Note: Descriptions are shown in the official language in which they were submitted.
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METHODS FOR REDUCING CORNEAL STAINING
IN CONTACT LENS WEARERS
Field of the Invention
The invention relates to contact lenses. In particular, the invention provides
lenses in which the occurrence of corneal staining in the lens wearer is
reduced.
Background of the Invention
The use of contact lenses for the correction of visual acuity, for cosmetic
purposes, or both is well known. Soft contact lenses are known, which lenses
generally are manufactured from materials including, without limitation,
hydrogels
and silicone hydrogels.
In normal use on the lens wearer's eye, a portion of the soft contact lens
overlies the wearer's cornea. Corneal cell damage that is observable by
corneal
staining, or upon instillation of a diagnostic dye onto the corneal surface,
may occur
in soft contact lens wearers. Of particularinterest is staining-resulting from
mechanical chaffing of the lens on the cornea. Such staining is considered a
precursor to corneal tissue splitting. Such damage has been observed in
wearer's of
lathe cut lenses, lenses made from materials having a Young's modulus of 40
psi or
greater, lenses with a single back surface curve, and lenses in which the
center
thickness; the peripheral thickness profile, or cross-sectional thickness, or
both is
greater than about 0.1 mm.
Additionally, corneal cell damage has been observed in wearer's of lenses
having certain geometries on their front or back surfaces. Particularly
problematic
geometries are those in which junctions between zones on the front or back
surface
of the lens creates surface discontinuities in the mid-peripheral area of the
lens. For
purposes of the invention, by mid-peripheral area is meant the non-optical
area,
outside of the optical zone, between the lens' geometric center and the lens
edge,
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which area overlies the cornea when the lens is on-eye. Typically, this area
will have
a radius of between about 3.5 and 6.5 mm from the lens' geometric center.
Finally,
corneal cell damage can result from lenses having areas over which the
thickness
profile is non-constant.
Corneal staining due to mechanical chaffing is most commonly found in the
superior region of the cornea, or the area of the cornea above the pupil, and
in the
inferior region, or region below the pupil. Thus, the cell damage is most
likely to
appear in the areas of the cornea that underlie the upper or lower eyelid. The
incidence of corneal staining varies from lens to lens based on the material
and design
of the lens, but can be as high as 50 % of lens wearers. Therefore, a need
exists for
lens designs in which the incidence of corneal staining is reduced or
eliminated.
Summary of the Invention
One aspect of the present invention is a contact lens, comprising at least one
surface comprising a design wherein a peak pressure is reduced.
Another aspect of the a method of designing a contact lens, comprising the
step of providing at least one surface wherein a peak pressure is reduced
More specifically, in one embodiment, there is provided a contact lens,
comprising at least one surface comprising a design wherein a peak pressure on
the
cornea of the wearer is reduced, wherein a radial thickness of the lens's mid-
peripheral area as measured between front and back lens surfaces and along a
direction orthogonal to the back surface, is distributed evenly along any
meridian
within 45 degrees of the vertical meridian of the lens, such that there is an
area
around the vertical meridian of the lens in which a cross-sectional thickness
of the
mid-peripheral area of the lens is constant, and said lens further comprising
rotational
stabilization provided by depressions or elevations formed on the surface of
the lens
away from the 90 degree meridian
In another embodiment, there is provided a method of designing a contact lens
wherein a peak pressure on the cornea of the wearer is reduced, said method
comprising the step of providing a lens wherein a radial thickness of the
lens's mid-
peripheral area as measured between front and back lens surfaces and along a
direction orthogonal to the back surface, is distributed evenly along any
meridian
DOCSTOR: 2734827\1
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2a
within 45 degrees of the vertical meridian of the lens, such that there is an
area
around the vertical meridian of the lens in which a cross-sectional thickness
of the
mid-peripheral area of the lens is constant, said lens further comprising
rotational
stabilization provided by depressions or elevations formed on the surface of
the lens
away from the 90 degree meridian.
Brief Description of the Drawings
Figure 1 is a magnified, cross-sectional view of a lens of the invention.
Figure 2 is a magnified plan view of the front surface of the lens of Figure
1.
Description of the Invention and Preferred Embodiments
The invention provides methods, and lenses produced by such methods, for
reducing the incidence of corneal staining in lens wearers. It is believed
that corneal
staining resulting from mechanical chaffing is most frequently the result of
peak
pressure on the cornea, meaning that an area of the cornea experiences a
higher force
imposed by an area of the lens, relative to the adjacent areas of the cornea.
Most
frequently, these areas of peak pressure occur under the lens wearer's
eyelids. Such
peak pressure is the result of one or more of the lens' thickness profiles, or
cross-
sectional thickness, material modulus, and junctions between the zones on the
lens'
surfaces.
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In one embodiment, the invention provides a contact lens comprising,
consisting essentially Of, or consisting of at least one surface comprising a
design
wherein a peak pressure is reduced.
One lens design of the invention provides an iso-thickness vertical profile.
By "iso-thickness vertical profile" is meant that the radial thickness of the
lens' mid-
peripheral area as measured between the front and back lens surfaces and along
a
direction orthogonal to the back surface, is distributed evenly along any
meridian
within 45 degrees of the vertical meridian (the 90-270 degree axis) of the
lens. The
iso-thickness vertical profile creates an area around the vertical meridian of
the lens
in which the cross-sectional thickness of the lens' mid-peripheral area is
constant.
Figure 1 depicts lens 10 embodying this design. Mid-peripheral areas 11 are
shown at the superior (top) and inferior (bottom) portions of the lens in
which areas
iso-thickness vertical profiles are used. Figure 2 depicts a plan view of the
lens
showing the superior-lying area 11.
The iso-thickness vertical profile may be achieved by offsetting the back
surface periphery with the front surface periphery to form the desired
profile. Such
a profile may be obtained by any number of design methods including, without
limitation, incorporating off-axis bevel curves or using multiple peripheral
zones.
Additionally, the design methods of United States Patent No. 6,595,640 .
As yet another alternative embodiment of the invention, the junctions
between the various zones on one or both of the lens' surfaces may be smoothed
so
as to eliminate slope discontinuities on the back surface. More specifically,
in this
embodiment the junction between curves on the back surface are such that the
first
order derivatives, i.e., the slopes of the curves at the junction, are equal.
Any
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number of methods may be used to obtain the smoothed junctions including,
without
limitation, blending two consecutive zones using conventional mathematical
techniques.
The lenses of the invention preferably are rotationally stabilized to maintain
their on-eye orientation. Suitable rotational stabilization includes prism
stabilization
including, without limitation, decentering of the lens' front surface relative
to the
back surface, prismatic balancing, thickening of the lower lens edge,
supporting the
to lens on the lower eyelid, forming depressions or elevations on the lens'
surface away
from the 90 degree meridian, and truncating the lens edge. Alternatively, or
in
combination with prism stabilization, the lens may be dynamically stabilized.
Dynamic stabilization includes reducing the thickness of the lens' outer
surface at
two symmetrically lying regions, thickening two regions in the horizontal
center
15 axis, and thinning, or slabbing off, top and bottom zones on the lens.
Typically, the
areas of stabilization are located in the lens' periphery meaning the non-
optical
portion of the lens surrounding the optic zone, but excluding the lens -edge
or
outermost portion of the lens relative to the geometric center.
20 The
invention may be used in designing single vision, multifocal and tone
lenses. Additionally, the invention may be used in designing lenses made from
any
suitable contact lens material. However, the invention may have its greatest
utility
in lenses that are either or boht rotationally stabilized by use of areas of
different
thicknesses in the lens' periphery and lenses made from high modulus material,
or
25 materials having a Young's modulus of about 40 psi, preferably about 60
psi, or
greater.
Exemplary high modulus lens materials include, without limitation hydrogels
including, without limitation, etafilcon A. Preferably, the invention is used
in lenses
30 made of silicone hydrogels meaning a material containing one or more
silicone-
containing components and one or more hydrophilic components, such as
galyfilcon.
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The one or more silicone-containing components and One or more
5 hydrophilic components can be any of the known components used in the
prior art to
make silicone hydrogels. The terms "silicone-containing component" and
"hydrophilic component" are not mutually exclusive, in that, the silicone-
containing
component can be somewhat hydrophilic and the hydrophilic component can
contain
some silicone.
A silicone-containing component is one that contains at least one [¨Si---
0¨Si] group, in a monomer, macromer or prepolymer. Preferably, the Si and
attached 0 are present in the silicone-containing component in an amount
greater
than 20 weight percent, and more preferably greater than 30 weight percent of
the
total molecular weight of the silicone-containing component. Useful silicone-
containing components preferably comprise polymerizable functional groups such
as
acrylate, methacrylate, acrylamide, methacrylamide, N-vinyl lactam, N-
vinylamide,
and styryl functional groups. Examples of silicone-containing components which
are useful in this invention may be found in U.S. Pat. Nos. 3,808,178;
4,120,570;
4,136,250; 4,153,641; 4,740,533; 5,034,461 and 5,070,215, and EP080539.
Further examples of suitable silicone-containing monomers are
polysiloxanylalkyl(meth)acrylic monomers including, without limitation,
methacryloxypropyl tris(trimethylsiloxy) silane, pentarnethyldisiloxanyl
methylmethacrylate, and methyldi(trimethylsiloxy)methaeryloxymethyl silane.
One preferred class of silicone-containing components is a
poly(organosiloxane) prepolymer such as a, co-bismethacryloxypropyl poly-
dimethylsiloxane. Another preferred example is mPDMS
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(monomethacryloxypropyl terminated mono-n-butyl terminated
polydimethylsiloxane). Another useful class of silicone containing components
includes silicone-containing vinyl carbonate or vinyl carbamate monomers
including, without limitation, 1,3-bis[4-(vinyloxycarbonyloxy)but-1-
yl]tetramethyl-
isiloxane 3-(vinyloxycarbonylthio) propyl-ltris (trimethylsiloxysilane]; 3-
[tris(trimethylsiloxy)silyl] propyl allyl carbamate; 3-
[tris(trimethylsiloxy)wilyl]
propyl vinyl carbamate; trimethylsilylethyl vinyl carbonate; and
trimethylsilylmethyl
vinyl carbonate.
0 CH3 CH3CH3 0
CH2=--CH¨Ot 0(CH2)44¨ li¨(CH2)10¨CH=----CH2
L-13 L13 L13
10
Hydrophilic components include those which are capable of providing at
least about 20% and preferably at least about 25% water content to the
resulting lens
when combined with the remaining reactive components. Suitable hydrophilic
components may be present in amounts between about 10 to about 60 weight%
15 based upon
the weight of all reactive components. About 15 to about 50 weight %
and more preferably between about 20 to about 40 weight %. The hydrophilic
monomers that may be used to make the polymers of this invention have at least
one
polymerizable double bond and at least one hydrophilic functional group.
Examples
of polymerizable double bonds include acrylic, methacrylic, acrylamido,
20
methacrylamido, fumaric, maleic, styryl, isopropenylphenyl, 0-vinylcarbonate,
0-
vinylcarbamate, allylic, 0-vinylacetyl and N-vinyllactam and N-vinylamido
double
bonds. Such hydrophilic monomers may themselves be used as crosslinking
agents.
"Acrylic-type" or "acrylic-containing" monomers are those monomers containing
the acrylic group
25 wherein R
is H or CH3, R' is H, alkyl or carbonyl, and X is 0 or N, which are also
known to polymerize readily, such as N,N-dimethylacrylamide (DMA), 2-
hydroxyethyl acrylate , glycerol methacrylate, 2-hydroxyethyl methacrylamide,
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polyethyleneglycol monomethacrylate, methacrylic acid, acrylic acid and
mixtures thereof.
Hydrophilic vinyl-containing monomers which may be incorporated into the
hydrogels of the present invention include monomers such as N-vinyl lactams
(e.g.
N-vinyl pyrrolidone (NVP)), N-vinyl-N-methyl acetamide, N-vinyl-N-ethyl
acetamide, N-vinyl-N-ethyl formamide, N-vinyl formamide, N-2-hydroxyethyl
vinyl
carbamate, N-carboxy-13-alanine N-vinyl ester, with NVP being preferred.
Other hydrophilic monomers that can be employed in the invention include
polyoxyethylene polyols having one or more of the terminal hydroxyl groups
replaced with a functional group containing a polymerizable double bond.
Examples include polyethylene glycol with one or more of the terminal hydroxyl
groups replaced with a functional group containing a polymerizable double
bond.
Examples include polyethylene glycol reacted with one or more molar
equivalents of
an end-capping group such as isocyanatoethyl methacrylate ("IBM"), methacrylic
anhydride, methacryloyl chloride, vinylbenzoyl chloride, or the like, to
produce a
_ _
polyethylene polyol having one or more terminal polymerizable olefinic groups
bonded to the polyethylene polyol through linking moieties such as carbamate
or
ester groups.
Still further examples are the hydrophilic vinyl carbonate or vinyl carbamate
monomers disclosed in U.S. Pat. No.5,070,215, and the hydrophilic oxazolone
monomers disclosed in U.S. Pat. No. 4,190,277. Other suitable hydrophilic
monomers will be apparent to one skilled in the art. More preferred
hydrophilic
monomers which may be incorporated into the polymer of the present invention
include hydrophilic monomers such as N,N-dimethyl acrylamide (DMA), 2-
hydroxyethyl acrylate, glycerol methacrylate, 2-hydroxyethyl methacrylamide, N-
vinylpyn-olidone (NVP), and polyethyleneglycol monomethacrylate. Most
preferred
hydrophilic monomers include DMA, NVP and mixtures thereof.
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Curing of the lens material may be carried out by any convenient method.
For example, the material may be deposited within a mold and cured by thermal,
irradiation, chemical, electromagnetic radiation curing and the like and
combinations
thereof. Preferably, molding is carried out using ultraviolet light or using
the full
spectrum of visible light. More specifically, the precise conditions suitable
for
curing the lens material will depend on the material selected and the lens to
be
formed. Suitable processes are disclosed in U.S. Patents Nos. 4,495,313,
4,680,336,
4,889,664, 5,039,459, and 5,540,410 .
The contact lenses of the invention may be formed by any convenient
method. One such method uses a lathe to produce mold inserts. The mold inserts
in
turn are used to form molds. Subsequently, a suitable lens material is placed
between the molds followed by compression and curing of the resin to form the
lenses of the invention. One ordinarily skilled in the art will recognize that
any
other number of known methods may be used to produce the lenses of the
invention.
