CN109241680A - Human eye biomethanics analogy method under state of weightlessness based on finite element - Google Patents
Human eye biomethanics analogy method under state of weightlessness based on finite element Download PDFInfo
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Abstract
本发明公开了一种基于有限元的失重状态下的人眼生物力学模拟方法，其步骤如下：1）对眼球进行简化与假设，建立人眼三维几何模型；2）确定人眼生物力学特性；3）确定材料的性质和设定在失重状态下的参数；4）对人眼三维几何模型进行有限元网格划分,设定有限元模型的边界条件；5）设定失重下人眼受作用的方式与作用的数值，并用波前理论对视觉质量进行判定。本发明能够解决无法进行准确测量人眼生物力学数据的问题，得到失重状态下的人眼生物力学准确数据，从而可以帮助人们更好地研究眼组织生物力学特点，为眼组织生物力学研究提供了一种有效的辅助研究方法且具有重要意义。
The invention discloses a method for simulating human eye biomechanics in a weightless state based on finite elements. The steps are as follows: 1) simplify and assume the eyeball, and establish a three-dimensional geometric model of the human eye; 2) determine the biomechanical characteristics of the human eye; 3) Determine the properties of the material and set the parameters in the weightless state; 4) Perform finite element mesh division on the three-dimensional geometric model of the human eye, and set the boundary conditions of the finite element model; 5) Set the human eye under the effect of weightlessness The method and effect of the numerical value, and use the wavefront theory to determine the visual quality. The invention can solve the problem that the biomechanical data of the human eye cannot be accurately measured, and obtain the accurate data of the biomechanics of the human eye in a weightless state, thereby helping people to better study the biomechanical characteristics of the eye tissue, and providing the research on the biomechanics of the eye tissue. An effective auxiliary research method and is of great significance.
Description
Technical field
The present invention relates to the finite element analysis technology of eyeball in biomedicine, especially a kind of weightless shape based on finite element
Human eye biomethanics analogy method under state.
Background technique
Finite element analysis is widely used in field of ophthalmology, and it is raw that finite element model can help people preferably to study ocular tissue
Object mechanics feature.Therefore, by establishing more perfect ideal eyeball phantom and complicated eyeball, eye biomethanics is carried out quasi-
Really analysis is remarkably improved the repeatability and accuracy of related ophthalmology experiment, reduces research cost, the diagnosis to eye disease
Treatment, research have important meaning.
The eyes are the organs of sight, one of most important sense organ.The mankind can be from complicated external environment by eyes
In, perceive and obtain information abundant.Ground ophthalmology disease such as cataract etc., matter that is serious and influencing people's life
Amount, and space microgravity eye injury not only brings serious harm to spacefarer's body, also seriously threatens the completion of space mission.
2011 or so, NASA started entitled " eye injury and intracranial pressure " (Vision Impairment and Intracranial
Pressure, VIIP) correlative study, it is intended to by being exposed to microgravity space environment for a long time, spacefarer is arriving at ground for research
The variation of its ocular structure and distant vision, near vision before and after ball.Studies have shown that under space flight microgravity environment, eye structure and function
Can change include papilledema, that eyeball becomes flat, choroid gauffer, retina cotton-wool spots, vagina nervi optici is swollen
Swollen, near point far moves, and will cause eye permanent damage under serious conditions.It is main for the research for microgravity environment eye injury
Be unfolded with experimental method, experimental cost is high, individual difference obvious, space testing cost height few by spacefarer's sample size etc. because
Element limitation, correlative study data do not have generality and progress is slower, and correlative study is restricted.
Summary of the invention
The present invention is to solve asking for the human eye biomechanical data that accurately can not be measured and be obtained under state of weightlessness
It inscribes, the human eye biomethanics analogy method under a kind of state of weightlessness based on finite element of proposition.
The purpose of the present invention is what is be achieved through the following technical solutions.Human eye biology under state of weightlessness based on finite element
Mechanical simulation method, which is characterized in that its step are as follows:
1) eyeball simplify and it is assumed that establishing human eye 3-D geometric model；
2) human eye biomechanics characteristic is determined；
3) property of material and the parameter being set under state of weightlessness are determined；Its process are as follows:
(1) through, there is good linear dependence, calculating to obtain linear regression side between data processing intracranial pressure and intraocular pressure
Journey:
IOP=0.934*ICP+3.705；
In formula: ICP is intracranial pressure, and IOP is intraocular pressure；
(2) according to above-mentioned equation of linear regression, to the pressure of 14.91~31.73mmHg of application in human eye, and human eye is constrained
Outer surface；
4) FEM meshing is carried out to human eye 3-D geometric model, sets the boundary condition of finite element model；Its mistake
Journey are as follows:
(1) human eye biomethanics geometrical model is input in finite element analysis software, selecting unit type, setup unit
Density carries out grid dividing, and the size of grid is less than or equal to 0.20mm；
(2) intraocular pressure preliminary examination value is set as 15mmHg, then carries out intra-ocular pressure increment simulation to cornea model, and correspondence is set
Time series is set, intraocular pressure difference is 1mmHg between adjacent time sequence, then carries out intra-ocular pressure increment mould to cornea model
Calculated result that is quasi-, being obtained after analysis processing simulation；It selects posterior surface of cornea and sclera inner surface for acting surface load, constrains people
The outer surface of eye finite element model；
5) numerical value of setting weightless lower human eye mode affected and effect, carries out finite element solving, root inside human eye
It is calculated according to the resulting stress-strain of each node of human eye interior tissue unit-displacement as a result, to obtain human eye interior tissue unit
Stress-strain-Displacements Distribution figure；Quantitative analysis human ocular tissues under state of weightlessness cornea front and rear surfaces change in displacement as a result,
And the change of the wave front aberration variation and visual quality caused by obtaining, process are as follows: human eye interior tissue is subjected to finite element
It solves, using the analysis result data of finite element software, function combined stress-strain-displacement diagram is inserted into, wherein to stress-
Strain-displacement diagram carries out export data, and related data and normal data are compared, and the change of analysis cornea displacement leads to angle
Film wave front aberration changes and affects the amount and characteristic of aberration, and is determined with wave front principle visual quality,
Complete the human eye biomethanics analogy method under a kind of state of weightlessness based on finite element；
Further, the detailed process of human eye 3-D geometric model is established in the step 1) are as follows:
(1) using the corresponding three-dimensional coordinate data of programming cornea upper and lower surface in MATLAB software, obtaining has cornea three
Tie up information data；Using the comprehensive eye anterior segment analysis system clinical measurement corneal topography of Pentacam, cornea front and rear surfaces are obtained
Height difference data；Using the height difference data with cornea three-dimensional information data and cornea front and rear surfaces and combine with reference to bent
Face and corneal thickness establish the geometrical model of individuation eye cornea；Wherein the eyeball of human eye is axisymmetric ellipsoid, human eye
The surfaces externally and internally of cornea is ellipsoid；
Wherein, anterior surface of cornea function are as follows:
Posterior surface of cornea function are as follows:
In formula: R` is the radius of curvature of anterior surface of cornea fit sphere, and R`` is the curvature half of posterior surface of cornea fit sphere
Diameter, X, Y are the coordinate of umbilical point, and Ci ' is zernike coefficient, and Zi is zernike polynomial；
(2) set scleral thickness be it is uniform, inside and outside wall is ellipsoid, and determines the axial length size of data measured by clinical,
The human eye appearance model of foundation；
(3) parametrization is carried out using known lens diameter, thickness, nuclear diameter, core thickness and core offsets parameter to build
Mould, and merged by above-mentioned parameter with the geometry physical characteristic parameter of actual measurement, obtain entity morphology model；
(4) above-mentioned entity morphology model is subjected to analytical integration, and establishes complete individuation human eye in modeling software
Biomechanical model；
Human eye biomechanics characteristic is determined in the step 2) are as follows:
It by eyeball tissue is approximately meet linear change each under below-G conditions using cornea as isotropic material processing
To the elastomer of the same sex, assumed according to substance uniformity in substance continuum hypothesis in eyeball tissue, eyeball tissue, eyeball tissue
The isotropism of interior substance mechanical characteristic assumes, linear elasticity assumes and small deformation assume the density of setting cornea, elasticity modulus with
And Poisson's ratio.
Further, the detailed process of human eye 3-D geometric model is established in the step 1) are as follows:
(1) using the corresponding three-dimensional coordinate data of programming cornea upper and lower surface in MATLAB software, obtaining has cornea three
Tie up information data；Using the comprehensive eye anterior segment analysis system clinical measurement corneal topography of Pentacam, cornea front and rear surfaces are obtained
Height difference data；Using the height difference data with cornea three-dimensional information data and cornea front and rear surfaces and combine with reference to bent
Face and corneal thickness establish the geometrical model of individuation eye cornea；Wherein the eyeball of human eye is axisymmetric ellipsoid, human eye
The surfaces externally and internally of cornea is ellipsoid；
Wherein, anterior surface of cornea function are as follows:
Posterior surface of cornea function are as follows:
In formula: R` is the radius of curvature of anterior surface of cornea fit sphere, and R`` is the curvature half of posterior surface of cornea fit sphere
Diameter, X, Y are the coordinate of umbilical point, and Ci ' is zernike coefficient, and Zi is zernike polynomial；
(2) set scleral thickness be it is uniform, inside and outside wall is ellipsoid, and determines the axial length size of data measured by clinical,
The human eye appearance model of foundation；
(3) it is parameterized using the characteristic parameter that known lens diameter, thickness, nuclear diameter, core thickness and core deviate
Modeling, is merged with the geometry physical characteristic parameter of actual measurement by above-mentioned parameter, obtains entity morphology model；
(4) above-mentioned entity morphology model is subjected to analytical integration, and establishes complete individuation human eye in modeling software
Biomechanical model；
Human eye biomechanics characteristic is determined in the step 2) are as follows:
(1) at using cornea as non-uniform, anisotropic, nonlinear and viscoelasticity complex biological mechanics material
Reason；The non-linear stress-strain relationship of cornea obeys following formula:
σ=A (e^ α ε -1)；
Wherein: σ is stress, and ε is strain, and A, α are material constant；
The viscoelasticity feature of cornea is obtained by stress relaxation curve, and calculates empirical equation:
Y=-0.0157ln (t)+0.9785；
Wherein: y is that accumulative modulus is normalized when ratio of elongation is 1.5, and t is the time；
(2) density for determining each human ocular tissues including cornea, iris, sclera, crystalline lens and suspensorium, by above-mentioned formula
Determine the biomechanics characteristic of human ocular tissues.
Further, the detailed process of human eye 3-D geometric model is established in the step 1) are as follows:
(1) it using the eyes of patients related data for carrying out corneal laser surgery clinically measured, and then constructs postoperative
The normal human eye 3-D geometric model of recovery；Utilize the corresponding three-dimensional coordinate number of programming cornea upper and lower surface in MATLAB software
According to obtaining has cornea three-dimensional information data；Eye anterior segment analysis system clinical measurement corneal topography is integrated using Pentacam,
Obtain the height difference data of cornea front and rear surfaces；Simultaneously using the height difference data with cornea three-dimensional information data and front and rear surfaces
And reference surface and corneal thickness are combined, establish the geometrical model of individuation eye cornea；Wherein the eyeball of human eye is axial symmetry
Ellipsoid, the surfaces externally and internally of the cornea of human eye is ellipsoid；
Wherein, anterior surface of cornea function are as follows:
Posterior surface of cornea:
In formula: R` is the radius of curvature of anterior surface of cornea fit sphere, and R`` is the curvature half of posterior surface of cornea fit sphere
Diameter, X, Y are the coordinate of umbilical point, and Ci ' is zernike coefficient, and Zi is zernike polynomial；
(2) set scleral thickness be it is uniform, inside and outside wall is ellipsoid, and determines the axial length size of data measured by clinical,
The human eye appearance model of foundation；
(3) using known lenticular characteristic parameter: lens diameter, thickness, nuclear diameter, core thickness, core deviate this five
A ginseng is merged with the geometry physical characteristic parameter of actual measurement by these parameters to carry out parametric modeling, obtains entity shape
States model；
(4) model is subjected to analytical integration, and establishes complete individuation human eye biomechanical model in modeling software；
Human eye biomechanics characteristic is determined in the step 2) are as follows:
It by eyeball tissue is approximately meet linear change each under below-G conditions using cornea as isotropic material processing
To the elastomer of the same sex, assumed according to substance uniformity in substance continuum hypothesis in eyeball tissue, eyeball tissue, eyeball tissue
The isotropism of interior substance mechanical characteristic assumes, linear elasticity assumes and small deformation assumes the density of setting cornea, elasticity modulus with
And Poisson's ratio.
The detailed process of human eye 3-D geometric model is established in the step 1) are as follows:
(1) it using the eyes of patients related data for carrying out corneal laser surgery clinically measured, and then constructs postoperative
The normal human eye 3-D geometric model of recovery；Utilize the corresponding three-dimensional coordinate number of programming cornea upper and lower surface in MATLAB software
According to obtaining has cornea three-dimensional information data；Eye anterior segment analysis system clinical measurement corneal topography is integrated using Pentacam,
Obtain the height difference data of cornea front and rear surfaces；Simultaneously using the height difference data with cornea three-dimensional information data and front and rear surfaces
And reference surface and corneal thickness are combined, establish the geometrical model of individuation eye cornea；Wherein the eyeball of human eye is axial symmetry
Ellipsoid, the surfaces externally and internally of the cornea of human eye is ellipsoid；
Wherein, anterior surface of cornea function are as follows:
Posterior surface of cornea function are as follows:
In formula: R` is the radius of curvature of anterior surface of cornea fit sphere, and R`` is the curvature half of posterior surface of cornea fit sphere
Diameter, X, Y are the coordinate of umbilical point, and Ci ' is zernike coefficient, and Zi is zernike polynomial；
(2) set scleral thickness be it is uniform, inside and outside wall is ellipsoid, and determines the axial length size of data measured by clinical,
The human eye appearance model of foundation；
(3) it is parameterized using the characteristic parameter that known lens diameter, thickness, nuclear diameter, core thickness and core deviate
Modeling, is merged with the geometry physical characteristic parameter of actual measurement by above-mentioned parameter, obtains entity morphology model；
(4) model is subjected to analytical integration, and establishes complete individuation human eye biomechanical model in modeling software；
The step 2) determines the detailed process of human eye biomechanics characteristic are as follows:
(1) anisotropic using cornea as non-uniform, at nonlinear and viscoelasticity complex biological mechanics material
Reason；The non-linear stress-strain relationship of cornea obeys following formula:
σ=A (e^ α ε -1)；
Wherein: σ is stress, and ε is strain, and A, α are material constant；
The viscoelasticity feature of cornea is obtained by stress relaxation curve, and calculates empirical equation:
Y=-0.0157ln (t)+0.9785；
Wherein: y is that accumulative modulus is normalized when ratio of elongation is 1.5, and t is the time；
(2) density for determining each human ocular tissues including cornea, iris, sclera, crystalline lens, suspensorium, by above
Formula determines the biomechanics characteristic of human ocular tissues.
The present invention, which is able to solve, can not carry out the problem of accurately measuring human eye biomechanical data, obtain under state of weightlessness
Human eye biomethanics accurate data, so as to help people preferably to study ocular tissue's biomechanics characteristic.The present invention is to people
Intraocular part tissue carries out finite element solving, calculated according to the resulting stress-strain of each node of human ocular tissues' unit-displacement as a result,
To obtain stress-strain-Displacements Distribution figure of human eye interior tissue unit；According to stress-strain-displacement distribution results,
The variation of aberration and it is further utilized to prediction to the visual quality of human eye caused by the variation of quantitative analysis displacement, thus
So that the present invention is provided a kind of effective support study dies method for ocular tissue's biomechanics Research and is of great significance.
Detailed description of the invention
Fig. 1 is flow chart of the invention；
Fig. 2 is the schematic diagram of human eye 3-D geometric model in the present invention；
Fig. 3 is to carry out FEM meshing figure to human-eye model in the present invention；
Fig. 4 is the human eye Displacements Distribution front view in the present invention.
Specific embodiment
Below in conjunction with drawings and examples, the invention will be further described.Referring to Fig. 1 to Fig. 4.
Embodiment 1: the human eye biomethanics analogy method under the state of weightlessness based on finite element, specifically according to the following steps
Preparation:
Step 1: eyeball simplify and it is assumed that establishing human eye 3-D geometric model；
Step 2: human eye biomechanics characteristic is determined；
Step 3: the property of material and the parameter being set under state of weightlessness are determined；
Step 4: progress FEM meshing (as shown in Figure 3) (as shown in Figure 2) to human eye 3-D geometric model, if
Determine the boundary condition of finite element model；
Step 5: the numerical value of setting weightless lower human eye mode affected and effect carries out finite element inside human eye and asks
Solution is calculated according to the resulting stress-strain of each node of human eye interior tissue unit-displacement as a result, to obtain group inside human eye
Knit stress-strain-Displacements Distribution figure (as shown in Figure 4) of unit；Quantitative analysis human ocular tissues are before and after cornea under state of weightlessness
Surface displacement result of variations, and obtain the change of caused wave front aberration variation and visual quality；One kind is completed to be based on
Human eye biomethanics analogy method under the state of weightlessness of finite element.
Present embodiment effect: the human eye biomethanics mould under a kind of state of weightlessness based on finite element proposed by the present invention
Quasi- method, can obtain the human eye biomethanics accurate data under state of weightlessness, so as to help people preferably to study eye group
Knit biomechanics characteristic.The present invention carries out finite element solving to human eye interior tissue, according to obtained by each node of human ocular tissues' unit
Stress-strain-displacement calculate as a result, to obtaining stress-strain-Displacements Distribution of human eye interior tissue unit；According to answering
Power-strain-displacement distribution results, quantitative analysis displacement variation caused by aberration variation and be further utilized to people
The prediction of the visual quality of eye, so that the present invention be made to provide a kind of effective support study dies side for ocular tissue's biomechanics Research
It method and is of great significance.
Embodiment 2: unlike the first embodiment: in step 1 to eyeball simplify with it is assumed that establish human eye three-dimensional several
The process of what model are as follows:
(1) it using the eyes of patients related data for carrying out corneal laser surgery clinically measured, and then constructs postoperative
The normal human eye 3-D geometric model of recovery.Do not consider that the tissue such as optic tract is asymmetric caused by eyeball configuration
It influences, ignores the small asymmetry in ball portions place, it is believed that eyeball is axisymmetric ellipsoid；It is approximately considered the inside and outside of cornea
Surface is ellipsoid；The geometric parameter that the foundation of this patent human eye geometrical model uses is in human eye the classic and clinical geometric parameters base
On plinth, on the basis of Rational Simplification and hypothesis, the simplification and hypothesis done, which are built upon, guarantees that interpretation of result is correct
On the basis of.
(2) using the corresponding three-dimensional coordinate data of programming cornea upper and lower surface in MATLAB software, obtaining has cornea three
Tie up information data；Using the comprehensive eye anterior segment analysis system clinical measurement corneal topography of Pentacam, cornea front and rear surfaces are obtained
Height difference data；Using the height difference data with cornea three-dimensional information data and front and rear surfaces and combine reference surface and
Corneal thickness establishes the geometrical model of individuation eye cornea.Wherein the eyeball of human eye is axisymmetric ellipsoid, the canthus of human eye
The surfaces externally and internally of film is ellipsoid；
Wherein, cornea front and rear surfaces function is respectively as follows:
Anterior surface of cornea:
Posterior surface of cornea:
In formula: R` is the radius of curvature of anterior surface of cornea fit sphere, and R`` is the curvature half of posterior surface of cornea fit sphere
Diameter, X, Y are the coordinate of umbilical point, and Ci ' is zernike coefficient, and Zi is zernike polynomial.
(3) set scleral thickness be it is uniform, inside and outside wall is ellipsoid, and determines the axial length size of data measured by clinical,
The human eye appearance model of foundation.
(4) using known lenticular characteristic parameter: lens diameter, thickness, nuclear diameter, core thickness, core deviate this five
A parameter carries out parametric modeling, is merged with the geometry physical characteristic parameter of actual measurement by these parameters, obtains true
The stronger entity morphology model of property.
(5) model is subjected to analytical integration, and establishes complete individuation human eye biomechanical model in modeling software；
Other steps and parameter are same as Example 1.
Embodiment 3: unlike embodiment 1,2: defining human eye biomechanics characteristic in step 2 are as follows: cornea has not
Uniformly, anisotropic, nonlinear and viscoelasticity complex biological mechanical characteristic.Comprising different thin in ocular tissue
Born of the same parents, the different fiber of performance, the cytoplasm etc. of flowing, their position and direction are unevenly distributed, cause on different directions
The mechanical characteristic of ocular tissue is different, and here it is the anisotropy of ocular tissue.Cornea has typical anisotropic Biological Strength scholarship and moral conduct
To show different stress and deformation behaviour in the long axis and short-axis direction of cornea.Have along short-axis direction cornea higher
Viscoelasticity and viscoplasticity, elongation is also greater than long axis direction, and then has higher elasticity along long axis soft tissue machine direction
Modulus and tensile ultimate strength；A variety of ocular tissues " stress-strain " under experimental conditions simultaneously do not meet stringent linear relationship,
So that ocular tissue cannot take fixed elasticity modulus within the scope of big internal pressure.The non-linear stress-strain relationship of cornea obey with
Wherein σ is stress to lower formula σ=A (e^ α ε -1), and ε is strain, and A, α are material constant；Eyeball tissue is by various cells, iuntercellular
Matter composition, it is believed that its interior substance is continuity；Cornea tissue internal clearance is filled by liquid completely, it is believed that is that can not press
The material of contracting.The viscoelasticity feature of cornea is provided by stress relaxation curve, meet empirical equation y=-0.0157ln (t)+
0.9785, wherein y is that accumulative modulus is normalized when ratio of elongation is 1.5, and t is the time.Other steps and parameter and embodiment 1,2
It is identical.
Embodiment 4: the human eye biomethanics analogy method under a kind of state of weightlessness based on finite element, specifically according to
Lower step preparation:
Step 1: eyeball simplify and it is assumed that establishing human eye 3-D geometric model；
(1) do not consider that optic tract etc. organizes the asymmetric influence caused by eyeball configuration, ignore ball portions
The small asymmetry in place, it is believed that eyeball is axisymmetric ellipsoid；The surfaces externally and internally for thinking cornea is ellipsoid；This patent people
The geometric parameter that the foundation of eye geometrical model uses is on the basis of human eye the classic and clinical geometric parameter, in Rational Simplification and hypothesis
On the basis of come, the simplification and hypothesis done be built upon guarantee interpretation of result it is correct on the basis of.
(2) using the corresponding three-dimensional coordinate data of programming cornea upper and lower surface in MATLAB software, obtaining has cornea three
Information data is tieed up (to use A=load (' cloud3d.dat ')；% reading data %X, Y, Z axis coordinate x=A (:, 1)；Y=A
(；, 2)；Z=A (；, 3) and Figure, surf (X, Y, Z)；% three-dimensional coordinate)；Utilize the comprehensive eye anterior segment analysis system of Pentacam
Clinical measurement corneal topography, (Pentacam can measure the height difference data of acquisition cornea front and rear surfaces within less than 2 second time
With analysis 25000/138000 data point of anterior ocular segment, wheel measuring can obtain more data in corneal center, make in cornea
The measurement data result of the heart is more accurate)；Using the height difference data with cornea three-dimensional information data and front and rear surfaces and
In conjunction with reference surface and corneal thickness, the geometrical model of individuation eye cornea is established.Wherein the eyeball of human eye is axisymmetric
Ellipsoid, the surfaces externally and internally of the cornea of human eye are ellipsoid；
Wherein, cornea front and rear surfaces function is respectively as follows:
Anterior surface of cornea:
Posterior surface of cornea:
R` is the radius of curvature of anterior surface of cornea fit sphere in formula, and R`` is the curvature half of posterior surface of cornea fit sphere
Diameter, X, Y are the coordinate of umbilical point, and Ci ' is zernike coefficient, and Zi is zernike polynomial.
(3) set scleral thickness be it is uniform, inside and outside wall is ellipsoid, and determines the axial length size of data measured by clinical,
The human eye appearance model of foundation.
(4) using known lenticular characteristic parameter: lens diameter, thickness, nuclear diameter, core thickness, core deviate this five
A parameter carries out parametric modeling, is merged with the geometry physical characteristic parameter of actual measurement by these parameters, obtains true
The stronger entity morphology model of property.
(5) model is subjected to analytical integration, and establishes complete individuation human eye biomechanical model in modeling software；
Step 2: human eye biomechanics characteristic is determined are as follows:
It carries out needing accurately to calculate human ocular tissues when simulation calculates, in valuable intraocular pressure ranges, " answer
The curvilinear characteristic performance of power-strain " curve is not obvious, and apparent linear relationship is presented；For eyeball tissue,
The composition of itself has very strong regularity, it is believed that it is isotropic.Cornea is substantially a kind of orthotropy
Material, it is main to needs input the stress on X, tri- directions Y, Z when accurately calculating that there are three elasticity in three orthogonal directions
One emergent property or three elasticity modulus main values.But due to the limitation of current experiment condition and experimental technique, only one direction
On stress-strain curve and a direction elasticity modulus.And elasticity modulus in the other direction is found under study for action
Difference is little.Therefore, we are herein using cornea as isotropic material processing.In conclusion within the scope of certain pressure intensity, i.e.,
It is also assumed that eyeball tissue meets linear change, isotropic elastomer under below-G conditions.I.e. it abides by five bases
This hypothesis: substance continuum hypothesis in eyeball tissue；Substance uniformity assumes in eyeball tissue；Substance mechanics is special in eyeball tissue
Property isotropism assume；Linear elasticity assumes；Small deformation assumes.
| Material properties | Human ocular tissues |
| Mechanical property | Line elastomer anisotropy |
| Density (Kg/m3) | 1030 |
| Young's modulus (MPa) | 1.8 |
| Poisson's ratio | 0.49 |
Step 3: determining the property of material and the parameter being set under state of weightlessness is；
(1) under reduced gravity situations, hydrostatic pressing disappears and body fluid head is to movement, since hydrostatic pressing disappears, human body body fluid everywhere
The identical about 100mmHg of pressure.Compared with normal environment state (normal intraocular tension value is 11-21mmHg), head pressure is increased
30mmHg。
(2) think that intraocular pressure (IOP) is 15mmHg under normal gravity environment in research, intracranial pressure (ICP) is approximately
12mmHg；Intracranial pressure (ICP) is increased to 30mmHg under weightlessness, and there is good linear correlations between intracranial pressure and intraocular pressure
Property, it through data processing and calculates, analyzes to obtain equation of linear regression: IOP=0.934*ICP+3.705.
Step 4: human eye accurate three-dimensional geometrical model is imported in finite element software, carries out FEM meshing (as schemed
Shown in 3), the finite element model boundary condition constructed needed for being set according to actual conditions；
Human eye biomethanics geometrical model is input in finite element analysis software, selecting unit type, setup unit is close
Degree, using free mesh, it is contemplated that the thickness of shell only has 0.62mm, and the placement differences in spatial distribution and space are very big,
Therefore, be avoid generate deformity grid, the size of grid should be less than or be equal to 0.20mm, should select " free orientation unit " with
Conducive to the grid for more reasonably, conveniently obtaining qualification.It is confirmed in calculating, selects such division condition, grid dividing energy
Obtain satisfied result.Intraocular pressure preliminary examination value is set as 15mmHg, this is a normal intraocular pressure, then carries out to cornea model
Intra-ocular pressure increment simulation, in 15 time serieses, each time series intraocular pressure increases by 1 millimetres of mercury, then with having
Limit meta software is analyzed and processed the calculated result after obtaining simulation.Apply pressure on geometrical model, is subject to due to cornea
Intraocular pressure be aqueous humor transmitting uniform liquid pressure, so the pressure values of cornea interior surface in all respects be all it is identical,
Select posterior surface of cornea for acting surface load, intraocular pressure value range is 10-22mmHg (1mmHg=under normal condition
133.322pa).FEM meshing figure such as Fig. 3 is carried out to human-eye model.
Step 5: the numerical value of setting weightless lower human eye mode affected and effect carries out finite element inside human eye and asks
Solution is calculated according to the resulting stress-strain of each node of human eye interior tissue unit-displacement as a result, to obtain group inside human eye
Knit stress-strain-Displacements Distribution figure of unit；Quantitative analysis human ocular tissues cornea front and rear surfaces change in displacement under state of weightlessness
As a result, and showing that caused wave front aberration changes the change with visual quality；
Human eye interior tissue is subjected to finite element solving, using the analysis result data of finite element software, function is inserted into and closes
Export data are carried out to stress-strain-displacement diagram at stress-strain-displacement diagram, and wherein, by related data and normal number
According to comparing, the change of analysis cornea displacement causes cornea wave front aberration to change and affects amount and the spy of aberration
Property, the caused advanced irregular aberration effects visibility range of big pupil, reduces the resolution ratio and imaging of retina
Quality, and then change visual quality.Therefore, visual quality can be determined according to wave front principle.
Claims (5)
1. the human eye biomethanics analogy method under the state of weightlessness based on finite element, which is characterized in that its step are as follows:
1) eyeball simplify and it is assumed that establishing human eye 3-D geometric model；
2) human eye biomechanics characteristic is determined；
3) property of material and the parameter being set under state of weightlessness are determined；Its process are as follows:
(1) through, there is good linear dependence, calculating to obtain equation of linear regression between data processing intracranial pressure and intraocular pressure:
IOP=0.934*ICP+3.705；
In formula: ICP is intracranial pressure, and IOP is intraocular pressure；
(2) according to above-mentioned equation of linear regression, to the pressure of 14.91~31.73mmHg of application in human eye, and human eye appearance is constrained
Face；
4) FEM meshing is carried out to human eye 3-D geometric model, sets the boundary condition of finite element model；Its process are as follows:
(1) human eye biomethanics geometrical model is input in finite element analysis software, selecting unit type, setup unit is close
Degree carries out grid dividing, and the size of grid is less than or equal to 0.20mm；
(2) intraocular pressure preliminary examination value is set as 15mmHg, then intra-ocular pressure increment simulation is carried out to cornea model, when being correspondingly arranged
Between sequence, intraocular pressure difference is 1mmHg between adjacent time sequence, intra-ocular pressure increment simulation then is carried out to cornea model, point
The calculated result obtained after analysis processing simulation；Select posterior surface of cornea and sclera inner surface for acting surface load, constraint human eye has
Limit the outer surface of meta-model；
5) numerical value of setting weightless lower human eye mode affected and effect, carries out finite element solving, according to people inside human eye
The resulting stress-strain of each node of intraocular part organizational unit-displacement calculates as a result, to obtain answering for human eye interior tissue unit
Power-strain-Displacements Distribution figure；Quantitative analysis human ocular tissues under state of weightlessness cornea front and rear surfaces change in displacement as a result, and
The change of wave front aberration variation and visual quality caused by out, process are as follows: human eye interior tissue is subjected to finite element solving,
Using the analysis result data of finite element software, it is inserted into function combined stress-strain-displacement diagram, wherein to stress-strain-
Displacement diagram carries out export data, and related data and normal data are compared, and the change of analysis cornea displacement leads to reflection,corneal
Preceding aberration changes and affects the amount and characteristic of aberration, and is determined with wave front principle visual quality, i.e., complete
At the human eye biomethanics analogy method under a kind of state of weightlessness based on finite element.
2. the human eye biomethanics analogy method under the state of weightlessness according to claim 1 based on finite element, feature
It is, the detailed process of human eye 3-D geometric model is established in the step 1) are as follows:
(1) using the corresponding three-dimensional coordinate data of programming cornea upper and lower surface in MATLAB software, obtaining has cornea three-dimensional letter
Cease data；Using the comprehensive eye anterior segment analysis system clinical measurement corneal topography of Pentacam, the height of cornea front and rear surfaces is obtained
Spend difference data；Using the height difference data with cornea three-dimensional information data and cornea front and rear surfaces and combine reference surface and
Corneal thickness establishes the geometrical model of individuation eye cornea；Wherein the eyeball of human eye is axisymmetric ellipsoid, the canthus of human eye
The surfaces externally and internally of film is ellipsoid；
Wherein, anterior surface of cornea function are as follows:
Posterior surface of cornea function are as follows:
In formula: R` is the radius of curvature of anterior surface of cornea fit sphere, and R`` is the radius of curvature of posterior surface of cornea fit sphere,
X, Y are the coordinate of umbilical point, and Ci ' is zernike coefficient, and Zi is zernike polynomial；
(2) set scleral thickness be it is uniform, inside and outside wall is ellipsoid, and determines the axial length size of data measured by clinical, is established
Human eye appearance model；
(3) parametric modeling is carried out using known lens diameter, thickness, nuclear diameter, core thickness and core offsets parameter, and
It is merged by above-mentioned parameter with the geometry physical characteristic parameter of actual measurement, obtains entity morphology model；
(4) above-mentioned entity morphology model is subjected to analytical integration, and establishes complete individuation human eye biology in modeling software
Mechanical model；
Human eye biomechanics characteristic is determined in the step 2) are as follows:
It by eyeball tissue is approximately meet linear change each to same under below-G conditions using cornea as isotropic material processing
Property elastomer, assumed according to substance uniformity in substance continuum hypothesis in eyeball tissue, eyeball tissue, object in eyeball tissue
The isotropism of matter mechanical characteristic assumes, linear elasticity assumes and small deformation assumes to set density, elasticity modulus and the pool of cornea
Loose ratio.
3. the human eye biomethanics analogy method under the state of weightlessness according to claim 1 based on finite element, feature
It is:
The detailed process of human eye 3-D geometric model is established in the step 1) are as follows:
(1) using the corresponding three-dimensional coordinate data of programming cornea upper and lower surface in MATLAB software, obtaining has cornea three-dimensional letter
Cease data；Using the comprehensive eye anterior segment analysis system clinical measurement corneal topography of Pentacam, the height of cornea front and rear surfaces is obtained
Spend difference data；Using the height difference data with cornea three-dimensional information data and cornea front and rear surfaces and combine reference surface and
Corneal thickness establishes the geometrical model of individuation eye cornea；Wherein the eyeball of human eye is axisymmetric ellipsoid, the canthus of human eye
The surfaces externally and internally of film is ellipsoid；
Wherein, anterior surface of cornea function are as follows:
Posterior surface of cornea function are as follows:
In formula: R` is the radius of curvature of anterior surface of cornea fit sphere, and R`` is the radius of curvature of posterior surface of cornea fit sphere,
X, Y are the coordinate of umbilical point, and Ci ' is zernike coefficient, and Zi is zernike polynomial；
(2) set scleral thickness be it is uniform, inside and outside wall is ellipsoid, and determines the axial length size of data measured by clinical, is established
Human eye appearance model；
(3) parametric modeling is carried out using the characteristic parameter of known lens diameter, thickness, nuclear diameter, core thickness and core offset,
It is merged by above-mentioned parameter with the geometry physical characteristic parameter of actual measurement, obtains entity morphology model；
(4) above-mentioned entity morphology model is subjected to analytical integration, and establishes complete individuation human eye biology in modeling software
Mechanical model；
Human eye biomechanics characteristic is determined in the step 2) are as follows:
(1) using cornea as non-uniform, anisotropic, nonlinear and viscoelasticity complex biological mechanics material processing；
The non-linear stress-strain relationship of cornea obeys following formula:
σ=A (e^ α ε -1)；
Wherein: σ is stress, and ε is strain, and A, α are material constant；
The viscoelasticity feature of cornea is obtained by stress relaxation curve, and calculates empirical equation:
Y=-0.0157ln (t)+0.9785；
Wherein: y is that accumulative modulus is normalized when ratio of elongation is 1.5, and t is the time；
(2) density for determining each human ocular tissues including cornea, iris, sclera, crystalline lens and suspensorium, is determined by above-mentioned formula
The biomechanics characteristic of human ocular tissues.
4. the human eye biomethanics analogy method under the state of weightlessness according to claim 1 based on finite element, feature
It is, the detailed process of human eye 3-D geometric model is established in the step 1) are as follows:
(1) it using the eyes of patients related data for carrying out corneal laser surgery clinically measured, and then constructs postoperative extensive
Multiple normal human eye 3-D geometric model；Using programming the corresponding three-dimensional coordinate data of cornea upper and lower surface in MATLAB software,
Obtaining has cornea three-dimensional information data；Using the comprehensive eye anterior segment analysis system clinical measurement corneal topography of Pentacam, obtain
Take the height difference data of cornea front and rear surfaces；Using the height difference data with cornea three-dimensional information data and front and rear surfaces and
In conjunction with reference surface and corneal thickness, the geometrical model of individuation eye cornea is established；Wherein the eyeball of human eye is axisymmetric
Ellipsoid, the surfaces externally and internally of the cornea of human eye are ellipsoid；
Wherein, anterior surface of cornea function are as follows:
Posterior surface of cornea:
In formula: R` is the radius of curvature of anterior surface of cornea fit sphere, and R`` is the radius of curvature of posterior surface of cornea fit sphere,
X, Y are the coordinate of umbilical point, and Ci ' is zernike coefficient, and Zi is zernike polynomial；
(2) set scleral thickness be it is uniform, inside and outside wall is ellipsoid, and determines the axial length size of data measured by clinical, is established
Human eye appearance model；
(3) utilize known lenticular characteristic parameter: lens diameter, thickness, nuclear diameter, core thickness, core deviate this five ginsengs
Parametric modeling is carried out, is merged by these parameters with the geometry physical characteristic parameter of actual measurement, obtains entity morphology mould
Type；
(4) model is subjected to analytical integration, and establishes complete individuation human eye biomechanical model in modeling software；
Human eye biomechanics characteristic is determined in the step 2) are as follows:
It by eyeball tissue is approximately meet linear change each to same under below-G conditions using cornea as isotropic material processing
Property elastomer, assumed according to substance uniformity in substance continuum hypothesis in eyeball tissue, eyeball tissue, object in eyeball tissue
The isotropism of matter mechanical characteristic assumes, linear elasticity assumes and small deformation assumes to set the density of cornea, elasticity modulus and pool
Loose ratio.
5. the human eye biomethanics analogy method under the state of weightlessness according to claim 1 based on finite element, feature
It is, the detailed process of human eye 3-D geometric model is established in the step 1) are as follows:
(1) it using the eyes of patients related data for carrying out corneal laser surgery clinically measured, and then constructs postoperative extensive
Multiple normal human eye 3-D geometric model；Using programming the corresponding three-dimensional coordinate data of cornea upper and lower surface in MATLAB software,
Obtaining has cornea three-dimensional information data；Using the comprehensive eye anterior segment analysis system clinical measurement corneal topography of Pentacam, obtain
Take the height difference data of cornea front and rear surfaces；Using the height difference data with cornea three-dimensional information data and front and rear surfaces and
In conjunction with reference surface and corneal thickness, the geometrical model of individuation eye cornea is established；Wherein the eyeball of human eye is axisymmetric
Ellipsoid, the surfaces externally and internally of the cornea of human eye are ellipsoid；
Wherein, anterior surface of cornea function are as follows:
Posterior surface of cornea function are as follows:
In formula: R` is the radius of curvature of anterior surface of cornea fit sphere, and R`` is the radius of curvature of posterior surface of cornea fit sphere,
X, Y are the coordinate of umbilical point, and Ci ' is zernike coefficient, and Zi is zernike polynomial；
(2) set scleral thickness be it is uniform, inside and outside wall is ellipsoid, and determines the axial length size of data measured by clinical, is established
Human eye appearance model；
(3) parametric modeling is carried out using the characteristic parameter of known lens diameter, thickness, nuclear diameter, core thickness and core offset,
It is merged by above-mentioned parameter with the geometry physical characteristic parameter of actual measurement, obtains entity morphology model；
(4) model is subjected to analytical integration, and establishes complete individuation human eye biomechanical model in modeling software；
The step 2) determines the detailed process of human eye biomechanics characteristic are as follows:
(1) using cornea as non-uniform, anisotropic, nonlinear and viscoelasticity complex biological mechanics material processing；
The non-linear stress-strain relationship of cornea obeys following formula:
σ=A (e^ α ε -1)；
Wherein: σ is stress, and ε is strain, and A, α are material constant；
The viscoelasticity feature of cornea is obtained by stress relaxation curve, and calculates empirical equation:
Y=-0.0157ln (t)+0.9785；
Wherein: y is that accumulative modulus is normalized when ratio of elongation is 1.5, and t is the time；
(2) density for determining each human ocular tissues including cornea, iris, sclera, crystalline lens, suspensorium, by above formula
Determine the biomechanics characteristic of human ocular tissues.
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