| Pathological myopia is a common blinding eye disease,but its pathogenesis has not been fully elucidated so far,so the lack of effective treatment for the cause of myopia has become a difficulty in the prevention and control of myopia,which needs further study.There are many difficulties in traditional myopia research methods,such as difficulty in animal model manufacturing,high research cost,long research cycle,many influencing factors,and difficulty in avoiding ethical risks.Therefore,in this study,COMSOL Multiphysics,a multi physical field simulation software based on the finite element method is used to build a digital model of pathological myopia,to simulate and analyze the influence of sclera thickness,area,curvature and other parameters in posterior staphyloma area on the occurrence and development of pathological myopia,and to preliminarily explore the application value and prospect of medical simulation technology in pathological myopia related research.Part One Three dimensional reconstruction of corneoscleral and finite element preprocessingObjective: to reconstruct the three-dimensional corneoscleral with the eye image data,and to prepare for the next finite element solution.Methods: 3D reconstruction and image analysis were carried out with the software attached to the image examination equipment,or the data was exported to invesalius 3 or MICs software in DICOM(digital imaging and communications in medicine)format for 3D reconstruction.The three-dimensional model of the corneoscleral was repaired,noise reduced and curved.The model was assembled and the mesh was preliminarily divided.The corneoscleral model was imported into the COMSOL multiphysics software,and the finite element mesh was processed twice and other mesh characteristics were assigned to complete the pre-processing of the corneoscleral finite element model.Results: a three-dimensional solid model of the corneoscleral was finally formed which could be used for the finite element calculation and analysis.Summary: CT can display the whole contour of the corneosclera better,but it is not enough to show the details of the local sclera.It is recommended to reconstruct the whole corneosclera by CT data,and to register and fuse with the data of the posterior sclera obtained by OCT,so as to obtain a three-dimensional model that takes into account the overall shape and local details.3D-MRI is an ideal tool for 3D reconstruction of eye content,which can indirectly reflect the shape of the inner surface of sclera and the extent of sclera expansion,but it can not replace CT in 3D reconstruction of corneoscleral.CBCT has the characteristics of low radiation,high accuracy and isotropy,which is very suitable for the examination and follow-up of pathological myopia,and has a good application prospect in ophthalmology.Part Two The influence of scleral thickness on the axial growth of patients with posterior staphylomaObjective: to simulate the effect of the thickness of sclera on the axial growth under different intraocular pressures.Methods: intraocular pressure was set at 15 mmhg,20mmhg and 30 mmhg respectively.The thickness of sclera in the putative area of posterior scleral staphyloma(a circle with a diameter of 4mm)was gradually reduced,and the distribution of sclera displacement was obtained under different conditions until the axial growth reached 2mm.Results: when the intraocular pressure was 15 mm Hg and the diameter of the posterior scleral staphyloma was 4 mm,if the sclera thickness was reduced from 0.8 mm to 0.37 mm,the axial length of the eye would be extended by 2 mm.When intraocular pressure was 20 mmhg and 30 mmhg,the corresponding sclera thickness was 0.42 mm and 0.57 mm.Summary: the thickness of sclera is closely related to the ability to resist deformation.Even if the strength of sclera is not considered to decrease,the change of sclera thickness alone can cause the obvious increase of ocular axis after exceeding a certain degree.When evaluating the risk of progression of pathological myopia,the thickness of sclera should be one of the monitoring indicators.Part Three The influence of the area of posterior staphyloma on the growth of ocular axisObjective: to simulate the effect of the area change of posterior staphyloma on the axial growth under different intraocular pressures.Methods: intraocular pressure was set to 15 mmhg,20mmhg and 30 mmhg respectively,and the initial sclera thickness of the posterior staphyloma area was set to 0.4mm.Assuming that the posterior staphyloma area was regular circle and the initial diameter was 2mm,the diameter of the posterior staphyloma area was gradually increased,and the sclera displacement distribution nephogram under different posterior staphyloma area was obtained,and the trend of the axial growth with the diameter was analyzed.Results: with the increase of the diameter of the posterior staphyloma area,the axial elongation of the eye increased nonlinearly.When the diameter of the posterior staphyloma area changes from 2mm to 4mm,the axial elongation is slow.When the diameter is more than 4mm,the axial growth speed increases with the increase of the diameter of the posterior staphyloma area.Summary: the diameter(area)of the grape swelling area is closely related to the growth rate of the ocular axis.When the diameter of the posterior staphyloma area exceeds 4mm,the growth rate of the ocular axis will increase significantly.The area of staphyloma is another important index to evaluate the risk of progression of pathological myopia.Part Four The influence of eyeball shape on the stress distribution of scleraObjective: To compare the local stress of sclera with the same thickness but different shape(curvature).Methods: the intraocular pressure was set to 20 mm Hg,the diameter of the posterior staphyloma area was set to 6mm,and the sclera thickness of the posterior staphyloma area was set to 0.4mm.The stress distribution of the regular spherical shell structure model and the individualized model reconstructed from the clinical image data were calculated respectively,and the local stress of the two models were compared and analyzed.Results: the stress concentration of the local sclera was obvious in myopic patients.In the range of 6 mm diameter of the posterior pole of the eyeball,compared with the standard spherical shell model,the stress difference of the local sclera was up to 5-8 times.Summary: due to the difference of scleral curvature,even in clinical emmetropia,the distribution of scleral stress is not uniform,which is more obvious in some myopia.In the area of stress concentration,whether the scleral remodeling can be initiated by the way of "stress-biological signal transmission",thus affecting the occurrence and development of myopia deserves further study.Part Five The influence of air pollutants on the safety of contact lensObjective: to apply multi physical field simulation method to study myopia.Methods: after the three-dimensional model of contact lens was established,the adsorption and deposition process of air pollutants on the front surface of contact lens was simulated by multi physical simulation method,and the results were compared with the clinical trial.Results: when PM2.5 particles were the main air pollutants,the air pollution below medium level would not increase the wearer’s intolerance to the contact lens or increase the related complications,but also had no significant impact on the optical performance of the contact lens.Summary: multi physical field coupling analysis can greatly expand the application of computer simulation technology in myopia research,but the possible errors in the modeling process are also increasing.When using the method of multi physical field simulation to study myopia,we must be careful in the analysis of simulation results,and attach great importance to the comparison of simulation prediction results and clinical research results.Conclusions:1.For myopia modeling and simulation research,there is no perfect single-mode imaging technology at present.To obtain 3D images that take into account the overall shape and local details,OCT / CT / MRI and other data should be registered and fused by multi-mode imaging technology.2.The thickness of sclera is closely related to its anti deformation ability.Even if the decrease of sclera intensity is not considered,the simple change of sclera thickness can cause the obvious increase of ocular axis after exceeding a certain degree.When evaluating the risk of progression of pathological myopia,sclera thickness should be one of the monitoring indicators.3.The diameter(area)of posterior staphyloma is closely related to the growth rate of ocular axis.With the increase of the diameter of the posterior scleral staphyloma area,the axial elongation showed a non-linear increasing trend.When the diameter of the staphyloma area was more than 4mm,the risk of axial growth increased significantly.4.There is obvious local stress concentration in sclera in myopic patients.Whether this kind of stress concentration can lead to sclera remodeling in the way of "force biological signal transmission" and thus initiate the occurrence and development of myopia deserves further study.5.With the development of myopia research,simple mechanical simulation has been unable to meet the needs of related research.In most cases,multi physical field coupling simulation must be used to simulate specific clinical problems. |
