Title of Invention	METHODS FOR DESIGNING CONTACT LENSES
Abstract	A method for designing a soft contact lens, comprising the steps of shaping a back surface of a lens to inversely correspond to a corneal shape, providing an aspheric front surface, and optimizing an optical performance of the front surface for one or more or all of pupil size, field, and lens centration using computer modelling using an eye model and a ray trace program; characterized in that: the step of optimizing comprises selecting an eye model and modifying the distance from the back of the eye lens to the retina of the eye model to represent a particular prescription; adding a spherical surface, representing the front surface of a contact lens, to the eye model to provide a lens-eye model; modifying the spherical front surface of the lens-eye model to an aspheric surface; adding object fields to the lens-eye model; setting a plurality of configurations of the lens-eye model representing different pupil sizes and lens decentrations; generating a merit function representing the optical performance of the lens-eye model at the object fields and configurations; initiating an optimisation routine; and changing the parameters of the front surface during the optimisation routine to minimize the merit function, thereby improving optical performance of the lens-eye model.

Title of Invention

METHODS FOR DESIGNING CONTACT LENSES

Abstract

A method for designing a soft contact lens, comprising the steps of shaping a back surface of a lens to inversely correspond to a corneal shape, providing an aspheric front surface, and optimizing an optical performance of the front surface for one or more or all of pupil size, field, and lens centration using computer modelling using an eye model and a ray trace program; characterized in that: the step of optimizing comprises selecting an eye model and modifying the distance from the back of the eye lens to the retina of the eye model to represent a particular prescription; adding a spherical surface, representing the front surface of a contact lens, to the eye model to provide a lens-eye model; modifying the spherical front surface of the lens-eye model to an aspheric surface; adding object fields to the lens-eye model; setting a plurality of configurations of the lens-eye model representing different pupil sizes and lens decentrations; generating a merit function representing the optical performance of the lens-eye model at the object fields and configurations; initiating an optimisation routine; and changing the parameters of the front surface during the optimisation routine to minimize the merit function, thereby improving optical performance of the lens-eye model.

Full Text	TITLE: Methods for designing contact lenses. FIELD OF THE INVENTION: The invention relates to methods for designing contact lenses. In particular, the invention provides methods taking into account the effects of field and decentration when the lens is on-eye. BACKGROUND OF THE INVENTION: The use of soft contact lenses for correction of visual acuity -defects is widely accepted. Typically, soft contact lenses are designed in air using simple, paraxial modeling. This method of lens design fails to take into account the effects of field and decentration when the contact lens wraps on the cornea resulting in suboptimal lens performance. Therefore, a need exists for method of lens design that improve lens performance. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS: Figure 1 is a depiction of decentration locations used in one embodiment of the design method of the invention. Figure 2 is a power curve for a lens of the invention. Figure 3 is a chart of the on-axis spot comparison of the lenses of the example. Figure 4 is a chart of the off-axis spot comparison of the lenses of the example. DETAILED DESCRIPTION OF THE INVENTION: The invention provides methods for design and production of contact lenses that take into account one or more of pupil size, field, and decentration. It is a discovery of the invention that, by taking these factors into account in lens design, a near diffraction limited contact lens can be designed, which lens has performance when off-axis, or decentered, that is superior to conventional soft contact lenses. By "near diffraction limited" is meant that the on-axis, centered performance of the lens is greater than about 80% of the diffraction limit of the lens plus eye. Additionally, the monofocal lenses designed using the method of the invention provide performance that minimizes the wearer's normally required optical cylinder without the need to include toricity in the lens due to the sharper image provided by the lens, which compensates for some of the blurring of image due to the wearer's cylinder. As yet another advantage, the lenses can be used to provide accommodation for near and intermediate distance tasks for emerging presbyopes. More specifically, the lenses may be useful for correcting near vision acuity of individuals who need less than about 1.75 diopters, preferably less than or equal to about 1.5 diopters of add power. In one embodiment, the invention provides a method of designing a soft contact lens according to claim 1 comprising, consisting essentially of and consisting of the steps of shaping a back surface of a lens to substantially inversely match a corneal shape, providing an aspheric front surface and optimizing the optical performance of the front surface of the lens for one or more of pupil size, field and lens centration. By "substantially inversely match" is meant that the back surface of the lens is substantially superimposable over the topography of the cornea. By "field" is meant a line of sight that enters the lens at an angle. The front surface of the lens designed according to the invention is an aspheric surface. Conventional aspheric lens surfaces are designed by providing a spherical surface and then adding a conic constant to the sag equation for the surface. In the present lens, preferably the aspheric surface is provided by taking a spherical surface and adding a conic constant to the sag equation along with a third or higher, preferably third to eight, numbered term in the power function. Alternately, the lens may be provided by describing it as a rotation about the optical axis of a decentered conic or odd asphere. In either method of describing the surface, the parameters to be varied in the design of the lens are the amount of decentration, the conic constant, the radius and the power terms. The spherical term, conic constant and higher order terms may be optimized using an appropriate merit function in an optical code design. Suitable optical design software is commercially available and includes, without limitation, ZEMAX™, CODE V™, OSLO™, and the like One ordinarily skilled in the art will recognize that the merit function will vary depending on the lens design code used and the optical parameters of the contact lens including, without limitation, refractive index and constraints on the lens thickness. The conic constant, aspheric values and power function used will vary depending on the prescription of the lens wearer and the design optimization preferences. However, a preferred range for the conic constant is-12.00 to about 3.00. In one embodiment of the lens designed according to the invention, the radius, conic constant, and aspheric terms are described according to the following equation: wherein Z is the sag of the surface; C is the curvature of the surface, which curvature is one divided by the radius of the surface of Y is the distance from the surface's geometric center;' K is the conic constant; and a is an aspheric term. In this embodiment, a terms of third through the eighth power are used. For a 3.5 diopter embodiment of this design, the values are as follows: R = 8.578046 mm; K = -5.708632; α1= 0; α2 = 0; α3 = 5.583403E-3; α4= -6.85069E-3; α5=6.107366E-3; α6= -2.68785E-3; α7= 6.08763 8E-4; and α8= -5.56538E-5. The back curve, or back surface, of the lenses designed according to the invention substantially inversely corresponds to a corneal shape. Preferably, the surface substantially inversely corresponds to an average corneal shape of a population of individuals. This back surface may be designed by any convenient method. By way of example, a standard corneal shape that is a population average corneal shape may be developed using a library of corneal topographies for a population. Suitable information relating to population corneal shapes are available from any number of sources including, without limitation, Atchison, David A. and George Smith, "Optics of the Human Eye", Butter-Heinemann, pp 15-18 (2000). Alternatively, the corneal shape of an individual's cornea may be used, which shape may be determined using any suitable corneal shape measuring device including, without limitation, a KERATRON™ device. The population average or individual corneal profile may be described mathematically including, without limitation, by the use of Zernike coefficients, polynomial power terms, Taylor series, Fourier series, conies, and the like. As yet another alternative, a corneal shape having radius of about 7.85 mm with a conic constant of -0.260 may be used, which values are derived from known measured values and represent the nominal values of a typical eye. The resulting lens is then optimized using a ray tracing program such as ZEMAX for performance in a plurality of fields. Preferably, the surface is optimized using centered and decentered fields. Figure 1 depicts a centered lens and the decentration fields used for the above-described embodiment. The centered, on axis lens 10 at 0 degrees is shown along with decentration 11 at +0.5 mm horizontal, decentration 12 at -0.5 mm horizontal, decentration 13 at +0.5 mm vertical and decentration 14 at -0.5 mm horizontal. Although an infinite number of configurations in any number of directions may be used, preferably, the lens is optimized centered relative to a pupil and at eight decentered configurations. The decentered values may be chosen to represent assumed random decentering of the lens on the eye with no decentration preference in any direction. Preferably, no less than four directions for decentration optimization are used, which directions are up, relative to the lens' center point and along the 90 degree axis, down along the 270 degree axis, left along the 180 degree axis and right along the 0 degree axis. The lens may be further optimized for different pupil sizes. Any number of pupil sizes may be used. Preferably, two pupil sizes, 3 and 5 mm respectively, are used, which sizes approximate population averages for low and high illumination lighting conditions. Because pupil size varies with illumination, at larger pupil sizes resulting from low illumination conditions, more aberrations will be experienced by the lens wearer. Also, typically spot size increases with pupil size in the human eye. Thus, by optimizing for more than one pupil size, lens performance may be improved. The pupil sizes 3 and 5 mm were used with the above-described decentration embodiments, shown in Figure 1, for a total of 10 configurations, each with 5 fields. Using these 10 configurations, the front surface shape parameters were varied by the ray tracing program to optimize the lens-eye system using the defined merit function, which was Modulation Transfer Function ("MTF") at 50 and 100 cycles for all fields and configurations. By optimizing for both centered and decentered conditions and fields, aberrations introduced into the image by lens decentering and fields may be reduced. Optimization of the lens surface is carried out using computer modeling using an eye model and a ray trace program. Preferably, the eye model used is a model that represents the 5th and 95th percentile eyes in addition to the average eye. Suitable ray trace programs include, without limitation, those found in ZEMAX, CODE V, OSLO, and the like. A merit function is used for each value of pupil size and centration and decentration. One ordinarily skilled in the art will recognize that the merit function selected will be determined based on the desired lens design. Merit functions that optimize optical performance criteria such as spot size, MTF, OTF, Strehl Ratio, encircled energy, RMS wavefront error, and the like and combinations thereof also may be used. Figure 2 depicts the power curve for a contact lens designed for 3 and 5 mm pupils and accounting for fields of 0 degrees and +/- 5 degrees in X and Y and 0.5 mm decentration in X and Y using the design approach of the invention. The plot is an average of several designs from piano to minus 3.5 diopters. Optimization is carried out wherein an eye model is selected and the distance from the back of the eye lens to the retina in the model is modified to represent a particular prescription. A spherical surface, representing the anterior surface of a contact lens is added to the eye model, and the surface is modified to an aspheric surface, like the surface represented by Equation I. Various object fields are added to the model and multiple configurations are then set that represent different, selected pupil sizes and lens decentrations. A merit function is generated representing the performance of the lens-eye model combination at the various fields and configurations. The parameters of the lens surface are changed to variables and the optimization routine in the optical design program is initiated to minimize the merit function improving optical performance of the lens-eye model. The lens of the invention provides performance for off-axis object points when the lens is decentered that is superior to conventional soft contact lenses. Additionally, the lenses of the invention provide some correction for the wearer's optical cylinder that minimizes or substantially eliminates the need to include optical cylinder correction for the lens wearer. The lenses designed according to the invention may be made from any suitable lens forming material for manufacturing hard or soft contact lenses. Illustrative materials for formation of soft contact lenses include, without limitation, silicone elastomers, silicone-containing macromers including, without limitation, those disclosed in United States Patent Nos. 5,371,147, 5,314,960, and 5,057,578 incorporated in their entireties by reference, hydrogels, silicone-containing hydrogels, and the like and combinations thereof. More preferably, the surface is a siloxane, or contains a siloxane functionality including, without limitation, polydimethyl siloxane macromers, methacryloxypropyl siloxanes, and mixtures thereof, silicone hydrogel or a hydrogel. Illustrative materials include, without limitation, acquafilcon, etafilcon, genfilcon, lenefilcon, senefilcon, balafilcon, lotrafilcon, or galyfilcon. Curing of the lens material may be carried out by any convenient method. For example, the material may be deposited within a mold and cured by thermal, irradiation, chemical, electromagnetic radiation curing and the like and combinations thereof. Preferably, molding is earned out using ultraviolet light or using the full spectrum of visible light. More specifically, the precise conditions suitable for curing the lens material will depend on the material selected and the lens to be formed. Suitable processes are disclosed in U.S. Patents Nos. 4,495,313, 4,680,336, 4,889,664, 5,039,459, and 5,540,410. The contact lenses designed according to the invention may be formed by any convenient method. One such method uses a lathe to produce mold inserts. The mold inserts in turn are used to form molds. Subsequently, a suitable lens material is placed between the molds followed by compression and curing of the resin to form the lenses of the invention. One ordinarily skilled in the art will recognize that any other number of known methods may be used to produce the lenses. EXAMPLES: The performance of a lens designed according to the method of the invention and a lens designed using a paraxial optical design method in air were compared. The paraxial design, Lens A, was an ACUVUE® 2 BRAND etafilcon lens of-3.00 diopters. The Lens A design was wrapped onto a nominal cornea using Finite Element Analysis ("FEA") techniques. The lens shape resulting from the FEA was then loaded into the ZEMAX optical ray trace program. Figures 3 and 4 are charts below comparing the 0 and 5 degree field RMS spot size at up to ± - 0.5 diopters from the central design point of the wrapped Lens a design to a lens design of the invention, Lens B. Lens B is a -3.00 diopters etafilcon lens. The merit function used for Lens B was the RMS spot size at focus, with a ± 5 degree field and a 0.5 mm decentration in ± X and ± Y directions. At these decentered conditions, the fields were optimized for RMS spot size at a O degree field and at ± 5 degrees fields in X and Y. The total number of configurations used was 10 and all conditions were at 2.5 and 4.5 mm apparent pupils. Figures 3 and 4 show that the design of the invention had a superior, or smaller, RMS spot size at a 4 mm apparent pupil for up to 0.5 diopters from the design point as compared to Lens A. WE CLAIM: 1. A method for designing a soft contact lens, comprising the steps of shaping a back surface of a lens to inversely correspond to a corneal shape, providing an aspheric front surface, and optimizing an optical performance of the front surface for one or more or all of pupil size, field, and lens centration using computer modelling using an eye model and a ray trace program; characterized in that: the step of optimizing comprises selecting an eye model and modifying the distance from the back of the eye lens to the retina of the eye model to represent a particular prescription; adding a spherical surface, representing the front surface of a contact lens, to the eye model to provide a lens-eye model; modifying the spherical front surface of the lens-eye model to an aspheric surface; adding object fields to the lens-eye model; setting a plurality of configurations of the lens-eye model representing different pupil sizes and lens decentrations; generating a merit function representing the optical performance of the lens-eye model at the object fields and configurations; initiating an optimisation routine; and changing the parameters of the front surface during the optimisation routine to minimize the merit function, thereby improving optical performance of the lens-eye model. 2. The method as claimed in claim 1, wherein the aspheric surface is provided by taking a spherical surface and adding a conic constant to a sag equation along with a third or higher numbered term in a power function. 3. The method as claimed in claim 1, wherein the aspheric surface is provided by taking a spherical surface and adding a conic constant to a sag equation along with a third to eight numbered term in a power function. 4. The method as claimed in claim 1, wherein the conic constant is -12.00 to about -3.00. 5. The method as claimed in claim 1, wherein optimizing is carried out using a lens centered relative to a pupil and a plurality of decentered values relative to the pupil. 6. The method as claimed in claim 1, wherein optimizing is carried out using a lens centered relative to a pupil and between 4 and 8 decentered values relative to the pupil. 7. The method as claimed in claim 5, wherein the optimizing further comprises optimizing for a plurality of pupil sizes. 8. The method as claimed in claim 5, wherein optimizing is carried out using a plurality of fields. 9. The method as claimed in claim 5, wherein the optimizing further comprises optimizing for pupil sizes of 3 and 5 mm. ABSTRACT Title: Methods for designing contact lenses. A method for designing a soft contact lens, comprising the steps of shaping a back surface of a lens to inversely correspond to a corneal shape, providing an aspheric front surface, and optimizing an optical performance of the front surface for one or more or all of pupil size, field, and lens centration using computer modelling using an eye model and a ray trace program; characterized in that: the step of optimizing comprises selecting an eye model and modifying the distance from the back of the eye lens to the retina of the eye model to represent a particular prescription; adding a spherical surface, representing the front surface of a contact lens, to the eye model to provide a lens-eye model; modifying the spherical front surface of the lens-eye model to an aspheric surface; adding object fields to the lens-eye model; setting a plurality of configurations of the lens-eye model representing different pupil sizes and lens decentrations; generating a merit function representing the optical performance of the lens-eye model at the object fields and configurations; initiating an optimisation routine; and changing the parameters of the front surface during the optimisation routine to minimize the merit function, thereby improving optical performance of the lens-eye model.

Full Text

TITLE:
Methods for designing contact lenses.
FIELD OF THE INVENTION:
The invention relates to methods for designing contact lenses. In particular,
the invention provides methods taking into account the effects of field and
decentration when the lens is on-eye.
BACKGROUND OF THE INVENTION:
The use of soft contact lenses for correction of visual acuity -defects is widely
accepted. Typically, soft contact lenses are designed in air using simple,
paraxial modeling. This method of lens design fails to take into account the
effects of field and decentration when the contact lens wraps on the cornea
resulting in suboptimal lens performance. Therefore, a need exists for method
of lens design that improve lens performance.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 is a depiction of decentration locations used in one embodiment of
the design method of the invention.
Figure 2 is a power curve for a lens of the invention.
Figure 3 is a chart of the on-axis spot comparison of the lenses of the
example.
Figure 4 is a chart of the off-axis spot comparison of the lenses of the
example.
DETAILED DESCRIPTION OF THE INVENTION:
The invention provides methods for design and production of contact lenses
that take into account one or more of pupil size, field, and decentration. It

is a discovery of the invention that, by taking these factors into account in
lens design, a near diffraction limited contact lens can be designed, which lens
has performance when off-axis, or decentered, that is superior to conventional
soft contact lenses. By "near diffraction limited" is meant that the on-axis,
centered performance of the lens is greater than about 80% of the diffraction
limit of the lens plus eye.
Additionally, the monofocal lenses designed using the method of the
invention provide performance that minimizes the wearer's normally
required optical cylinder without the need to include toricity in the lens due
to the sharper image provided by the lens, which compensates for some of
the blurring of image due to the wearer's cylinder. As yet another
advantage, the lenses can be used to provide accommodation for near and
intermediate distance tasks for emerging presbyopes. More specifically,
the lenses may be useful for correcting near vision acuity of individuals who
need less than about 1.75 diopters, preferably less than or equal to about
1.5 diopters of add power.
In one embodiment, the invention provides a method of designing a soft
contact lens according to claim 1 comprising, consisting essentially of and
consisting of the steps of shaping a back surface of a lens to substantially
inversely match a corneal shape, providing an aspheric front surface and
optimizing the optical performance of the front surface of the lens for one or
more of pupil size, field and lens centration.
By "substantially inversely match" is meant that the back surface of the lens is
substantially superimposable over the topography of the cornea. By "field" is
meant a line of sight that enters the lens at an angle.

The front surface of the lens designed according to the invention is an
aspheric surface. Conventional aspheric lens surfaces are designed by
providing a spherical surface and then adding a conic constant to the sag
equation for the surface. In the present lens, preferably the aspheric
surface is provided by taking a spherical surface and adding a conic
constant to the sag equation along with a third or higher, preferably third to
eight, numbered term in the power function. Alternately, the lens may be
provided by describing it as a rotation about the optical axis of a decentered
conic or odd asphere.
In either method of describing the surface, the parameters to be varied in
the design of the lens are the amount of decentration, the conic constant,
the radius and the power terms. The spherical term, conic constant and
higher order terms may be optimized using an appropriate merit function in
an optical code design. Suitable optical design software is commercially
available and includes, without limitation, ZEMAX™, CODE V™, OSLO™,
and the like One ordinarily skilled in the art will recognize that the merit
function will vary depending on the lens design code used and the optical
parameters of the contact lens including, without limitation, refractive index
and constraints on the lens thickness.
The conic constant, aspheric values and power function used will vary
depending on the prescription of the lens wearer and the design
optimization preferences. However, a preferred range for the conic constant
is-12.00 to about 3.00.
In one embodiment of the lens designed according to the invention, the
radius, conic constant, and aspheric terms are described according to the
following equation:

wherein Z is the sag of the surface;
C is the curvature of the surface, which curvature is one divided by the radius of
the surface of
Y is the distance from the surface's geometric center;'
K is the conic constant; and
a is an aspheric term.
In this embodiment, a terms of third through the eighth power are used. For a
3.5 diopter embodiment of this design, the values are as follows:
R = 8.578046 mm;
K = -5.708632;
α1= 0;
α2 = 0;
α3 = 5.583403E-3;
α4= -6.85069E-3;
α5=6.107366E-3;
α6= -2.68785E-3;
α7= 6.08763 8E-4; and
α8= -5.56538E-5.
The back curve, or back surface, of the lenses designed according to the
invention substantially inversely corresponds to a corneal shape. Preferably,
the surface substantially inversely corresponds to an average corneal shape of
a population of individuals. This back surface may be designed by any
convenient method. By way of example, a standard corneal shape that is a

population average corneal shape may be developed using a library of corneal
topographies for a population. Suitable information relating to population
corneal shapes are available from any number of sources including, without
limitation, Atchison, David A. and George Smith, "Optics of the Human Eye",
Butter-Heinemann, pp 15-18 (2000). Alternatively, the corneal shape of an
individual's cornea may be used, which shape may be determined using any
suitable corneal shape measuring device including, without limitation, a
KERATRON™ device. The population average or individual corneal profile
may be described mathematically including, without limitation, by the use of
Zernike coefficients, polynomial power terms, Taylor series, Fourier series,
conies, and the like. As yet another alternative, a corneal shape having radius
of about 7.85 mm with a conic constant of -0.260 may be used, which values
are derived from known measured values and represent the nominal values of
a typical eye.
The resulting lens is then optimized using a ray tracing program such as
ZEMAX for performance in a plurality of fields. Preferably, the surface is
optimized using centered and decentered fields. Figure 1 depicts a centered
lens and the decentration fields used for the above-described embodiment.
The centered, on axis lens 10 at 0 degrees is shown along with decentration
11 at +0.5 mm horizontal, decentration 12 at -0.5 mm horizontal,
decentration 13 at +0.5 mm vertical and decentration 14 at -0.5 mm
horizontal. Although an infinite number of configurations in any number of
directions may be used, preferably, the lens is optimized centered relative to a
pupil and at eight decentered configurations. The decentered values may be
chosen to represent assumed random decentering of the lens on the eye with
no decentration preference in any direction. Preferably, no less than four
directions for decentration optimization are used, which directions are up,
relative to the lens' center point and along the 90 degree axis, down along the
270 degree axis, left along the 180 degree axis and right along the 0 degree
axis.

The lens may be further optimized for different pupil sizes. Any number of pupil
sizes may be used. Preferably, two pupil sizes, 3 and 5 mm respectively, are
used, which sizes approximate population averages for low and high
illumination lighting conditions. Because pupil size varies with illumination, at
larger pupil sizes resulting from low illumination conditions, more aberrations will
be experienced by the lens wearer. Also, typically spot size increases with pupil
size in the human eye.
Thus, by optimizing for more than one pupil size, lens performance may be
improved. The pupil sizes 3 and 5 mm were used with the above-described
decentration embodiments, shown in Figure 1, for a total of 10 configurations,
each with 5 fields. Using these 10 configurations, the front surface shape
parameters were varied by the ray tracing program to optimize the lens-eye
system using the defined merit function, which was Modulation Transfer
Function ("MTF") at 50 and 100 cycles for all fields and configurations. By
optimizing for both centered and decentered conditions and fields, aberrations
introduced into the image by lens decentering and fields may be reduced.
Optimization of the lens surface is carried out using computer modeling
using an eye model and a ray trace program. Preferably, the eye model
used is a model that represents the 5th and 95th percentile eyes in addition
to the average eye. Suitable ray trace programs include, without limitation,
those found in ZEMAX, CODE V, OSLO, and the like.
A merit function is used for each value of pupil size and centration and
decentration. One ordinarily skilled in the art will recognize that the merit
function selected will be determined based on the desired lens design.
Merit functions that optimize optical performance criteria such as spot size,
MTF, OTF, Strehl Ratio, encircled energy, RMS wavefront error, and the like

and combinations thereof also may be used. Figure 2 depicts the power curve
for a contact lens designed for 3 and 5 mm pupils and accounting for fields of 0
degrees and +/- 5 degrees in X and Y and 0.5 mm decentration in X and Y
using the design approach of the invention. The plot is an average of several
designs from piano to minus 3.5 diopters.
Optimization is carried out wherein an eye model is selected and the distance
from the back of the eye lens to the retina in the model is modified to represent
a particular prescription. A spherical surface, representing the anterior surface
of a contact lens is added to the eye model, and the surface is modified to an
aspheric surface, like the surface represented by Equation I. Various object fields are
added to the model and multiple configurations are then set that represent different,
selected pupil sizes and lens decentrations. A merit function is generated
representing the performance of the lens-eye model combination at the various fields
and configurations. The parameters of the lens surface are changed to variables and
the optimization routine in the optical design program is initiated to minimize the merit
function improving optical performance of the lens-eye model.
The lens of the invention provides performance for off-axis object points when the
lens is decentered that is superior to conventional soft contact lenses. Additionally,
the lenses of the invention provide some correction for the wearer's optical cylinder
that minimizes or substantially eliminates the need to include optical cylinder
correction for the lens wearer.
The lenses designed according to the invention may be made from any suitable lens
forming material for manufacturing hard or soft contact lenses. Illustrative materials for
formation of soft contact lenses include, without limitation, silicone elastomers,
silicone-containing macromers including, without limitation, those disclosed in United
States Patent Nos. 5,371,147, 5,314,960, and 5,057,578 incorporated in their
entireties by reference, hydrogels, silicone-containing hydrogels, and the like and

combinations thereof. More preferably, the surface is a siloxane, or contains a
siloxane functionality including, without limitation, polydimethyl siloxane macromers,
methacryloxypropyl siloxanes, and mixtures thereof, silicone hydrogel or a hydrogel.
Illustrative materials include, without limitation, acquafilcon, etafilcon, genfilcon,
lenefilcon, senefilcon, balafilcon, lotrafilcon, or galyfilcon.
Curing of the lens material may be carried out by any convenient method. For
example, the material may be deposited within a mold and cured by thermal,
irradiation, chemical, electromagnetic radiation curing and the like and combinations
thereof. Preferably, molding is earned out using ultraviolet light or using the
full spectrum of visible light. More specifically, the precise conditions suitable
for curing the lens material will depend on the material selected and the lens to
be formed. Suitable processes are disclosed in U.S. Patents Nos. 4,495,313,
4,680,336, 4,889,664, 5,039,459, and 5,540,410.
The contact lenses designed according to the invention may be formed by any
convenient method. One such method uses a lathe to produce mold inserts.
The mold inserts in turn are used to form molds. Subsequently, a suitable lens
material is placed between the molds followed by compression and curing of
the resin to form the lenses of the invention. One ordinarily skilled in the art will
recognize that any other number of known methods may be used to produce
the lenses.
EXAMPLES:
The performance of a lens designed according to the method of the invention
and a lens designed using a paraxial optical design method in air were
compared. The paraxial design, Lens A, was an ACUVUE® 2 BRAND etafilcon
lens of-3.00 diopters. The Lens A design was wrapped onto a nominal cornea

using Finite Element Analysis ("FEA") techniques. The lens shape resulting
from the FEA was then loaded into the ZEMAX optical ray trace program.
Figures 3 and 4 are charts below comparing the 0 and 5 degree field RMS spot
size at up to ± - 0.5 diopters from the central design point of the wrapped Lens
a design to a lens design of the invention, Lens B. Lens B is a -3.00 diopters
etafilcon lens. The merit function used for Lens B was the RMS spot size at
focus, with a ± 5 degree field and a 0.5 mm decentration in ± X and ± Y
directions. At these decentered conditions, the fields were optimized for
RMS spot size at a O degree field and at ± 5 degrees fields in X and Y.
The total number of configurations used was 10 and all conditions were at
2.5 and 4.5 mm apparent pupils.
Figures 3 and 4 show that the design of the invention had a superior, or
smaller, RMS spot size at a 4 mm apparent pupil for up to 0.5 diopters from
the design point as compared to Lens A.

WE CLAIM:
1. A method for designing a soft contact lens, comprising the steps of shaping a
back surface of a lens to inversely correspond to a corneal shape, providing an
aspheric front surface, and optimizing an optical performance of the front surface
for one or more or all of pupil size, field, and lens centration using computer
modelling using an eye model and a ray trace program; characterized in that:
the step of optimizing comprises selecting an eye model and modifying the
distance from the back of the eye lens to the retina of the eye model to
represent a particular prescription;
adding a spherical surface, representing the front surface of a contact lens, to the
eye model to provide a lens-eye model;
modifying the spherical front surface of the lens-eye model to an aspheric
surface;
adding object fields to the lens-eye model;
setting a plurality of configurations of the lens-eye model representing different
pupil sizes and lens decentrations;
generating a merit function representing the optical performance of the lens-eye
model at the object fields and configurations;

initiating an optimisation routine; and
changing the parameters of the front surface during the optimisation routine to
minimize the merit function, thereby improving optical performance of the lens-eye
model.
2. The method as claimed in claim 1, wherein the aspheric surface is provided
by taking a spherical surface and adding a conic constant to a sag equation
along with a third or higher numbered term in a power function.
3. The method as claimed in claim 1, wherein the aspheric surface is provided by
taking a spherical surface and adding a conic constant to a sag equation along with
a third to eight numbered term in a power function.
4. The method as claimed in claim 1, wherein the conic constant is -12.00 to
about -3.00.
5. The method as claimed in claim 1, wherein optimizing is carried out using a
lens centered relative to a pupil and a plurality of decentered values relative to
the pupil.
6. The method as claimed in claim 1, wherein optimizing is carried out using a
lens centered relative to a pupil and between 4 and 8 decentered values
relative to the pupil.

7. The method as claimed in claim 5, wherein the optimizing further comprises
optimizing for a plurality of pupil sizes.
8. The method as claimed in claim 5, wherein optimizing is carried out using a
plurality of fields.
9. The method as claimed in claim 5, wherein the optimizing further comprises
optimizing for pupil sizes of 3 and 5 mm.

ABSTRACT

Title: Methods for designing contact lenses.
A method for designing a soft contact lens, comprising the steps of shaping a
back surface of a lens to inversely correspond to a corneal shape, providing an
aspheric front surface, and optimizing an optical performance of the front surface
for one or more or all of pupil size, field, and lens centration using computer
modelling using an eye model and a ray trace program; characterized in that: the
step of optimizing comprises selecting an eye model and modifying the
distance from the back of the eye lens to the retina of the eye model to
represent a particular prescription; adding a spherical surface, representing the
front surface of a contact lens, to the eye model to provide a lens-eye model;
modifying the spherical front surface of the lens-eye model to an aspheric
surface; adding object fields to the lens-eye model; setting a plurality of
configurations of the lens-eye model representing different pupil sizes and lens
decentrations; generating a merit function representing the optical performance
of the lens-eye model at the object fields and configurations; initiating an
optimisation routine; and changing the parameters of the front surface during
the optimisation routine to minimize the merit function, thereby improving optical
performance of the lens-eye model.

METHODS FOR DESIGNING CONTACT LENSES

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