Calculation of post-lens pressure profile for contact lens
View Patent ↗A system for facilitating contact lens design comprises an input unit for input of design parameters, and a processing unit for calculating a post-lens pressure profile based on the design parameters. The processing unit is arranged, in use, to perform a finite model calculation allowing for large deflection and non-linear geometry effects in the deformation of a model lens shape. Preferably the finite element model calculation utilizes solid elements of modelling the lens shape. A contact comprising a high Young's modulus material such as silicone hydrogel can be designed to have a maximum corneal or limbal post-lens pressure valve of less than 250 Pa.
1. A system for facilitating contact lens design before manufacture, the system comprising:
an input unit configured for input of model design parameters based solely on at least one from a group consisting of model designs and model measurements, and
a processing unit for calculating a post-lens pressure profile based on the model design parameters, the post-lens pressure profile is calculated with respect to a model representation of a standard eye, wherein the post-lens pressure profile is calculated by applying a frictionless sliding contact approximation between the model contact lens and the model eye, wherein the frictionless sliding contact approximation comprises a small distance separation between the lens and the eye;
wherein the processing unit is arranged, in use, to perform a finite element model calculation allowing for large deflection/non-linear geometry effects in the deformation of a model lens shape, wherein the finite element model calculation utilizes solid elements for modeling the lens shape,
wherein the model lens and eye parameters are defined by applying a pressure evenly across the contact lens surface, examining pressure peaks identified from the pressure application, evaluating continuity of the pressure peaks and repeating the process if not acceptably continuous, and analyzing the height of the pressure peaks.
2. A system as claimed in claim 1 , wherein a lens material of the contact lens to be modeled is a high oxygen permeability (Dk) material, and the processing unit is arranged to model the lens at an elasticity representative of the intended lens material.
3. A system as claimed in claim 2 , wherein the intended lens material is modeled at a Young's modulus value representative of silicone hydrogel of a range from about 0.8 to 2 MPa.
4. A system as claimed in claim 3 , wherein the finite element model calculation comprises second order elements, whereby, in use, second-order properties of the model lens are considered by the system.
5. A system as claimed in claim 3 , wherein the processing unit is arranged, in use, such that a 2-D axisymmetric geometry is applied to a lens/eye interaction problem in the calculation of the post-lens pressure profile.
6. A system as claimed in claim 3 , wherein the processing unit is arranged, in use, to calculate the post-lens pressure profile based on a closed eye, steady-state finite element model calculation.
7. A system as claimed in claim 3 , wherein the corneoscleral surface is represented as a rigid body in the finite element model calculation.
8. A system as claimed in claim 3 , wherein a shape of the comeoscleral surface is approximated based on an ellipsoid-and-sphere formulation in the finite element model calculation.
9. A method of calculating a post-lens pressure profile based on model design parameters based solely on at least one from a group consisting of model designs and model measurements, comprising performing a finite element model calculation allowing for large deflection/non-linear geometry effects in the deformation of a model lens shape, wherein the finite element model calculation utilizes solid elements for modeling the lens shape, wherein the post-lens pressure profile is calculated before manufacture with respect to a model representation of a standard eye, wherein the post-lens pressure profile is calculated by applying a frictionless sliding contact approximation between the model contact lens and the model eye, wherein the frictionless sliding contact approximation comprises a small distance separation between the lens and the eye, wherein the model lens and eye parameters are defined by applying a pressure evenly across the contact lens surface, examining pressure peaks identified from the pressure application, evaluating continuity of the pressure peaks and repeating the process if not acceptably continuous, and analyzing the height of the pressure peaks.
10. A method as claimed in claim 9 , wherein a lens material of the contact lens to be modeled is a high oxygen permeability (Dk) material, and the lens is modeled at an elasticity representative of the intended lens material.
11. A method as claimed in claim 10 , wherein the intended lens material is modeled at a Young's modulus value representative of silicone hydrogel of a range from about 0.8 to 2 MPa.
12. A method as claimed in claim 11 , wherein the finite element model calculation comprises second order elements, whereby second-order properties of the model lens are considered.
13. A method as claimed in claim 11 , wherein a 2-D axisymmetric geometry is applied to a lens/eye interaction problem in the calculation of the post-lens pressure profile.
14. A method as claimed in claim 11 , wherein the post-lens pressure profile is based on a closed eye, steady-state finite element model calculation.
15. A method as claimed in claim 11 , wherein the comeoscleral surface is represented as a rigid body in the finite element model calculation.
16. A method as claimed in claim 11 , wherein a shape of the comeoscleral surface is approximated based on an ellipsoid-and-sphere formulation in the finite element model calculation.