Variable transmissivity annular mask lens for the treatment of optical aberrations

An annular mask lens for the treatment of optical aberrations such as but not limited to night myopia, spherical aberration, aniridia, keratoconus, corneal scarring, penetrating keratoplasty, and post refractive surgery complication. The lens has an annular mask having an aperture larger than conventional pinhole contact lens. The aperture having a "soft" inside edge and which mask has a gradually increasing transmissivity radially toward the outer edge of the mask.

FIELD OF THE INVENTION 
This invention concerns an annular mask lens. The size of the aperture 
defined by the annular mask of the lens of the present invention function 
to reduce peripheral aberrations and distortion. The aperture is of a size 
greater conventional "pinhole" contact lenses which produce refractive 
correction. The aperture is sized for improving the vision of individuals 
with night myopia, spherical aberration, aniridia, keratoconus, corneal 
scarring, prolate cornea, penetrating keratoplasty, post refractive 
surgery complication, etc. The aperture is of a sufficient size so as not 
to be effective as or a substitute for refractive correction. 
BACKGROUND OF THE INVENTION 
Contact lenses are commonplace today. Most individuals with average 
refractive errors can quickly and easily acquire and use these lenses in 
place of prescription eye glasses. For presbyopic individuals, designers 
have attempted to develop "pinhole" contact lenses. These lenses endeavor 
to utilize the known theories of pinhole imaging, commonly understood in 
optics as a method to reduce visual deficiencies. Pinhole mask intraocular 
lenses also exist for cataract patients (e.g., U.S. Pat. No. 4,955,904 
issued to Atebara et al.). A pinhole mask lens conventionally has a clear 
aperture of up to 4 millimeters in diameter. The annular mask lenses are 
generally characterized as having a sharp demarcation at the inside and 
outside edges of the annular mask. 
The prior art has focused on the use of "pinhole" contacts for presbyopic 
individuals (e.g., PCT Publication No. WO 95/08135 published Mar. 23, 
1995). However, there is a long felt need for treatment of patients with 
optical aberration problems, for example, night myopia, which is an 
increase in refractive error due to the dilation of the pupil and the 
effect of spherical aberration. Also, increased spherical aberration in 
patients having radial keratotomy and photo-refractive keratectomy due to 
prolate geometry of the cornea following surgery and aberrations due to 
corneal distortion and scarring resulting from trauma or genetic 
conditions including keratoconus. Conventional pinhole contact lens can 
not adequately address these problems because the loss of retinal 
illumination due to the pinhole aperture offsets the peripheral distortion 
benefit. 
SUMMARY OF THE INVENTION 
The present invention provides, in one aspect, a contact lens with a 
transparent lens body having an annular mask which gradually increases in 
transmissivity radially and which defines an aperture whose diameter is of 
sufficient size so as not to be effective as or a substitute for 
refractive correction. In other words, the aperture does not provide 
pinhole effect correction (i.e., refractive substitute correction for 
myopia, presbyopia, hyperopia, etc.). In a preferred aspect the annular 
mask reduces or eliminates the effects of night myopia, spherical 
aberration (i.e., "halos"), aniridia, keratoconus, corneal scaring, 
penetrating keratoplasty or post refractive surgery complications (among 
others) by utilizing an annular mask having a "soft" inside edge and that 
gradually increases the transmissivity radially toward the outer edge of 
the mask. A lens according to the present invention eliminates or reduces 
diffraction effects at the inside and outside edges of the annular mask, 
thereby avoiding a reduction in visual acuity caused by diffraction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described with respect to a contact lens, 
but as will be appreciated by one of ordinary skill in the art, the 
elements of the present invention include any lens, including but not 
limited to contact lenses (including rigid or hard lenses, hybrid lenses, 
hydrogel lenses and gel lenses that do or do not contain water), 
intraocular lenses, intracorneal lenses, anterior chamber lenses, etc. 
which are all encompassed by the present invention. 
Currently, the tinted pattern on some conventional masked lenses have a 
clear demarcation between the opaque zone and the partially opaque or 
transparent zones. Under dim light conditions the iris of the wearer may 
be dilated to a pupil size greater than the opaque ring. This can create 
an annular window for forming a "structural halo" which may be visually 
disturbing. This is believed to be due to the defocused light passing 
through the annulus of the partially opaque ring or passing around the 
outer edge of the opaque ring on a conventional masked lens. 
The present invention eliminates the halo by diminishing the distinct 
demarcation between the opaque and the partially opaque zones or at the 
outer edge of the opaque ring by radially "tapering" the opacity of the 
tinted pattern (FIG. 1). In accordance with the present invention, the 
lens body 12 has a surface configured (e.g., with a concave form) to 
conform to the eye curvature of the wearer. The lens body 12 has a second 
surface 16 with a convex form. Optionally, the second surface 16 can be 
optically configured to correct the vision of the wearer selectively at a 
focus between and including far and near objects. 
The contact lens 10 has an annular mask 18 of continuously variable 
transmissivity according to the particular needs of a given wearer. The 
annular mask 18 is arranged to form an aperture 20 at the wearer's optical 
line-of-sight. The aperture 20 is preferably arranged to be concentric 
with the wearer's pupil, which could be off-center with respect to the 
center of the lens body. The aperture 20 is sized to reduce peripheral 
aberrations and distortions while maximizing retinal illumination. In 
other words, the aperture is sized to correct optical aberrations with 
minimal energy starvation to the retina. The aperture is typically of a 
size greater than conventional "pinhole" contact lenses which produce 
refractive correction by reducing the retinal blur circle to allow for 
simultaneous focus of near and distance vision. Therefore, the aperture of 
the present invention is of sufficient size so as not to be effective as 
or a substitute for refractive correction. Preferably, the diameter of the 
aperture is about 3.5 millimeters or larger, more preferably about 4.0 
millimeters or larger, more preferably about 4.2 millimeters or larger for 
individuals having average sized pupils in medium light conditions. The 
size of the aperture is chosen to be as large as possible for a given 
wearer while still providing a mask region of sufficient size to treat the 
conditions described above. However, some individuals have paracentral 
corneal distortions, therefore, in some instances the aperture diameter 
may be about 2.0 millimeters or larger, preferably about 3.0 millimeters 
or larger, (which is within the range of conventional pinhole contact 
lens) but not be effective as or a substitute for refractive correction, 
such as for presbyopia. 
In one embodiment (FIG. 1), the mask region 18 whether in the form of a 
coating or other structure, can have various selected levels of 
transmissivity. Opacity in the annular mask is generally desired for 
maximum visual sharpness as visual dimness or energy starvation is 
generally not a problem with the present invention because the aperture 
diameter is sized so large relative to the wearer's pupil. However, some 
wearers may want or need more light energy transmitted through the annular 
mask region 18 to avoid a sense of visual dimness (i.e. to attain more 
brightness) in medium to low light conditions. For example, the lens 10 
(FIG. 1) transmits less light energy towards the central portion 34 of the 
mask region 18 and transmits relatively more light energy towards the 
outer edge 26 of the mask region. In one embodiment, the transmissivity 
transition for the annular mask 18 from less light energy to more light 
energy utilizes a Gaussian and/or pseudo-Gaussian function to eliminate 
any sharp demarcation at the edge of the mask region or between the outer 
edge 26 and any clear region that may exist if the mask region does not 
extend all the way to the outer region of the lens to avoid the adverse 
diffraction effects. The transmissivity in the annular mask region can 
follow any predetermined mathematical function or not be defined by a 
mathematical function. 
In one embodiment, the tapered (progressive) mask pattern has a clear 
central aperture and the transmissivity of the mask increases gradually 
from 0% transmissivity at the edge of the clear central aperture to the 
periphery of the mask. The variation in transmissivity is symmetrical to 
the axis through the center of the aperture. The aperture 20 typically is 
greater than the diameter at which diffraction effects start to degrade 
image quality. In general, the benefits achieved can be destroyed by 
diffraction if small apertures relative to pupil size are incorporated 
into the lens. Such small apertures that have these adverse results 
include radial slits and scalloped patterns. Diffraction can actually 
increase the blurring of the retina/image such that the wearer's vision is 
degraded rather than improved. Thus, to maintain retinal illumination and 
reduce diffraction effects, typically the lower limit of an aperture in a 
usable contact lens is above about 3.5 millimeters, more preferably above 
about 4.0 millimeters, more preferably above about 4.2 millimeters. 
In one embodiment, the present invention also utilizes a "soft edge" 32 at 
the junction of the clear aperture 20 and the annular mask 18. This can be 
accomplished by either reducing the transmittance of the central aperture 
as a function of increasing radial position, or by decreasing the 
transmissivity of the annular mask as a function of increasing radial 
position. 
In one embodiment, the present invention eliminates the sharp edge (i.e., 
abrupt demarcation) by apodizing the aperture. The transmittance function 
of the aperture 20 on lens 10 (FIG. 1) can be a Gaussian apodized aperture 
or pseudo-Gaussian apodized aperture described by the function: 
EQU I(r)=e.sup.-r/c).spsp.x 
where I(r) is the transmissivity amplitude for the aperture 20 as a 
function of the radial position, r, and c is the effective radius of the 
aperture. The effective radius is of sufficient size to reduce peripheral 
aberrations and distortions but not to be effective as or a substitute for 
refractive correction. Preferably, the effective radius is in the range 
from about 2.0 to about 4.2 millimeters, and more preferably in the range 
from about 3.5 to about 4.0 millimeters, and x is chosen from the range 
2&lt;.times..ltoreq.5. The effective radius is chosen for a particular 
patient based on the type of optical distortion and the location of that 
distortion. For example, corneal topography can be utilized to identify 
the location and severity of keratoconus. Then, c would be chosen based on 
that location. The function is referred to as Gaussian when x equals 2 and 
as pseudo-Gaussian for values greater than 2 and preferably no more than 
10. 
To this point, the aperture apodization as been described as either a 
Gaussian or pseudo-Gaussian function. However, the present invention is 
not limited to a Gaussian or a pseudo-Gaussian function to produce the 
"soft edge" effect. Any number of functions can be used, such as, but not 
limited to linear, exponential, parabolic, any combination of these, etc. 
In addition, the present invention is not limited to "soft edges" that are 
defined by a mathematical function. It is with the scope of the invention 
that the "soft edge" be defined as any decreasing transmissivity that has 
diffraction-reducing effect. It is within the scope of the invention that 
the "soft edge" be defined as any decreasing transmissivity that 
essentially begins at about 100% and decreases to about 20% or less within 
a distance in the range of about 0.05 millimeters or greater to about 1.0 
millimeters or less, more preferably, decreases to about 10% or less 
within that distance, more preferably, decreases to about 1% or less 
within that distance. Likewise, more preferably decreases to about 20% or 
less within a distance in the range of about 0.1 millimeters or greater to 
about 1.0 millimeters or less, more preferably decreases to about 10% or 
less in that distance, more preferably decreases to about 1% or less in 
that distance. Likewise, more preferably decreases to about 20% or less 
within a distance in the range of about 0.15 millimeters or greater to 
about 0.4 millimeters or less, more preferably decreases to about 10% or 
less in that distance, more preferably decreases to about 1% or less in 
that distance. 
FIG. 2 illustrates the transmissivity for one embodiment of the lens of 
FIG. 1. The transmissivity at the center of the lens starts at 100% then 
decreases according to the principles above until reaching a 
transmissivity below which the mask is opaque or performs as essentially 
opaque. Preferably, the transmissivity stays at that level for a width of 
between about 1.0 millimeters to about 4.0 millimeters, preferably about 
1.5 to 2.0 millimeters, then increase in transmissivity to the outer "soft 
edge" 26 or to the edge of the lens. Preferably, the transition in "soft 
edge" 32 is more rapid than the transition through central portion 34 in 
the annular mask to its outer portion 26. 
An optimal tapering profile of the opaque mask will be related to the pupil 
sizes and the retinal illumination required for the wearer. 
Since the lens may not always center over the wearer's pupil, the lens is 
preferably fitted first, and the position of the annulus 18 noted, and the 
lens 10 then made to special order according to the fitting so the annulus 
18 centers over the wearer's pupil. Alternatively, the lens can be 
mass-produced to fit a generalized population of wearers or to fit several 
sets of generalized wearers. In a preferred embodiment, the lens body 12 
is weighted (e.g., with a prism ballast) or shaped to center the aperture 
20 at the optimal location on the eye of the wearer, and to reduce the 
movement of the contact 10 on the wearer's eye, preferably to less than 
approximately one and one-half millimeters. Accordingly, the lens 10 is 
held in a relatively constant position on the eye of the wearer, thereby 
maximizing the lens 10 for central vision while reducing the possibility 
of a reduction in the peripheral field by decentering and other excessive 
movements. 
In addition, the radial width of the annular mask 18, from the inside edge 
32 to the outside edge 26, is preferably between about 0.95 millimeters or 
greater and about 4.5 millimeters or less. It will be appreciated that the 
annular mask can extend to the outside edge of the lens and thus its width 
would be determined by the diameter of the lens. The radial width is sized 
in the practice of the invention to accommodate the normal function of the 
human pupil while being effective in treating the above-listed conditions. 
The lens body 12 can be constructed with material to form a hard, gas 
permeable lens, or, alternatively, to form a soft contact lens, e.g., with 
a flexible soft polymer material. Combinations of these materials are also 
suitable to form a composite contact. The outer diameter of the contact 
lens body 12 is approximately seven to eighteen millimeters, depending 
upon the wearer's eye size. Likewise, the lens body can be constructed 
with materials suitable for producing anterior chamber lenses, intraocular 
lenses, intracorneal lenses, etc. It can be appreciated that the 
dimensions of the annular mask 18 can be adjusted for a particular wearer. 
For example, the annular mask 18 can be sized for a particular pupil. 
Those skilled in the art will appreciate that the mask regions of the lens 
can be constructed in several ways. In one embodiment, an opaque spinning 
mask 44 is used to produce an annular mask like the one shown in FIG. 1. 
The apparatus used with the spinning mask 44 is shown diagrammatically in 
FIG. 3. The method as described with respect to FIG. 3, can be used to 
produce a variably transmissive annular mask of any desirable profile 
depending on the pattern of the spinning mask used. A light source 40 and 
condenser lens 42 provide back illumination to mask 44 which is spun by 
motor 46. The spinning mask 44 as an object is imaged through relay lens 
48 and imaging lens 50 onto the lens 10 using a photo-reactive dye or 
coating in or on the lens. The opaque mask has several light transmitting 
"petals" extending radially outward from a central region. The profile of 
the variably transmissive annular mask on the resulting lens is controlled 
by changing the shape of the design of the "petals". As the mask is 
spinning about an axis symmetric to the petal pattern, the image of the 
spinning mask becomes an apodized pattern on the lens with continuously 
variable gray tones. 
Another embodiment, similar to that just described, utilizes a beamsplitter 
60 as illustrated diagrammatically in FIG. 4, to combine the apodized 
aperture pattern with a second spinning mask 62 of any desirable pattern 
using another projection system branch. In this embodiment, a tapered 
(i.e., reverse apodized) annular mask pattern is implemented in the second 
branch of the projection system to produce a masked lens as shown in FIG. 
1 having diffraction-reducing edges on the inside of the annular mask and 
the outside of the annular mask. 
A mask 64 with a plurality of opaque petals 66 on a light-transmitting 
substrate disk 68 (FIG. 5) is illuminated by a light source 70 and 
condenser lens 72 (FIG. 4). A magnified or demagnified image of the mask 
64 is formed on the lens 10 by relay and imaging lenses 74, 76. As the 
mask 64 is spinning about an axis symmetric to the blade pattern, the 
image of the spinning mask becomes a brightness-tapered pattern with 
continuous gray tones. The brightness tapered profile of the image is 
controlled by the design of the shape of the petals. A second mask 62 of 
any desirable pattern, such as shown in FIG. 5, is illuminated by a second 
light source 80 and condenser lens 82. A second magnified or demagnified 
image is formed on the lens 10 by relay and imaging lenses 84, 76 and 
beamsplitter 60. The final image is a combined image of the individual 
images superimposed on the lens 10. By controlling the brightness of the 
light sources and/or exposure time for each mask, a combined image of any 
desired transmissivity pattern can be produced in the lens. 
In another embodiment, a transparent dome 86 (FIG. 6) having a 
light-occluding portion 88 is used to produce the annular mask pattern in 
the lens. The dome 86 has a groove machined into the top of the dome 
beginning at a depth of about 0.1 millimeters deep in the region 
surrounding an area not machined out that will form the central aperture 
on the lens and rapidly increasing to a depth of about 1.0 millimeters at 
a diameter of about 3.5 millimeters then gradually decreasing to a depth 
of 0.1 millimeters at an outside diameter of 5.5 millimeters. The groove 
is filled with black blocking wax to form light occluding portion 88. In 
use, the lens 10 is emersed in a Diazo dye solution (HD-61; see full 
chemical name in Example 1) and then placed on the dome 86 in position so 
that the light-occluding portion of the dome is in the position where the 
resulting annular mask should be on the finished lens. Light 90 is shone 
from beneath the dome until all exposed areas of the lens become 
discolored. A typical light source is a HA 6000 halogen ELH or ENX lamp. 
The lens is then placed into phloroglucinol solution in which the areas of 
the lens corresponding to the light-occluding part of the dome turn black 
and form a continually variable shade of gray resulting in an annular mask 
pattern such as shown in FIG. 1. 
In another embodiment, the lens 10 is positioned correctly on an opaque 
dome 92 in housing 98, and then contacted with a dam ring 94 to hold dye 
solution 96 (FIG. 7). Dye solution is placed in the dam ring and allowed 
to permeate the lens from the top side of the lens only. Dye is allowed to 
diffuse into the lens only to a depth necessary to produce the desired 
intensity, and not all the way through the thinnest section of the lens. 
After the dye has penetrated the lens 10, the dam ring is removed and the 
dye rinsed off the surface quickly with water. A light restricting mask 
100 is then placed over the lens 10 and the dye in the lens is 
desensitized by exposure to light (FIG. 8). The mask 100 is produced on a 
computer monitor with a commercially available graphics program. Then 
either printed out on clear film or a slide is made with a 35 millimeter 
camera of the computer-generated mask pattern. The slide film is then used 
as the mask 100. Alternatively, the mask 100 can be produced by methods 
such as but not limited to selection of appropriate neutral density or 
color filters, metal deposition, such as sputtering, vacuum deposition, 
printing, spraying, etc. 
In order to achieve a more graduated or tapered edge, the mask can be 
raised slightly above the lens, so that a diffused edge will form from 
light diffraction effects. By varying the distance of the mask from the 
lens, the light intensity, duration of exposure to the light, and quality 
of light in the lens, different tapering effects may be produced in the 
lens. 
Another practice uses a variably transmissive coating applied to, or 
manufactured with, the lens body. Yet another practice generates the 
annular mask with a plurality of light-blocking dots, which in total 
reduce the transmission of light energy through the annulus to the 
selected transmissivity. Another practice uses a shutter-like mechanical 
device (not shown) with several shutter blades arranged to provide masking 
in three concentric annular regions corresponding to the inner soft edge, 
the opaque portion and the outer soft edge. The opaque region will be 
fixed with 1% transmissivity or less. The transmissivity of the inner soft 
edge and the outer soft edge can be varied with the speed of the shutter 
blades opening and closing and with the shape of the shutter blades. 
Other practices for forming the annular mask include other Diazo contact 
printing processes, mesoprints, and reactive and vat dyes. Other practices 
for forming the annular mask include a variety of methods for disrupting 
the surface or refractive properties of the lens in the area of the 
annular mask. For example, lasers or chemical etchants, or physical 
abrasives, are effectively used to disrupt the optical surface of the 
contact to change the transmission in the annular mask region to form the 
annular mask. Suitable techniques for disrupting and creating such optical 
surfaces are described in U.S. Pat. No. 4,744,647, entitled "Semi-Opaque 
Corneal Contact Lens or Intraocular Lens and Method of Formation". 
Another embodiment for achieving the variably transmissive annular mask 
utilizes PAD FLEX.TM. or Italio Plate methodology, which is well-known to 
those skilled in the art. In PAD FLEX.TM. printing, for example, a 
silicone tip contacts an Italio plate engraved with a selectable pattern 
and filled with ink. The tip acquires the image from the Italio plate and 
then transfers the image without distortion onto a wide range of curved 
surfaces, such as a contact lens. 
In another method of imparting the annular mask to the contact lens, the 
mask comprises a pigment suspended in a solvent material which is applied 
to the surface of a contact lens mold, and the contact lens is cast and 
polymerized thereabouts. This means that the mask is incorporated into the 
body of the lens as part of the contact lens surface or into the lens body 
in the region immediately adjacent to the lens surface. 
Suitable pigments for use with this method include: 
______________________________________ 
Color Index Chemical Name 
______________________________________ 
Pigment Black 7 
Carbon Black 
Pigment Black 11 
Iron Oxide 
Pigment Brown 6 
Iron Oxide 
Pigment Red 101 
Iron Oxide 
Pigment Yellow 42 
Iron Oxide 
Pigment White #6 
Titanium Oxide 
Pigment Green #17 
Chromic Oxide 
Pigment Blue #36 
Chromium-Aluminum-Cobaltous Oxide 
Pigment Green #7 
Poly chloro copper phthalocyanine 
Pigment Blue #15 
Copper phthalocyanine 
Pigment Violet #23 
3, amino-9-ethyl carbazole-chloranil 
______________________________________ 
Furthermore, the above mentioned pigments may be mixed with one another to 
produce the desired variably transmissive mask. Likewise, precipitated vat 
dyes, including precipitated version of those disclosed earlier may be 
used as suitable pigments in the above method. 
In another embodiment for incorporating the variably transmissive mask into 
the body of the lens, pigment is dispersed in a polymerisable medium which 
is then applied to the surface of a contact lens casting mold and the 
contact lens is cast and polymerized thereabouts. In this particular 
instance as the main body of the lens is polymerized so is the 
polymerisable medium in which pigment is incorporated into the contact 
lens as part of the surface of the contact lens or immediately adjacent 
thereto. 
The pigments which may be used with this particular arrangement of the 
present invention include those disclosed above for use with the earlier 
disclosed methods, which may be dispersed in the same monomeric materials 
as that from which the contact lens is formed. 
In another embodiment, a rod of polymeric material is formed, which rod has 
a band of variably transmissive material throughout its length, this rod 
is then cut into buttons from which the contact lenses are then machined. 
In its simplest form this method may be used to produce individual buttons 
and not a rod. 
A contact lens constructed in accordance with the invention is colored, 
tinted, or otherwise shaded, when appropriate, by methods known in the 
art. This coloring or tinting can be cosmetic, as it often is for many 
wearers of common contact lenses. It can also reduce the sometimes 
objectionable appearance of the annular mask 18 when viewed on the eye of 
the wearer. For example, the invention provides for an annulus that is 
matched to the wearer's iris. It also provides for an annulus that 
enhances or changes the appearance of the wearer's iris, if desired. A 
further enhancement can include a limbal ring as described in U.S. Pat. 
No. 5,302,978 which is incorporated herein by reference in its entirety. 
It will be understood that changes may be made in the above constructions 
without departing from the scope of the invention. For example, the 
arrangement and size of the annular mask 18, can be selected for a 
particular wearer to optimize the visual correction available. In another 
example, the contact lens body 12 can be constructed with a yellow 
appearance, giving the wearer a physiological impression of brighter 
lighting. Those skilled in the art will appreciate that the invention can 
also aid wearers suffering from other vision deficiencies and disorders. 
EXAMPLE 1 
A contact lens in accordance with FIG. 1 was produced with the following 
procedure. A 1% sensitizer solution was formed by dissolving 1.0 grams of 
4-diazo-[4'-toluyl]-mercapto-2,5-diethoxybenzene zinc chloride (also 
referred to as Diazo-15 or HD-61) in 100.0 grams of de-ionized water and 
sonicating for 15 to 20 minutes. A 1% developer solution was formed by 
dissolving 1.0 grams of phloroglucinol dihydrate in 100.0 grams of 
de-ionized water and sonicating for 15-20 minutes. The solutions were 
filtered using 0.45 micron filter paper prior to use. Prior to tinting, 
the lens was equilibrated in water for at least 1 hour. The lens was then 
pat dry and dropped in a vial containing about 6-8 milliliters of 
sensitizer. The front curve of the lens was uppermost. The lens was left 
in the solution for 3 minutes. The lens was removed, rinsed with water and 
pat dry. The lens was positioned on a dome and the imaging mask pattern 
placed over the lens on the dome. The dome was then placed over a type ENX 
HA 6000 Halogen light source for 2 minutes. The lens was then removed from 
the dome and placed in the developer solution for 2 minutes. The lens was 
then rinsed with clean water and processed via the usual extraction and 
hydration processes. 
The foregoing has described the principles, preferred embodiments and modes 
of operation of the present invention. However, the invention should not 
be construed as being limited to the particular embodiments discussed. 
Thus, the above-described embodiments should be regarded as illustrative 
rather than restrictive, and it should be appreciated that variations may 
be made in those embodiments by workers skilled in the art without 
departing from the scope of the present invention as defined by the 
following claims.