Computer-implemented method, computer program and system for determining ophthalmic parameters - Patents.com

Abstract

A computer-implemented method, computer program, system, and method for analyzing time-velocity curves and calculating ophthalmic parameters based on the time-velocity curves.

Description

[Technical Field]

[0001] The present disclosure relates to computer-implemented methods, computer programs, systems and methods for determining ophthalmic parameters such as intraocular pressure, corneal thickness, tear film thickness, and corrected intraocular pressure. [Background technology]

[0002]

[0002] The cornea is the outermost transparent layer of the eye and plays a key role in human vision. It accounts for approximately 70% of the eye's refractive power, particularly in the central region where light passes toward the retina. The central corneal thickness (CCT), which is the thickness of the central portion of the cornea, is the most important factor in corneal stability. The CCT thickness averages 530±10 μm in humans and ranges from 300 to 1500 μm in animals, depending on the species. This thickness value is used by ophthalmologists in clinical routines as a diagnostic parameter for diseases such as glaucoma, as well as a preoperative parameter for surgical procedures such as refractive surgery and corneal transplants.

[0003] In a healthy eye, the cornea is covered by a thin layer of viscous liquid called the tear film. The tear film is approximately 5 μm thick and covers the outer mucosal surface of the eye. The tear film forms the interface between the ocular surface and the surrounding environment. When the tear film is too thin, a condition called dry eye disease occurs. Symptoms range from mild eye burning and itching to severe corneal perforation.

[0004]

[0004] Intraocular pressure is the pressure caused by the constant regeneration of fluid within the eye, and increases in diseases such as glaucoma.

[0005]

[0005] Glaucoma is a chronic, end-stage disease that, if left untreated, can cause irreversible damage to the eye. Patients with glaucoma gradually lose central vision until complete degeneration occurs. Individuals with elevated intraocular pressure are at increased risk of developing glaucoma. While timely diagnosis of the disease can effectively improve disease management, delayed diagnosis can result in permanent damage and require more complex treatment.

[0006]

[0006] Intraocular pressure (IOP) is an ocular diagnostic parameter that plays an important role in the timely diagnosis of ocular diseases such as glaucoma. Accurate measurement of IOP helps improve the diagnosis of glaucoma patients.

[0007]

[0007] Due to the direct measurement of IOP through the corneal interface, CCT influences the measurement of intraocular pressure. This is systematically ignored due to the lack of a reliable technique for simultaneous measurement of CCT and IOP. As a result, IOP measurements are often accompanied by systematic errors. IOP values ​​can be defined in two ways: a) uncorrected IOP and b) corrected IOP.

[0008]

[0008] Uncorrected IOP is measured using a fixed, preset CCT reference value, i.e., 530 μm, without taking into account the actual thickness of the cornea. For example, U.S. Patent Application Publication No. 2018 / 368681 A1 describes an apparatus and method for measuring uncorrected IOP. Existing devices for measuring uncorrected IOP, while generally inexpensive, lack sufficient accuracy, especially when measuring in eyes that have previously undergone refractive surgery and therefore have a thinner CCT than normal. IOP inaccuracy is also a problem when measuring in a variety of animals with a wide range of CCTs.

[0009]

[0009] Corrected intraocular pressure is a parameter used to normalize the effect of central corneal thickness on intraocular pressure relative to a specific reference thickness. Corrected intraocular pressure is more accurate and important than uncorrected intraocular pressure, and requires more expensive and sophisticated equipment. Current technology measures corneal thickness and uncorrected intraocular pressure independently, and then calculates corrected IOP from the measured parameters. Each of these measurements requires expensive equipment.

[0010]

[0010] Today, there is a growing demand for laser surgical procedures (surface ablation), such as LASIK (laser in-situ keratomileusis), LASEK (laser subepithelial keratectomy), and PRK (photorefractive keratectomy), and the corneal thickness of patients who have undergone such interventions is significantly thinner. These patients are at risk of IOP underestimation and therefore misdiagnosis of glaucoma if the IOP is measured uncorrected.

[0001] Therefore, there is a clear need for a simpler, faster, and less expensive method of measuring ophthalmic parameters such as corrected intraocular pressure. Summary of the Invention

[0011]

[0011] It is an object of the present disclosure to provide a computer-implemented method for determining ophthalmic parameters such as intraocular pressure, corneal thickness, tear film thickness, and corrected intraocular pressure.

[0012] Another object is to provide a computer program, system and method for calculating such ophthalmic parameters.

[0013]

[0013] The invention is defined by the accompanying independent claims. Non-limiting embodiments will become apparent from the dependent claims, the accompanying drawings and the following description.

[0014] According to a first aspect, there is provided a computer-implemented method for analyzing a time-velocity curve comprising registered velocities and times of a probe body during movement of the probe body in a first direction towards the outer corneal surface of a subject's eye, during impact of an end of the probe body with the outer corneal surface when it comes to a complete stop on the eye, and during rebound movement of the probe body in a second direction opposite the first direction, the method comprising the steps of calculating the intraocular pressure of the eye as the slope of the time-velocity curve between the time when the end of the probe body first impacts the outer corneal surface and the time when the probe body comes to a complete stop on the eye; and calculating a velocity V of the probe body on the time-velocity curve at the moment of contact of the end of the probe body with the outer corneal surface. rand the velocity V of the probe body in the time-velocity curve at the moment when the probe body leaves the outer surface of the cornea during the bouncing movement of the probe body in the second direction. b and calculating the central corneal thickness using:

[0015] The probe body has no velocity in either the first or second direction when it comes to a complete stop at the eye.

[0016]

[0016] Here, the central area of ​​the outer surface of the cornea refers to the area in the center of the pupil of the eye, and the diameter of the central area can be less than 2 mm.

[0017] The velocity V of the probe body at the moment of contact of the tip of the probe with the outer surface of the cornea is r and the velocity V of the probe body at the moment the end of the probe body leaves the outer surface of the cornea during the bouncing movement of the probe body in the second direction. b The central corneal thickness is calculated from the speed-velocity curve using any nonlinear, linear, or piecewise linear function of the time-velocity curve.

[0018] The intraocular pressure obtained is the so-called uncorrected intraocular pressure, which is obtained without taking into account the actual thickness of the cornea. When calculating this pressure, the gradient can be measured as the average gradient, for example by using three uniformly distributed points on the gradient.

[0019]

[0019] In eyes that have previously undergone refractive surgery and have a thinner than normal corneal thickness, the uncorrected intraocular pressure may be incorrect. Furthermore, corneal thickness varies widely in different animals.

[0020] In this computer-implemented method, the uncorrected intraocular pressure and the central corneal thickness are calculated from the same time-rate curve, and the computer-implemented method may then use both values ​​to calculate the corrected intraocular pressure.

[0021] According to a second aspect, there is provided a computer program comprising instructions which, when executed by a computer, cause a computer to perform an analysis of a time-velocity curve comprising registered velocities and times of the probe body during movement of the probe body in a first direction towards the outer corneal surface of the subject's eye, during impact of the end of the probe body with the outer corneal surface when it comes to a complete halt on the eye, and during rebound movement of the probe body in a second direction opposite to the first direction, wherein the computer calculates the intraocular pressure of the eye as the slope of the time-velocity curve between the time when the end of the probe body first impacts the outer corneal surface and the time when the probe body comes to a complete halt on the eye, and the velocity V of the probe body in the time-velocity curve at the moment of contact of the end of the probe body with the outer corneal surface is calculated. r and the velocity V of the probe body in the time-velocity curve at the moment when the probe body leaves the outer surface of the cornea during the bouncing movement of the probe body in the second direction. b A computer program is provided that causes a computer to calculate central corneal thickness using:

[0022]

[0022] In this computer-implemented method or computer program, D=C·exp(τ)+L (where C and L are constants) τ=(V r 2 -v b 2 )(1-exp(-K logp)) / V r 2 (where K is a constant) and The central corneal thickness may be calculated from the above formula.

[0023]

[0023] C, L, and K are constants that can be determined from time-rate curves obtained using an artificial eye model with adjustable intraocular pressure and different central corneal thicknesses. Alternatively, the constants can be determined from time-rate curves of eyes of freshly deceased animals, such as cows, by creating different corneal thicknesses by cutting the cornea, as well as by pressurizing the eye with aspiration or by injecting liquid into the eye. Three reference settings may be used to obtain the values ​​of C, L, and K: a corneal thickness of 30 μm and intraocular pressures of 10, 20, and 30 mmHg; a corneal thickness of 530 μm and intraocular pressures of 10, 20, and 30 mmHg; and a corneal thickness of 1500 μm and intraocular pressures of 10, 20, and 30 mmHg.

[0024]

[0024] The computer program may further include instructions that cause the computer to calculate a corrected intraocular pressure using the calculated corneal thickness and intraocular pressure.

[0025]

[0025] The computer-implemented method may further include calculating a corrected intraocular pressure using the calculated corneal thickness and intraocular pressure.

[0026]

[0026] Corrected intraocular pressure is a parameter used to unify the effect of central corneal thickness on intraocular pressure. Corrected intraocular pressure is more accurate and important than uncorrected intraocular pressure. Typically, measuring corrected intraocular pressure requires expensive and sophisticated equipment. With current technology, corneal thickness and uncorrected intraocular pressure can be calculated from the exact same time-rate curve, and then the corrected pressure can be calculated using the calculated parameters. Therefore, this computer-implemented method and computer program present a simple, fast, and cost-effective way to determine corrected intraocular pressure.

[0027] Based on the calculated corneal thickness and intraocular pressure, a new curve (velocity, time) is reconstructed and simulated using sophisticated algorithms and geometric equations, and the corrected intraocular pressure is determined from this new curve.

[0028]

[0028] The computer program may further include instructions that cause the computer to calculate the tear film thickness on the outer surface of the cornea from the time-rate curve, where the tear film thickness L is calculated as follows:

[0029]

[0029]

number

[0030]

[0030] V(t) is the velocity-time profile of the probe body registered during the collision-rebound path of the probe body from the time when the end of the probe body collides with the eye and comes to a complete stop at the eye until the probe body leaves the eye. (T t ,V t ) is the time when the end of the probe body first impacts the tear film on the outer surface of the cornea, and (T c ,V c ) is the point at which the end of the probe body first impacts the outer surface of the cornea.

[0031]

[0031] The computer-implemented method may further include calculating the tear film thickness on the outer surface of the cornea from the time-velocity curve, where the tear film thickness L is calculated as follows:

number

[0032] In a healthy eye, the cornea is covered by a thin layer of viscous fluid, the tear film, thought to be approximately 5 μm thick. The tear film forms the interface between the ocular surface and the surrounding environment. When the tear film is insufficiently thick, a condition known as dry eye disease results. Symptoms range from mild itchy eyes to severe corneal perforation.

[0033]

[0033] According to the above-described computer-implemented method and computer program, the exact same time-rate curves can be used to calculate the tear film thickness, corneal thickness, intraocular pressure, and corrected intraocular pressure.

[0034] According to a third aspect, there is provided a system for determining an ophthalmic parameter of a subject, comprising a probe and a processor, the processor registering a velocity and time of the probe body during movement of the probe body in a first direction towards the outer corneal surface of the subject's eye, during impact of an end of the probe body with the outer corneal surface when it comes to a complete stop on the eye, and during a rebound movement of the probe body in a second direction opposite to the first direction; calculating, based on a curve obtained from the registered velocity and time of the probe body, the intraocular pressure of the eye as the slope between the time when the end of the probe body first impacts the outer corneal surface and the time when the probe body comes to a complete stop on the eye; and calculating, based on the time-velocity curve, the velocity V of the probe body at the moment of contact of the end of the probe body with the outer corneal surface. r and the velocity V of the probe body at the moment the end of the probe body leaves the outer surface of the cornea during the bouncing movement of the probe body in the second direction. b and calculating the central corneal thickness using the calculated corneal thickness.

[0035] The probe is positioned such that the end of the probe body is a distance from the outer corneal surface, such distance being, for example, 3 to 8 mm, before the probe body is moved in a first direction toward a central area of ​​the outer corneal surface.

[0036] The end of the probe body may be adapted to impinge on the outer corneal surface in a direction substantially perpendicular to the outer corneal surface and the pupil, meaning that the direction may be exactly perpendicular or may deviate from exactly perpendicular by up to ±2.5°.

[0037] Corneal thickness measurements are considered reliable when performed within the vicinity of the center of the cornea, approximately 1 mm. Outside this circle, the measured thickness may not represent the central corneal thickness.

[0038] In the above-described system, the probe may include a magnetic probe body having a first end and an opposite second end, and a non-magnetic tube having a first end and an opposite second end, the magnetic probe body being slidably disposed therein, the first end of the probe body and the first end of the tube being oriented in the same direction. A magnetic field may be present that is configured to move the probe body in a first direction from a first position on the tube to a second position, at least to the second position where the first end of the probe body extends from the first end of the tube, and the first end of the probe body may be configured to impact the outer surface of the cornea of ​​the subject's eye at the second position.

[0039]

[0039] The system may further include an optical unit positioned at the second end of the non-magnetic tube and aligned concentrically with the tube, configured so that light emitted from the optical unit passes through the non-magnetic tube, passes toward the first end of the non-magnetic tube, and is directed toward an outer corneal surface positioned perpendicularly at a distance from the first end of the tube, where it is reflected from the outer corneal surface to indicate the area on the outer corneal surface where the first end of the probe collides with the outer corneal surface.

[0040]

[0040] The optical unit may be adapted to control the position of impact of the end of the probe body with the outer corneal surface by emitting light in a direction toward the outer corneal surface, which is the direction of movement of the probe body as it moves toward the outer corneal surface, before moving the probe body toward the outer corneal surface, and the light reflected from the outer corneal surface indicates the area on the outer corneal surface where the end of the probe body will impact the outer corneal surface. Optionally, the position where the end of the probe body impacts the outer corneal surface can be adjusted by adjusting the position of the probe body relative to the outer corneal surface based on the position indicated by the light on the outer corneal surface.

[0041] The light may be emitted using a cylindrical, concentric optical path aligned with the path of the probe body, for example, by using an LED light source to produce a circular light approximately 2.6 mm in diameter at the corneal surface, indicating the area where the probe body impinges on the outer corneal surface.

[0042]

[0042] Thus, the area of ​​the corneal surface that is impacted by the end of the probe body may be the central area of ​​the cornea.

[0043] If the reflected light indicates that the surface where the end of the probe body strikes the outer corneal surface is already in the center of the outer corneal surface, no adjustment is necessary.

[0044]

[0044] The emitted light may be synchronous light.

[0045] The optical unit may be disposed inside a non-magnetic tube.

[0046]

[0046] The above-described system may further comprise a display for displaying the calculated ophthalmic parameters.

[0047] The ophthalmic parameters displayed may be one or more of intraocular pressure, central corneal thickness, corrected corneal pressure, and tear film thickness.

[0048]

[0048] According to a fourth aspect, there is provided a method for determining an ophthalmic parameter of a subject, the method comprising the steps of: providing a probe body having a first end and an opposite second end; positioning the probe body so that the end of the probe body is a distance from the outer corneal surface of the subject's eye; moving the probe body in a first direction towards a central area of ​​the outer corneal surface until the end of the probe body impacts the outer corneal surface and comes to a complete stop on the eye; and registering the velocity and time of the probe body during the impact path of the probe body as it moves in the first direction, during the time when the probe body impacts the outer corneal surface and comes to a complete stop on the eye, and during the bounce path of the probe body as it moves from a complete stop on the eye in a second direction opposite the first direction until it leaves the eye. Also, based on the curve obtained from the registered velocity of the probe and time, the intraocular pressure of the eye is calculated as the slope between the time when the end of the probe body first impacts the outer surface of the cornea and the time when the probe body comes to a complete stop in the eye, and based on said time-velocity curve, the velocity V of the probe body at the moment of contact of the end of the probe body with the outer surface of the cornea is calculated. r and the velocity V of the probe body at the moment the end of the probe body leaves the outer surface of the cornea during the rebound of the probe body in the second direction. b and are used to calculate the central corneal thickness.

[0049]

[0049] This method may also include the step of calculating a corrected intraocular pressure based on the calculated intraocular pressure and corneal thickness.

[0050]

[0050] This method may be performed using the system described above. [Brief explanation of the drawings]

[0051] [Figure 1]

[0051] Figure 1 shows a system comprising a magnetic probe body configured to move through a magnetic field, the device being used to measure ophthalmic parameters of a patient's eye based on the registered velocity and time of the probe body during movement of the probe body, during impact with the outer surface of the cornea of ​​the eye (impact phase), and during rebound of the probe.

[0052] [Figure 2] FIG. 2 shows the system of FIG. 1 arranged in a casing.

[0053] [Figure 3]

[0053] Figure 3 is a graph of the velocity versus time of the probe body of the system shown in Figure 1 at different positions on the eye, including a) the position where the probe body collides with the tear film covering the outer surface of the cornea, b) the position where the probe body collides with the outer surface of the cornea, c) the position where the probe body comes to rest on the eye, and d) the position where the probe body leaves the eye.

[0054] [Figure 4] FIG. 4 is a schematic diagram illustrating a method for measuring ophthalmic parameters of a subject.

[0055] [Figure 5]

[0055] Figures 5 and 6 are graphs of the same type as those shown in Figure 3, reconstructed using values ​​of corneal thickness and intraocular pressure calculated from the original graph (solid line), and are reconstructed graphs (dashed lines) used to calculate corrected intraocular pressure. [Figure 6]

[0055] Figures 5 and 6 are graphs of the same type as those shown in Figure 3, reconstructed using values ​​of corneal thickness and intraocular pressure calculated from the original graph (solid line), and are reconstructed graphs (dashed lines) used to calculate corrected intraocular pressure. Detailed Description of the Invention

[0056]

[0056] The central corneal thickness (CCT), which is the thickness of the central part of the cornea, is the most important factor in corneal stability, and is 530±10 μm on average in humans and 300-1500 μm in animals, depending on the species. This thickness value is not only used in clinical routine by ophthalmologists as a diagnostic parameter for diseases such as glaucoma, but also as a procedural preoperative parameter for surgical procedures such as refractive surgery and corneal transplantation.

[0057] In a healthy eye, the cornea is covered by a thin layer of viscous fluid, the tear film (approximately 5 μm thick). The tear film forms the interface between the ocular surface and the surrounding environment. When the tear film is too thin, a condition called dry eye disease occurs. Symptoms range from mild itching to severe corneal perforation.

[0058]

[0058] Intraocular pressure is the pressure caused by the constant regeneration of fluid within the eye, and increases in the presence of diseases such as glaucoma.

[0059]

[0059] Accurate measurement of intraocular pressure helps improve diagnosis in glaucoma patients. Intraocular pressure can be defined in two ways: a) uncorrected or b) corrected pressure.

[0060]

[0060] Uncorrected pressure is measured without taking into account the actual thickness of the cornea, and therefore is not sufficiently accurate, especially when measuring in eyes that have previously undergone refractive surgery and have thinner than normal corneas.

[0061]

[0061] Corrected intraocular pressure is a parameter used to unify the effect of central corneal thickness on intraocular pressure. Corrected intraocular pressure is more accurate and important than uncorrected intraocular pressure and has traditionally required more expensive and sophisticated equipment. In current technology, corneal thickness and uncorrected intraocular pressure are measured independently, and then the corrected pressure is calculated from the measured parameters.

[0062]

[0062] Below, we describe a computer-implemented method, computer program, system 1, and method for calculating ophthalmic parameters such as corneal thickness, tear film thickness, uncorrected intraocular pressure, and corrected intraocular pressure from the exact same time-velocity curve.

[0063]

[0063] Figure 1 shows a non-invasive system 1 comprising a magnetic probe 2 configured to move in a magnetic field. The system can be used to measure ophthalmic parameters of the eye of a human or animal patient. Figure 2 shows the system of Figure 1 with a display 20 arranged on the casing for displaying the calculated ophthalmic parameters. Figure 4 shows a schematic diagram of how the system can be used to measure ophthalmic parameters.

[0064]

[0064] The system 1 includes a magnetic probe 2 having a first end 2a and an opposite second end 2b. The probe may be disposed in a non-magnetic tube 4 having a first end 4a and an opposite second end 4b. The magnetic probe 2 may be slidably disposed in the non-magnetic tube, with the probe first end 2a and the tube first end 4a oriented in the same direction. The probe 2 is configured to move in a magnetic field. The magnetic field may be provided by a pair of coils 6a, 6b.

[0065] 1, the magnetic field may accelerate the probe 2 in a first direction within the tube 4, causing the first end 2a of the probe 2 to extend from the first end 4a of the tube 4. Also, the first coil 6a may be activated by applying a voltage to push the probe in the first direction.

[0066]

[0066] A probe body 2 is provided (100), and the probe 2 is positioned (101) so that a first end 2a of the probe 2 is a certain distance from the outer surface of the cornea of ​​the subject's eye, whereby the magnetic field causes the probe 2 to move in a first direction toward a central area of ​​the outer surface of the cornea until the first end 2a impacts the outer surface of the cornea in a direction perpendicular to the surface and comes to a complete stop on the eye (the impact path of the probe body 2). A probe body 2 is provided (100), and the first end 2a of the probe 2 may be positioned (101) so that the first end 2a of the probe 2 is a certain distance (e.g., 3 to 8 mm) from the outer surface of the cornea of ​​the subject's eye.

[0067]

[0067] When the probe body 2 comes into contact with the outer surface of the cornea of ​​the eye, it starts to decelerate and bounces off the eye. As a result, a voltage determined by the intraocular pressure is induced in the second coil 6b. This voltage and velocity of the probe body 2 may be detected by the second coil 6b and registered by the processor 5 (103). The waveform of the resulting registered amplified signal (velocity-time) at the output of the second coil 6b is shown in the graph of Figure 3. At position a), the probe body 2 collides with the tear film covering the outer surface of the cornea; at position b), the probe body collides with the outer surface of the cornea; at position c), the probe body stops at the eye; and at position d), the probe body leaves the eye (i.e., the first end 2a of the probe 2 retracts from the outer surface of the cornea due to the absence of a uniform tear film in the rebound path of the probe body 2).

[0068] A computer program may be used that includes instructions that, when executed by a computer, cause the computer to perform an analysis of a time-velocity curve such as the curve shown in Figure 3. The time-velocity curve may be registered using the system described above, or may be registered using another system that provides the same type of speed-velocity curve.

[0069] The computer program causes the computer to calculate the intraocular pressure p of the eye as the slope of the time-velocity curve between (b) the moment when the end of the probe body 2 first impacts the outer surface of the cornea and (c) the moment when the probe body 2 comes to a complete stop on the eye, and calculates the velocity V of the probe body 2 on the time-velocity curve at (b) the moment when the end 2a of the probe body 2 comes into contact with the outer surface of the cornea. r and the velocity V of the probe body 2 in the time-velocity curve at the moment when the probe body 2 leaves the outer surface of the cornea during the rebound movement of the probe body 2 in the second direction. b and may be used to allow a computer to calculate the central corneal thickness D.

[0070]

[0070] The computer program may be adapted to be used by the processor 5. The calculations performed by the computer program may be displayed on the display 20.

[0071] A computer-implemented method may be used to analyze a time-velocity curve such as that shown in Figure 3. The time-velocity curve may be registered using the system described above, or may be registered using another system that provides the same type of speed-velocity curve. The computer-implemented method calculates the intraocular pressure p of the eye as the slope of the time-velocity curve between (b) the moment when the end of the probe body 2 first impacts the outer surface of the cornea and (c) the moment when the probe body 2 comes to a complete stop on the eye, and calculates the velocity V of the probe body 2 on the time-velocity curve at the moment (b) of contact of the end 2a of the probe body 2 with the outer surface of the cornea. r and the velocity V of the probe body 2 in the time-velocity curve at the moment when the probe body 2 leaves the outer surface of the cornea during the rebound movement of the probe body 2 in the second direction. band calculating the central corneal thickness D using the above-described method. This computer-implemented method may be used by processor 5. Calculations performed in this computer-implemented method may be displayed on display 20. The time-velocity curve may be registered using the system described above, or may be registered using another system that provides the same type of time-velocity curve.

[0072]

[0072] The central corneal thickness D is, for example, D=C·exp(τ)+L (where C and L are constants) τ=(V r 2 -v b 2 )(1-exp(-K logp)) / V r 2 (where K is a constant and V r is the velocity of the probe 2 at the moment (b) of contact of the first end 2a of the probe 2 with the outer surface of the cornea in the collision path of the probe body 2, and V b is the velocity of the probe body 2 at the moment when the first end 2 a of the probe body 2 leaves the outer surface of the cornea in the rebound path of the probe body 2), It may be calculated from (105).

[0073] The intraocular pressure obtained as above is the so-called uncorrected intraocular pressure, which is obtained without taking into account the actual thickness of the cornea. When calculating this pressure, the gradient is calculated as the average gradient p = Δprobe speed / Δtime The pressure may be measured as ρ = ρ ⁢ ...

[0074] The area under the curve in the collision path is the amount of longitudinal movement of the probe body into the eye. The area under the curve in the bounce path is equal to the area under the collision path. Intraocular pressure is inversely related to the amount of longitudinal movement of the probe body in the collision or bounce path (see Figure 3).

[0075]

[0075] The probe body 2 may be a magnetic iron rod and may have a plastic cap (probe tip) at its first end 2a. Two coils 6a, 6b are present in a non-magnetic tube 4 (which may be in the form of a pulley cylinder). When each coil is excited with an electric pulse, a relatively strong magnetic field is generated inside the non-magnetic tube 4, causing the probe body 2 to move within the tube 4. The non-magnetic tube 4 may be constructed of aluminum.

[0076]

[0076] Corneal thickness has a very direct logical relationship to the rate of loss of mechanical energy of the probe body 2 after impacting the outer surface of the cornea. The energy loss is determined by calculating the difference between the compressibility at the moment of contact with the eye and the acceleration at the moment the eye is decompressed.

[0077]

[0077] A portion (less than 10%) of these kinetic energy losses is due to the formation of intraocular pressure by the viscoelastic fluid (gel-like fluid) inside the eye, and the amount of energy loss due to the gel-like fluid inside the eye is equal to the magnitude of the pressure. The lower the pressure inside the eye, the greater the loss, and the higher the pressure, the smaller the loss. If the compression velocity at the moment of contact with the eye is V r and the velocity of the probe body at the moment it leaves the eye is V b is.

[0078]

[0078] Compression kinetic energy E at both moments r (compressive kinetic energy at the time of impact), kinetic energy E when the probe body leaves the eye b In addition, the energy loss and corneal thickness are given by the following equations:

[0079]

[0079] E r =0.5mV r 2 , and E b =0.5mV b 2 , and E tp =(E r -E b )=0.5m(V b 2 -V r 2 )

[0080]

[0080] E tp has the total amount of energy loss related to corneal thickness (more than 90% of the total loss) and intraocular pressure (the gel-like fluid inside the eye (less than 10% of the total energy loss)), and E p is the energy loss rate due to intraocular pressure, E t is the amount of energy loss by the cornea, and m is the mass. Therefore, the amount of energy loss by the cornea can be calculated using the following formula: E t =E tp (1-exp(-K logp)) (where K is a constant, p is the intraocular pressure, exp is the mathematical exponential function, log is the mathematical logarithm function, and E t is the energy loss through the cornea, and E tp is the total energy loss due to the cornea and intraocular pressure) Eyes and E t / E r The amount of corneal thickness indicates the thickness of the cornea, and the amount of corneal thickness correlates with the amount of energy loss by the cornea.

number

[0081] The constants C and L can be determined in a pre-calibration procedure of the device to allow for measurement of a wide range of corneal thicknesses, typically ranging from 100 micrometers to 1500 micrometers. In the system setup, C and L can have values ​​of, for example, 781 and 805, respectively.

[0082] In the example above, V r = 2 m / s, V b Using parameters and constants with values ​​of =1.6 m / s, K=3, p=7 mmHg, C=781, and L=-805, the central corneal thickness D was calculated to be 530 micrometers.

[0083]

[0083] The method may further include, before moving (102) the probe body 2 toward the outer corneal surface (b), controlling (101b) the position of impact (b) of the first end 2a with the outer corneal surface by emitting light in a direction toward the outer corneal surface, which is the direction of movement of the probe body 2 when moving (102) toward the outer corneal surface. The light reflected from the outer corneal surface indicates the area on the outer corneal surface where the first end 2a of the probe 2 impacts the outer corneal surface. Thereafter, optionally, the position of the probe 2 relative to the outer corneal surface is adjusted based on the position indicated by the light on the outer corneal surface, thereby adjusting the position of the probe 2 relative to the outer corneal surface.

[0084] An optical unit 7 may be disposed at the second end 4b of the non-magnetic tube 4 to emit light, the light being configured to pass through the non-magnetic tube 4, pass toward the first end 4a of the non-magnetic tube 4, and be reflected toward the outer corneal surface (b) positioned perpendicularly at a distance from the first end 4a of the tube 4, thereby indicating the area on the outer corneal surface where the first end 2a of the probe body 2 impinged upon the outer corneal surface. The emitted light is visible to the patient, thereby indicating to the user of the device the location of the light impinging upon the ocular surface. The user uses the reflected light from the patient's eye to subjectively locate the central vertical position of the patient's eye.

[0085]

[0085] The method may further include calculating (106) by the processor the tear film thickness L on the outer surface of the cornea, where L is determined from:

number

[0086]

[0086] The lacrimal layer (tear film) is an intermediate liquid between the cornea and air, and is a substance (liquid) different from the cornea (solid) and air (gas). It has a compressive movement and a compression stopping coefficient different from the compressive stopping coefficient in the corneal layer. The compressive coefficient in the cornea is ε c , the compressibility coefficient in the tear film is ε t , the compressibility coefficient in air is ε a If , then the following holds: ε a <ε t <ε c The result is an acceleration at compression stop, i.e., the same slope as the velocity-time curve resulting from flexion. The return in the graph shown in Figure 3 is as follows: Slope is the compression acceleration. Slope a <Slope t <Slope c As a result, the point of compression from the air to the first point of the tear or eye layer (T t , V r ) and then the point of compression at the cornea (T c , V c ), the magnitude of the compression distance at these two points, i.e., the tear film thickness, can be calculated as follows:

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[0087] Based on / using the calculated corneal thickness D and intraocular pressure p, a corrected intraocular pressure Pc may be calculated 107. This may be performed as follows, and is shown in the graphs of Figures 5 and 6:

[0088] 5 shows as solid lines the registered velocity and time of the probe body 2 during the collision path of the probe during its movement in a first direction, during its collision with the outer surface of the cornea and its complete stop at the eye, and during the rebound path of the probe body 2 in a second direction opposite the first direction. In this example, the corneal thickness determined by this signal was 580 μm and the calculated intraocular pressure was 20 mmHg.

[0089] This measurement signal can then be reconstructed for a "normal" corneal thickness of 530 μm (the average human corneal thickness is 530±10 μm) and an intraocular pressure of less than 20 mmHg. When the measured corneal thickness is as thick as 580 μm, the pressure readings from the instrument are higher, so a pressure of less than 20 mmHg is used.

[0090] The measured signal can be reconstructed as a reconstructed signal (dashed line in FIG. 5) as follows: 1) V when the corneal thickness is 530 microns b is found from the equation for τ (see above). 2) V r is the V obtained for the measurement signal r is the same as 3) The gradient rate of the bounce path of the probe body 2 is the measured and reconstructed value V b and time. 4) The magnitude of the velocity over time in the bounce path of the probe body is calculated point by point based on the gradient rate and the actual signal. 5) The area under the reconstruction curve in the bounce path of the probe body is calculated (the amount of dip of the probe on the surface of the eye). 6) The amount of drop during the impact phase is the same as during the rebound phase. 7) The ratio of the gradient rate of the impact phase to the gradient rate of the rebound phase is calculated based on the actual measurement signal (the biomechanical properties of the cornea) and is assumed to be the same as the reconstructed signal. Then, the gradient rate of the impact phase is calculated. 8) The velocity-time curve is reconstructed for the impact phase based on the slope rate and signal dip of the impact phase. 9) Corrected intraocular pressure is calculated by using the reconstruction curve.

[0091]

[0091] The corrected intraocular pressure CP may then be calculated from the reconstructed curve as the slope shown in Figure 5 between the point (b') when the first end 2a of the probe body 2 first impacts the outer surface of the cornea and the point (c) when the probe body 2 comes to a complete stop on the eye.

[0092]

[0092] Figure 6 shows an example of a corneal thickness of 450 μm obtained from the registered velocity-time signal and a calculated intraocular pressure of 20 mmHg. This signal was reconstructed based on a corneal thickness of 530 μm and an intraocular pressure of more than 20 mmHg (because a thinner cornea would result in a lower pressure measurement from the device), and is shown as a dashed line in Figure 6. CP is then calculated from the reconstructed curve as the slope shown in Figure 6 between (b') when the first end 2a of the probe 2 first impacts the outer surface of the cornea and (c) when the probe body 2 comes to a complete stop in the eye.

[0093]

[0093] To increase the accuracy of the calculation, the calculated parameter may be the average of multiple (eg, 2 to 4) measurements or time-velocity curves.

[0094]

[0094] The system may be adapted for use without the need for anesthetic eye drops.

[0095]

[0095] The first coil 6a may be activated for approximately 10 ms, generating a magnetic field that moves the probe body 2 toward the eye at a constant, steady speed over the first approximately 10 mm of movement. The magnitude of the speed is monitored by the second coil 6b. After impacting the tear film, the end 2a of the probe body 2 impacts the outer surface of the cornea. The probe body compresses the cornea until it comes to a complete stop at the corneal surface (impact phase). The intraocular pressure then causes the probe body to move in the opposite direction (bounce phase) until it has completely left the eye. The speed profile of the impact and bounce phases is registered by the system. If the processor detects that the probe body 2 has left the eye, activation of the second coil 6b (within approximately 100 ms) returns the probe to its starting position.

[0096]

[0096] The total time for the impact and rebound phase on the target is around 1 ms when the uncorrected intraocular pressure is 70 mmHg, and around 5 ms when the uncorrected intraocular pressure is 7 mmHg.

[0097]

[0097] To control the speed of the probe body 2, the first coil 6a and the second coil 6b may be activated multiple times in succession at short intervals, such as between 2 ms and 3 ms and between 4 ms and 5 ms, respectively. If the speed of the probe body deviates from a specific value, a warning may be displayed to the system user, for example on the display 20. This process is performed only once for the entire measurement consisting of multiple trials.

[0098]

[0098] The system 1 may be a portable system or a desktop system. [Item of invention] [Item 1] 1. A computer-implemented method for analyzing a time-velocity curve comprising registered velocities and times of a probe body (2) during movement of the probe body (2) in a first direction towards an outer corneal surface (b) of a subject's eye (c), during impact of an end (2a) of the probe body (2) with the outer corneal surface (b) when coming to a complete stop at the eye (c), and during rebound movement of the probe body (2) in a second direction opposite to the first direction, comprising: calculating the intraocular pressure (p) of the eye as the slope of the time-velocity curve between the time when the end of the probe body (2) first impacts the outer corneal surface (b) and the time when the probe body (2) comes to a complete stop in the eye (c); The velocity V of the probe body (2) on the time-velocity curve at the moment of contact of the end (2a) of the probe body (2) with the outer surface of the cornea (b) r and a velocity V of the probe body (2) in the time-velocity curve at the moment when the probe body (2) leaves the outer surface of the cornea during the bouncing movement of the probe body (2) in the second direction. b and calculating the central corneal thickness (D) using 11. A computer-implemented method comprising: [Item 2] 1. A computer program comprising instructions that, when executed by a computer, cause the computer to perform an analysis of a time-velocity curve comprising registered velocities and times of the probe body (2) during movement of the probe body in a first direction towards the outer corneal surface of a subject's eye, during impact of the end (2a) of the probe body (2) with the outer corneal surface (b) when it comes to a complete stop at the eye (c), and during rebound movement of the probe body (2) in a second direction opposite to the first direction, causing the computer to calculate the intraocular pressure (p) of the eye as the slope of the time-velocity curve between the time when the end of the probe body (2) first impacts the outer corneal surface (b) and the time when the probe body (2) comes to a complete stop in the eye (c); The velocity V of the probe body (2) on the time-velocity curve at the moment of contact of the end (2a) of the probe body (2) with the outer surface of the cornea (b) r and a velocity V of the probe body (2) in the time-velocity curve at the moment when the probe body (2) leaves the outer surface of the cornea during the bouncing movement of the probe body (2) in the second direction. b and causing the computer to calculate the central corneal thickness (D) using the formula: [Item 3] The central corneal thickness (D) is D=C·exp(τ)+L (where C and L are constants) τ=(V r 2 -v b 2 )(1-exp(-K logp)) / V r 2 (where K is a constant) and 3. The computer-implemented method or computer program according to item 1 or 2, wherein the method or program is calculated from: [Item 4] 4. The computer program according to any one of items 1 to 3, further comprising instructions for causing the computer to calculate a corrected intraocular pressure (CP) using the calculated corneal thickness (D) and the intraocular pressure (p). [Item 5] 4. The computer-implemented method according to any one of items 1 to 3, further comprising the step of calculating a corrected intraocular pressure (CP) using the calculated corneal thickness (D) and the intraocular pressure (p). [Item 6] and further comprising instructions for causing the computer to calculate a tear film thickness (L) on the outer surface of the cornea from the time-rate curve, the tear film thickness (L) being:

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Claims

1. 1. A computer-implemented method for analyzing a time-velocity curve comprising registered velocities and times of a probe body (2) during movement of the probe body (2) in a first direction towards an outer corneal surface (b) of a subject's eye (c), from when an end (2a) of the probe body (2) impacts the outer corneal surface (b) until it comes to a complete stop at the eye (c), and during a rebound movement of the probe body (2) in a second direction opposite to the first direction, comprising: calculating the intraocular pressure (p) of the eye as the slope of the time-velocity curve between the time when the end of the probe body (2) first impacts the outer corneal surface (b) and the time when the probe body (2) comes to a complete stop in the eye (c); The velocity V of the probe body (2) on the time-velocity curve at the moment of contact of the end (2a) of the probe body (2) with the outer surface of the cornea (b) ｒ and a velocity V of the probe body (2) in the time-velocity curve at the moment when the probe body (2) leaves the outer surface of the cornea during the bouncing movement of the probe body (2) in the second direction. ｂ and calculating the central corneal thickness (D) using 11. A computer-implemented method comprising:

2. 1. A computer program comprising instructions that, when executed by a computer, cause the computer to perform an analysis of a time-velocity curve comprising registered velocities and times of the probe body (2) during movement of the probe body (2) in a first direction towards the outer corneal surface (b) of a subject's eye (c), from when an end (2a) of the probe body (2) impacts the outer corneal surface (b) until it comes to a complete stop at the eye (c), and during a rebound movement of the probe body (2) in a second direction opposite to the first direction, causing the computer to calculate the intraocular pressure (p) of the eye as the slope of the time-velocity curve between the time when the end of the probe body (2) first impacts the outer corneal surface (b) and the time when the probe body (2) comes to a complete stop in the eye (c); The velocity V of the probe body (2) on the time-velocity curve at the moment of contact of the end (2a) of the probe body (2) with the outer surface of the cornea (b) ｒ and a velocity V of the probe body (2) in the time-velocity curve at the moment when the probe body (2) leaves the outer surface of the cornea during the bouncing movement of the probe body (2) in the second direction. ｂ and causing the computer to calculate the central corneal thickness (D) using

3. The central corneal thickness (D) is D = C exp(τ) + L (where C and L are constants); τ=(V ｒ ２ -V ｂ ２ )(1-exp(-K logp)) / V ｒ ２ (where K is a constant) and The computer-implemented method of claim 1 , wherein the calculation is performed from

4. The central corneal thickness (D) is D = C exp(τ) + L (where C and L are constants); τ=(V ｒ ２ -V ｂ ２ )(1-exp(-K logp)) / V ｒ ２ (where K is a constant) and The computer program of claim 2, wherein the calculation is performed from

5. 5. The computer program of claim 2 or 4, further comprising instructions for causing the computer to calculate a corrected intraocular pressure (CP) using the calculated corneal thickness (D) and the intraocular pressure (p).

6. 4. The computer-implemented method of claim 1, further comprising calculating a corrected intraocular pressure (CP) using the calculated corneal thickness (D) and the intraocular pressure (p).

7. and further comprising instructions for causing the computer to calculate a tear film thickness (L) on the outer surface of the cornea from the time-rate curve, the tear film thickness (L) being: [Equation 1] It is calculated from V(t) is the velocity-time profile of the probe body (2) registered during the impact-rebound path of the probe body (2) from the moment the end (2 a) of the probe body (2) impacts the eye to the moment the end (2 a) of the probe body (2) comes to a complete stop at the eye and leaves the eye; (T ｔ , V ｔ ) is the time when the end (2a) of the probe body (2) first collides with the tear film (a) on the outer surface of the cornea; (T ｃ , V ｃ 6. The computer program according to claim 2, wherein the first collision point (2a) of the end (2a) of the probe body (2) with the outer surface (b) of the cornea is reached.

8. and calculating a tear film thickness (L) on the outer surface of the cornea from the time-rate curve, wherein the tear film thickness (L) is: [Equation 2] It is calculated from V(t) is the velocity-time profile of the probe body (2) registered during the impact-rebound path of the probe body (2) from the moment the end (2 a) of the probe body (2) impacts the eye to the moment the end (2 a) of the probe body (2) comes to a complete stop at the eye and leaves the eye; (T ｔ , V ｔ ) is the time when the end (2a) of the probe body (2) first collides with the tear film (a) on the outer surface of the cornea; (T ｃ , V ｃ 7. The computer-implemented method of claim 1, wherein the first impact of the end (2a) of the probe body (2) with the outer corneal surface (b) occurs at time t1.

9. A system (1) for determining ophthalmic parameters of a subject, comprising a probe (11) and a processor (10), the processor comprising: registering the velocity and time of the probe body (2) of the probe (11) during movement of the probe body (2) in a first direction towards the outer corneal surface (b) of the subject's eye (c), from when the end (2a) of the probe body (2) impacts the outer corneal surface (b) until it comes to a complete stop at the eye (c), and during the rebound movement of the probe body (2) in a second direction opposite to the first direction; calculating the intraocular pressure (p) of the eye based on a curve obtained from the registered velocity of the probe body (2) and time as the slope between the time when the end (2a) of the probe body (2) first impacts the outer corneal surface (b) and the time when the probe body (2) comes to a complete stop on the eye (c); Based on the registered time-velocity curve including the velocity and time of the probe body (2), the velocity V of the probe body (2) at the moment of contact of the end (2a) of the probe body (2) with the outer surface (b) of the cornea is calculated. ｒ and a velocity V of the probe body (2) at the moment when the end (2a) of the probe body (2) leaves the outer surface of the cornea during the bouncing movement of the probe body (2) in the second direction. ｂ and calculating the central corneal thickness (D) using A system (1) configured to perform the following.

10. The probe body (2) a magnetic probe body (2) having a first end (2a) and an opposite second end (2b); a non-magnetic tube (4) having a first end (4a) and an opposite second end (4b), the magnetic probe body (2) being slidably disposed therein, the first end (2a) of the probe body (2) and the first end (4a) of the tube (4) being oriented in the same direction; a magnetic field configured to move the probe body (2) in a first direction from a first position in the tube to a second position where at least the first end (2 a) of the probe body (2) extends from the first end (4 a) of the tube (4); Equipped with 10. The system (1) of claim 9, wherein the first end (2a) of the probe body (2) is configured to impact an outer corneal surface (b) of the subject's eye at the second position.

11. 11. The system of claim 10, wherein an optical unit is disposed at the second end of the non-magnetic tube and is concentrically aligned with the tube, and wherein light emitted from the optical unit passes through the non-magnetic tube, passes toward the first end of the non-magnetic tube, and is directed toward an outer corneal surface that is positioned perpendicularly at a distance from the first end of the tube, where it is reflected from the outer corneal surface and indicates an area on the outer corneal surface where the first end of the probe body collides with the outer corneal surface.

12. The system (1) according to any one of claims 9 to 11, further comprising a display (20) for displaying the calculated ophthalmic parameters.

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