Title of Invention

DESIGN OF A SOFT CONTACT LENS BASED UPON NOVEL METHODS OF CORNEAL TOPOGRAPHIC ANALYSIS

Abstract A method is provided which is used to design soft contact iens via corneal topographic analysis. The topography of the cornea is matched to a corresponding topography of a soft contact lens. A geometrical transformation which maps the corneal elevation onto the back surface of an unflexed soft contact lens is used to minimize errors induced by flexure of the lens. The mapping transformation takes into account the effects of flexure. As a result, the contact lens has a back surface with a curvature which matches the specific elevations of the cornea, while the front surface can be spherical or any desired symmetrical or asymmetrical shape.
Full Text DESIGN OF A SOFT CONTACT LENS BASED UPON NOVEL METHODS OF
CORNEAL TOPOGRAPHIC ANALYSIS
FIELD OF THE INVENTION
The present invention generally relates to soft contact lenses and a method of
designing such lenses. More specifically, the present invention relates to a suit contact lens and the
design ot'such a lens using novel methods of corneal topographic analysis
BACKGROUND OF THE INVENTION
The curvature of an unflexed soft contact lens, such as a lens placed in physiological
saline solution, is different than the curvature of the same lens placed on the cn e. This change in
cui-\'ature is often reteired to as tlexure'. (See. e.g.. .A..G. Bennet. "Power Changes In Soft Contact
I enses Due To Bending"", The Ophthalmic Optician. 16:939-945. 1976, the rontents of which are
mcorporated herein by reference). In the case of thin soft lenses placed on a i>Dical eye. this change
in curvature does not substantially affect the lens power. However, in the case of thick lenses of
high positive power, bifocal soft lenses, or for subjects with corneal ahnoirnalities (e.g., due to
keratoconusi. the change in power due to flexure may be signitlcant
SUMMARY OF THE INVENTION
The present invention matches the topography of iiie cornea to a conesponding
topography of a soft contact lens. A geometrical transformation is used which maps the cornea!
elevation onto the back surface of an unflexed soft contact lens in such a wa\ that the enor induced
by flexure of the lens is minimized. The mapping transformation takes into account the effects of
flexure. The resulting contact lens has a back surface having a curvature which matches the specific
elevations of the cornea, while the front surface can be spherical or any desired symmetrical or
asymmetrical shape.
According to the present invention, a geometrical transformation is used v/hich maps
the corneal elevations, measured by a videokeratoscope, for example, into the back surface of an
unflexed lens. The mapping is performed in such a way that the error introduced by flexure is
minimized. The approach of the present invention utilizes a number of simplifications in achieving
the desired lens design. The tlrst simplification is that corneal elevations (i.e., difference away from
an underlying best fit snhere) are taken as being much smaller than the apical radius of curvature of
the cornea. The second simplification is that the lens material, when flexured, is uniformly deformed
and all points on the lens stay in the same azimuthal angle. These simplifications help in achieving
a practical engineering solution to the design of such lenses.
The mapping procedure is performed in two steps. First, the elevations of the cornea
are mapped to a larger scale surface having a radius of curvature corresponding to that of an unflexed
soft contact lens. Second, the scaled up elevation information is scaled down using an area
preser\ing transformation.
Other features and advantages of the present invention will become apparent from
the iollov\ing detailed description, taken in conjunction with the accompanying drawings which
illustrate, by way of example, the features of the present invention.
DESCRIPTION OF THE DRAWINGS
Figure I is an illustration of the actual corneal elevations and their best spherical fit
(in a least squares sense), denoted by f(x) and g(x), respectively;
Figure 2 is an illustration of the original elevation. f(9), the best spherical fit for the
original elevation. g(9). the scaled up elevation, f'(0), and the best spherical fit for the scaled up
elevation. g'"(9);
Figure 3 is an illustration of the original corneal elevation. f(9), the scaled up
elevation, f "(9), and the scaled down elevation. f'XQ), along with the best spherical fits, g(9) and
g''(e);
Figure 4 is an illustration of an example where the original corneal elevations are
modeled by a sphere v.ith a superimposed two dimensional sine function;
Figure ^ is an illustration of the scaled up version of the corneal elevations illustrated
in Figure 4; and
Figure t^> is an illustration of the scaled down version of the corneal elevations
obtained using Equation (4).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
According to the present invention, arbitrar>- corneal topographic information is
acquired about a subject's eye. This information is acquired, tor example, using a corneal
topographer which has high resolution along the z-axis, above and below the mean spherical surface
of the cornea. This intbrmation is then mathematicallv transformed into elevation data. The
elevation data may then be transformed onto a grid pattern, which may be rectilinear, polar
concentric, or of a spiral format which corresponds to the mechanism by which the surface of the
lens or lens mold may be tooled using a CNC (computer numenc control) lathe, mill or bit
addressable device. The surface which is tooled or lathed may be the surface of a non hydrated
corneal contact lens polymer button or an injection molded tool insert. The surface may also be
tooled or lathed using a programmable laser ablation device.
Initially, the elevation data is applied to the soft contact lens model in its unflexed
state. .Also, the elevation data may be applied to the contact lens back surface only, the front surface
only, or some defined combination oi the front and back surfaces.
Next, the elevation data is transformed by taking into account soft lens flexure (i.e.,
wrap) when the lens is placed on the eye Typically, soft lenses are flatter, e.g.. by 1.0-1.5 mm. than
the cornea that they are placed on. Thus, both elevation and wrap must be considered when utilizing
the original corneal topographic data to make a soft contact lens surface or mold insert.
The flexure transformed elevation data may be mapped onto a CNC gnd partem and
used to make a lens or a mold tool surface. The resulting lens utilizing such information will be a
lens which exhibits fluctuations in thickness on the gnd pattern which may or may not be
rotationally symmetrical about the center of the lens. When the manufactured soft lens wraps
perfectly to the underlying cornea, the fluctuations in surface elevation (i.e., above and below the
mean spherical surface of the cornea) will typically disappear. In this way, corneal irregularities may
be neutralized and optical aberrations due to irregular corneal topography may likewise be
substantially eliminated. To achieve any additional degree of optical <:orrection. such a spherical> or astigmatic focus, appropnate curvatures may be incorporated in the front surface, hack surface,
or both front and back surfaces of the lens.
For practical considerations, it is assumed that the ideal cornea is spherical. In such
a case, the actual corneal elevations and their best spherical fit (in a least squares sense). are denoted
by f(x) and g(xi, respectively, as shown in Figure 1. The function e(x) is part of a sphere having
radius R,.
In general, the radius R. of the unflexed soft contaci lens is spherical and is larger
than that of the best spherical fit, g(x). Accordingly, the first step is to transibrm the corneal
elevations f(x) into a larger scale for which the best spherical fit will have a radius equal to R,, One
approach in simplifying the transformation is to represent the function f(x) in polar coordinates as
f(9). Then, using a scale factor, a = R^/R,. the scaled version ot the corneal elevation may be
expressed as:
f"(e) = af(0) (1)
Figure 2 illustrates the original elevation, f(9), the best spherical lit tor the originaJ
elevation, g(9), the scaled up elevation, f "(9), and the best spherical fit for the scaled up elevation,
g'"(9).
In the second stage, the scaled up corneal elevation t" '(9) is scaled down so that the
area covered by the soft lens corresponds to the area of the cornea. In a iwo dimensional case, this
scaling down is obtained according to the following relationship;
-4-
f'>(e) = a' f"[(e-7i/2)/a + 7t.'2] + R:(l-l/al (2)
Figure ]¦ illustrates the original corneal elevation, f(9). the scaled up elevation, f' '(9),
and the scaled down elevation. f-'(0), along with the best spherical fits, g(6) and g'"(0).
The mapping transformations given in Equations (1) and (2) are not restricted to the
case where the cornea and the back surface of the contact lens are spherical. Rather, the tme corneal
and lens curvatures, as measured by a videokeratoscope, may be used to calculate the scale parameter
a as a ratio between the lens and the corneal radius of cur\'ature. In the general case, the scale
parameter will be a function of 9. i.e., u = R.(e)/R|(G) = a(Q).
The mapping transformation discussed above may be generalized to the case of three
dimensional transformation. In such a case, the corneal elevations may be represented by a function.
f(6.(p), where Q and (p represent the azimuth and elevation angle, respectively. As discussed above,
the original elevation data is scaled up from a radius of curvature R, (6,(p) onto a surface having a
radius of curvature R^ iG.cp) using the following transfonnation relationship:
f"(e,(p) = af(e,(p) (1)
where a = R,(G.(p)/R|(B,(p).
Figure 4 illustrates an example where the original comeal elevations are modeled ba sphere with a superimposed two dimensional sine function. Figure 5 illustrates the scaled up
version of the comeal elevations illustrated m Figure 4. obtained using Equation (3 ) above.
To obtain a desired back surface of the soft contact lens, the function f "(B,cp) is scaled
back down, as discussed above. However, m the three dimensional case, there are a number of
options to choose from in performing the scaling operation such that the area is preserved. For
example, if it is assumed that the deformation of the material is uniformly radial, the scaling may
be performed by scaling the elevation angle only, leaving the original azimuth angle. This is
expressed in the follov/ing relationship:
Figure 6 illustrates the scaled dovvn version of the corneal elevations obtained using
Equation (4).
While forms of the invention have been illustrated and described, it will be apparent
tc those skilled in the art that various modifications and improvements may be made without
departing from the spirit and scope of the invention. As such, it is not intended that the invention
be limited, except as by the appended claims.
WE CLAIM
1. A method for forming a soft contact lens, comprising the following steps:
acquiring corneal topographic data of an eye using a corneal topographer;
transforming the topographical data into elevation data;
mapping the elevation data into a grid pattern;
utilizing the grid pattern to form a surface of the lens;
applying the elevation data to a topography of the soft contact lens in an
unflexed state; and
transforming the elevation data from a scaled up state to a scaled down
state by taking into account the lens in a flexed state.
2. The method as claimed in claim 1, wherein said step of utilizing comprises
tooling the surface of the lens via one of a CNC lathe, mill and bit
addressable device.
3. The method as claimed in claim 2, wherein said surface comprises one of
a non hydrated corneal lens polymer button and an injection molded tool
insert.
4. The method as claimed in claim 1, wherein said utilizing comprises tooling
the surface of the lens via a programmable laser ablation device.
5. The method as claimed in claim 1, further comprising the following step
of:
incorporating curvatures into at least one of a back surface, a front
surface and a back and front surface of the lens.
6. The method as claimed in claim 5, wherein said step of incorporating
comprises the following step of:
transforming corneal elevations of the lens into scaled up corneal
elevations to obtain an optimum spherical fit for original corneal
elevations.
7. The method as claimed in claim 6, wherein said step of transforming
corneal elevations is performed according to a relationship:
f wherein a is R2/R1, f(6) is the corneal elevations in polar coordinates,
f^^^(9) is the scaled up corneal elevations, Ri is a radius of the lens in a
flexed state and R2 is a radius of the lens in an unflexed state.
8. The method as claimed in claim 7, wherein Ri is a radius of the lens
flexed on the cornea of the eye.
9. The method as claimed in claim 6, further comprising the following step
of:
8
scaling down the scaled-up corneal elevations to obtain an area covered
by the lens which corresponds to a cornea of the eve.
10. The method as claimed in claim 9, wherein the area covered by the lens
which corresponds to the cornea of the eye is a back surface of the lens.
11.The method as claimed in claim 9, wherein said scaled step down is
performed according to a relationship:

wherein a'^ is Ri/R;:, f^^'(0) is a scaled down corneal elevation, f^^^(9) is
the scaled up corneal elevations, Ri is a radius of the lens in a flexed state
and R2 is a radius of the lens in an unflexed state.
12.The method as claimed in claim 11, wherein Ri is a radius of the lens
flexed on the cornea of the eye.
13. The method as claimed in claim 6, wherein said transforming corneal
elevation is performed according to a relationship:

wherein u is R2(6, 0)/ Ri(9,0), (6) is an azimuth angle, is an elevation
angle, f^^^(6,*), is the scaled up corneal elevations, f(8,cti) is three
dimensional corneal elevations, Ri(6, state and R2(6, ) is a radius of the lens in an unflexed state.
14.The method as claimed in claim 13, wherein Ri(e,0) is a radius of the
lens flexed on the cornea of the eye.
15.The method as claimed in claim 6, further comprising the following step
of:
scaling down the scaled up corneal elevations to obtain a desired back
surface of the lens.
16. The method as claimed in claim 15, wherein said step of scaling down
comprises scaling only an elevation angle to obtain a desired back surface
curvature of the lens.
17. The method as claimed in claim 16, wherein said step of scaling only the
elevation angle is performed according to a relationship:

wherein a"^ is Ri(6,0)/ R2(6,0), (6) is an azimuth angle, O is an elevation
angle, f^^^(6,*) is the scaled down corneal elevations, f^^\Q,) is the
scaled up corneal elevations, Ri(9,0) is a radius of the lens in a flexed
state and R2(6,0) is a radius of the lens in an unflexed state.
18.The method as claimed in claim 17, wherein Ri(e, lens flexed on the cornea of the eye.
19. A soft contact lens formed according to the method as claimed in claim 1.
20. A soft contact lens formed according to the method as claimed in claim 5.
21. A soft contact lens formed according to the method as claimed in claim 6.
22. A soft contact lens formed according to the method as claimed in claim 7.
23. A soft contact lens formed according to the method as claimed in claim 9.
24. A soft contact lens formed according to the method as claimed in claim
10.
25. A soft contact lens formed according to the method as claimed in claim
11,
26. A soft contact lens formed according to the method as claimed in claim
13.
27. A soft contact lens formed according to the method as claimed in claim
15.
28. A soft contact lens formed according to the method as claimed in claim
16.
29. A soft contact lens formed according to the method as claimed in claim 17.


A method is provided which is used to design soft contact iens via corneal topographic
analysis. The topography of the cornea is matched to a corresponding topography of a soft contact
lens. A geometrical transformation which maps the corneal elevation onto the back surface of an
unflexed soft contact lens is used to minimize errors induced by flexure of the lens. The mapping
transformation takes into account the effects of flexure. As a result, the contact lens has a back
surface with a curvature which matches the specific elevations of the cornea, while the front surface
can be spherical or any desired symmetrical or asymmetrical shape.

Documents:

in-pct-2002-333-kol-abstract.pdf

in-pct-2002-333-kol-claims.pdf

in-pct-2002-333-kol-correspondence.pdf

in-pct-2002-333-kol-description (complete).pdf

in-pct-2002-333-kol-drawings.pdf

in-pct-2002-333-kol-examination report.pdf

in-pct-2002-333-kol-form 5.pdf

in-pct-2002-333-kol-granted-abstract.pdf

in-pct-2002-333-kol-granted-claims.pdf

in-pct-2002-333-kol-granted-correspondence.pdf

in-pct-2002-333-kol-granted-description (complete).pdf

in-pct-2002-333-kol-granted-drawings.pdf

in-pct-2002-333-kol-granted-examination report.pdf

in-pct-2002-333-kol-granted-form 1.pdf

in-pct-2002-333-kol-granted-form 18.pdf

in-pct-2002-333-kol-granted-form 26.pdf

in-pct-2002-333-kol-granted-form 3.pdf

in-pct-2002-333-kol-granted-form 5.pdf

in-pct-2002-333-kol-granted-priority document.pdf

in-pct-2002-333-kol-granted-reply to examination report.pdf

in-pct-2002-333-kol-granted-specification.pdf

in-pct-2002-333-kol-international preliminary examination report.pdf

in-pct-2002-333-kol-international publication.pdf

in-pct-2002-333-kol-international search report.pdf

in-pct-2002-333-kol-pct request form.pdf

in-pct-2002-333-kol-receipt copy.pdf

in-pct-2002-333-kol-specification.pdf


Patent Number 239404
Indian Patent Application Number IN/PCT/2002/333/KOL
PG Journal Number 12/2010
Publication Date 19-Mar-2010
Grant Date 17-Mar-2010
Date of Filing 11-Mar-2002
Name of Patentee JOHNSON & JOHNSON VISION CARE, INC.
Applicant Address 7500 CENTURION PARKWAY, SUITE 100, JACKSONVILLE, FL
Inventors:
# Inventor's Name Inventor's Address
1 COLLINS MICHAEL J. LOT 8, MT. NEBO RD., MT. NEBO, QUEENSLAND 4520
2 DAVIS BRETT A. 3/48 RIALTO ST., COOPAROO, QUEENSLAND 4151
3 ROSS DENWOOD F 1401 STARLIGHT COURT, JACKSONVILLE, FL 32259
4 ROFFMAN JEFFREY H 307 EDGEWATER BRANCH DRIVE, JACKSONVLE, FL 32259
PCT International Classification Number B29D 11/00
PCT International Application Number PCT/US2000/21592
PCT International Filing date 2000-08-08
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 09/372,715 1999-08-11 U.S.A.