U.S. patent application number 10/920963 was filed with the patent office on 2005-02-24 for ophthalmic lens with optimal power profile.
Invention is credited to Andino, Rafael Victor, Lindacher, Joseph Michael, Morgan, Courtney Flem.
Application Number | 20050041203 10/920963 |
Document ID | / |
Family ID | 34216007 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050041203 |
Kind Code |
A1 |
Lindacher, Joseph Michael ;
et al. |
February 24, 2005 |
Ophthalmic lens with optimal power profile
Abstract
An ophthalmic lens includes an optical zone having a center and
a spaced-apart periphery. The optical zone has a first corrective
power range in a first region and a second corrective power range
in an annular region surrounding the first optical zone. The second
corrective power is corrective of spherical aberration of an eye.
The optical zone has a power profile that gradually changes from
the first corrective power to the second corrective power. A
central progressive zone that provides intermediate vision
correction may be applied to a central region of the lens. The
progressive zone has a diameter that is less than or equal to the
diameter of an aperture of a pupil when subjected to bright
light.
Inventors: |
Lindacher, Joseph Michael;
(Lawrenceville, GA) ; Morgan, Courtney Flem;
(Alpharetta, GA) ; Andino, Rafael Victor;
(Lawrenceville, GA) |
Correspondence
Address: |
CIBA VISION CORPORATION
PATENT DEPARTMENT
11460 JOHNS CREEK PARKWAY
DULUTH
GA
30097-1556
US
|
Family ID: |
34216007 |
Appl. No.: |
10/920963 |
Filed: |
August 18, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60496456 |
Aug 20, 2003 |
|
|
|
Current U.S.
Class: |
351/159.42 |
Current CPC
Class: |
G02C 7/028 20130101;
G02C 7/042 20130101; G02C 7/044 20130101 |
Class at
Publication: |
351/168 |
International
Class: |
G02C 007/06 |
Claims
What is claimed is:
1. An ophthalmic lens, comprising an optical zone having a center
and a spaced-apart periphery, the optical zone having a first
corrective power range in a first region and a second corrective
power range in an annular region that surrounds the first region
the lower limit of the first corrective power range being equal
approximately to the manifest corrective refractive power for an
eye; the upper limit of the second corrective power range being
equal approximately to the manifest corrective refractive power for
the eye; the second corrective power range having negative
spherical aberration varying with diameter and being less than the
manifest corrective refractive power for an eye at the periphery of
the optical zone, the optical zone having a power profile such that
the optical power of the optical zone decreases from the center to
the periphery of the optical zone.
2. The ophthalmic lens of claim 1, wherein the first region is
coaxial with the center.
3. The ophthalmic lens of claim 1, wherein the annular region is
coaxial with the center.
4. The ophthalmic lens of claim 1, wherein the surface of the first
region is described by a spline function and the surface of the
annular region is described by a polynomial or conic function.
5. The ophthalmic lens of claim 1, wherein the upper limit of the
first corrective power range is 2 to 6 diopters greater than the
manifest corrective refractive power for the eye.
6. The ophthalmic lens of claim 1, wherein corrective power at a 6
mm diameter is 0.5 to 2 diopters less than the manifest corrective
refractive power for an eye.
7. The ophthalmic lens of claim 1, wherein the optical zone has an
axis and wherein the axis of the optical zone is aligned to a
line-of-sight of an eye.
8. The ophthalmic lens of claim 2, wherein the first region is a
circular zone having a first diameter no greater than a diameter of
a pupil exposed to bright light.
9. The ophthalmic lens of claim 8, wherein the first diameter is
less than 2.0 mm.
10. The ophthalmic lens of claim 9, wherein the upper limit of the
first corrective power range is 2 to 6 diopters greater than the
manifest corrective refractive power for the eye, and wherein
corrective power at a 6 mm diameter is 0.5 to 2 diopters less than
the manifest corrective refractive power for an eye.
11. A method of designing an ophthalmic lens having a center and a
spaced-apart periphery that is coaxial with the optical axis of the
ophthalmic lens, comprising the steps of: (a) generating a
description of a power profile of the lens so that the lens has a
first corrective power range in a first central circular region
with a first diameter and so that the lens has a second corrective
power range in an annular region extending outwardly from the first
diameter to a second diameter being the outer diameter of the
annular region, the second corrective power range having negative
spherical aberration varying with diameter and being less than the
manifest corrective refractive power for an eye; (b) generating in
a recursive manner a spline function to define the surface of the
first central circular region; and (c) generating a polynomial or
conic function that describes a surface that is tangent to the
surface of the first optical zone. wherein the surface of the first
central circular region is tangent to the surface of the annular
region, and wherein the surfaces described by the spline function
and the polynomial or conic function provide the power profile of
the lens.
12. The method of claim 11, wherein the first diameter is no
greater than a diameter of a pupil exposed to bright light.
13. A method of manufacturing a lens, comprising the steps of: (a)
determining a power profile of a lens having a first corrective
power range for intermediate vision correction in a central optical
zone having a first diameter and a second corrective power range in
an annular optical zone extending outwardly from the central
optical zone to a second diameter, the second corrective power
range capable of correcting spherical aberration of an eye; (b)
generating a model of a lens having the power profile; and (c)
fabricating a tool, mold or lens on a 3-axis lathe to create
surfaces and optical surface corresponding to the prescribed
optical power profile
14. The method of claim 13, wherein the first corrective power
range comprises a corrective power used for "computer vision."
15. The method of claim 13, wherein the central optical zone has a
diameter that is less than 2 mm.
16. The method of claim 13, wherein the annular optical zone
comprises a surface that is described by a polynomial or conic
function.
17. The method of claim 13, wherein the central optical zone
comprises a surface that is described by a spline function.
18. The method of claim 17, wherein the upper limit of the first
corrective power range is 2 to 6 diopters greater than the manifest
corrective refractive power for the eye.
19. The method of claim 17, wherein corrective power at a 6 mm
diameter is 0.5 to 2 diopters less than the manifest corrective
refractive power for an eye.
Description
[0001] This application claims the benefits under 35 USC .sctn.
119(e) of U.S. provisional application No. 60/496,456, filed Aug.
20, 2003, incorporated by reference in its entirety. This
application incorporates by reference co-pending U.S. patent
application Ser. No. 10/616,378, entitled "Method for Manufacturing
a Contact Lens", filed on Jul. 9, 2003, commonly assigned to the
asignee of the present application, the disclosure of which is
incorporated herein in its entirety.
[0002] The present invention relates to ophthalmic lenses and, more
specifically to an ophthalmic lens having an optimal power profile
for vision.
BACKGROUND OF THE INVENTION
[0003] Contact lenses are ophthalmic lenses worn on the anterior
cornea that are widely used for correcting many different types of
vision deficiencies. These include defects such as near-sightedness
(myopia) and far-sightedness (hypermetropia), astigmatism, and
defects in near range vision usually associated with aging
(presbyopia). A typical single vision contact lens has a real or
virtual focus, which is the point at which parallel rays of light
focus when the lens is placed perpendicular to the parallel rays,
and an optical axis, which is an imaginary line drawn from the
focus to the center of the optical zone of the lens. A posterior
surface of the contact lens fits against the cornea and an opposite
anterior surface has an optical zone that refracts light to correct
vision. In the case of a typical spherical lens, the optical zone
has a single radius of curvature, whereas the distance from any
point on the optical zone to a point on the optical axis referred
to as the center of curvature.
[0004] The optical zone is typically at the central section of the
contact lens that corrects the refractive error of the wearer.
[0005] A typical human eye, as a result of the optical
characteristics of the cornea and crystal lens, inherently exhibits
an increasing amount of spherical aberration as the diameter of the
pupil expands. Typically, the spherical aberration, of an adult, is
about one diopter for a 6 mm diameter pupil, while the spherical
aberration is slightly less than two diopters for an 8 mm pupil,
regardless of the eye's sphero-cylindrical manifest refraction.
Spherical aberration typically results in degraded night
vision--when the pupils are dilated. FIG. 1A is a diagram 10
showing the power of lenses designed with spherical or toric
surfaces for +6 diopters 12, 0 diopters 14 and -10 diopters 16. The
variation in power across the optical zone, or pupil, is the
spherical aberration of the lens. The dashed line 14 depicts the
nominal amount of spherical aberration of the eye for an individual
with a plano refraction.
[0006] Individuals including computer users or individuals at the
onset of presbyopia require an intermediate corrective power for
viewing objects, such as computer screens, at a range of about two
to three feet. Generally, light from a computer monitor causes the
diameter of the pupil to contract (myosis). While there exist
contact lenses that provide intermediate correction, having to
change back and forth between normal lenses and intermediate lenses
is awkward for the user. Intermediate mono-vision is not well
tolerated by most individuals.
[0007] Therefore, there is a need for a contact lens that corrects
the spherical aberration of the eye.
[0008] There is also a need for a contact lens that provides
intermediate correction under certain circumstances, but that also
provides distance vision correction that is not compromise.
SUMMARY OF THE INVENTION
[0009] The disadvantages of the prior art are overcome by the
present invention, which, in one aspect, is an ophthalmic lens that
includes an optical zone having a center and a spaced-apart
periphery. The optical zone has a first corrective power range in a
first region and a second corrective power range in an annular
region that surrounds the first region. The lower limit of the
first corrective power range is around a manifest refractive power.
The second corrective power range comprises negative spherical
aberrations varying with diameter and is smaller than the manifest
refractive power. The optical zone has a power profile in which the
corrective powers of the lens decreases from the center to the
periphery.
[0010] The optical zone has a first variable optical power
corrective zone in a first region nearly coaxial to the center and
a second corrective power zone in an annular region that is coaxial
with the center and surrounds the first variable optical power
corrective zone. The second corrective region corrects spherical
aberration, of the eye, in a predetermined amount at a 6 mm
diameter pupil. The surface of the first region is defined by a
spline to provide the optimal power profile for intermediate
vision. The lower limit (i.e., the optical power at the boundary of
the first region with the annular region) of the first power
profile range is approximately equal to the manifest distance
refractive power. The optical zone has a power profile that
gradually changes from the first corrective power to the second
corrective power. The surface of first corrective power region is
tangent to the surface of the annular region. In the first
embodiment, the first optical power zone may be a perturbation to
the optical zone of the base curve. In the second embodiment, the
first optical zone may be a perturbation to the front curve.
[0011] In another aspect, the invention is a method of making an
ophthalmic lens, in which a power profile of a lens is determined
so that the lens has a first variable corrective power zone at a
point adjacent the optical axis and so that the lens has a second
corrective power zone adjacent the periphery and surrounding the
first corrective power zone. The second corrective power zone can
corrects spherical aberration of an eye. A model of a lens having
the power profile is generated. A lens, mold or tool is turned on a
lathe to create an object having a shape that conforms to the
model.
[0012] In another aspect, the invention is a method of designing an
ophthalmic lens having an optical axis and a spaced-apart periphery
that is coaxial or nearly coaxial with the optical axis. A
description of a power profile of the lens is generated so that the
lens has a first corrective power zone at a point adjacent the
optical axis and so that the lens has a second corrective power
zone adjacent the periphery and surrounding the first corrective
power zone. The second corrective zone corrects spherical
aberration, of the eye, in a predetermined amount at a 6 mm
diameter. The surface of the first corrective power is defined by a
spline function to create the optimal power profile. The first
power zone description is sampled at a predetermined number of
evenly spaced points across the lens and a spline function is fit
through the points to create the variable power profile. A
fourth-order polynomial that describes the second optical power
zone. The optical powers of the first optical zone, the variable
ADD zone, are always equal to or higher than the optical power of
the base lens correction.
[0013] In another aspect, the invention is an ophthalmic lens
having an optical axis, a central optical zone and a peripheral
optical zone surrounding the central optical zone. The central
optical zone has a first diameter and a first corrective power
range corresponding to near and intermediate vision. The peripheral
optical zone has a second diameter that is greater than the first
diameter. The peripheral optical zone is coaxial or nearly coaxial
with the central optical zone and provides distance intermediate
vision correction.
[0014] These and other aspects of the invention will become
apparent from the following description of the preferred
embodiments taken in conjunction with the following drawings. As
would be obvious to one skilled in the art, many variations and
modifications of the invention may be effected without departing
from the spirit and scope of the novel concepts of the
disclosure.
BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS
[0015] FIG. 1A is a power profile diagram showing prior art
spherical aberration curves for three types of lenses as a function
of distance from the line of sight.
[0016] FIG. 1B is a power profile diagram showing corrective power
curves for three types of lenses according to one embodiment of the
invention, as a function of distance from the line of sight.
[0017] FIG. 1C is a power profile diagram showing corrective power
curves for three types of lenses according to one embodiment of the
invention in which a progressive zone has been added central to the
lens, as a function of distance from the center of the cornea.
[0018] FIG. 1D is a diagram showing an alternative power
profile.
[0019] FIG. 1E is a diagram showing an alternative power
profile.
[0020] FIG. 2 is a conceptual diagram showing use of a grid to
select points of a map of a lens model.
[0021] FIG. 3 is front view of a lens according to one aspect of
the invention.
[0022] FIG. 4A is a cross-sectional view of a lens according to a
second aspect of the invention.
[0023] FIG. 4B is a cross-sectional view of an alternative
embodiment of a lens according to the invention.
[0024] FIG. 4C is a cross-sectional view of a lens according to the
invention, as applied to an eye.
DETAILED DESCRIPTION OF THE INVENTION
[0025] As used herein "manifest refraction" means a user's
subjective best correction for an eye. The "manifest corrective
refractive power" means a refractive power required for achieving a
user's subjective best correction for an eye.
[0026] As used herein "negative spherical aberration" in reference
to a lens means that the optical power decreases as the value of
diameter increases. The amount of spherical aberration depends on
the diameter. For a lens having a negative spherical aberration,
its optical power at the center is larger than an optical power at
any diameter. It should be understood that where a lens having a
negative power (e.g., -6 diopters), its optical power at any
diameter is more negative than its optical power at the center.
[0027] One embodiment of the invention is a lens that cancels the
nominal amount of spherical aberration of the eye, which is
approximately 1 diopter at a 6 mm diameter pupil for an adult,
regardless of the eye's sphero-cylindrical manifest refraction.
Lenses according to the invention have a power profile as shown in
FIG. 1B, a power profile diagram 100 showing correction as a
function of distance from the center of the cornea. Curve 102 is
for an eye requiring +6 diopters of correction (i.e., manifest
refractive power), curve 104 is for a normal eye not otherwise
requiring correction, and curve 106 is for an eye requiring -10
diopters of correction (i.e., manifest refractive power).
Essentially, in this embodiment of the invention the optical power
of the lens decreases outwardly from the center to the outer
periphery such that the optical power at a 6 mm diameter is one
diopter smaller than the nominal amount of correction (i.e.,
manifest refractive power) for the eye.
[0028] In one embodiment, as shown in FIG. 1C, a central (also
referred to as progressive) zone 110 may be added to the lens. The
central zone 110 provides intermediate vision correction 112 in a
region central to the lens, whereas a peripheral zone 106c provides
correction for spherical aberration. When a user is in front of a
computer screen, the light from the screen will cause the user's
pupil to contract (myosis) roughly to the point where the pupil is
subtended by the central zone 110 and, thus, the lens provides
intermediate correction that is optimal for computer usage. When
the user is in low light situations (scotopic viewing), the central
zone 110 has little effect on the user's vision because the
aperture of the pupil dilates to the point where most of the light
entering the eye is outside of the central zone 110. When the user
is in bright light conditions, such a in sunlight, the user's pupil
contracts to the point where the focusing effect causes most
objects to be in focus, irrespective of the effect of the central
zone 110. For an optical system, the depth of focus is inversely
proportional to the pupil diameter. Thus, distant objects in bright
light are in focus. FIGS. 1D and 1E show alternative power
profiles. The ADD function (the amount of power added to the lens
and the functional shape of the ADD zone) for the lens profile 106d
shown in FIG. 1D would typically have a diameter of 1.5 mm to 3 mm,
whereas ADD function for the lens profile 106e shown in FIG. 1E
would typically have a diameter of less than about 2.2 mm,
preferably from about 1.0 mm to about 1.8 mm.
[0029] A lens according to one embodiment of the invention can be
preferably designed by generating a model 202 of a lens. The model
includes a description of an optical zone 216 on one of the two
opposite surfaces of the lens. The optical zone 216 has a region
204 coaxial or nearly coaxial to the center 214 and a annular
region 208 that is coaxial with the center 214 and adjacent to the
periphery 206. The region 204 provides optical powers (a first
optical power range) for intermediate correction. The annular
region 208 has varying optical powers (a second optical power
range) being smaller than the manifest corrective refractive power
and includes negative spherical aberration to compensate for the
spherical aberration of an eye. The optical zone 216 has a power
profile that gradually changes from the center to the periphery of
the optical zone 216. After a desired power profile is determined,
one can generate a mathematical description to define the surface
of the optical zone 216, which provide the desired optical power
profile, according to any known suitable methods. For example, the
mathematical description to define the surface of the optical zone
216 can be generated in a recursive manner. A desired power profile
of the lens can be sampled at a predetermined number of evenly
spaced points 212 across the lens. A grid 210 may preferably used
to define the evenly-space points 212, at each of which there is
one curvature to provide one optical power. A fourth-order
polynomial (or a conic function) is generated that connect each of
the evenly-spaced points located in the annular region 208 and
describes a surface providing the varying optical powers, using a
conventional computer-based analysis tool. A spline function is
generated that connects each of the evenly spaced points 212 within
the first power zone 204 and describes a surface providing the
first optical power range, using a conventional computer-based
analysis tool. The surface of the first optical zone 204 is tangent
to the surface of the annular region 208. The surfaces described by
the spline and the fourth-order polynomial is then used by a
conventional contact lens lathe system or functionally equivalent
system to manufacture a lens. Preferably, the second corrective
power will equal the manifest refractive power less 1 diopter at a
6 mm zone diameter, to cancel the nominal spherical aberration of
the average eye across the diameter of the cornea. Where the
optical zone 216 is rotationally symmetric, the surface of the
optical zone can be formed by rotating a curve around an axis
passing through the center 214.
[0030] The embodiment using intermediate correction is shown in
FIG. 3. In this embodiment, the lens 302 includes an optic zone 316
having a center 314 and a peripheral zone 306. The central zone 310
is predominately central to the optic zone 316. Cross-sectional
views of several embodiments of a lens 402 according to the
invention are shown in FIGS. 4A-4D. Each embodiment includes a lens
402 having a posterior surface 408 and an opposite anterior surface
406. The lens also has an optic zone 414 and may have a non-optic
region 404 at the extreme periphery of the lens to provide complete
corneal coverage. The optic zone 414 includes a central region 416
and an annular region 410 that is nearly coaxial with the central
region 416. As shown in FIG. 4A, the topography of at least a
portion of the anterior side 406 in the central region 416 may be
manipulated to add the progressive zone 412a. Similarly, as shown
in FIG. 4B, the progressive zone 412b may be formed by manipulating
the topography of the posterior side 408. A lens 402 applied to an
eye 12 is shown in FIG. 4C. Typically, the lens may be stabilized
using a double slab-off design, a prism ballast or a non-prism
ballast design.
[0031] The ADD function in the progressive zone 310 will, most
likely, be a function of the wearer's age. However, the ideal lens
will also correspond to the wearer's lifestyle. The ideal amount of
spherical aberration of the periphery of the lens will typically be
designed to be more negative for older (presbyopic)
individuals.
[0032] An ophthalmic lens of the invention can be designed using
any known, suitable optical design system. Exemplary optical
computer aided design systems for designing an optical model lens
includes, but are not limited to ZEMAX (ZEMAX Development
Corporation.). Preferably, the optical design will be performed
using a tool such as ZEMAX (ZEMAX Development Corporation). The
design of the optical model lens can be transformed by, for
example, a mechanical computer aided design (CAD) system, into a
set of mechanical parameters for making a physical lens. Any know
suitable mechanical CAD system can be used in the invention. The
design of an optical model lens may be translated back and forth
between the optical CAD and mechanical CAD systems using a
translation format which allows a receiving system, either optical
CAD or mechanical CAD, to construct NURBs (nonuniform rational
B-splines) or Beizier surfaces of an intended design. Exemplary
translation formats include, but are not limited to, VDA (verband
der automobilindustrie) and IGES (Initial Graphics Exchange
Specification). By using such translation formats, overall surface
of lenses can be in a continuous form that facilitates the
production of lenses having radially asymmetrical shapes. Beizier
and NURBs surface are particular advantageous for a lens having a
plurality of zones including optical zone and non-optical zones
because multiple zones can be blended, analyzed and optimized. More
preferably, the mechanical CAD system is capable of representing
precisely and mathematically high order surfaces. An example of
such mechanical CAD system is Pro/Engineer from Parametric
Technology.
[0033] When transforming the design of an optical model lens into a
set of mechanical parameters, common feature parameters of a family
of ophthalmic lenses can be incorporated in the lens designing
process. Examples of such parameters include shrinkage, non-optical
edge zone and its curvature, center thickness, range of optical
power, and the like.
[0034] An ophthalmic lens of the invention may be produced by any
convenient manufacturing means, including, for example, a
computer-controllable manufacturing device, molding or the like. A
"computer controllable manufacturing device" refers to a device
that can be controlled by a computer system and that is capable of
producing directly an ophthalmic lens or an optical tool for
producing an ophthalmic lens. Any known, suitable computer
controllable manufacturing device can be used in the invention.
Exemplary computer controllable manufacturing devices includes, but
are not limited to, lathes, grinding and milling machines, molding
equipment, and lasers. Preferably, a computer controllable
manufacturing device is a two-axis lathe with a 45.degree. piezo
cutter or a lathe apparatus disclosed by Durazo and Morgan in U.S.
Pat. No. 6,122,999 (herein incorporated by reference in its
entirety), or is a numerically controlled lathe, for example, such
as Optoform.RTM. ultra-precision lathes (models 30, 40, 50 and 80)
having Variform.RTM. or Varimax piezo-ceramic fast tool servo
attachment from Precitech, Inc.
[0035] Preferably, contact lenses are molded from contact lens
molds including molding surfaces that replicate the contact lens
surfaces when a lens is cast in the molds. For example, an optical
cutting tool with a numerically controlled lathe may be used to
form a metallic optical tool incorporating the features of the
anterior surface of a contact lens of the invention. The tool is
then used to make anterior surface molds that are then used, in
conjunction with posterior surface molds, to form the lens of the
invention using a suitable liquid lens-forming material placed
between the molds followed by compression and curing of the
lens-forming material.
[0036] Preferably, an ophthalmic lens of the invention or the
optical tool to be used for making the same is fabricated by using
a numerically controlled lathe, for example, such as Optoform.RTM.
ultra-precision lathes (models 30, 40, 50 and 80) having
Variform.RTM. or Varimax piezo-ceramic fast tool servo attachment
from Precitech, Inc.
[0037] As an illustrative example, production of a translating
contact lens having a ramped ridge zone having a latitudinal ridge
is created via the following process. First, a user defines a set
of parameters, such as a surface tolerance, a concentricity
tolerance, orientation of the lens design, the number of
semi-diameter spokes to be generated for each of the anterior and
posterior surfaces, creating zero point at 0,0, orientation of
Z-axis, and type of lens surface (concave or convex surface) to be
converted into a geometry. A "surface tolerance" refers to the
allowed position-deviation of a projected point from an ideal
position on a surface of a lens design. The deviation can be in the
direction either parallel or perpendicular to the central axis of a
lens design. A "concentricity tolerance" refers to the allowed
deviation of a point from a given arc. A "semi-diameter spoke"
refers to a radiating outwardly from the central axis and is
perpendicular to the central axis and projected onto the surface.
"Evenly-spaced semi-diameter spokes" means that all semi-diameter
spokes radiate outwardly from the central axis and separate from
each other by one equal angle. A "point spacing" refers to a
distance between two points along the semi-diameter spoke.
[0038] Second, a user determines the point density to be projected
onto the surface of the lens design (for example, the anterior
surface) along each of the number of evenly-spaced semi-diameter
spokes in a direction parallel to the central axis. A semi-diameter
spoke at an azimuthal angle corresponds to the feature that
deviates most from the base conic surface, and is selected as the
semi-diameter probing spoke. Evenly-spaced points are projected
along the semi-diameter probing spoke, in which each pairs of
points are separating by a point spacing of typically 10 microns.
Then all of the projected points are divided into a series of
groups, with each group composed of three consecutive points, a
first point, a middle point, and a third point. Each of the points
can belong to either one group or two groups. One group is analyzed
at a time from the central axis to the edge, or from the edge to
the central axis, from the curvature of the surface at the middle
point of the group by comparing a distance between the middle point
and a line linking the first point and the third point of the
corresponding group with the predetermined surface tolerance. If
the distance between the middle point and the line linking the
first and third points of the group is larger than the
predetermined surface tolerance, the curvature of the surface at
that point is sharp and an additional point is projected between
the first and the middle points in that group. The point spacing
between the first and additional points is equal to point spacing
between the additional and middle points. After adding an
additional point, all of the points included the newly added point
is regrouped again and the curvature of the surface at the middle
point of each of the series of groups is analyzed. Such iterative
procedure is repeated until the distance between the middle point
of each of the series of groups and the line linking the first and
the third points of corresponding group along the probing spoke is
equal to or less than the predetermined surface tolerance. In this
manner, the number of the points to be projected onto the surface
of the lens design along each of the desired number of
evenly-spaced semi-diameter spokes and point spacing for a series
of pairs of neighboring points are determined.
[0039] The above-determined number of points is then projected onto
the anterior surface of the lens design along each of 24, 96 or 384
semi-diameter spokes, in the preferred embodiment. Other numbers of
spokes are possible. For each of the semi-diameter spokes, a
semi-meridian that is continuous in first derivative is generated.
The semi-meridian includes a series of arcs and, optionally,
straight lines wherein each arc is defined by fitting at least
three consecutive points into a spherical mathematical function
within a desired concentricity tolerance. Each of the straight
lines is obtained by connecting at least three consecutive points.
Preferably, the arc-fitting routine is started from the central
axis to the edge. Similarly, conversion of the posterior surface of
the lens design into a geometry can be carried out according to the
above-described procedure.
[0040] After converting the lens design to a geometry of a contact
lens to be produced in a manufacturing system, a mini-file, or
equivalent format, containing both the information for the header
and the information about the geometry of the lens is generated.
This mini-file also contains a zero semi-meridian that is based on
the average height of each of the other meridians at each of radial
locations and that gives the Variform or Varimax a zero position on
which it can base its oscillation calculations. In this mini-file,
all semi-meridians have the same number of zones. This is
accomplished by copying the last zone of a semi-meridian for a
number of times to equalize the numbers of zones for all meridians.
After the mini-file is completed, it is loaded into an
Optoform.RTM. ultra-precision lathe (models 30, 40, 50 or 80)
having Variform.RTM. piezo-ceramic fast tool servo attachment and
run to produce a translating contact lens.
[0041] Although various embodiments of the invention have been
described using specific terms, devices, and methods, such
description is for illustrative purposes only. The words used are
words of description rather than of limitation. It is to be
understood that changes and variations may be made by those skilled
in the art without departing from the spirit or scope of the
present invention, which is set forth in the following claims. In
addition, it should be understood that aspects of the various
embodiments may be interchanged either in whole or in part.
Therefore, the spirit and scope of the appended claims should not
be limited to the description of the preferred versions contained
therein.
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