U.S. patent application number 12/229125 was filed with the patent office on 2009-02-26 for presbyopic treatment system.
Invention is credited to Joseph Michael Lindacher, Shyamant Ramana Sastry.
Application Number | 20090051870 12/229125 |
Document ID | / |
Family ID | 40032824 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090051870 |
Kind Code |
A1 |
Lindacher; Joseph Michael ;
et al. |
February 26, 2009 |
Presbyopic treatment system
Abstract
A method and system for treating Presbyopia and pre-Presbyopia
are provided that do not compromise the wearer's intermediate or
distance vision. The system is a lens and a lens series, wherein
the power profiles of the lenses are tailored to provide an amount
of positive ADD power in the near vision zone that is slightly less
than that which is normally required for near vision accommodation,
while also providing an amount of negative spherical aberration in
the peripheral optical zone. The dynamic ocular factors of the
wearer's eye work in conjunction with the positive ADD power
provided by the central optical zone and with the effective ADD
gained from the negative spherical aberration provided by the
peripheral optical zone to induce a minimally discernible amount of
blur that is tuned to maximize the wearer's depth of focus.
Inventors: |
Lindacher; Joseph Michael;
(Suwanee, GA) ; Sastry; Shyamant Ramana; (Suwanee,
GA) |
Correspondence
Address: |
CIBA VISION CORPORATION;PATENT DEPARTMENT
11460 JOHNS CREEK PARKWAY
DULUTH
GA
30097-1556
US
|
Family ID: |
40032824 |
Appl. No.: |
12/229125 |
Filed: |
August 20, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60957183 |
Aug 22, 2007 |
|
|
|
61125215 |
Apr 23, 2008 |
|
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|
Current U.S.
Class: |
351/159.41 |
Current CPC
Class: |
G02C 7/044 20130101;
G02C 7/047 20130101; G02C 7/042 20130101; G02C 7/066 20130101; G02C
2202/08 20130101; G02C 7/027 20130101; G02C 7/061 20130101; G02C
7/041 20130101; G02C 7/024 20130101; G02C 7/028 20130101 |
Class at
Publication: |
351/169 |
International
Class: |
G02C 7/06 20060101
G02C007/06 |
Claims
1. A lens for treating Presbyopia comprising: a central optical
zone having a power profile that provides an ADD power ranging from
a maximum ADD power of between about 0 diopters and about 2.4
diopters and a minimum ADD power of between about 0 diopters and
0.2 diopters; a peripheral optical zone having an inner
semi-diameter of about 2 millimeters (mm) and an outer
semi-diameter of about 3 mm, the peripheral optical zone having a
power profile that provides an amount of negative spherical
aberration, a difference between the amount of negative spherical
aberration provided by the power profile at the inner semi-diameter
and the amount of negative spherical aberration provided by the
power profile at the outer semi-diameter ranging from a minimum
absolute value of about 0.65 diopters and a maximum absolute value
of about 1.25 diopters; and a transition zone interposed between
and connected to the central optical zone and the peripheral
optical zone, the transition zone providing a transition between
the central optical zone and the peripheral optical zone, the
transition zone having a power profile that is continuous.
2. The lens of claim 1, wherein said difference between the amount
of negative spherical aberration provided by the power profile at
the inner semi-diameter and the amount of negative spherical
aberration provided by the power profile at the outer semi-diameter
has an absolute value of about 0.85 diopters.
3. The lens of claim 1, wherein the power profile of the central
optical zone is continuous.
4. The lens of claim 3, wherein the power profile of the peripheral
optical zone is continuous.
5. The lens of claim 1, wherein the maximum ADD power provided by
the power profile of the central optical zone is about 1.6
diopters.
6. The lens of claim 1, wherein the maximum ADD power provided by
the power profile of the central optical zone is about 0.9
diopters.
7. The lens of claim 1, wherein the maximum ADD power provided by
the power profile of the central optical zone is about 0.3
diopters.
8. The lens of claim 1, wherein a rate of power change in the
central optical zone is discontinuous at the interconnection of the
central optical zone and the transition zone.
9. The lens of claim 1, wherein a rate of power change in the
peripheral optical zone is continuous.
10. The lens of claim 9, wherein a rate of change in the central
optical zone is substantially constant.
11. The lens of claim 1, wherein the lens is a toric multifocal
lens.
12. A lens series comprising lenses for treating Presbyopia, each
lens of the series comprising: a central optical zone having a
power profile that provides a selected amount of ADD power; a
peripheral optical zone having a power profile that provides a
selected amount of negative spherical aberration; a transition zone
interposed between and connected to the central optical zone and
the peripheral optical zone, the transition zone providing a
transition between the central optical zone and the peripheral
optical zone; and wherein each lens of the series has a power
profile that is defined by a mathematical function, each of the
mathematical functions being identical except that the dc bias
terms for each lens of the series are different.
13. The lens series of claim 12, wherein the power profile has a
rate of power change in the central optical zone that is
discontinuous at the interconnection of the central optical zone
and the transition zone.
14. The lens series of claim 12, wherein the power profile has a
rate of power change in the peripheral optical zone that is
continuous between a semi-diameter of about 2 millimeters (mm) from
a center of the lens and a semi-diameter of about 3 mm from the
center of the lens.
15. The lens series of claim 12, wherein the power profile has a
rate of power change in the peripheral optical zone that has an
absolute value that ranges from about 0.50 diopters to about 1.00
diopters at a distance of about 2.0 millimeters (mm) from a center
of the lens and has an absolute value that ranges from about 0.75
diopters to about 1.50 diopters at a distance of about 3.0 mm from
the center of the lens.
16. The lens series of claim 15, wherein the power profile has a
rate of power change in the peripheral optical zone that has an
absolute value of about 0.65 diopters at a distance of about 2.0 mm
from the center of the lens and that has an absolute value of about
1.00 diopters at a distance of about 3.0 mm from the center of the
lens.
17. The lens series of claim 12, wherein the power profile has a
rate of power change in the central optical zone that has an
absolute value that ranges from about 0.15 diopters to about 0.8
diopters at a distance of about 0.5 millimeters (mm) from a center
of the lens and has an absolute value that ranges from about 0.3
diopters to about 2.0 diopters at a distance of about 1.0 mm from
the center of the lens.
18. The lens series of claim 12, wherein the transition zone has a
power profile that is continuous.
19. A method for providing a lens series for treating Presbyopia
comprising: selecting a power profile for a lens series that
provides ADD power in the central optical zone and negative
spherical aberration in the peripheral optical zone; and for each
lens of the lens series, provide the selected power profile with a
different dc bias term such that all lenses have the same power
profile except that the dc bias term of the profile is different
for each lens of the series.
20. The method of claim 19, further comprising: fitting a first eye
of the wearer with a first lens of the series; and fitting the
second eye of the wearer with a second lens of the series.
21. A method for designing at least a first lens for treating
Presbyopia comprising: selecting a power profile for a central
optical zone of the lens that provides an ADD power ranging from a
maximum ADD power of between about 0 diopters and about 2.4
diopters and a minimum ADD power of between about 0 diopters and
0.2 diopters; selecting a power profile for a peripheral optical
zone of the lens that provides an amount of negative spherical
aberration between a semi-diameter of about 2 millimeters (mm) from
a center of the lens and a semi-diameter of about 3 mm from the
center of the lens, a difference between the amount of negative
spherical aberration provided by the power profile at the inner
semi-diameter and the amount of negative spherical aberration
provided by the power profile at the outer semi-diameter ranging
from a minimum absolute value of about 0.65 diopters and a maximum
absolute value of about 1.25 diopters; and selecting a power
profile for a transition zone interposed between and connected to
the central optical zone and the peripheral optical zone, the
transition zone providing a transition between the central optical
zone and the peripheral optical zone, wherein the power profile
that is selected for the transition zone is continuous.
22. The method of claim 21, wherein said difference between the
amount of negative spherical aberration provided by the power
profile at the inner semi-diameter and the amount of negative
spherical aberration provided by the power profile at the outer
semi-diameter has an absolute value of about 0.85 diopters.
Description
[0001] This application claims the benefits under 35 USC 119(e) of
U.S. Provisional Patent Application Nos. 60/957,183 filed Aug. 22,
2007 and 61/125,215 filed Apr. 23, 2008, herein incorporated by
reference in their entireties.
TECHNICAL FILED OF THE INVENTION
[0002] The invention relates to a system for treating Presbyopia.
More particularly, the invention relates to a lens and a lens
series that can be worn by a person to correct, or treat, symptoms
of Presbyopia.
BACKGROUND OF THE INVENTION
[0003] Presbyopia is a gradual loss of accommodation of the visual
system of the human eye. This is due to an increase in the modulus
of elasticity and growth of the crystalline lens of the eye that is
located just behind the iris and the pupil. Tiny muscles in the eye
called ciliary muscles pull and push the crystalline lens, thereby
causing the curvature of the crystalline lens to adjust. This
adjustment of the curvature of the crystalline lens results in an
adjustment of the eye's focal power to bring objects into focus. As
individuals age, the crystalline lens of the eye becomes less
flexible and elastic, and, to a lesser extent, the ciliary muscles
become less powerful. These changes result in inadequate adjustment
of the lens of the eye (i.e., loss of accommodation) for various
distances, which causes objects that are close to the eye to appear
blurry.
[0004] In most people, the symptoms of Presbyopia begin to become
noticeable under normal viewing conditions at around age 40, or
shortly thereafter. However, Presbyopia actually begins to occur
before the symptoms become noticeable and increases throughout a
person's lifetime. In general, a person is deemed "symptomatic"
when the residual accommodation is less than that required for one
to read. Typical reading distance requires an accommodation ADD of
2.0 to 3.0 Diopters. Eventually, the residual accommodation is
reduced to the point at which the individual becomes an absolute
Presbyope after age 50. Symptoms of Presbyopia result in the
inability to focus on objects close at hand. As the lens hardens,
it is unable to focus the rays of light that come from nearby
objects. People that are symptomatic typically have difficulty
reading small print, such as that on computer display monitors, in
telephone directories and newspaper advertisements, and may need to
hold reading materials at arm's length.
[0005] There are a variety of non-surgical systems that are
currently used to treat Presbyopia, including bifocal spectacles,
progressive (no-line bifocal) spectacles, reading spectacles,
bifocal contact lenses, and monovision contact lenses. Surgical
systems include, for example, multifocal intraocular lenses (IOLs)
and accommodation IOLs inserted into the eye and vision systems
altered through corneal ablation techniques. Each of these systems
has certain advantages and disadvantages relative to the others.
With bifocal spectacles, the top portion of the lens serves as the
distance lens while the lower portion serves as the near vision
lens. Bifocal contact lenses generally work well for patients who
have a good tear film (i.e., moist eyes), good binocular vision
(i.e., ability to focus both eyes together), good visual accuity
(i.e., sharpness) in each eye, and no abnormalities or disease in
the eyelids. The bifocal contact lens wearer must invest the time
required to maintain contact lenses, and generally should not be
involved in occupations that impose high visual demands on the
person. Furthermore, bifocal contact lenses may limit binocular
vision. In addition, bifocal contact lenses are relatively
expensive, in part due to the time it takes the patient to be
accurately fitted.
[0006] An alternative to spectacles and bifocal contact lenses are
monovision contact lenses. With monovision contact lenses, one lens
of the pair corrects for near vision and the other corrects for
distance vision. For an emmetropic individual, i.e., an individual
who does not require distance vision correction, only a single
contact lens is worn in one eye to correct for near vision. With
non-emmetropic individuals, one of the monovision contact lenses
sets the focus of one eye, typically the dominate eye, at distance
and the other lens adds a positive power bias to the other eye. The
magnitude of the positive power bias depends on the individual's
residual accommodation and near vision requirements. Individuals
with low ADD requirements typically adapt very well to monovision
contact lenses. Advantages of monovision are patient acceptability,
convenience, and lower cost. Disadvantages include headaches and
fatigue experienced by the wearer during the adjustment period and
decreases in visual accuity, which some people find unacceptable.
As the ADD difference is increased, a loss of depth perception,
night vision and intermediate vision limits its effectiveness of
monovision systems.
[0007] Simultaneous vision multifocal contact lenses are also used
to treat Presbyopia. Types of multifocal contact lenses include,
but are not limited to, center distance power designs, center near
power designs, annular power designs, diffractive power designs,
and the like. Center near power designs are multifocal, or
progressive, contact lenses used to treat Presbyopia. These lenses
have a near vision zone in the center of the lens that extends
outwardly a distance away from the center of the lens and a
distance vision zone that is on the periphery of the lens and is
concentric with and surrounds the near vision zone. With more
modern multifocal contact lenses, known as progressive contact
lenses, the transition between the near and distance vision regions
is more gradual than in earlier designs. The ADD power is highest
in the near vision region of the lens and lowest or zero in the
distance vision region of the lens. In the transition region, the
power continuously decreases from near vision ADD power to distance
vision ADD power (or no ADD power) as the lens transitions from the
near vision zone to the distance vision zone.
[0008] While multifocal lenses generally are effective at treating
symptoms of Presbyopia, there are many disadvantages associated
with multifocal lenses. Multifocal lenses designed to treat
symptoms of Presbyopia normally have relatively high ADD powers in
the near vision zone of the lens to provide the correction needed
for near vision. The high ADD power in the near vision zone can
result in visual artifacts, or ghost images, that affect the
wearer's intermediate vision and can result in other problems that
compromise the wearer's distance vision.
[0009] Another shortcoming of current Presbyopic treatment systems
is that most are ineffective at treating pre-Presbyopia, or
emerging Presbyopia. Even prior to the symptoms of Presbyopia
becoming readily noticeable to a person, that person may be
experiencing pre-Presbyopia symptoms, such as inability of the
vision system of the eye to accommodate in conditions of darkness
or low lighting. Progressive multifocal lenses with very high near
vision ADD powers are not suitable for use to treat pre-Presbyopia.
CooperVision, Inc., a company headquartered in Fairport, N.Y.,
recently began testing a contact lens that it claims is effective
at treating pre-Presbyopia, but insufficient information is
currently available about this product to verify that the lens is
actually effective at treating pre-Presbyopia.
[0010] Accordingly, a need exists for a system for treating
Presbyopia and pre-Presbyopia that is effective and that does not
compromise the wearer's intermediate or distance vision through the
stages of Presbyopia.
SUMMARY OF THE INVENTION
[0011] The invention provides a lens and a lens series for treating
Presbyopia and pre-Presbyopia. Each lens comprises a central
optical zone, a peripheral optical zone and a transition zone. The
central optical zone has a power profile that provides an ADD power
ranging from a maximum ADD power of between about 0 diopters and
about 2.4 diopters and a minimum ADD power of between about 0
diopters and 0.2 diopters. The peripheral optical zone has a power
profile that provides an amount of negative spherical aberration
between a semi-diameter of about 2 mm and a semi-diameter of about
3 mm. The difference between the amount of negative spherical
aberration provided at the inner semi-diameter of the peripheral
optical zone and the amount of negative spherical aberration
provided at the outer semi-diameter of the peripheral optical zone
ranges from a minimum absolute value of about 0.65 diopters and a
maximum absolute value of about 1.25 diopters. The transition zone
of the lens is interposed between and connected to the central
optical zone and the peripheral optical zone and provides a
transition between the central optical zone and the peripheral
optical zone. The transition zone has a power profile that is
continuous.
[0012] The invention provides a method for designing a lens series
for treating Presbyopia wherein each lens of the series has a power
profile that provides the central optical zone with a selected
amount of ADD power and that provides the peripheral optical zone
with a selected amount of negative spherical aberration. A
transition zone is interposed between and connected to the central
optical zone and the peripheral optical zone, and provides a
transition between the central optical zone and the peripheral
optical zone. The power profiles for each lens are defined by the
same mathematical function, except that the dc bias terms in the
function for each lens of the series are different.
[0013] In accordance with another embodiment, the invention
provides a method for designing a lens for treating Presbyopia
comprising selecting a power profile for a central optical zone of
the lens, selecting a power profile for a peripheral optical zone
of the lens, and selecting a power profile for a transition zone of
the lens. The power profile of the central optical zone is selected
to provide an ADD power ranging from a maximum ADD power of between
about 0 diopters and about 2.4 diopters and a minimum ADD power of
between about 0 diopters and 0.2 diopters. The peripheral optical
zone has a power profile that provides an amount of negative
spherical aberration between a semi-diameter of about 2 mm and a
semi-diameter of about 3 mm. The difference between the amount of
negative spherical aberration provided at the inner semi-diameter
of the peripheral optical zone and the amount of negative spherical
aberration provided at the outer semi-diameter of the peripheral
optical zone ranges from a minimum absolute value of about 0.65
diopters and a maximum absolute value of about 1.25 diopters. The
transition zone is interposed between and connected to the central
optical zone and the peripheral optical zone and provides a
transition between the central optical zone and the peripheral
optical zone. The power profile selected for the transition zone is
continuous.
[0014] These and other features and advantages of the invention
will become apparent from the following description, drawings and
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates a plan view of a contact lens in
accordance with an illustrative embodiment of the invention.
[0016] FIG. 2 illustrates a plot of three different power profiles
that represent examples of power profiles that are suitable for the
lens shown in FIG. 1.
[0017] FIG. 3 illustrates a plot of three different curves that
represent the rates of change of the three profiles shown in FIG. 2
in diopters/mm across the central optical zone.
[0018] FIG. 4 illustrates a plot of a portion of the power profile
in the peripheral optical zone shown in FIG. 1 extending from about
2.0 mm to about 3.0 mm from the center of the lens.
[0019] FIG. 5 illustrates a plot of a curve 81 that represents the
rate of change of the profile shown in FIG. 4 in diopters/mm across
the peripheral optical zone.
[0020] FIG. 6 illustrates two power profiles of two lenses of the
same series that have different dc bias terms in accordance with an
embodiment of the invention.
[0021] FIG. 7 illustrates a flowchart that represents the method of
the invention in accordance with an illustrative embodiment for
providing a lens series for treating Presbyopia.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0022] The invention relates to a treatment system for treating
Presbyopia and pre-Presbyopia that does not compromise the wearer's
intermediate or distance vision. For ease of discussion, the terms
"Presbyopia" and "pre-Presbyopia" will be referred to hereinafter
as simply "Presbyopia". The invention is directed to a lens series
comprising lenses that are tailored to provide an amount of
positive ADD power in the central optical zone that is tuned to the
residual accommodation and the dynamics of the individual's visual
system and to provide an amount of negative spherical aberration in
the peripheral optical zone. As an eye accommodates for a near
vergence, the pupil constricts (myosis) and the spherical
aberration of the optical system becomes more negative. These
dynamic ocular factors act to increase the depth of focus of the
individual's visual system. In essence, these dynamic ocular
factors work in conjunction with the positive ADD power provided by
the central optical zone of the lens and with the effective ADD
gained from the negative spherical aberration provided by the
peripheral optical zone of the lens to induce a minimally
discernible amount of blur. The combination of all of these factors
results in a minimally discernible amount of blur that is tuned to
maximize the individual's depth of focus. The manner in which these
goals are achieved will now be described with reference to a few
illustrative embodiments of the invention.
[0023] The lenses of the invention are described herein in terms of
dioptric power profiles. A lens series is defined herein as the
range of ADD powers for a given ADD parameter. For example, a
typical spherical lens series has ADD powers that range from -10
diopters to +6 diopters in 0.25-diopter steps. An ADD parameter is
the aberration or dioptric power perturbation in the optical zone
needed to increase the depth of focus by a target magnitude. The
magnitude and functional form of the perturbation of a given ADD
parameter is targeted for a given magnitude of residual
accommodation. Thus, a particular ADD parameter is associated with
all of the lenses in a particular lens series. Multiple ADD
parameters are possible, and each ADD parameter targets a
particular stage of Presbyopia. All of the power profiles of a
given series are defined by the same equation, except that the dc
term of the equation is different for each lens of the lens series.
Therefore, a particular equation having particular coefficients and
mathematical operators corresponds to the ADD parameter, whereas
the dc term in that equation corresponds to the ADD power.
[0024] FIG. 1 illustrates a plan view of a contact lens 1 in
accordance with an illustrative embodiment of the invention. For
purposes of describing the principles and concepts of the
invention, it will be assumed that a contact lens in accordance
with the invention has at least a central optical zone 10, a
peripheral optical zone 20, and a transition zone 30 that bridges
the central optical zone 10 to the peripheral optical zone 20. For
these purposes, the entire optical zone of a contact lens in
accordance with the invention will be assumed to comprise the
central optical zone 10, the transition zone 30 and the peripheral
optical zone 20, although any of these zones may be made up of
multiple zones.
[0025] For a typical contact lens, the entire optical zone is about
7.0 to 8.0 millimeters (mm) in diameter. For the purposes of
describing the principles and concepts of the invention, it will be
assumed that the central optical zone ranges in diameter from about
2.0 to about 4.0 mm, and preferably is about 3.0 mm in diameter.
The peripheral optical zone 20 is an annulus surrounding the
central optical zone 10. Outside of the peripheral optical zone 20
is an outer peripheral region 25 that generally does not serve any
optical purpose, but serves the purpose of fitting the anterior
surface of the lens 1 to the surface of the eye. The entire lens 1,
including this outer peripheral region 25 is typically about 13.8
mm to about 14.60 mm in diameter.
[0026] FIG. 2 illustrates a plot of three different power profiles
40, 50 and 60 that represent examples of power profiles that are
suitable for the lens 1 shown in FIG. 1. The vertical axis in the
plot represents optical power in diopters and the horizontal axis
represents radius from the center of the lens outward in
millimeters. As stated above, in accordance with the invention, it
has been determined that Presbyopia can be effectively treated by
using a lens that provides an amount of positive ADD power in the
central optical zone that is slightly less than that which is
normally required for near vision accommodation if a selected
magnitude of negative spherical aberration is provided by the
peripheral optical zone. The reason that a lens having this type of
profile is effective at treating Presbyopia is that the selected
magnitude of negative spherical aberration provided by the
peripheral optical zone works in conjunction with the residual
accommodation of the individual's eye to extend the eye's depth of
focus, thereby improving near vision with minimally discernible
blur for intermediate vision or distance vision. More specifically,
the dynamic ocular factors of the eye work in conjunction with the
positive ADD power provided by the central optical zone of the lens
and with the effective ADD gained from the negative spherical
aberration provided by the peripheral optical zone of the lens to
induce a minimally discernible amount of blur that is tuned to
maximize the individual's depth of focus.
[0027] The power profiles 40, 50 and 60 each have a maximum ADD
power in the central optical zone, i.e., at the intercepts of the
curves on the vertical axis, and provide negative spherical
aberration in the peripheral optical zone of the lens. In the
example represented by FIG. 2, the maximum ADD power in the central
optical zone for profile 40 is about 0.3 diopters, the maximum ADD
power in the central optical zone for profile 50 is about 0.9
diopters, and the maximum ADD power in the central optical zone for
profile 60 is about 1.6 diopters. The invention is not limited to
these ADD powers. The maximum ADD power typically ranges from about
0 diopters to about 2.4 diopters at the center of the central
optical zone 10. The minimum ADD power typically ranges from about
0 diopters to about 0.2 diopters at the center of the central
optical zone 10. The amplitudes (i.e., the dc bias component) and
the functional forms of the ADD parameters that define the profiles
are designed to work with individuals' residual accommodation to
provide a smooth, constant visual acuity level through
vergence.
[0028] As indicated above, the power profile that is selected for
the wearer depends on the dynamic ocular factors of the wearer's
eye. A profile having a higher amplitude ADD in the central optical
zone will bring the near point closer, but will result in both
reduction in intermediate vision and more visual compromise through
vergence. Therefore, the maximum ADD power of the central optical
zone is selected based on the dynamic ocular factors of the eye so
that the selected ADD power and the effective ADD gained from the
negative spherical aberration provided by the peripheral optical
zone of the lens induce a minimally discernible amount of blur
tuned to maximize the individual's depth of focus.
[0029] The minimum ADD power in the central optical zone 10 occurs
at the boundary of the central optical zone 10 and the transition
zone 30. The distance from the lens center at which the central
optical zone 10 ends and the transition zone 30 begins will vary
depending on the lens design. As indicated above with reference to
FIG. 1, the central optical zone 10 typically has a diameter that
ranges from about 2.0 to about 4.0 mm and preferably is about 3.0
mm. This corresponds to a radial distance from the lens center,
i.e., a semi-diameter, of about 1.0 mm to about 2.0 mm. The minimum
ADD power of the central optical zone is selected based on the
dynamic ocular factors of the eye so that the selected minimum ADD
power and the effective ADD gained from the negative spherical
aberration provided by the peripheral optical zone of the lens
induce a minimally discernible amount of blur tuned to maximize the
individual's depth of focus. Negative spherical aberration, as that
term is used herein, means that light rays received through the
peripheral region of the pupil are focused behind the retina while
light rays received through the pupil center are focused on the
retina.
[0030] A lens having the profile 40 is generally intended for a
people experiencing symptoms of pre-Presbyopia, often referred to
as emerging presbyopes. In the central optical zone 10, the profile
40 has lower ADD powers than the ADD powers of profiles 50 and 60.
For an intermediate presbyope, i.e., a person who has begun to
experience symptoms of Presbyopia, which typically happens at
around age 40, the residual accommodation of the eye is typically
only slightly less than that required to focus clearly on objects
that are close to the eye. For these individuals, a lens having the
profile 50 would be suitable because the ADD power is slightly
greater than that provided by profile 40 in the central vision
zone, but still less than that which would traditionally by used
for these individuals. For more advanced presbyopic individuals, a
lens having profile 60 provides a higher ADD power across then
entire central optical zone than that provided by profiles 40 and
50, but still less ADD power than that traditionally used for
lenses designed for these individuals.
[0031] FIG. 3 illustrates a plot of three different curves 41, 51
and 61 that represent the rates of power change of the profiles 40,
50 and 60, respectively, shown in FIG. 2 in diopters/mm across the
central optical zone 10. The curves 41, 51 and 61 are obtained by
taking the first derivative of profiles 40, 50 and 60 from r=0 mm
to r=1.5 mm. The rate of power change in the central optical zone
should be appropriate for the eyes' residual accommodation. For
optimal vision, the rate of power change over the central optical
zone should be a smoothly varying function. The rate of power
change in the central optical zone typically has a minimum absolute
value of about 0.15 diopters and a maximum absolute value of about
0.8 diopters at a semi-diameter of about 0.5 mm from the center of
the lens. At a semi-diameter of about 1.0 mm from the center of the
lens, the rate of power change in the central optical zone
typically has a minimum absolute value of about 0.3 diopters and a
maximum absolute value of about 2.0 diopters.
[0032] It can be seen that for profile 40, the corresponding rate
of change 41 is constant (i.e., linear) across the central optical
zone 10. It can be seen that for profile 50, the corresponding rate
of change 51 increases in magnitude from the center of the lens out
to a radius of about 1.0 mm, but then is generally constant from a
radius of about 1.0 mm to a radius of about 1.45 mm. It can be seen
that for profile 60, the corresponding rate of change 61 increases
from the center of the lens out to a radius of about 1.0 mm, and
then decreases from a radius of about 1.0 mm out to a radius of
about 1.45 mm.
[0033] The invention is not limited to the profiles shown in FIG.
2. Different mathematical functions and/or different ADD powers
from those represented by profiles 40, 50 and 60 can be used to
define profiles that achieve the goals of the invention. The
mathematical functions that are used to define the power profiles
are not limited to any particular type or class of mathematical
function. Each profile may be defined by a single mathematical
function, such as a polynomial function, or it may be defined by a
piece-wise function made up of multiple mathematical functions. The
profiles may also be defined by other functions, such as, for
example, linear functions, spline functions (e.g., cubic splines
and bicubic splines), Seidel functions, Zernike functions, conic
functions and biconic functions.
[0034] For example, the curves 51 and 61 shown in FIG. 3 are
discontinuous at a radius of about 1.45 mm from the center of the
central optical zone 10. However, because the functions that
represent the profiles 50 and 60 shown in FIG. 2 are continuous and
therefore differentiable in the first derivative, the profiles 40,
50 and 60 are suitable for lens designs for Presbyopia treatment.
Because the profiles need not be differentiable in the second
derivative, a wider variety of mathematical functions may be used
to define the profiles, including piece-wise functions and
splines.
[0035] The invention is not limited with respect to the behavior of
the power profiles in the transition zone 30 (FIG. 1). Preferably,
the profile is continuous over the transition zone 30 to prevent
vision from being affected by artifacts, also commonly referred to
as ghosting. Another way of stating that the profile is continuous
over the transition zone 30 is to state that the profile is
differentiable in at least the first derivative over the transition
zone 30. For the higher ADD power profiles 50 and 60 shown in FIG.
2, the continuous changes in the rate curves 51 and 61 shown in
FIG. 3 from the center of the central optical zone 10 almost to the
transition zone 30 (1.5 mm from center) ensure that vision is not
degraded by visual artifacts or ghost images.
[0036] FIG. 4 illustrates a plot of a portion of the power profile
80 in the peripheral optical zone 20 extending from about 2.0 mm to
about 4.0 mm from the center of the lens 1 (FIG. 1). As indicated
above, the power profile in the peripheral optical zone 20 provides
an amount of negative spherical aberration. The amount of negative
spherical aberration will typically range from about -0.1 to about
-0.7 diopters at the boundary of the peripheral optical zone 20 and
the transition zone 30 to about -2.0 diopters to about -2.7
diopters at the boundary of the peripheral optical zone 20 and the
outer peripheral region 25. As indicated above, the effect of this
spherical aberration is that it provides an amount of effective ADD
that works in conjunction with the positive ADD provided by the
central optical zone 10 and the ocular dynamics of the eye to
induce a minimally discernible amount of blur tuned to maximize the
individual's depth of focus.
[0037] FIG. 5 illustrates a plot of a curve 81 that represents the
rate of power change of the profiles 40, 50 and 60 in diopters/mm
across the peripheral optical zone 20. The curve 81 is obtained by
taking the first derivative of any one of the profiles 40, 50 and
60 from r=2.0 mm to r=3.0 mm, i.e., by taking the first derivative
of the profile 80 shown in FIG. 4. The dashed lines 82 and 83
represent bounding functions that represent the typical power
ranges across the peripheral optical zone 20. It can be seen from
FIG. 5 that the rate of change across the peripheral optical zone
20 increases in magnitude in the direction away from the center of
the lens and has a magnitude of about -0.67 diopters/mm at a radius
of about 2 mm and a magnitude of about -1.00 diopters/mm at a
radius of about 3 mm. Although it cannot be seen in FIG. 5 due to
the X-axis stopping at a radius of 3 mm, the rate of change has a
magnitude of about -1.33 diopters/mm at a radius of about 4 mm.
Looking at the bounding functions 82 and 83, the rate of power
change across the peripheral optical zone 20 ranges in magnitude
from a magnitude of about -0.5 diopters/mm at a radius of about 2
mm to a magnitude of about -1.5 diopters/mm at a radius of about 3
mm at the boundary of the peripheral optical zone 20 and the
transition zone 30 to a maximum absolute value of about 1.5
diopters at the boundary of the peripheral optical zone 20 and the
outer peripheral region 25.
[0038] Since the spherical aberration of the eye is essentially
independent of refractive error, the negative spherical aberration
for a lens series preferably will be generally equal for all lenses
of the series or will vary only by a small amount over the
peripheral optical zone for different lenses of the series.
Providing the proper magnitude range of negative spherical
aberration in the peripheral optical zone 20 increases depth of
focus by providing a visually tolerable amount of image blur to
extend depth of focus while taking into account the pupil dynamics
of the visual system at vergence (myosis). As stated above,
negative spherical aberration, as that term is used herein, means
that light rays received through the peripheral region of the pupil
are focused behind the retina while light rays received through the
pupil center are focused on the retina. Equivalently stated, the
periphery of the pupil has less power than the center of the
pupil.
[0039] Defining the spherical aberration (SA) as the absolute value
of the difference in negative spherical aberration between a 2 mm
semi-diameter zone and a 3 mm semi-diameter zone, as shown in FIG.
5, then the preferred ranges of SA values are: [0040] SA(min)=0.65
diopters [0041] SA(max)=1.25 diopters [0042] SA(nominal)=0.85
diopters
[0043] Preferably, for all ADD parameters, spherical aberration in
the peripheral optical zone will be equal. For toric multifocal
lenses, the above ranges are valid along the Sphere meridians. The
peripheral optical zone 20 may be described by Zernike polynomials,
aspheric terms, or the equivalent. The power profile in the
peripheral optical zone 20 may be described by a quadratic or a
perturbed quadratic power function.
[0044] As stated above, for a given lens series, preferably each
lens will have a power profile defined the same ADD parameter, but
the dc bias term will be different for each lens of the series.
FIG. 6 illustrates two power profiles 90 and 91 of two lenses of
the same series that have different dc bias terms in accordance
with an embodiment of the invention. Thus, the mathematical
functions that define the profiles 90 and 91 are identical except
for the dc bias terms. The dc bias term corresponds to the location
at which the profile intersects the Y-axis. This value is obtained
by setting all of the X-axis terms of the function equal to zero
such that the value of the function corresponds to the dc bias
term, i.e., the constant in the equation.
[0045] In accordance with another embodiment of the invention, it
has been determined that over-plusing the near eye by a small
magnitude will sometimes result in an improvement in the treatment
of Presbyopia. In cases where the distance eye is the dominant eye
or has the least amount of astigmatism, over-plusing the near eye
by a small amount increases depth of focus. The term "over-plusing"
as that term is used herein, means fitting an eye with a lens
having a profile defined by the same ADD parameter as another lens
of the series used for the other eye, but that also has a greater
dc bias term than the other lens of the series. For example, with
reference to FIG. 6, the near eye would be fitted with a lens
having profile 91 whereas the distance eye would be fitted with a
lens having the profile 90.
[0046] Although the invention has been described above with
reference to contact lenses, the invention applies equally to
phakic or aphakic lenses, as well as to optical power profiles
created by performing corneal ablation. In addition, although the
invention has been described with reference to the simultaneous
vision lens shown in FIG. 1, lenses in accordance with the
invention may also be used for modified monovision since the power
profiles described herein reduce the disparity between distance and
near powers.
[0047] FIG. 7 illustrates a flowchart that represents the method of
the invention in accordance with an illustrative embodiment for
providing a lens series for treating Presbyopia. A lens series is
provided such that each lens of the series has a power profile that
provides ADD power in the central optical zone and negative
spherical aberration in the peripheral optical zone, as indicated
by block 101. The maximum ADD power preferably occurs at the center
of the central optical zone 10 (FIG. 1) and the minimum ADD power
preferably occurs at the boundary between the central optical zone
10 and the transition zone 30. For each lens of the lens series,
the respective power profile is provided with different dc bias
term, as indicated by block 102. Each lens of the lens series has a
power profile in the transition region that preferably is
continuous, as indicated by block 103, which means that the profile
in the transition region is differentiable in at least the first
derivative, but not necessarily in the second or higher
derivatives.
[0048] It should be noted that the invention has been described
with reference to a few preferred and illustrative embodiments and
that the invention is not limited to these embodiments. Persons
skilled in the art will understand that modifications can be made
to the embodiments described herein and that all such modifications
are within the scope of the invention. For example, persons skilled
in the art will understand, in view of the description provided
herein, that the invention is not limited to a lens having one of
the power profiles described above with reference to FIG. 2. As
indicated above a variety of mathematical functions and ADD
parameters may be used to described power profiles that meet the
objectives of the invention of treating Presbyopia without
sacrificing intermediate and/or distance vision. Also, although the
method described above with reference to FIG. 6 indicates separate
processes for selecting the power profiles for the central optical
zone, the peripheral optical zone and the transition zone, this may
be accomplished in a single process during which a single power
profile is selected that meets all of the requirements for each of
these zones.
* * * * *