U.S. patent application number 11/536305 was filed with the patent office on 2007-01-25 for contact lenses.
This patent application is currently assigned to COOPERVISION, INC.. Invention is credited to Arthur Back.
Application Number | 20070019155 11/536305 |
Document ID | / |
Family ID | 26889046 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070019155 |
Kind Code |
A1 |
Back; Arthur |
January 25, 2007 |
CONTACT LENSES
Abstract
A contact lens having a rotational stabilization mechanism
thereon, such as prism ballast, and a thickness profile that
reduces the torque imparted on the lens by the action of the
eyelids, especially for stabilizing toric lenses. The prism ballast
is provided on one or more portions of the anterior face of the
lens such that the lens body has a uniform thickness of within 10%
along horizontal cross-sections. The anterior face of the lens may
be segregated into a peripheral zone, an inner zone circumscribed
by the peripheral zone, and a central optic zone. The prism ballast
portion is provided within the inner zone, which may be further
subdivided into a superior portion, an intermediate portion
proximate the optic zone, and an inferior portion. The ballast
portion increases in thickness along a superior-inferior line
parallel to a vertical meridian, and has a substantially uniform
thickness perpendicular thereto. The peripheral zone may be
tapered, and have a rounded edge. The rate of thickness change
across any portion of the peripheral zone is less than about 250
.mu.m/mm.
Inventors: |
Back; Arthur; (Pleasanton,
CA) |
Correspondence
Address: |
FRANK J. UXA
STOUT, UXA, BUYAN & MULLINS, LLP
4 VENTURE, SUITE 300
IRVINE
CA
92618
US
|
Assignee: |
COOPERVISION, INC.
370 Woodcliff Drive, Suite 200
Fairport
NY
|
Family ID: |
26889046 |
Appl. No.: |
11/536305 |
Filed: |
September 28, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11188190 |
Jul 22, 2005 |
7133174 |
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11536305 |
Sep 28, 2006 |
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10827168 |
Apr 19, 2004 |
6971746 |
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11188190 |
Jul 22, 2005 |
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10171718 |
Jun 14, 2002 |
6857740 |
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10827168 |
Apr 19, 2004 |
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09818244 |
Mar 27, 2001 |
6467903 |
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10171718 |
Jun 14, 2002 |
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60193493 |
Mar 31, 2000 |
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Current U.S.
Class: |
351/159.02 |
Current CPC
Class: |
G02C 7/048 20130101;
G02C 7/04 20130101 |
Class at
Publication: |
351/161 |
International
Class: |
G02C 7/04 20060101
G02C007/04 |
Claims
1. A contact lens, comprising: an anterior surface, a posterior
surface, a peripheral edge, and a thickness defined as a distance
between the anterior surface and the posterior surface; a toric
optic zone; a second zone circumscribing the toric optic zone, the
second zone comprising a region of maximum thickness along a 225
degree meridian of the contact lens, wherein along the 225 degree
meridian, the distance between the region of maximum thickness and
the peripheral edge is less than about 1.4 mm.
2. The contact lens of claim 1 which is a fully molded contact
lens.
3. The contact lens of claim 1 which is a soft contact lens.
4. The contact lens of claim 3, further comprising a hydrophilic
material.
5. The contact lens of claim 3 which is made from a
hydroxyethylmethacrylate.
6. The contact lens of claim 1 which is a silicone hydrogel contact
lens.
7. The contact lens of claim 6, wherein the peripheral edge
comprises a rounded edge surface.
8. The contact lens of claim 1 which is a rotationally stabilized
contact lens.
9. The contact lens of claim 8 which is a contact lens selected
from the group consisting of prism ballasted contact lenses,
periballasted contact lenses, and dynamically stabilized contact
lenses.
10. The contact lens of claim 8, wherein the second zone further
comprises a midsection of the contact lens having a greater
thickness relative to a superior section and an inferior section of
the second zone.
11. The contact lens of claim 1, wherein the second zone further
comprises a second region of maximum thickness along a 270 degree
meridian, and along the 270 degree meridian, the distance between
the second region of maximum thickness and the peripheral edge is
less than about 2.1 mm.
12. The contact lens of claim 1, wherein the second zone further
comprises a second region of maximum thickness along a 180 degree
meridian, and along the 180 degree meridian, the distance between
the second region of maximum thickness and the peripheral edge is
less than about 1.3 mm.
13. The contact lens of claim 1, wherein the second zone further
comprises a second region of maximum thickness along a 270 degree
meridian, and a third region of maximum thickness along a 180
degree meridian, and along the 270 degree meridian, the distance
between the second region of maximum thickness and the peripheral
edge is less than about 2.1 mm, and along the 180 degree meridian,
the distance between the third region of maximum thickness and the
peripheral edge is less than about 1.3 mm.
14. The contact lens of claim 1, wherein the second zone comprises
at least one region having a substantially uniform horizontal
thickness.
15. The contact lens of claim 1, wherein, along the 225 degree
meridian, a rate of change of thickness from the region of maximum
thickness to the peripheral edge is less than about 250
.mu.m/mm.
16. The contact lens of claim 15, wherein, along the 225 degree
meridian, a rate of change of thickness from the region of maximum
thickness to the peripheral edge is less than about 200
.mu.m/mm.
17. The contact lens of claim 1, wherein the maximum thickness
along the 225 degree meridian of the lens is between about 200-400
.mu.m.
18. The contact lens of claim 17, wherein the maximum thickness
along the 225 degree meridian of the lens is between about 250-350
.mu.m.
19. A contact lens, comprising: a silicone hydrogel lens body
comprising an anterior surface, a posterior surface, a peripheral
edge, and a thickness defined as a distance between the anterior
surface and the posterior surface; a toric optic zone; a second
zone circumscribing the toric optic zone, the second zone
comprising a region of maximum thickness along a 180 degree
meridian of the contact lens, wherein along the 180 degree
meridian, the distance between the region of maximum thickness and
the peripheral edge is less than about 1.3 mm.
20. The contact lens of claim 19 which is a fully molded contact
lens.
21. The contact lens of claim 19, wherein the peripheral edge
comprises a rounded edge surface.
22. The contact lens of claim 19 which is a rotationally stabilized
contact lens.
23. The contact lens of claim 22 which is a contact lens selected
from the group consisting of prism ballasted contact lenses,
periballasted contact lenses, and dynamically stabilized contact
lenses.
24. The contact lens of claim 22, wherein the second zone further
comprises a midsection of the contact lens having a greater
thickness relative to a superior section and an inferior section of
the second zone.
25. The contact lens of claim 19, wherein the second zone further
comprises a second region of maximum thickness along a 270 degree
meridian, and along the 270 degree meridian, the distance between
the second region of maximum thickness and the peripheral edge is
less than about 2.1 mm.
26. The contact lens of claim 19, wherein the second zone further
comprises a second region of maximum thickness along a 225 degree
meridian, and along the 225 degree meridian, the distance between
the second region of maximum thickness and the peripheral edge is
less than about 1.8 mm.
27. The contact lens of claim 19, wherein the second zone comprises
at least one region having a substantially uniform horizontal
thickness.
28. The contact lens of claim 19, wherein, along any meridian, a
rate of change of thickness from the region of maximum thickness to
the peripheral edge is less than about 250 .mu.m/mm.
29. The contact lens of claim 28, wherein the rate of change of
thickness is less than about 200 .mu.m/mm.
30. A contact lens, comprising: a rotationally stabilized
silicone-hydrogel contact lens body comprising a centrally located
optic zone surrounding an optical axis of the lens body, and an
optic circumscribing zone comprising at least one region having a
substantially uniform horizontal thickness effective in
rotationally stabilizing the lens body about the optical axis of
the lens body when placed on an eye of an individual.
31. The contact lens of claim 30, wherein the lens body further
comprises a ballast.
32. The contact lens of claim 30, wherein the lens body includes a
midsection having a greater thickness relative to a superior
section and an inferior section of the lens body.
33. The contact lens of claim 30, wherein the lens body has a
maximum thickness at a region located between the optic zone and an
inferior edge of the lens body.
34. The contact lens of claim 30, wherein the lens body is
non-axisymmetric.
35. The contact lens of claim 30 which is a toric contact lens.
36. The contact lens of claim 30, wherein, along a 225.degree.
meridian, the distance between the optic circumscribing zone and
the peripheral edge is less than about 1.8 mm.
37. A contact lens, comprising: a non-axisymmetric lens body
comprising an anterior surface; a posterior surface; a peripheral
edge; an optic zone; and a ballast having a ballast periphery,
wherein along a 225 degree meridian of the lens body, the distance
between the ballast periphery and the peripheral edge is less than
about 1.4 mm.
38. The contact lens of claim 37 which is a fully molded contact
lens.
39. The contact lens of claim 37 which is a soft contact lens.
40. The contact lens of claim 39, further comprising a hydrophilic
material.
41. The contact lens of claim 39 which is made from a
hydroxyethylmethacrylate.
42. The contact lens of claim 37 which is a silicone hydrogel
contact lens.
43. The contact lens of claim 42, wherein the peripheral edge
comprises a rounded edge surface.
44. The contact lens of claim 37 which is a contact lens selected
from the group consisting of prism ballasted contact lenses,
periballasted contact lenses, and dynamically stabilized contact
lenses.
45. The contact lens of claim 37, wherein, along a 270 degree
meridian of the lens body, the distance between the ballast
periphery and the peripheral edge is less than about 2.1 mm.
46. The contact lens of claim 37, wherein, along a 180 degree
meridian of the lens body, the distance between the ballast
periphery and the peripheral edge is less than about 1.3 mm.
47. The contact lens of claim 37, wherein the lens body further
comprises a second zone circumscribing the optic zone and
comprising at least one region having a substantially uniform
horizontal thickness.
48. The contact lens of claim 37, wherein, along the 225 degree
meridian, a rate of change of thickness from the ballast periphery
to the peripheral edge is less than about 250 .mu.m/mm.
49. The contact lens of claim 48, wherein the rate of change of
thickness is less than about 200 .mu.m/mm.
50. The contact lens of claim 37, wherein the maximum thickness
along the 225 degree meridian of the lens body is between about
200-400 .mu.m.
51. The contact lens of claim 50, wherein the maximum thickness
along the 225 degree meridian of the lens body is between about
250-350 .mu.m.
52. A contact lens, comprising: a non-axisymmetric silicone
hydrogel lens body comprising an anterior surface; a posterior
surface; a peripheral edge; an optic zone; and a ballast having a
ballast periphery, wherein along the 180 degree meridian, the
distance between the ballast periphery the peripheral edge is less
than about 1.3 mm.
53. The contact lens of claim 52 which is a fully molded contact
lens.
54. The contact lens of claim 52, wherein the peripheral edge
comprises a rounded edge surface.
55. The contact lens of claim 52 which is a contact lens selected
from the group consisting of prism ballasted contact lenses,
periballasted contact lenses, and dynamically stabilized contact
lenses.
56. The contact lens of claim 52, wherein along a 270 degree
meridian of the lens body, the distance between the ballast
periphery and the peripheral edge is less than about 2.1 mm.
57. The contact lens of claim 52, wherein along a 225 degree
meridian of the lens body, the distance between the ballast
periphery and the peripheral edge is less than about 1.8 mm.
58. The contact lens of claim 52, wherein the lens body further
comprises a second zone circumscribing the optic zone and
comprising at least one region having a substantially uniform
horizontal thickness.
59. The contact lens of claim 52, wherein, along any meridian, a
rate of change of thickness from the ballast periphery to the
peripheral edge is less than about 250 .mu.m/mm.
60. The contact lens of claim 59, wherein the rate of change of
thickness is less than about 200 .mu.m/mm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of application Ser. No. 11/188,190,
filed Jul. 22, 2005, which is a continuation of application Ser.
No. 10/827,168, filed Apr. 19, 2004, now U.S. Pat. No. 6,971,746,
which is a continuation of application Ser. No. 10/171,718, filed
Jun. 14, 2002, now U.S. Pat. No. 6,857,740, which is a continuation
of application Ser. No. 09/818,244, filed Mar. 27, 2001, now U.S.
Pat. No. 6,467,903, which claims the benefit of U.S. provisional
application No. 60/193,493, filed Mar. 31, 2000. The disclosure of
each of these applications is incorporated in its entirety herein
by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to contact lenses and, in
particular, to an improved ballast, preferably a prism ballast, for
toric lenses that imposes a low-torque rotational correction on the
lens.
[0003] Astigmatism is a defect in the eye that is corrected by a
lens with a non-spherical prescription. The prescription, which is
usually expressed as cylinder on the patient's prescription order,
causes at least a portion of the surface of the lens to have the
shape of the toric segment. A torus is a surface or object defined
by the rotation of a circle about an axis other than its own. For
example, a donut has a toroidal shape. The toric portion of the
lens is a small oval-shaped section of the toroid, with a major
axis and a minor axis. As a result of this non-axi-symmetric
configuration, proper rotational orientation of the lens must be
maintained. It should be noted that other lenses, for instance that
provide bifocal or multi-focal correction, are non-axi-symmetric
and thus have a particular orientation outside of which performance
suffers.
[0004] Astigmatism is often associated with other refractive errors
such as myopia or hypermetropia, and so toric contact lenses often
also provide some spherical correction, negative or positive. While
the concave or posterior surface of a contact lens generally has a
spherical configuration, where the lens is used to correct
astigmatism the posterior surface will usually have the toric
configuration. That is, the curved portion of the posterior surface
of the lens has a major axis and a minor axis. The radius of
curvature of the posterior surface of the lens is larger in the
major-axis direction than in the minor-axis direction. The major
diameter of the toric surface is generally smaller in diameter than
the overall lens, and is cut into a starting spherical base curve.
Additionally, the anterior and/or posterior surface(s) of the
optical zone may include a spherical portion that contributes to a
distance refractive correction. The spherical correction is
typically provided on the exterior or anterior surface. Of course,
certain prescriptions provide the toric curve on the anterior
surface, with the spherical correction also on the anterior
surface, or on the posterior surface.
[0005] While spectacle lenses are held rigidly in place by a frame,
toric contact lenses must be stabilized so that the cylindrical
correction is stabilized in substantially the correct position on
the eye. Soft contact lenses which had been designed for use to
correct astigmatism are well-known in the art. Generally, these
lenses rely on some type of ballasting or stabilizing method to
cause the lens to be properly oriented in the eye. The ballast is
typically provided on a contact lens by incorporating structures
either on the front surface or on the back surface, or spread
between both surfaces. Such orientation structures utilize eyelid
forces generated during blinking. As the eyelids wipe across the
contact lens, they tend to squeeze the lens down and against the
cornea and displace elevated surface features.
[0006] A so-called "wedge" or "prism" ballast may be utilized
wherein the lower or inferior portion of the lens is relatively
thicker than the upper or superior portion. As a result, the upper
eyelid, which undergoes greater movement than the lower eyelid, and
thus exerts greater influence on the contact lens, tends to
displace the inferior portion of the contact lens downward,
inherently rotating the contact lens over the cornea into the
intended orientation. Alternatively, the lens may incorporate a
so-called "periballast" (short for peripheral ballast)
stabilization that involves a ballast region surrounding but
excluding the central optic.
[0007] For examples of prism ballast, see U.S. Pat. Nos. 4,573,774,
5,125,728, and 5,020,898, and PCT Publication No. WO 98/45749.
Another orientation structure for contact lenses includes the
provision of thin superior and inferior zones relative to a thicker
central zone. Such structures are shown in U.S. Pat. Nos.
4,095,878, and 5,650,837. Alternatively, channels or ridges may be
provided on the contact lens, such as seen in PCT publication No.
AU 92/00290.
[0008] U.S. Pat. No. 5,020,898 describes a toric contact lens with
ballast distributed outside the anterior optical zone such that the
ballast thickens from the top of the lens to two points of maximum
thickness proximate the lower peripheral edge.
[0009] U.S. Pat. No. 5,125,728 also describes a ballast portion
that increases from a superior part of the lens to a maximum
thickness in the lower periphery on each side thereof. The maximum
thickness of the ballast is located as close as possible to the
lens edge so that these portions fit over the peripheral cornea and
conjunctiva to limit lens rotation. A ballast-free corridor of
least resistance is provided in the vertical mid-section of the
lens above and below the central optical area. The patent asserts
that the ballast-free corridor in combination with the thicker
ballast and thicker portions close to the lens periphery provides
an improved stabilization mechanism.
[0010] Finally, PCT Publication No. WO 98/45749 describes a ballast
lens with a prism through the optical zone. The anterior and
posterior optical zone diameters are selected such that when
combined to form a lens, the thickness at the superior and inferior
junctions of the optical zone on the anterior face is
controlled.
[0011] In addition to the relative ability of a lens to orient
consistently on cornea, other factors affect the performance of the
various stabilization structures. For example, some structures are
better than others with respect to one or more of the following:
reducing the overall thickness across the toric contact lens for
the physiological benefit of the wearer, ease of manufacture,
reducing the lens parameter inventory, clinical performance
including wearer comfort and consistency of fitting between
refractive powers. With respect to wearer comfort, in general, the
thinner the lens and the smoother the surface, the more comfort
will be provided. In addition, it is known to provide a periphery
on the lens that is relatively thin and shaped for added
comfort.
[0012] The principal limitation of existing toric contact lens
designs is that orientation is highly variable and/or
uncomfortable, for a given design, between individual toric lens
wearers. Besides the lens design and lens material, patient factors
also influence the orientation of a toric contact lens on the eye
and contribute to this variability in lens orientation. Patient
factors such as blink characteristics and ocular parameters such as
eyelid, corneal, and conjuctival shape and anatomy may result in
undesired interaction (for example, asymmetry) or insufficient
interaction with the contact lens. However, many of the problems
associated with prior art mechanisms may be attributed to problems
with failure of the stabilization mechanism to maximize eyelid
interaction and reduce the variability of lens orientation between
individuals.
[0013] Despite much effort in this area, there is still a need for
a toric contact lens that has more consistent stabilization
features between individuals.
SUMMARY OF THE INVENTION
[0014] In accordance with the present invention, a contact lens
having improved thickness and ballast arrangement is provided. The
contact lens of the present invention reduces the known variability
of lens orientation from individual to individual. Further, the
lenses of the present invention provide more effective interaction
between the stabilization mechanism and the eyelid during blinking,
and preferably include a peripheral zone that is required for
wearer comfort.
[0015] In one aspect, therefore, the present invention provides a
contact lens, including a contact lens body having a generally
spherical base curvature with a convex anterior face, a concave
posterior face, and a peripheral edge therebetween. A peripheral
zone is defined adjacent the peripheral edge of the anterior face.
The body has a thickness between the anterior face and the
posterior face and is non-axi-symmetric so as to define a superior
edge and an inferior edge. Further, a vertical meridian is defined
from the superior edge toward the inferior edge and a horizontal
meridian is defined perpendicular thereto. The anterior face
defines a plurality of zones thereon, including an inner zone
circumscribed by the peripheral zone, and an optic zone defined
generally in the middle of the inner zone. Additionally, the lens
includes a prism ballast portion whereby the thickness increases
parallel to the vertical meridian from the superior edge toward the
inferior edge in at least a ballast portion of the inner zone. The
inner zone comprises a superior portion between the optic zone and
the superior extent of the inner zone, an inferior portion between
the optic zone and the inferior extent of the inner zone, and an
intermediate portion between the superior and inferior portions.
The ballast portion is defined within one or more of the superior,
intermediate, and inferior portions and has a series of consecutive
horizontal cross-sections exclusive of the peripheral zone and
optic zone spanning a distance along the vertical meridian of at
least 20% of the smallest dimension of the superior, intermediate,
and inferior portions as measured along the vertical meridian,
wherein each horizontal cross-section has a substantially uniform
thickness not varying by more than about 30 .mu.m or 20%, whichever
is greater in absolute terms. In one embodiment, the thickness of
the contact lens in each of the consecutive horizontal
cross-sections does not vary by more than about 15 .mu.m or about
10%, whichever is greater in absolute terms.
[0016] In one embodiment, the ballast portion is defined wholly
within only one of the superior, intermediate, and inferior
portions. In another embodiment, the ballast portion is defined
wholly within only two of the superior, intermediate, and inferior
portions. In still another embodiment, the ballast portion is
defined within all three of the superior, intermediate, and
inferior portions, or comprises the entire inner zone.
[0017] In a preferred embodiment, a rate of change of thickness in
the tapered peripheral zone is less than about 250 .mu.m/mm, more
preferably less than about 200 .mu.m/mm.
[0018] In an alternative embodiment, a contact lens of the present
invention comprises a contact lens body having a generally
spherical base curvature with a convex anterior face, a concave
posterior face, and a peripheral edge therebetween. A peripheral
zone is defined adjacent the peripheral edge of the lens that
tapers thinner toward the peripheral edge of the lens. The lens
body has a thickness between the anterior face and the posterior
face and is non-axi-symmetric so as to define a superior edge and
an inferior edge. A vertical meridian is defined from the superior
edge toward the inferior edge and a horizontal meridian is defined
perpendicular thereto. The anterior face defines a plurality of
zones thereon, including an inner zone circumscribed by the
peripheral zone and having a prism ballast portion therein, and an
optic zone defined generally in the middle of the inner zone,
wherein the thickness increases parallel to the vertical meridian
from the superior edge toward the inferior edge in at least the
prism ballast portion of the inner zone. Along a 225.degree.
meridian, the distance between the inner zone and the peripheral
edge is less than about 1.4 mm.
[0019] In accordance with one aspect of the invention, a molded
contact lens includes a fully molded contact lens body (i.e.,
molded on both the anterior and posterior faces) having the general
features as described above. As before, the molded lens has a prism
ballast portion in the inner zone and, along a 225.degree.
meridian, the distance between the inner zone and the peripheral
edge is less than about 1.8 mm. Alternatively, or desirably in
addition, and along a 270.degree. meridian, the distance between
the inner zone and the peripheral edge is less than about 2.1 mm,
while along a 180.degree. meridian, the distance between the inner
zone and the peripheral edge is less than about 1.3 mm.
[0020] Desirably, a band circumscribed by the peripheral zone and
around the optic zone is substantially annular. Namely, a superior
distance A is defined along the vertical meridian and within the
inner zone from the optic zone to the peripheral zone. An inferior
distance B is defined along the vertical meridian and within the
inner zone from the optic zone to the peripheral zone. For molded
prism ballasted lenses the band is annular within the range of 0.33
A.ltoreq.B.ltoreq.A, while for all prism ballasted lenses the
annular band is within the range of 0.55 A.ltoreq.B.ltoreq.A.
[0021] Each and every feature described herein, and each and every
combination of two or more of such features, is included within the
scope of the present invention provided that the features included
in such a combination are not mutually inconsistent.
[0022] The invention, together with additional features and
advantages thereof, may best be understood by reference to the
following description taken in connection with the accompanying
illustrative drawings in which like parts bear like reference
numerals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic front elevational view of a contact
lens according to the present invention illustrating various zones
defined thereon;
[0024] FIG. 2 (A-A' to E-E') illustrate a series of horizontal
cross-sections taken through the lens of FIG. 1;
[0025] FIG. 3 is a graph showing the varying thickness of the
contact lens of FIG. 1 taken along a vertical meridian Z-Z';
[0026] FIG. 4a is a schematic diagram of the contact lens of the
present invention having an exemplary topographical numerical
thickness map superimposed thereon;
[0027] FIG. 4b is a graph of a portion of the contact lens of the
present invention illustrating a discontinuity and angular
relationship between zones thereon;
[0028] FIGS. 5a-5d are elevational views of contact lenses of the
present invention each having a spherical anterior optical zone and
varying regions of substantially uniform horizontal thickness;
[0029] FIGS. 6a-6d are elevational views of contact lenses of the
present invention each having a toric anterior optical zone and
varying regions of substantially uniform horizontal thickness;
[0030] FIG. 7 is a schematic front elevational view of a contact
lens having a number of meridian lines superimposed thereon for
reference; and
[0031] FIG. 8 is a schematic front elevational view of a contact
lens of the prior art illustrating various zones defined
thereon.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] The present invention provides stabilized contact lenses,
especially contact lenses having a cylindrical correction for
astigmatism. More broadly, the present invention provides contact
lenses having elevated surfaces thereon that interact with the
blinking action of the eyelids to rotationally stabilize the lens.
The rotational stability is useful for any contact lens that is
non-axi-symmetric. For example, the rotational orientation of toric
lenses or multifocal lenses must be maintained for proper
correction. It should be understood, however, that rotational
stability may also be desirable for other specialized lenses.
[0033] In the following description, a number of surfaces and
thicknesses of the contact lenses of the present invention will be
described with reference to schematic elevational views of the
lenses, in that the lenses have been flattened. Contact lenses
typically possess an underlying spherical curvature, with the
anterior face being convex, and the posterior face being concave.
The various surfaces and optic zones are then either molded or
machined from the base sphere. For simplicity, the elevational
views shown herein are flattened, with the base sphere removed. In
this way, the lines of shading corresponding to the underlying
spherical curvature are removed so that the particular surfaces and
thicknesses of the present invention can be more clearly
illustrated. In a preferred embodiment, lenses of the present
invention have a negative spherical power distance correction, and
a toric surface for cylindrical correction.
[0034] An exemplary contact lens 20 of the present invention is
thus shown in schematic elevational view in FIG. 1 flattened
without shading to illustrate various zones thereon. The lens 20
includes a lens body of suitable soft or rigid material. Soft
contact lenses are typically made of a hydrophilic material such as
hydroxyethylmethacrylate, metallo-organic substances, silicone
rubbers, silicone hydrogels, urethanes, etc. Alternatively, a rigid
gas-permeable material such as siloxane acrylate or fluorosiloxane
acrylate may be used. The lens body has an overall spherical
curvature with a concave posterior face adapted to contact the
cornea opposite an outwardly-facing convex anterior face.
[0035] With reference to FIG. 1, the lens 20 includes an optic zone
22, a peripheral zone 24, and an inner zone 26 circumscribed by the
peripheral zone, wherein the optic zone 22 forms a portion of the
inner zone 26. Alternatively, the inner zone 26 may be defined
between the optic zone and the peripheral zone. As will be
described further herein, the optic zone 22 may be circular,
toroidal, or other special shapes. The peripheral zone 24 may have
a uniform radial dimension (width), or the radial dimension may
vary. In the exemplary illustrated embodiment, the peripheral zone
24 has a narrower radial dimension at a superior end 30, and a
wider radial dimension at an inferior end 32. Stated another way,
the inner zone 26 has a circular periphery or ballast periphery 34
that is slightly offset toward the top of the lens 20 along a
vertical meridian or centerline Z-Z' therethrough. It should be
noted that the clear delineations in the drawings between the optic
zone 22 peripheral zone 24 and inner zone 26 should not be taken to
imply that there is a discontinuity or corner at those locations,
and in fact the exemplary lens of the present invention possesses
gradually curved transitions between the zones.
[0036] A lens edge 36 defines the intersection of the anterior and
posterior faces. The peripheral zone 24 desirably exhibits a taper
so as to be thinner at the lens edge 36 than at the circular
ballast periphery 34. In this regard, the peripheral zone 24
preferably defines a partial conical surface (albeit, superimposed
on the underlying spherical curvature). Alternatively, the
peripheral zone 24 may define a partial spherical or other
curvature (i.e., shape), for example, any suitable curvature.
[0037] Various features of the lens 20 are believed to enhance
wearer comfort in comparison to other similar lenses. Indeed,
certain clinical trials resulted in findings that patients
responded more favorably to questions designed to ascertain a
comfort level of lenses made according to the present invention
than with respect to questions on the comfort level of similar
lenses.
[0038] The inner zone 26 may be segregated into three parts along
the vertical meridian Z-Z'. Specifically, a superior portion 40
extends between the upper extent of the ballast periphery 34 and
the upper extent of the optic zone 22, delineated by an imaginary
line 42, perpendicular to the vertical meridian Z-Z'. An
intermediate portion 44 extends between the perpendicular line 42
and a second perpendicular line 46 at the lower extent of the optic
zone 22. Finally, an inferior portion 48 extends between the
perpendicular line 46 and the lower extent of the ballast periphery
34. The optic zone 22 thus lies entirely within the intermediate
portion 44.
[0039] The superior portion 40, intermediate portion 44, and
inferior portion 48 are used in the present application to
segregate the inner zone 26 into discrete areas in which specific
ballast surfaces can be provided. It should be understood, however,
that the dividing lines 42, 46 between the areas may be shifted, or
may be non-linear, for that matter. In one aspect, the present
invention concerns particular ballast or prism ballast
surfaces/thicknesses in one or more portions of the inner zone 26,
which portions may be defined in a number of ways. Therefore, the
reader will understand that the portions 40, 44, and 48 are shown
as exemplary only. Desirably, iso-thickness ballast surfaces are
formed in at least 20% (measured as a percent of the vertical
dimension), preferably at least 50%, and more preferably at least
100%, of at least one of the portions 40, 44, and 48. More
specifically, an iso-thickness prism ballast portion is defined
within one or more of the superior, intermediate, and inferior
portions 40, 44, and 48 as a series of consecutive horizontal
cross-sections exclusive of the peripheral zone and optic zone
spanning a distance along the vertical meridian of at least 20% of
the smallest dimension of the superior, intermediate, and inferior
portions as measured along the vertical meridian. The term
"iso-thickness" means that each of the consecutive horizontal
cross-sections has a substantially uniform thickness not varying by
more than about 30 .mu.m or 20%, whichever is greater in absolute
terms. In a particularly preferred construction, ballast surfaces
are provided in at least two, more preferably all three of the
portions 40, 44, and 48.
[0040] The present invention pertains to contact lenses having
rotational stabilization mechanisms thereon, including those with
ballasts, e.g., prism ballasts, periballasts, and so-called
"dynamically stabilized" lenses. A ballasted lens provides some
raised surface contour over which the eyelid wipes to re-orient the
lens, generally about its optical axis. A prism ballast provides a
wedge or tapered ballast for interaction with the eyelids even in
the optic, while a periballast is exclusive of the optic. Dynamic
stabilization involves superior and inferior flats on the lens
leaving a thickened midsection to interact with the eye, as seen in
U.S. Pat. No. 4,095,878. Those of skill in the art will also
recognize that there may be other such stabilization mechanisms
with which the present invention could be advantageously used.
[0041] FIG. 1 also illustrates a number of representative
cross-sectional lines A-A', B-B', C-C', D-D', and E-E' extending
perpendicularly with respect to the vertical meridian Z-Z' (i.e.,
horizontally). These sections are illustrated in FIG. 2, with the
base spherical curvature shown. The present invention provides that
consecutive horizontal cross-sections shown in FIG. 2 that possess
ballast each has a substantially uniform or iso-thickness, except
in the optic zone 22 and peripheral zone 24. For example, one of
the cross-sections in FIG. 2 having ballast, such as D-D', has a
substantially uniform thickness. Alternatively, all of the cross
sections shown in FIG. 2 that possess ballast may have a uniform
thickness except in the optic zone 22 and peripheral zone 24.
[0042] Desirably, the sections of substantially uniform thickness
do not vary in thickness within one section by more than about 30
.mu.m or about 20% whichever is greater in absolute terms. In one
embodiment, the thickness of the sections varies by no more than
about 15 .mu.m or about 10%, such as by no more than about 10 .mu.m
or about 7%, whichever is greater. Such variations will be
understood to be sufficiently small that the sections can still be
regarded as being of "substantially uniform" thickness.
[0043] In an exemplary embodiment of the present invention, the
contact lens 20 has a so-called prism ballast superimposed thereon
within the entire inner zone 26. That is, from the intersection of
the ballast periphery 34 with the vertical meridian Z-Z' at the top
of the lens 20, to the intersection between the same two lines at
the bottom of the lens, the thickness generally increases. This
thickness distribution along the vertical meridian Z-Z' is
graphically illustrated in FIG. 3, with the superior end 30 of the
peripheral zone 24 shown at the right and the inferior end 32 shown
at the left. Starting at the right side, the taper of the
peripheral zone 24 within the superior end 30 from the edge 36 to
the upper extent of the ballast periphery 34 is seen. In the
superior portion 40, the thickness gradually increases to the
horizontal line 42. The thickness further increases through the
optic zone 22 to the horizontal line 46. The greatest thickness is
in the inferior portion 48 to the lower extent of the ballast
periphery 34. The lens again tapers downward within the peripheral
zone 24 between the ballast periphery 34 to the inferior edge
36.
[0044] The thickness distribution represented in FIG. 3 thus
corresponds to a prism ballast within the lens 20 that extends
through all of the superior portion 40, intermediate portion 44,
and inferior portion 48. Indeed, even the optic zone 22 exhibits
this prism ballast. Importantly, the present invention provides a
prism ballast in at least one of these portions 40, 44, 48 having
horizontal cross-sections of uniform thickness. Therefore, as seen
in FIG. 2, all of the cross-sections illustrated have uniform
thicknesses along their widths, except in the peripheral zone 24.
Of course, because of the increasing thickness in the
superior-inferior direction parallel to the vertical meridian Z-Z',
the thickness of each cross-section increases from cross-section
A-A' to cross-section E-E'.
[0045] The uniform thickness in the horizontal cross-sections helps
to stabilize lenses of the present invention, in contrast to
previous lenses. More specifically, lenses of the present invention
are suitable for a greater number of wearers than those of the
prior art because of the lower torque exerted by the eyelids on the
lens by virtue of the uniform thickness or iso-thickness
configuration. The iso-thickness ballast arrangement maximizes
eyelid interaction by achieving an even contact across each section
of the lens as the eyelid travels down and up the lens during
blinking. In contrast, the eyelid generates more rotational torque
during a normal blink when interacting with horizontal lens
sections of non-uniform thickness, as in the prior art. This is
because for a lens to orient appropriately on the eye the
lens-eyelid interaction should be maximized across the lens (i.e.,
across each horizontal cross-section) so that the lens is squeezed
into the desired orientation (overall orientation) and undergoes
minimal fluctuation during blinking (interblink orientation).
[0046] Prior art lenses, having narrow peaks or points of maximum
thickness on either side of the vertical meridian are more likely
to create a non-uniform lens-eyelid interaction across horizontal
sections. In addition, the horizontal distance between peaks of
maximum thickness in the prior art lenses typically increases from
a superior portion to the horizontal midline, and then decreases
from the mid-line to the inferior portion. This further varies the
lens-eyelid interaction forces.
[0047] The uniform thicknesses in the horizontal cross-sections of
the lens 20 have proven to enhance performance of the lenses in
comparison to other similar lenses in terms of maintaining a
correct rotational orientation in the eye. Clinical trials have
shown that there is less variability in the position of a location
mark on the lens over time. For example, groups of 20 people at a
time were studied to determine the positions of location marks over
time on various lenses in the eye, and the standard deviations of
the positions of the location marks were determined. The results
are that the standard deviation for lenses of the present invention
are measurably smaller than in other lenses, meaning the present
lenses had less rotational instability in the eye.
[0048] Exemplary values for the thickness of the contact lens 20
having the distribution as seen in FIG. 3 are provided in the
topographical depiction of FIG. 4a. It is understood that the
contact lens 20 shown in FIG. 4a is generally circular. In FIG. 4a,
the inner zone 26 is divided by horizontal and vertical grid lines
into a plurality of discrete units. Each horizontal row of units
has a uniform thickness throughout the inner zone 26. On the other
hand, the thickness along a vertical column of units generally
increases from the superior to the inferior. For example,
horizontal row 50 has a uniform thickness of 140 .mu.m other than
in the optic zone. Vertical column 52 has a thickness of 70 .mu.m
at the top, gradually increases to 280 .mu.m, and begins to
decrease just prior to the inferior portion of the peripheral zone
24. The values provided in FIG. 4a are exemplary and are suitable
for a soft hydrogel contact lens. The values for lenses made of
other materials may vary depending on the optical or other
properties of the particular material.
[0049] It will be understood by the reader that the discrete units
mapped in FIG. 4a represent the average thickness within each unit.
That is, the thickness down the lens 20 changes gradually, rather
than at a stepped border between units. More generally, although
the present application describes distinct zones or portions in
contact lenses, those zones are shown for clarity of description of
the invention only. It will be appreciated by those skilled in the
art that there are no sharp distinctions between these different
zones of the lens, but that they are instead smoothly blended into
one another.
[0050] FIG. 4a also illustrates the decreasing thickness or taper
of the lens 20 through the peripheral zone 24. For example, at the
inferior midpoint, the thickness decreases from 210-140-70 .mu.m.
This is also seen in the graph of FIG. 3. This taper within the
peripheral zone 24 provides a so-called comfort zone around the
edge of the lens 20. Because of the reduced thickness, movement of
the eyelids across the contact lens is facilitated, and there is
less irritation. Specifically, the eyelids more easily travel over
the tapered peripheral zone 24 than if there were a more abrupt
thickness change.
[0051] In an exemplary embodiment, the lens 20 has a corneal
fitting relationship to maintain the lens centered on the cornea.
The preferred lens has a diameter sufficient to achieve corneal
coverage, and optimum stability is provided so that the lens does
not become loose and unstable with gaze and blinking, which may
influence the comfort and vision of the wearer. The sagittal depth
(concave depth of the posterior face) for an optimum lens-cornea
fitting relationship is between about 3.0 and 5.0 mm over a lens
diameter of between about 13.0 mm and 16.0 mm. The lens diameter is
more preferably between about 13.5-14.8 mm. A preferred thickness
of the lens edge 36 is less than about 120 .mu.m, more preferably
about 90 .mu.m. In this respect, the thickness is measured radially
with respect to the curvature of the anterior face. The extreme
outermost extent of the edge 36 may incorporate a preferred
rounding of the anterior edge corner.
[0052] A plurality of meridian lines may be defined through the
center of the lens. In a preferred embodiment, for maximum wearer
comfort, the rate of change in lens radial thickness from the end
of the ballast zone 34 to the lens edge 36 (i.e., in the peripheral
zone 24) is less than about 250 .mu.m/mm along any meridian of the
lens. For example, in the topographical map of FIG. 4a, the rate of
change of thickness along any meridian and within the peripheral
zone 24 is less than about 250 .mu.m/mm. More preferably, the rate
of change in the peripheral zone 24 is less than about 200
.mu.m/mm.
[0053] The advantageous interaction between the peripheral zone 24
and the iso-thickness is further exemplified in the proximity to
the lens edge 36 of the point of maximum thickness, as variously
measured around the lens. To illustrate this principle, FIG. 7
shows various meridians through the optical axis and around the
lens in degrees, starting at the 3:00 o'clock position and moving
counterclockwise. Of course, with iso-thickness in the inner zone
26, the point of maximum thickness along any horizontal meridian
corresponds to the thickness along the entire horizontal meridian
excluding the optical zone. Therefore, the beginning of the inner
zone 26 and the point of maximum thickness along any meridian
always lies on the ballast periphery 34. However, because of the
preferred ballasting, the maximum thickness changes around the
ballast periphery 34.
[0054] For prism ballasted lenses in accordance with the present
invention, and along the 225.degree. meridian, the distance between
the point of maximum thickness (e.g., the ballast periphery 34) and
the lens edge 36 is no greater than about 1.4 mm, regardless of the
thickness. For any type of ballasted lens, the maximum thickness
along the 225.degree. meridian in accordance with the present
invention is between about 200-400 .mu.m, preferably between about
250-350 .mu.m, and more preferably about 320 .mu.m. Along the
270.degree. meridian, the distance between the point of maximum
thickness (e.g., the ballast periphery 34) and the lens edge 36 is
no greater than 1.8 mm, also regardless of the thickness, though a
thickness of about 320 .mu.m is preferred. For fully molded prism
ballasted lenses (i.e., molded on both the anterior and posterior
faces), and along a 225.degree. meridian, the distance between the
point of maximum thickness (e.g., the ballast periphery 34) and the
peripheral edge is less than about 1.8 mm, and desirably, along a
270.degree. meridian, the distance between the point of maximum
thickness and the peripheral edge is less than about 2.1 mm. Also,
along a 180.degree. meridian, the distance between the inner zone
and the peripheral edge is less than about 1.3 mm. In general, the
peripheral zone 24 of the lenses of the present invention is
relatively narrow in comparison to the prior art ballasted lenses,
yet because of the preferred thicknesses the comfort taper angle in
the peripheral zone 24 is relatively shallow, as mentioned
above.
[0055] Although the preferred lens of the present invention has
smooth, rounded transitions between different portions thereon,
discrete boundaries or corners are not excluded. For example, the
transition between the peripheral zone 24 and the inner zone 26 may
be defined by a rounded corner or discontinuity at the circular
ballast periphery 34. An example of the transition between the
ballast area 26 and the peripheral zone 24 (i.e., at 34) along the
meridian Z-Z' is seen in FIG. 3.
[0056] FIGS. 5a-5d illustrate several variations of the contact
lens of the present invention having different ballast portions
defined within the ballast zone. For purpose of explanation, the
reader will refer back to FIG. 1 for the definition of the various
portions (i.e., superior, intermediate, and inferior) of the inner
zone 26. FIG. 5a shows a contact lens 70 having a ballast portion
72 defined within the superior portion of the inner zone. Again,
the inner zone lies between an optic zone 74 and a peripheral zone
76. FIG. 5b illustrates a contact lens 80 of the present invention
having a ballast portion 82 defined within both the superior and
intermediate portions of the inner zone. FIG. 5c shows a contact
lens 90 having a ballast portion 92 defined within the entire inner
zone, through the superior, intermediate, and inferior portions
thereof. Finally, FIG. 5d illustrate a contact lens 100 having a
ballast portion 102 defined only within the inferior portion of the
inner zone.
[0057] Other variations not shown include a ballast portion defined
wholly within either the intermediate or inferior portions of the
inner zone, or within the intermediate and inferior portions
combined, exclusive of the superior portion. Also, the ballast
portion could surround the optic zone in a so-called "periballast"
arrangement, or could continue through the optic zone in a
so-called "prism ballast" arrangement.
[0058] FIGS. 6a-6d illustrate a number of other contact lenses of
the present invention having a cylindrical correction on the
anterior face thereof. More specifically, a toric optic zone 110 is
shown in each of the lenses oriented along a major axis 112 that is
rotated with respect to the superior-inferior axis of the lens. The
need for proper ballasting for the lenses is thus apparent to
maintain the proper offset orientation of the axis 112.
[0059] FIG. 6a shows a contact lens 120 having a ballast portion
122 beginning in the superior portion and continuing through both
the intermediate and inferior portions of the inner zone. FIG. 6b
shows a contact lens 130 having a ballast portion 132 located
entirely within the inferior portion of the inner zone. FIG. 6c
depicts a contact lens 140 having a ballast portion 142 wholly
within the intermediate portion of the inner zone. Finally, FIG. 6d
shows a lens 150 having a ballast portion 152 only within the
superior portion of the inner zone.
[0060] FIG. 8 shows a prism ballast lens of the prior art
(CooperVision Frequency Xcel (Encore) Toric) with lines demarking
the transitions between various zones drawn. Specifically, an optic
zone 200 is separated from a ballast zone 202 by a generally
circular inner line 204, and the ballast zone is separated from a
peripheral zone 206 by a generally circular outer line 208. While
the inner line 204 is approximately centered as expected on the
optical axis OA, the outer line 208 is offset upward along the
vertical meridian 210. As a result, the ballast zone 202 is wider
in the superior region than the inferior. Specifically, the
superior radial width A of the ballast zone 202 is significantly
greater than the inferior radial width B. Indeed, the superior
radial width A is more than twice the inferior radial width B.
[0061] In contrast, as seen in FIG. 1, the lenses of the present
invention have an inner zone 26 that is substantially annular, with
a radial dimension A that is within about 300% of the radial width
B. That is, for molded prism ballasted lenses the band is annular
and the relationship 0.33 A.ltoreq.B.ltoreq.A holds. Alternatively,
for all prism ballasted lenses the annular band is within the range
of 0.55 A.ltoreq.B.ltoreq.A.
[0062] It will be appreciated that the present invention may be
embodied in lenses having varying optical powers. For example, a
contact lens of present invention may have an optic power of about
between about -8 to about +8 diopters, although this range is not
to be considered limiting.
[0063] Additionally, the contact lenses according to the present
invention may also comprise stabilization features other than the
uniform thickness ballast arrangement. For example, the peripheral
zone may include a flattened region for dynamic stabilization, or
the lens may incorporate a periballast stabilization outside of the
central optic.
[0064] While this invention has been described with respect to
various specific examples and embodiments, it is to be understood
that the invention is not limited thereto and that it can be
variously practiced within the scope of the following claims.
* * * * *