorithm's output for noise-free input is identical to the input parameter triplet. For noisy input, the algorithm's output is a triplet that deviates slightly from the input parameter triplet. In other words, it is the best estimate of the input parameter triplet under realistic input conditions (i.e., with noise and non-ideal factors). This process is repeated 30 times for each triplet and frequency band combination. An example is shown below. Figure 8 As shown, the results are presented in scatter plot form.

[0053] Figure 8 A flowchart illustrating at least some embodiments according to this disclosure is shown. First, the illumination frequency band can be selected. Figure 8 shows the lowest frequency band. Then, you can select the parameter triplet. Figure 8 In the example, , , Then, a measurement model can be used to generate a noiseless measurement signal Γ(f). Random noise, denoted by parameter n1, can be generated to simulate measurement noise and added to the noiseless data, thus generating noisy data. Subsequently, an estimation algorithm can be used to estimate the operating parameters from the noisy data, resulting in three estimates, denoted as […]. , and .exist Figure 8 In the scatter plot above, as indicated by the arrow above, the estimated values ​​are plotted. Compared with the estimated The relationship. In Figure 8 The scatter plot below, as indicated by the arrow below, plots the estimated values. Compared with the estimated The relationship is shown. The actual parameters are superimposed in a circular form on the scatter plots above and below.

[0054] This process can then be repeated 30 times to form a distribution of the estimated parameters. In this way, the possible range of values ​​for the estimated parameters can be visualized, given the true parameters and the fact that the measurements are affected by real-world measurement noise.

[0055] Reference Figure 7 A key concern is that if the cornea suffers excessive loss at the irradiation frequency due to: (1) excessive water content, and / or (2) excessive corneal thickness, it may be possible to acquire only the reflected signal from the anterior surface of the cornea, and not the reflected signal from the posterior surface. This results in significant uncertainty in the estimation. This uncertainty may be so great that the measurement results become unusable.

[0056] for Figure 7 In the middle column, corresponding to the 220-330 GHz frequency band, considering data points with a free water content of approximately 62% and a total thickness of 580 μm, under normal measurement noise conditions, the estimated upstream water content range is approximately 21.4%-21.7%, with a total variation of approximately 0.3%. The estimated downstream water content range is approximately 60%-64%, with a total variation of approximately 4%, which may be sufficient or insufficient.

[0057] Furthermore, it can be deduced, at least from the data points corresponding to a posterior free water content of approximately 78% and a total thickness of 680 μm, that higher water content and greater corneal thickness lead to significant loss. Under normal measurement noise conditions, the estimated anterior water content range remains essentially constant at approximately 21.4%–21.7%, with a total variation of approximately 0.3%. However, the estimated posterior water content range is approximately 73%–87%, with a total variation of approximately 14%, which is insufficient to meet the accuracy requirements.

[0058] Combining the scatter plot of post-moisture content, some points show and A moderate positive correlation exists between some points, with a small range, while another set of points exhibits a very strong positive correlation with a very large range. According to embodiments of this disclosure, multiple measurements are used to provide sufficient measurement accuracy. For example,

[0059] • It can collect a set of measurements, such as 30 measurements;

[0060] • Parameter estimation can be performed for each measurement;

[0061] • Joint statistics of estimated pre-water content and estimated corneal thickness can be determined;

[0062] • It is possible to determine the joint statistics of the estimated back water content and the estimated corneal thickness;

[0063] • Potentially, the known corneal thickness could be used to reduce the dimension of the distribution to one dimension;

[0064] • The statistical characterization of parameter estimates from multiple measurements leads to sufficient measurement accuracy.

[0065] Regarding the issue of improving the signal-to-noise ratio (SNR) of a single measurement by extending the integration or averaging time, in practical applications, it is impossible to completely eliminate noise and measurement uncertainty through averaging over a sufficiently long period because the patient and their eyes are constantly moving. This motion manifests as noise or uncertainty in the data, with a magnitude significantly greater than the measurement noise. In other words, more averaging means a worse signal.

[0066] If multiple measurements are performed as suggested above, without analyzing the uncertainties in the extracted parameter set, and all measurement results are simply summed, the signal-to-noise ratio will not be improved to reduce uncertainty. This is because the slight differences in the physical location of the cornea between each measurement can cause the averaging process to lose coherence.

[0067] In some embodiments, optical coherence tomography (OCT) can be used for two reasons. First, it ensures that terahertz measurements of the cornea are obtained when the cornea is in the correct position. An OCT system can provide this information in real time, with a depth resolution of approximately 9 µm, about 1 / 100th of the wavelength. Second, OCT can also be used to obtain reference values ​​for corneal thickness.

[0068] It should be understood that the embodiments disclosed herein are not limited to the specific structures, process steps, or materials disclosed herein, but cover equivalent technical solutions that can be recognized by those skilled in the art. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0069] In this specification, references to "an embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of this disclosure. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing in different places in this specification do not necessarily refer to the same embodiment. When numerical values ​​are mentioned using terms such as, for example, "about" or "substantially," their precise values ​​are also disclosed.

[0070] In this document, for ease of description, multiple items, structural elements, components, and / or materials may be listed in a common list. However, such a list should be interpreted as each member being individually considered a separate and unique entity. Therefore, unless stated to the contrary, no individual member of the list should be considered factually equivalent to other members of the same list simply because it is included in the same group. Furthermore, various embodiments and examples of this disclosure are described herein in conjunction with alternatives to its components. It should be understood that these embodiments, examples, and alternatives should not be considered factual equivalents of each other, but rather should be regarded as independent and autonomous technical solutions embodied in this disclosure.

[0071] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the foregoing description, various specific details such as length, width, and shape have been set forth to provide a thorough understanding of the embodiments of this disclosure. However, those skilled in the art will recognize that this disclosure can be implemented without using one or more of the above-described specific details, or using other methods, components, materials, etc. In other instances, well-known structures, materials, or operations have not been shown or described in detail to avoid obscuring relevant aspects of this disclosure.

[0072] While the foregoing examples illustrate the principles of this disclosure in one or more specific applications, it will be apparent to those skilled in the art that various modifications in form, use, and implementation details may be made without inventive effort and without departing from the principles and concept of this disclosure. Therefore, this disclosure is not intended to be limited except as defined in the appended claims.

[0073] In this specification, the verbs “comprising” and “including” are used as open-ended qualifiers, neither excluding nor requiring the presence of undescribed features. Unless otherwise expressly stated, the features described in the dependent claims can be freely combined with each other. Furthermore, it should be understood that the use of “a” or “an” (i.e., the singular form) throughout this document does not exclude plural cases.

[0074] As used herein, “at least one of the following: ”, “at least one of ”, and similar expressions, wherein two or more elements are connected by “and” or “or”, means at least any one element, or at least any two or more elements, or at least all elements.

[0075] Industrial applicability

[0076] At least some embodiments of this disclosure can be applied to the determination of corneal water content.

[0077] List of abbreviations

[0078] Anterior Water Content (AWC)

[0079] CCT (Central Corneal Thickness)

[0080] CPWC Corneal Posterior Water Content

[0081] CTWC Corneal Tissue Water Content

[0082] EMT (Effective Media Theories)

[0083] Optical coherence tomography (OCT)

[0084] Posterior water content after PWC

[0085] RoC (Radius of Curvature)

[0086] SMT (Stratified Media Theory)

[0087] SNR (Signal to Noise Ratio)

[0088] List of reference numerals

[0089]

Claims

1. A measurement system for determining information about corneal water content, wherein, The system is configured as follows: - Irradiate the cornea with multiple terahertz beams and receive the backscattered beams of the multiple terahertz beams; - Determine the joint statistics of the backscattered beams of the multi-beam terahertz beam; as well as - Information about the corneal water content is determined based on the joint statistics.

2. The measurement system according to claim 1, wherein, The information regarding the corneal water content includes at least one of the corneal tissue water content gradient or the corneal thickness.

3. The measurement system according to claim 1 or 2, wherein, The measurement system also includes: - A terahertz emitter configured to irradiate the cornea using the multiple terahertz beams.

4. The measurement system according to any of the preceding claims, wherein, The measurement system also includes: - A terahertz receiver configured to receive the backscattered beams of the multiple terahertz beams.

5. The measurement system according to any of the preceding claims, wherein, The measurement system is also configured to: - Irradiate the cornea with the multi-beam terahertz wave with a frequency band between 100 GHz and 600 GHz, preferably between 140 GHz and 220 GHz, between 220 GHz and 330 GHz, or between 330 GHz and 500 GHz.

6. The measurement system according to any of the preceding claims, wherein, The number of the multiple terahertz beams is between 20 and 30, preferably about 30.

7. The measurement system according to any of the preceding claims, wherein, The number of terahertz beams is sufficient for processing material properties and for deconvolution of target positions and interference factors in the beam path.

8. The measurement system according to any of the preceding claims, wherein, The measurement system is also configured to: - The joint statistics are determined by calculating the average value of the backscattered beams of the multiple terahertz beams.

9. The measurement system according to any of the preceding claims, wherein, The measurement system is also configured to: - The joint statistics are determined by using particle swarm optimization on the backscattered beams of the multi-terahertz beams.

10. A method for determining information about corneal water content, comprising: - Irradiate the cornea with multiple terahertz beams and receive the backscattered beams of the multiple terahertz beams; - Joint statistics are determined at least based on the backscattered beams of the multi-beam terahertz beams; as well as - Information about the corneal water content is determined based on the joint statistics.

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