U.S. patent application number 10/371853 was filed with the patent office on 2003-07-03 for contact lens and process for fitting.
Invention is credited to Dunn, Stephen A..
Application Number | 20030123024 10/371853 |
Document ID | / |
Family ID | 21711419 |
Filed Date | 2003-07-03 |
United States Patent
Application |
20030123024 |
Kind Code |
A1 |
Dunn, Stephen A. |
July 3, 2003 |
Contact lens and process for fitting
Abstract
A contact lens with a central region (10) that is optimally less
than approximately 1.9 millimeters in diameter and that is
preferably overcorrected by approximately 25% to 100% over the
correction needed for reading. Unexpectedly, the central region
(10) does not impair distance vision, but compensates for
presbyopia and therefore alows a user to focus on objects within a
range of near and intermediate distances. A method for fitting the
contact lens is also provided.
Inventors: |
Dunn, Stephen A.; (Honolulu,
HI) |
Correspondence
Address: |
EDWARDS & ANGELL, LLP
P.O. Box 9169
Boston
MA
02209
US
|
Family ID: |
21711419 |
Appl. No.: |
10/371853 |
Filed: |
February 20, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10371853 |
Feb 20, 2003 |
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09212904 |
Dec 16, 1998 |
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6540353 |
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09212904 |
Dec 16, 1998 |
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08716199 |
Sep 27, 1996 |
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5864379 |
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60004567 |
Sep 29, 1995 |
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Current U.S.
Class: |
351/159.05 |
Current CPC
Class: |
A61F 9/007 20130101;
A61F 2/164 20150401; A61F 2/1613 20130101; G02C 7/021 20130101;
G02C 7/042 20130101; G02C 7/044 20130101; A61F 2/1618 20130101 |
Class at
Publication: |
351/160.00R ;
351/159; 351/161 |
International
Class: |
G02C 007/02; G02C
007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 1996 |
WO |
PCT/US96/15589 |
Claims
What is claimed is:
1. A contact lens, comprising: a circular central region
overcorrected for near vision, wherein said central region is small
enough to avoid impairing distance vision; at least one ring shaped
transition region extending radially outward from said central
region; a ring shaped outer region extending radially outward from
said transition region corrected for distance vision; and a ring
shaped carrier region extending radially outward from said outer
region; wherein said transition region provides at least a partial
diopter shift over said transition region between said
overcorrection of said central region and said distance correction
of said outer region.
2. A contact lens according to claim 1, wherein said central region
is between approximately 1 millimeter and approximately 2.5
millimeters in diameter.
3. A contact lens according to claim 2, wherein said central region
is between approximately 1.5 millimeters and approximately 1.9
millimeters.
4. A contact lens according to claim 1, wherein said central region
has a diameter of less than approximately 1.9 millimeters.
5. A contact lens according to claim 2, wherein said central region
has a diameter of approximately 1.5 millimeters.
6. A contact lens according to claim 2, wherein said central region
has a diameter of approximately 1.9 millimeters.
7. A contact lens according to claim 1, wherein said central region
is overcorrected for near vision by approximately 25% to
approximately 100%.
8. A contact lens according to claim 1, wherein said lens has at
least a first transition region and a second transition region.
9. A contact lens according to claim 8, wherein said lens has two
transition regions and each of said transition regions is
approximately 0.5 millimeters wide.
10. A contact lens according to claim 8, wherein said transition
regions are aspherical.
11. A contact lens according to claim 8, wherein said transition
regions are spherical.
12. A contact lens according to claim 8, wherein said diopter shift
across said first transition region is at a first constant radial
rate and said diopter shift across said second transition region is
at a second constant radial rate.
13. A contact lens according to claim 8, wherein said first
transition region provides a diopter shift of approximately 1.6
diopters, said second transition region provides a diopter shift of
approximately 1.2 diopters, and said outer region provides a
diopter shift of approximately 0.9 diopters.
14. A contact lens according to claim 8, wherein said first
transition region provides a diopter shift of approximately 1.1
diopters, said second transition region provides a diopter shift of
approximately 0.8 diopters, and said outer region provides a
diopter shift of approximately 0.6 diopters.
15. A contact lens according to claim 1, wherein said outer region
has a diameter of approximately 8 millimeters.
16. A contact lens according to claim 1 wherein optical correction
of at least one of said regions is provided by a material with
differing indices of refraction in different portions.
17. A contact lens according to claim 1, wherein said lens is made
from materials selected from the group consisting of conventional
soft lens material, rigid gas permeable contact lens material, or
hard contact lens material.
18. An intraocular implant, comprising: a circular central region
overcorrected for near vision, wherein said central region is small
enough to avoid impairing distance vision; at least one ring shaped
transition region extending radially outward from said central
region; a ring shaped outer region extending radially outward from
said transition region corrected for distance vision; and a carrier
region extending radially outward from said outer region; wherein
said transition region provides at least a partial diopter shift
over said transition region between said overcorrection of said
central region and said distance correction of said outer
region.
19. A refractive surgical procedure, comprising: shaping a human
cornea to provide: a circular central region overcorrected for near
vision, wherein said central region is small enough to avoid
impairing distance vision; at least one ring shaped transition
region extending radially outward from said central region; a ring
shaped outer region extending radially outward from said transition
region corrected for distance vision; wherein said transition
region provides at least a partial diopter shift over said
transition region between said overcorrection of said central
region and said distance correction of said outer region.
20. A contact lens having a pupil area, comprising: a central
accommodation zone covering approximately half of said pupil area
overcorrected for near vision by between approximately 25% to
approximately 100%; at least one concentric transition region
extending radially outward from said accommodation region; and a
concentric outer region extending radially outward from said
transition region corrected for distance vision; wherein said
transition region provides at least a partial diopter shift over
said transition region between said overcorrection of said central
accommodation zone and said distance correction of said outer
region.
21. A contact lens according to claim 20, having an add power of
between approximately 3.5 and approximately 3.9 diopters.
22. A contact lens according to claim 20, having an add power of
approximately 3.7 diopters.
23. A contact lens according to claim 20, having an add power of
between approximately 2 and approximately 3.5 diopters.
24. A contact lens according to claim 20, having an add power of
between approximately 2.4 and 2.8 diopters.
25. A contact lens according to claim 20, having an add power of
approximately 2.6 diopters.
26. A process for aligning a central region of a contact lens,
comprising: marking a centered spot on a diagnostic contact lens;
and detecting whether a user's pupils would be aligned with said
central region.
27. A process according to claim 26, wherein said spot has a
diameter of approximately 1.9 millimeters.
Description
TECHNICAL FIELD
[0001] This invention relates to a contact lens that restores the
ability to focus on objects within a range of distances near to the
user (referred to as "natural accommodation"), while retaining the
ability to see distant objects. More specifically, this invention
relates to a contact lens with a conventional spherical concave
surface conforming to the curvature of the eye (base curve) and
having a non-conventional convex surface (optic curve) combining
spherical and non constant aspherical curvature resulting in an
optical system that provides true monocular presbyopic correction
(correction of presbyopia in each eye independently, instead of
partial or full distance correction in one eye and partial or full
near correction in the other) and restores the phenomenon of
"natural accommodation." Additionally, the invention affords a
methodology of fitting that substantially reduces the skill and
experience required by the contact lens fitter to a very basic
level while affording a high degree of clinical success and patient
satisfaction.
[0002] Normally between the ages of 40 and 45, presbyopia or old
sightlessness is brought about by loss of elasticity of the
crystalline lens of the eye, causing blurred vision at near points
due to the reduction of the ability of the eye's natural lens to
accommodate the changes in curvature necessary to focus on both
near and distant objects.
[0003] When a person is free of presbyopia, the eye retains its
full range of natural accommodation. This type of person's vision
can be corrected by eyeglasses or contact lenses providing only the
correction required for distance vision, and natural accommodation
would automatically provide correction for near and intermediate
distance vision.
BACKGROUND ART
[0004] For the contact lens wearer who requires presbyopic (or near
vision) correction, in addition to distance correction, a variety
of options have been available. These individuals may be fitted
with single vision contact lenses corrected for distance, and wear
reading glasses for near correction. Another alternative is to
provide a contact lens for one eye that is corrected for distance
vision and to provide a contact lens for the other eye that is
corrected for near vision (this practice is referred to as
monovision because only one eye is corrected for near vision), or
the fitting of bifocal or multifocal contact lenses.
[0005] During the 1950's, a variety of contact lenses were designed
for the correction of presbyopia. These contact lenses, although
very innovative in design, met with only limited success because
the only readily available material was Poly Methyl Methacrylate
(Plexiglass), also known as PMMA, which does not transmit oxygen.
As bifocal and multifocal designs of the period were quite thick
and heavy compared to conventional distance correction contact
lenses, these presbyopic contact lenses were uncomfortable to wear
for substantial periods of time. Additionally, the fitting of these
bifocal and multifocal contact lenses required considerable time
and skill on the part of the contact lens fitter.
[0006] During the 1970's, both soft contact lenses and rigid gas
permeable (RGP) contact lenses were introduced. With the
availability of these new materials, renewed enthusiasm brought
about several new designs for contact lenses for the correction of
presbyopia.
[0007] RGP materials provide oxygen transmission through the lens
material itself, and afforded new hope for the earlier designs
developed in PMMA material. However, lens thickness and resultant
patient discomfort continued to be a problem.
[0008] One of the early benefits recognized with soft contact
lenses was the comfort and ease of fitting and, for this reason, by
1995 approximately 85% of new contact lens wearers are being fitted
with soft contact lenses. As soft contact lenses command such a
large share of the contact lens market, it is natural that
considerable effort would be made to develop bifocal and multifocal
contact lens designs in soft contact lens material.
[0009] There are two types of contact lens designs for the
correction of presbyopia--Alternating (or Translating) and
Simultaneous.
[0010] (1) in the alternating (or translating) vision technique,
the lenses are very similar in design to bifocal eyeglass lenses in
that the wearer sees through the distance segment in the upper
portion of the lens when looking straight ahead and sees through a
lower near vision segment when the eye (moves) to look down.
Alternating vision lenses have proven to be successful in RGP
designs, but have met with little success when designed in soft
contact lenses.
[0011] Perhaps the reason that alternating vision soft contact lens
designs were not as successful as the same design concept in RGP
materials was because lens translation is necessary for this design
to be successful. The translation from distance to near is achieved
through the mechanical action of the lens resting on the lower
eyelid and, when the eye looks down, the lens remains stable on the
lower eyelid causing the pupil of the eye to translate from the
distant vision portion of the lens to the near vision portion of
the lens. Soft lens material by its nature caused this modality to
fail as there was insufficient rigidity in the soft lens to remain
properly positioned on the lower eyelid and often the lens would
slip underneath the lower eyelid during translation.
[0012] (2) Simultaneous vision bifocal or multifocal contact lenses
are either concentric or aspheric in design with focal power
changing through different areas of the lens. Lenses are fitted so
that distance, intermediate and near zones focus images
simultaneously on the retina of the eye and the brain then
separates out the image desired.
[0013] Theoretically, with adaptation, the ability to change focus
naturally from near to far with no blurring in between can be
achieved with simultaneous vision lenses in both RGP and soft
contact lenses.
[0014] As alternating presbyopic designs proved to be unsuccessful
in soft contact lens designs, most of the development work with
soft contact lenses was done in the area of simultaneous presbyopic
correction with concentric designs or aspheric designs.
[0015] During the 1980's, several designs of concentric and
aspheric soft contact lenses were introduced. Soft aspheric
multifocal contact lenses typically provided relatively weak
reading addition power and therefore worked best in early
presbyopia.
[0016] Reading addition powers are referred to by eye care
professionals as "add" power, and represent the difference between
the distance correction and near correction prescribed by an eye
care professional for eyeglasses- or contact lenses. Accordingly, a
prescription of "-3 with a +2 add" (which would be typical for
moderate presbyopia) would mean that distance vision requires -3
diopters of correction, and near vision requires an additional 2
diopters of plus correction, resulting in -1 diopters of near
vision correction. In conventional monovision, the dominant eye
would be fitted with a -3 distance correction lens, and the other
eye would be fitted with a -1 near correction lens.
[0017] This type of solution is often satisfactory in early
presbyopia because the user still has some remaining visual
accommodation and the needed add power is usually between +0.75 and
+1.25, which is usually low enough for the brain to comfortably
select the desired image in most people. However, conventional
monovision becomes less satisfactory as presbyopia becomes more
advanced because the needed add power increases and visual
accommodation has deteriorated further, so that the visual
imbalance exceeds the brain's ability to select the desired image
from the appropriate eye.
[0018] Typically, early presbyopes, would be between the age of 40
and 45, and would require add power of between +1.00 and +1.50
diopters. Moderate presbyopes would usually be between 45 and 55
years and would require add power of between +1.50,and +2.00
diopters. Mature presbyopes would usually be older than age 55 and
require an add power of between +2.00 and +3.00 diopter.
[0019] The add corrective power of current aspheric multifocal
contact lens designs is usually limited to only +0.75 to +1.25
diopters because the brain must be able to separate out the desired
image (and also suppress the undesired images) from the multiple
images (near, intermediate or distant) being simultaneously focused
by the multifocal contact lens design. In order to achieve this
suppression, the images cannot be too different from each other.
However, if aspheric corrections are increased in attempts to
achieve higher add powers, the images become too different for the
brain to suppress the undesired images, resulting in blurred
vision. Even at add powers of +0.75 to +1.25 diopters, many
patients suffer some blurring or ghosting with multifocal contact
lens designs because their brains are not able to completely
separate the desired image while simultaneously completely
suppressing the undesired images.
[0020] Some contact lens fitters may attempt to use aspheric
designs to achieve near distance correction of up to +2.00 diopters
(or more) by undercorrecting the distance vision of the
non-dominant eye by between 0.25 and 1.00 diopters, thereby
theoretically providing up to +2.00 diopters (or more) of near
vision correction, instead of the +0.75 to +1.25 diopter correction
that would be provided if that eye had been fully corrected for
distance vision with an aspheric multifocal contact lens. The
dominant eye would be corrected to maximum distance acuity in such
a situation. However, this creates even more blurring and ghosting.
This technique is called modified monovision.
[0021] Aspheric optics have been incorporated on both the front and
back surfaces of soft contact lenses. However, it is believed that
front surface aspherical multifocal soft contact lenses provide
better presbyopic correction. Still, only limited success is
achieved because providing add power of +0.75 to +1.25 (or more)
usually results in reduced distance acuity. For this reason, many
contact lens fitters find it necessary, when using aspheric soft
multifocal contact lenses, to undercorrect the distance power in
one eye to improve near vision, while correcting the other eye
fully for distance vision, as discussed above. When attempting to
fit moderate to mature presbyopes, this modified monovision almost
always results in a visual compromise similar to that of
conventional monovision.
[0022] Concentric multifocal lens designs have an advantage over
aspheric designs in the fitting and correcting of more mature
presbyopes requiring add power of more than +1.25 diopters,
primarily due to the availability of higher add power correction
and central power zones of different diameters. Concentric soft
multifocal contact lenses have been made with the central distant
correction zones and central near correction zones. In the latter
designs, the central power zones would be corrected by the amount
prescribed to correct near vision. It is believed that central near
add zones have been more successful at correcting presbyopia than
central distance zones, when incorporated in concentric multifocal
soft lens designs. Although concentric center add multifocal
designs have the ability to correct higher add power requirements,
most individuals fitted with this type of lens experience moderate
to significant amounts of visual discomfort due to ghosting of
images or a 3-D effect, at near distances. These effects diminish
with adaptation, but still cause a high portion of wearers to
discontinue the use of this type of presbyopic contact lens.
[0023] The reality of the existing art of presbyopic correction
with simultaneous vision contact lenses is that no currently
available lens system, be it aspheric or concentric, provides
monocular multifocal correction for moderate to mature presbyopia.
In most cases, some form of modified monovision is required in an
attempt to satisfy the visual requirement for near and far vision.
To this end almost all currently available presbyopic contact lens
manufacturers indicate in their fitting manuals the requirement of
compensating one eye more for near and the other eye more for
distance correction. This is the norm rather than the exception.
Additionally, no currently available multifocal contact lens has
the ability to restore the phenomena of natural accommodation and
successful results are difficult to achieve and require
considerable time and experience on the part of the fitter.
[0024] It is therefore an object of this invention to provide true
multifocal correction for moderate and mature presbyopes requiring
up to +3.00 diopters of add power without the need to compensate
one eye for near and the other eye for distance.
[0025] It is a further object of this invention to provide rapid
patient adaptation with minimal initial visual discomfort.
[0026] It is a still further object of this invention to provide a
presbyopic optical system that restores the phenomenon of natural
accommodation.
[0027] It is a still further object of this invention to provide a
system of fitting and methodology that allows a contact lens fitter
with little or no multifocal contact lens fitting experience to
achieve a very high degree of success and patient satisfaction.
DISCLOSURE OF INVENTION
[0028] These and other objects are achieved by a contact lens
having a central circular region (an "accommodation zone" or "sweet
spot" named zone 1) that is overcorrected for near vision, and that
is small enough that it does not impair distance vision.
Preferably, a plurality of concentric transition regions (or
rings), optimally two (named zone 2 and zone 3, progressing
radially outwardly), are provided between the sweet spot and the
outer region (or ring) of the lens (named zone 4), which is
corrected for distance vision. Preferably, the sweet spot has a
diameter of between approximately 1.0 millimeters and approximately
2.5 millimeters, preferably between approximately 1.5 millimeters
and approximately 1.9 millimeters, and optimally either
approximately 1.5 millimeters or approximately 1.9 millimeters.
Preferably, the transition rings (zones 2 and 3) are each
approximately 0.5 millimeters wide. Preferably also, the remaining
portion of the lens (zone 4.) extends radially outward from the
outermost transition ring to at least approximately 8 millimeters.
Because the human pupil cannot expand beyond approximately 8
millimeters in diameter, the portion of the lens extending more
than approximately 8 millimeters radially outward from the center
is not an optical portion and functions only as a carrier.
[0029] Preferably, the sweet spot is spherical and is overcorrected
by between 25% and 100% over the near vision correction prescribed
for the user. Preferably, the remaining optical portions of the
lens are aspheric, with different diopter shifts over different
regions. Optimally, for high add power, zone 2 provides a diopter
shift of approximately 1.6 diopters, zone 3 provides a diopter
shift of approximately 1.2 diopters, and zone 4 provides a diopter
shift of approximately 0.9 diopters. For low add power, optimally
zone 2 provides a diopter shift of approximately 1.1 diopters, zone
3 provides a diopter shift of approximately 0.8 diopters, and zone
4 provides a diopter shift of approximately 0.6 diopters.
[0030] The contact lens manufacturing lathe disclosed in the
example below provided contact lenses that achieved the desired
results. However, some experimentation may be necessary to achieve
the desired result with different equipment, but this
experimentation should not be undue.
[0031] The invention incorporates both concentric and aspheric
design principles and can be produced with a high add power
correction or a low add power correction. In addition, the lens
system offers two accommodation zone diameters for different sized
pupils to achieve maximum near point acuity without reduction in
distance visual acuity.
[0032] The higher add power lens has a power transition of 3.7
diopters across the usable optic zone, and the low add power lens
has a power transition of 2.6 diopters across the usable optic
zone.
[0033] The accommodation zone should cover approximately 50% of the
pupil area for maximum success in distant, intermediate and near
visual acuity. The accommodation zone functions to restore the
phenomenon of natural accommodation by creating a very small area
of over magnification in the center of the pupil of approximately
25% to 100% over the near vision correction required by the
indicated reading add power. Surprisingly, distance vision will not
be substantially impaired if the accommodation zone covers 50% or
less of the pupil area. Further, the function of natural
accommodation will be restored to an unexpectedly great extent.
[0034] Although the inventor is not sure (and the validity and
enforceability of any patent issuing hereon shall not be affected
by the accuracy or inaccuracy of this explanation), the inventor
believes that, in near vision, a user's pupils constrict, so that
the accommodation zone occupies a large enough portion of the pupil
area for the accommodation zone to become effective. Normal reading
correction is prescribed for approximately 15 inches (approximately
38 centimeters). Accordingly, the overcorrection of the
accommodation zone (sweet spot) allows the user to see from 8
inches to 15 inches, thus restoring the function of natural
accommodation. In distance vision, however, the pupil will be
normally dilated, so that the accommodation zone is small enough
that the brain ignores the image generated by it. The constriction
of the pupil for near vision is known as "accommodative pupil
response."
[0035] The accommodation zone is blended to the distance zone 4 via
two zones of non constant aspherocity which allows true monocular
correction of near, intermediate and distant vision. Near vision
correction, when tested at the standard distance of approximately
15 inches (approximately 0.38 centimeters) offers normal best
corrected acuity and when reading material is brought closer to the
eyes, up to about eight inches (approximately 20 centimeters), near
acuity remains stable and often improves due to the increased near
power created by the sweet spot.
[0036] Due to the non constant aspheric transition from the sweet
spot to zone 4, adaptation problems associated with prior designs
of concentric or aspheric multifocal contact lenses are
substantially reduced or eliminated completely.
[0037] Historically, the fitting of multifocal contact lenses has
been more an art than a science as the variables associated with
fitting presbyopic contact lenses are considerable. Often success
has only been achieved through the process of trying many different
lenses on the patient in the hope of finding a lens that generates
a good presbyopic response. The contact lens fitter's degree of
experience in the fitting of multifocal lenses has also been a key
to achieving a successful fitting with good visual results.
[0038] The fitting of lenses according to this invention requires
accurate centering of the lens over the pupil of the eye in order
to achieve the expected results. To determine the location of the
sweet spot relative to the pupil is often difficult because the
pupil may not be aligned with the center of the cornea or for other
reasons. Thus, the invention also incorporates the use of a
diagnostic trial lens with a white ring corresponding in diameter
and location to the sweet spot. The exact position of the center of
the contact lens can be determined and the relative position of the
sweet spot to the pupil and the percentage of pupil covered by the
sweet spot is easily observed. The use of the diagnostic lens
allows the fitter to very quickly determine the proper sweet spot
size, which increases the chances of successful fitting. For
example, if the accommodation zone does not align within the pupil,
the fitter knows that the standard lens design will not work and a
custom lens design with an offset accommodation zone will be
required.
[0039] Other objects, features and advantages of the present
invention will become more, fully apparent from the following
detailed description of the presently preferred embodiments for
carrying out the invention and the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0040] FIG. 1 is a top elevational schematic view of a presently
preferred embodiment of a contact lens according to the present
invention for a person who needs a high degree of reading
correction (high add power) and a larger sweet spot;
[0041] FIG. 2 is a top elevational schematic view of a presently
preferred embodiment of a contact lens according to the present
invention for a person who needs a high degree of reading
correction (high add power) but a smaller sweet spot;
[0042] FIG. 3 is a top elevational view of a contact lens according
to the present invention for a person who needs a lesser degree of
reading correction (low add power) and a larger sweet spot; and
[0043] FIG. 4 is a top elevational view of a contact lens according
to the present invention for a person who needs a lesser degree of
reading correction (low add power) and a smaller sweet spot.
BEST MODES FOR CARRYING OUT INVENTION
[0044] The presently preferred best modes for carrying out the
present invention are illustrated by way of example in FIGS. 1 to
4.
[0045] Referring to FIG. 1, shown is a first preferred embodiment
of a contact lens CL according to the present invention. The
contact lens CL is divided into a central circular region and four
concentric ring shaped regions. The central region 10 will be
referred to as zone 1, the accommodation zone, or the sweet spot.
The immediately adjacent first ring shaped region 20 will be
referred to as zone 2. The second ring shaped region 30 immediately
adjacent to zone 2 will be referred to as zone 3. The third ring
shaped region 40 immediately adjacent to zone 3 will be referred to
as zone 4.
[0046] The maximum diameter of a human pupil when it is fully
dilated is approximately 8 millimeters, so that the ring shaped
region 50 of the contact lens extending radially outwardly from
zone 4 is not an optical surface, but merely functions as a carrier
to maintain the optical surface of zones 1 through 4 in
position.
[0047] Structurally, the zones can be described as follows. Zone 1
is preferably approximately 1.5 to 1.9 millimeters in diameter.
Zone 2 and zone 3 are both preferably approximately 0.5 millimeters
in width. Zone 4 preferably extends outwardly from a radius of
approximately 2.5 millimeters to approximately 2.9 millimeters to
approximately 8 millimeters. Thus, the lens can be described as
having a central sweet spot (zone 1), two 0.5 millimeter
intermediate zones (zones 2 and 3), and a distance zone (zone 4)
extending outwardly from the intermediate zones to the edge of the
optical portion of the contact lens (approximately 8 millimeters
radially outwards from the center). The total diameter of the
contact lens CL will be approximately 13 to approximately 16
millimeters for a soft contact lens, so that the carrier 50 will
normally extend from approximately 8 millimeters outwards to
approximately 13.5 millimeters to approximately 15.0 millimeters,
and optimally 14.5 millimeters.
[0048] If this invention is practiced in connection with a hard
contact or RGP lens, the total diameter of the contact lens CL
would be between approximately 7.0 millimeters and approximately
11.0 millimeters, and typically between approximately 8.0
millimeters and approximately 10.5 millimeters, and optimally
approximately 9.5 millimeters.
[0049] Zone 1, the sweet spot, is preferably spherical, although it
can be aspherical. Zones 2, 3 and 4 are preferably aspherical in
order to accommodate transitions in corrective power across these
zones.
[0050] Conventional contact lenses consist of a carrier with a
central lens portion. The central lens portion is usually corrected
for distance vision. This is described in U.S. Pat. No. 4,119,2312,
Evans, which is hereby incorporated by reference.
[0051] The present invention differs from conventional multifocal
contact lenses in that a small central portion of the lens is
overcorrected beyond the correction that would be necessary for
reading. This central portion, the sweet spot or accommodation
zone, is small enough so that, surprisingly, it does not impair
distance vision when the user is looking at distant objects, but it
restores the ability to focus on near objects within a substantial
range of distances from the wearer, such as, between 8 inches and
15 inches. It is believed that the transition zones restore the
ability to focus as follows: zone 2 restores the intermediate
visual acuity between approximately 15 inches and approximately 36
inches, and zone 3 restores the intermediate visual acuity between
approximately 36 inches and full distance correction
(infinity).
[0052] In determining the appropriate curvatures for the various
zones in the contact lens CL, the correction to restore distance
vision must be determined first. The distance power correction is
then applied to zone 4. The distance power correction is usually
within a range between +20.00 diopters to -20.00 diopters.
[0053] After the distance correction is determined, the amount of
correction for near vision ("add power") should be calculated. A
person with early to moderate presbyopia would be prescribed a low
additional reading power of up to +1.75 diopters (referred to as a
"low add"). A moderate to advanced presbyope would require a
reading correction from 1.75 to 2.75 diopters (referred to as a
"high add").
[0054] For a high add presbyope, the aggregate change in powers
across the various zones is preferably approximately 3.7 diopters.
For a low add presbyope, the aggregate change in powers across the
various zones is preferably approximately 2.6 diopters
(approximately 70% of the total diopter shift for a high add).
[0055] The corrective power of the various zones preferably does
not remain constant within each zone. Instead, for a high add
presbyope, it is preferred that there be as 1.6 diopter shift
across zone 2, a 1.2 diopter shift across zone 3 and a 0.9 diopter
shift across zone 4, so that the total diopter shift across zones
2, 3, and 4 is 3.7 diopters.
[0056] Because the sweet spot is so small, and because it must be
centered in the pupil in order for the invention to function
properly, the contact lens CL must be precisely manufactured in
order to be sure the sweet spot is properly centered over the
center of the pupil. In order to accomplish this critical
centering, it is preferred to mark a 1.9 millimeter centered spot,
preferably white, on a pair of trial diagnostic contact lenses.
With such a pair of trial diagnostic contact lenses, it is possible
to detect whether a user's pupil is off center (and other
problems), so that the contact lens of the present invention can be
properly manufactured to center the sweet spot over the pupil.
[0057] The inventor has discovered that an overcorrected central
portion of between approximately 1 to approximately 2.5
millimeters, and preferably approximately 1.5 to approximately 1.9
millimeters (optimally either 1.5 millimeters or 1.9 millimeters)
in diameter does not substantially impair distance vision of a
contact lens. Surprisingly, the inventor also has discovered that
overcorrecting the central portion beyond the correction needed for
near vision, restores an unexpectedly large portion of the function
of natural accommodation of the eye so that focus can be achieved
over a range of near distances.
[0058] Although, other contact lenses are known with central areas
that are differently corrected than distance portions, those
central segments are either larger than the present invention's
"sweet spot," or they do not overcorrect the sweet spot, or
both.
[0059] It is preferred that the various zones have constant widths
even if the size of the sweet spot differs. Thus, if the sweet spot
is 1.9 millimeters in diameter, the diameters of zones 2, 3, and 4
would all be approximately 0.4 millimeters greater than the
corresponding diameters in a lens with a 1.5 millimeter diameter
sweet spot. It is also preferred that the diopter shifts between
zones 2, 3, and 4 remain constant regardless of the size of the
sweet spot for mature presbyopes. FIG. 2 shows a contact lens
according to the present invention with a smaller sweet spot.
[0060] For early presbyopia, the amounts of the diopter shifts
across zones 2, 3, and 4 are preferably approximately 70% of the
diopter shifts for mature presbyopes. Thus, the preferred aggregate
diopter shift for early presbyopes is approximately 70% of the
diopter shifts for mature presbyopes. Thus, the aggregate diopter
shift across zones 2, 3, and 4 would be approximately 2.6 diopters;
the diopter shift across zone 2 will be approximately 1.1 diopters;
the diopter shift across zone 3 would be approximately 0.8 diopters
and the diopter shift across zone 4 would be approximately 0.6
diopters. FIGS. 3 and 4 show contact lenses for early presbyopes
with large and small sweet spots.
[0061] Although it is presently preferred to have intermediate zone
2 and 3, it is not known whether the presence of such zones is
critical to the invention. Further, it is not known whether the
manner in which the diopter shift is achieved by the aspheric shape
of the various zones is critical. At present, it is preferred that
the diopter shift take place at a constant radial rate in each
zone, so that there is a different constant diopter shift rate in
each of zones 2, 3, and 4. However, it is also possible that the
benefits of this invention may be achievable by using varying
diopter shift rates within a zone, or to increase or decrease the
number of zones.
[0062] Further, it is not believed to be critical that the diopter
shifts be effected by shaping the contact lens. For example, it is
possible to achieve the diopter shift by using material with
differing indices of refraction in various different portions of
the lens. Indeed, with appropriate control over the diffusion of
materials with different indices of refraction during molding of
contact lenses, it is possible that the present invention could be
practiced with a lens that is spherical or that does not have
differently formed lens portions.
[0063] The sweet spot is preferably overcorrected between 25% and
approximately 100% stronger than the prescribed reading correction
requirement.
[0064] For example, for a high add, it would be preferred that the
sweet spot be from 3.5 to 5 diopters more plus add power than the
distance zone (zone 4), between 3.5 to approximately 3.9 diopters
being even more preferred, and approximately 3.7 diopters being
optimal. For a low add, it would be preferred that the sweet spot
be from 2.0 to 3.5 diopters more plus add power than the distance
zone (zone 4), with between approximately 2.4 and approximately 2.8
diopters being more preferred, and optimally approximately 2.6
diopters.
EXAMPLE 1
[0065] A Microturn 9000 three axis radius lathe with aspheric
surface cutting capabilities has been used to make contact lenses
according to the present invention with base curves of 8.6
millimeters wet (6.6 millimeters dry). The lenses were manufactured
dry from Ocufilcon B (a 53% water content material) and were
hydrated afterwards. Therefore compensating calculations were made
to achieve the appropriate hydrated parameters, such as base curve,
radial expansion, linear expansion, power changes due to changes in
index of refraction caused by hydration. When hydrating Ocufilcon
B, the linear expansion parameter is approximately 1.35, the radial
expansion parameter is approximately 1.30, and the power change
parameter is approximately 0.57. The settings for the various radii
of curvature in the various zones (for dry manufacturing using
Ocufilcon B) are shown in the following cutting charts:
1 Zone 1 2 3 4 CENTER 1.10 1.50 1.90 6.00 DIA. C.T. DIST. POWER
1.40 1.80 2.20 6.00 DIA. C.T. POWER 8.60 high add minus power p1
6.73 6.98 7.17 7.30 .16 -.25 6.77 7.02 7.21 7.35 .16 -.50 6.83 7.06
7.25 7.40 .16 -.75 6.86 7.11 7.29 7.46 .16 -1.00 6.90 7.15 7.33
7.50 .16 -1.25 6.93 7.18 7.37 7.53 .16 -1.50 6.96 7.22 7.41 7.58
.16 -1.75 7.00 7.25 7.45 7.62 .16 -2.00 7.05 7.29 7.49 7.66 .15
-2.25 7.09 7.33 7.53 7.70 .15 -2.50 7.13 7.37 7.58 7.75 .15 -2.75
7.17 7.41 4.62 7.79 .15 -3.00 7.21 7.46 7.67 7.84 .14 -3.25 7.24
7.51 7.71 7.89 .14 -3.50 7.28 7.56 7.76 7.94 .14 -3.75 7.31 7.60
7.80 7.99 .14 -4.00 7.35 7.65 7.85 8.04 .13 -4.25 7.38 7.70 7.90
8.07 .13. 8.60 high add plus power p1 6.73 6.98 7.17 7.30 .16 +.25
6.71 6.95 7.13 7.27 .17 +.50 6.68 6.91 7.09 7.23 .17 +.75 6.65 6.87
7.05 7.19 .17 +1.00 6.62 6.84 7.02 7.16 .17 +1.25 6.59 6.80 6.98
7.12 .17 +1.50 6.56 6.77 6.94 7.08 .17 +1.75 6.52 6.73 6.90 7.04
.18 +2.00 6.49 6.70 6.87 7.00 .18 +2.25 6.46 6.66 6.83 6.96 .18
+2.50 6.44 6.63 6.80 6.93 .18 +2.75 6.40 6.59 6.76 6.89 .18 +3.00
6.37 6.56 6.72 6.85 .19 +3.25 6.34 6.53 6.69 6.80 .19 +3.50 6.31
6.50 6.66 6.75 .19 +3.75 6.28 6.47 6.62 6.73 .20 +4.00 6.26 6.44
6.59 6.70 .20 +4.25 6.23 6.41 6.56 6.67 .20 8.60 low add plus power
p1 6.73 6.93 7.06 7.17 .16 +.25 6.70 6.89 7.02 7.13 .17 +.50 6.67
6.85 6.98 7.10 .17 +.75 6.63 6.82 6.93 7.06 .17 +1.00 6.60 6.79
6.89 7.02 .17 +1.25 6.58 6.74 6.86 6.98 .17 +1.50 6.56 6.70 6.84
6.95 .17 +1.75 6.52 6.67 6.80 6.91 .17 +2.00 6.49 6.64 6.77 6.87
.18 +2.25 6.46 6.61 6.73 6.83 .18 +2.50 6.43 6.58 6.70 6.79 .18
+2.75 6.40 6.55 6.66 6.75 .18 +3.00 6.37 6.52 6.63 6.72 .19 +3.25
6.34 6.48 6.60 6.68 .19 +3.50 6.31 6.45 6.57 6.65 .20 +3.75 6.28
6.42 6.54 6.62 .20 +4.00 6.26 6.39 6.51 6.59 .20 +4.25 6.23 6.36
6.47 6.56 .20 8.60 low add minus power p1 6.73 6.93 7.06 7.17 .16
-.25 6.77 6.96 7.10 7.21 .16 -.50 6.81 7.00 7.14 7.25 .16 -.75 6.85
7.03 7.18 7.29 .16 -1.00 6.89 7.07 7.22 7.33 .16 -1.25 6.93 7.11
7.25 7.37 .16 -1.50 6.97 7.15 7.29 7.41 .16 -1.75 7.01 7.19 7.33
7.45 .16 -2.00 7.05 7.24 7.37 7.50 .15 -2.25 7.08 7.28 7.41 7.54
.15 -2.50 7.12 7.32 7.46 7.58 .15 -2.75 7.16 7.36 7.51 7.62 .15
-3.00 7.20 7.40 7.55 7.67 .14 -3.25 7.23 7.44 7.59 7.71 .14 -3.50
7.27 7.48 7.64 7.76 .14 -3.75 7.31 7.52 7.68 7.80 .14 -4.00 7.35
7.57 7.73 7.85 .13 -4.25 7.39 7.61 7.77 7.89 .13
[0066] It is preferred that the contact lenses conform to industry
standards for inside radii, which for soft contact lenses are
presently between 7.5 and 9.5 millimeters, and typically between
8.30 millimeters and 8.6 millimeters. For RGP and hard lenses, the
industry standard inside radii are between 7.0 millimeters and 8.5
millimeters, and typically between 7.3 and 8.2 millimeters.
[0067] It is presently preferred that the contact lens of the
present invention comprise conventional soft contact lens material,
such as Ocufilcon B with 53% water content, because contact lenses
have been successfully manufactured using this material. However,
any conventional soft or rigid contact lens material may be used to
practice the invention (as long as appropriate compensations are
made for parameters that may change during hydration for soft
contact lens material). The inventor believes that Benz 55G or
Methafilcon A may be as good as, or better than, Ocufilcon B in the
practice of the present invention, but no lenses according to the
present invention have yet been made with these materials.
[0068] While the present invention has been disclosed in connection
with the presently preferred embodiments described herein, it
should be understood that there may be other embodiments which fall
within the spirit and scope of the invention as defined by the
claims. For example, this invention can be practiced with contact
lenses that are made by any method now known or hereafter invented,
including (but not limited to) molding, spin casting, or extruding.
This invention also can be applied to intraocular lens implants and
refractive surgical procedures (including radial keratotomy, photo
refractive keratotomy, and corneal implantation) that reshape the
cornea. Furthermore, this invention can be practiced in combination
with spherical or astigmatic (toric) contact lenses. Toric lens
prescriptions comprise spherical power corrections, usually between
+20 and -20 diopters (commonly between +8 and -8 diopters), and
cylindrical power corrections, usually between 0.5 diopters and 10
diopters (commonly between 1 and 4 diopters). The present invention
can be practiced within this entire range of toric (astigmatic)
lens prescriptions. Accordingly, no limitations are to be implied
or inferred in this invention except as specifically and explicitly
set forth in the claims.
INDUSTRIAL APPLICABILITY
[0069] This invention can be used whenever it is desired to provide
a contact lens that corrects for distance vision as well as near
and intermediate vision.
* * * * *