U.S. patent application number 17/444186 was filed with the patent office on 2022-04-07 for broadview natural addition lens.
The applicant listed for this patent is Michael Walach. Invention is credited to Michael Walach.
Application Number | 20220107509 17/444186 |
Document ID | / |
Family ID | 1000006223324 |
Filed Date | 2022-04-07 |
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United States Patent
Application |
20220107509 |
Kind Code |
A1 |
Walach; Michael |
April 7, 2022 |
BROADVIEW NATURAL ADDITION LENS
Abstract
An ophthalmic lens apparatus has a visual field of a plurality
of horizontal meridians each having constant optical power. The
optical power of the visual field continuously varies from a top
portion of the lens to a bottom portion of the lens by the
horizontal meridians being arranged with their midpoints along a
generally vertical focal length deceleration curve across the
visual field and at least some adjacent horizontal meridians having
different optical powers. widths of the horizontal meridians across
the lens decrease from a top end of the focal length deceleration
curve toward a bottom end of the focal length deceleration curve,
and the lens surface beyond the horizontal ends of the meridians
provides visual comfort to a user of the lens by providing smooth
gradients of defocus without sharp edges, image jumps, waviness or
distortions of image.
Inventors: |
Walach; Michael; (Largo,
FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Walach; Michael |
Largo |
FL |
US |
|
|
Family ID: |
1000006223324 |
Appl. No.: |
17/444186 |
Filed: |
July 31, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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17194811 |
Mar 8, 2021 |
11126012 |
|
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17444186 |
|
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63086089 |
Oct 1, 2020 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02C 7/065 20130101 |
International
Class: |
G02C 7/06 20060101
G02C007/06 |
Claims
1. An ophthalmic lens apparatus comprising: a visual field of a
plurality of horizontal meridians each having constant optical
power; wherein the optical power of the visual field continuously
varies from a top portion of the lens to a bottom portion of the
lens by the horizontal meridians being arranged with their
midpoints along a generally vertical focal length deceleration
curve that extends across the height of the visual field and by at
least some adjacent horizontal meridians having different optical
powers; wherein widths of the horizontal meridians across the lens
decrease from a top end of the focal length deceleration curve
toward a bottom end of the focal length deceleration curve, and the
lens surface beyond the horizontal ends of the meridians provides
visual comfort to a user of the lens by providing smooth gradients
of defocus without sharp edges, image jumps, waviness or
distortions of image.
2. The apparatus of claim 1, wherein the focal length deceleration
curve follows a major design backbone of the visual field and is no
less than 14 millimeters (mm) long.
3. The apparatus of claim 2, wherein widths of the horizontal
meridians near a midpoint of the focal length deceleration curve
are no less than 8 mm.
4. The apparatus of claim 3, wherein widths of the horizontal
meridians near a portion of the focal length deceleration curve
corresponding to a mid-near gaze are no less than 15 mm.
5. The apparatus of claim 1, wherein each meridian proceeding along
the focal length deceleration curve from a top end toward a bottom
end has a shorter focal length than a preceding adjacent
meridian.
6. The apparatus of claim 5, wherein differences in focal length
between adjacent meridians are greater toward a midpoint of the
focal length deceleration curve than toward either the top end or
the bottom end.
7. The apparatus of claim 1, wherein a difference in focal length
between meridians along a 1 mm length of the focal length
deceleration curve is no greater than 0.25 Diopter in total.
8. The apparatus of claim 1, wherein adjacent meridians are spaced
apart along the focal length deceleration curve by no more than 0.1
mm.
9. The apparatus of claim 1, wherein the focal length deceleration
curve is about 30 mm long.
10. The apparatus of claim 1, wherein the focal length deceleration
curve extends within about 20.degree. from vertical.
11. The apparatus of claim 10, wherein the focal length
deceleration curve extends between about 3.degree. and about
15.degree. from vertical.
12. The apparatus of claim 11, wherein the focal length
deceleration curve extends between about 3.degree. and about
5.degree. from vertical.
13. The apparatus of claim 10, wherein the focal length
deceleration curve proceeds generally toward an inner edge of the
lens from a top end of the focal length deceleration curve to a
bottom end of the focal length deceleration curve.
14. The apparatus of claim 1, wherein the top end of the focal
length deceleration curve is at least 3 mm below a top edge of the
lens.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of "Broadview Natural
Addition Lens," U.S. patent application Ser. No. 17/194,811, filed
Mar. 8, 2021, which in turn is a non-provisional of, and claims the
priority, of "Broadview Natural Addition Lens," U.S. Provisional
Pat. Appl. 63086089, filed Oct. 1, 2020. The complete disclosures
of the aforesaid U.S. patent application Ser. No. 17/194,811 and
U.S. Provisional Pat. Appl. 63/086,089 are expressly incorporated
herein by reference in their entireties for all purposes.
FIELD
[0002] This invention relates to the field of ophthalmic
lenses.
BACKGROUND
[0003] Eyeglasses are used to treat several kinds of refractive
errors (known in the field as "ametropias") suffered by human
beings. Eyes that do not suffer such ametropias are said to be
"emmetropic." In emmetropic eyes, images viewed by a subject focus
on the subject's retina, which is a light-sensing membrane located
at the back surface of the interior of the globe of the eye.
Furthermore, this focus is maintained whether the subject views
objects at far or near distances (the "object distance"). The focus
is accomplished in part by the crystalline lens of the eye, which
is a converging lens (known in the field as a "plus" power lens),
located between the front surface of the eye (the "cornea") and the
retina. Rays of light which emanate from objects diverge; at object
distances of six meters or more, the rays that reach a subject's
eyes are roughly parallel. The plus power of the crystalline lens
brings these rays into focus on the retina.
[0004] As the object distance decreases, the rays that form an
image in the eye increasingly include divergent rays, so that in
order for an image of the object to continue to focus on the
retina, the crystalline lens must change shape to increase its
converging ("plus") power. This ability is called "accommodation"
(or "accommodation at near"). The crystalline lens is contained
within a flexible capsule, attached to the globe by the ciliary
muscles, which relax when a subject views an object at a distance.
This causes the crystalline lens to become more round (in
cross-section; the plus power of a lens is directly related to the
steepness of its curvature). However, as the crystalline lens
grows, it increases in volume as a person ages, and at some point,
usually around the age of forty years, the capsule in effect fills
up, causing the assembly of lens and capsule to lose its
flexibility. In this case, although the ciliary muscles continue to
contract when a subject views a nearby object, the lens can no
longer change shape adequately, confined as it is to the engorged
capsule. This condition is known as "presbyopia" (from the Greek
for "old eyes"), and most humans suffer from it sometime after the
age of forty years.
[0005] Untreated, presbyopia manifests in subjects as a
progressively diminishing ability to focus on objects at near
distances. This is most often a serious problem, requiring
treatment, for subjects trying to read, because reading material is
almost always held at a near distance, on the order of forty
centimeters. In modern times, subjects may notice a diminishing
ability to see at typical object distances for computer screens
(around fifty-five centimeters).
[0006] Presbyopia does not happen all at once; a subject may first
notice an inability to focus at very close (i.e., close than
reading) distances, or may notice difficulty reading, but still be
able to see a computer screen.
[0007] Eyeglass lenses that treat presbyopia exist in the prior
art. In all cases, these lenses work by affording more than one
power on a single lens, so that by viewing near objects through the
area of the lens that affords increased plus power, the subject
can, in effect, replace the increased plus power that would, in a
non-presbyopic eye, be provided by accommodation.
[0008] The "increased plus power" afforded by such lenses is
referred to in the field as the "addition" (sometimes "near
addition," "reading addition," or simply, "add"). Such lenses are
generally known in the field as "multifocal" lenses. Existing
multifocal designs can be generally categorized as "segmented" and
"non-segmented," which differentiates between lenses on which the
area affording the addition is visible (in which case the area is
referred to as a "segment"), and those on which the area affording
the addition is not visible, other than upon very close examination
or measurement. In the common vernacular of the trade, "seg" is
used to refer to the area affording near focus, and "add" is used
to refer to both the area affording near focus, and the dioptric
magnitude of the additional plus power.
[0009] With very few exceptions, whether segmented or
non-segmented, the add is located on the lens below the distance
area, simply because historically, near objects, especially books,
are most often positioned in a subject's hands. Further, the
positioning of the add must take into account the fact that our
eyes converge when viewing near objects (so that both eyes point to
the object).
[0010] Existing segmented designs, such as bifocals (which afford
one distance power and one near power), and trifocals (which afford
an intermediate power between the distance and near powers, both in
terms of the physical locations of the segments and the magnitudes
of the powers) having segments of various shapes and sizes, have
been produced for many decades.
[0011] Non-segmented designs include "power variation" lenses,
which afford multiple powers on a single lens. Subcategories of
power variation lenses include "progressive power" (or simply
"progressive") lenses, wherein distance and near power areas are
provided, connected by a "corridor" of progressively increasing
power; "degressive" lenses, which have a similar form as
progressive lenses, but which are primarily intended for near and
intermediate use; and "assistive" lenses, which are intended
primarily for distance use, but which afford some relief for
emerging presbyopes.
[0012] Existing designs have drawbacks. Many eyeglass wearers
believe that segments are visible signs of advancing age, so that
segmented multifocals are cosmetically undesirable. Both segmented
and non-segmented designs must be fit carefully, which requires
substantial skill on the part of the practitioner doing the
fitting, whether the practitioner is an optician, optometrist, or
in some cases, a trained clerk (i.e., not a licensed professional).
Fitting includes the positioning of the segment, or of the
specified fitting point (which all existing power variation lenses
have) in a frame so that the features of the lens design are
positioned properly in front of the subject's eyes. The accuracy of
fitting is critical, and this is especially true of progressive
power lenses. In the case of progressive power lenses, the fitting
point must be positioned precisely in front of the subject's eyes
so that as the subject views increasingly near objects, his eyes
will track the progressive corridor. Because the areas of the lens
on either side of the corridor are distorted, if the position of
the corridor is but slightly off, either vertically or
horizontally, the subject will experience distorted vision.
[0013] Currently, the fitting of multifocal lenses requires that
the practitioner take three measurements. The first two are the
distance between the subject's pupils at distance gaze, and at near
gaze (known as the "Far P.D." and "Near P.D."; where "P.D." stands
for "Pupillary Distance"). These two measurements are therefore
properties of the subject's physiognomy. There are various devices
designed to aid in taking this measurement, although many
practitioners manage to take the measurement with a ruler. The
third measurement is the "fitting height", also known as the height
of the Layout Reference Point ("LRP"), and it is measured relative
to the shape of the frame into which the lenses are to be fitted.
This requires that the position of the LRP be measured while the
patient wears the frame (which must be adjusted to fit the patient
as it will ultimately be worn), from the lowest point on the lens,
to a certain point on the patient. The appropriate location for
this certain point on the patient varies among lens categories, but
for example, in the case of progressive power lenses, it is usually
the center of the pupil. Unsurprisingly, that third measurement is
difficult to take and is therefore frequently inaccurate, leading
to a suboptimal result for the subject, namely, the subject will
not obtain comfortable vision at all object distances. There are
devices which can assist in making these measurements, but they are
expensive and time-consuming to use, and therefore, unpopular.
SUMMARY OF THE INVENTION
[0014] An aspect of this disclosure provides a multifocal power
variation lens that provides comfortable vision at all object
distances normally encountered in everyday life for the wearer of
frames fitted with such lenses. More particularly, aspects of the
invention provide a lens that mitigates the effects of presbyopia
for the wearer of eyeglasses in which such a lens has been
fitted.
[0015] Presbyopia occurs in emmetropic, myopic, and hyperopic eyes
alike. (Persons who have these characteristics are referred to in
the field as "emmetropes," "myopes," "hyperopes," and
"presbyopes"). Embodiments of the invention advantageously treat
presbyopia in all cases.
[0016] Thus, embodiments of the invention advantageously provide a
new class of power variation lens, which provides more natural
vision for presbyopes than existing classes of lenses, and which,
by virtue of its characteristics, obviates the need to measure the
height of the fitting point, thereby simplifying fitting, and
increasing the likelihood of a successful fit and outcome.
[0017] Thus, one aspect of the invention provides an ophthalmic
lens apparatus comprising: a visual field of a plurality of
horizontal meridians each having constant optical power; wherein
the optical power of the visual field continuously varies from a
top portion of the lens to a bottom portion of the lens by the
horizontal meridians being arranged with their midpoints along a
generally vertical focal length deceleration curve across the
visual field and at least some adjacent horizontal meridians having
different optical powers; wherein the focal length deceleration
curve follows a major design backbone of the visual field and is at
least 20 millimeters (mm) long.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The invention can be best understood by those having
ordinary skill in the art by reference to the following detailed
description when considered in conjunction with the accompanying
drawings.
[0019] FIG. 1 depicts a broadview natural addition lens fit into a
frame, and a visual field of the lens, according to an exemplary
embodiment.
[0020] FIG. 2 depicts in a schematic a side view of the lens of
FIG. 1, showing various degrees of add power for viewing objects at
various distances, according to an exemplary embodiment.
[0021] FIG. 3 depicts in a schematic a power curve of the lens of
FIG. 1 at various heights along the lens surface, according to an
exemplary embodiment.
[0022] FIG. 4 depicts a prior art progressive lens fit into a
frame, and a visual field of the prior art progressive lens using a
checkerboard pattern.
[0023] FIG. 5 depicts the lens of FIG. 1 fit into a frame, and a
visual field of the lens using a checkerboard pattern.
[0024] FIG. 6 depicts, in a plan view, a formula for determining
widths of the visual field at various vertical positions on the
lens of FIG. 1, based on common object viewing distances and
sizes.
DETAILED DESCRIPTION
[0025] Reference will now be made in detail to an exemplary
embodiment of the invention, which is illustrated in the
accompanying drawings.
[0026] FIG. 1 depicts in a schematic a lens 12, according to an
exemplary embodiment, as fit in a typical frame 10. A user's eye 20
is depicted in a position that typifies conventional frame fitting.
Areas 30, 32, 34 on the lens include horizontal meridians 40 of
differing optical power that extend from end to end across each
area. Thus, at each of the meridians 40 the lens 12 has a different
curvature to provide a different plus power. The meridians 40 are
arranged crosswise along a generally vertical focal length
deceleration curve 42 that connects the areas 30, 32, 34. The areas
30, 32, 34 are identified for viewing distant objects 50,
intermediate objects 52, and near objects 54. Bars 58 have varying
thicknesses that show (in approximate, relative terms) varying
magnification of uniform horizontal lines when viewed through
different parts of the lens 12. Portions of the bars 58 inside the
areas 30, 32, 34 are clear and focused; portions of the bars 58
outside the areas 30, 32, 34 are stippled to indicate defocus. Note
the bars show no discontinuity or bending. This point is reinforced
by the checkerboard image shown in FIG. 5.
[0027] In a conventional progressive lens, optical power is
essentially constant in an upper (distance) region and in a lower
(near) region, which are connected by a relatively short
"progressive corridor" of typically 7-14 mm in length and no more
than about 8 mm in perceived width.
[0028] By contrast, in one or more embodiments the lens 12 has
smoothly varying optical power in a visual field not less than 10
mm wide, typically about 20 mm wide, which extends along a focal
length deceleration curve 42 at least 20 mm in length proceeding
from about 3-10 mm below the top of frame down toward the bottom of
frame. Thus, at any point along the focal length deceleration curve
42, the change in optical power according to distance along the
focal length deceleration curve (the "acceleration of optical
power" or "focal length deceleration rate") is sufficiently small
that even a presbyopic eye can naturally without strain accommodate
it within the funnel-shaped field of vision. The focal length
deceleration curve 42 is generally vertical, i.e. within about
20.degree. from vertical. In one or more embodiments the focal
length deceleration curve 42 extends between about 3.degree. and
about 15.degree. from vertical; in particular embodiments, between
about 3.degree. and about 5.degree. from vertical. In one or more
embodiments, the focal length deceleration curve 42 proceeds
generally toward an inner edge of the lens from a top end of the
focal length deceleration curve to a bottom end of the focal length
deceleration curve. The major design backbone of the lens runs
along the focal length deceleration curve 42.
[0029] Referring to FIG. 2, rays 60 show the amounts of additional
plus power provided at various meridians of the lens 12
corresponding to different viewing angles (infinity gaze 1, mid-far
gaze 2, far-intermediate gaze 3, intermediate gaze 4, mid-near gaze
5, or near gaze 6). The rays 60 get thicker descending the lens,
corresponding to increasing add or plus power. Thus, in one or more
embodiments of the present invention the meridians are stacked from
distance power in the uppermost meridian to near power in the
bottom meridian.
[0030] A power curve 62, shown in FIG. 3, describes the increase or
"acceleration" of "add" power from left (zero add) to right (full
add) as the wearer's gaze descends the lens 12 from infinity gaze 1
(about 3-8 mm below the eyebrows or top of frame) toward near gaze
6 (about 30 mm below the top of frame). Note the relatively slow
acceleration of add power from infinity to mid-far gaze 2, a more
rapid increase of add power from mid-far gaze through intermediate
gaze 4, and then again a relatively slow acceleration of add power
from intermediate gaze to near gaze 6. Thus, as the wearer's gaze
proceeds down the face of the lens 12, they encounter gradually
decreasing curvature of the back surface. Although the increase of
add power from mid-far gaze through intermediate gaze is shown as
generally linear, any shape of smooth curve is suitable.
[0031] Traditionally, as shown for example in FIG. 4 using a
standard checkerboard pattern, progressive lens designs have
accommodated the sharply different curvatures of near and distant
fields of view by providing clear vision in an "hourglass" shape 70
with areas of astigmatism and distortion 72 to either side of the
hourglass. The astigmatic areas of the lens surface induce waviness
and "swim" that discomfort wearers. Unwanted or induced astigmatic
lens areas are a principal reason for non-adoption of progressive
lenses by presbyopes who could benefit from such lenses. Note that
in the image of FIG. 4, the area of clear vision 70 and the areas
of astigmatism 72 are separated by dashed lines that are not
present in the original photograph. These lines are provided only
for clarity of understanding.
[0032] Referring back to FIG. 1, as plus power is gradually added
down the face of the lens 12, a design according to an exemplary
embodiment accommodates the differing curvatures of the lens by
providing areas of defocus 80 to either side of a focused field of
view or "funnel" 82 that is defined by the gradually diminishing
horizontal widths of the meridians 40 from top to bottom of the
lens. An aspect of the invention is the discovery that the areas of
defocus 80 (i.e. vision correction that is less than what the eye
requires) are more tolerated by lens wearers than are the areas of
astigmatism 72.
[0033] Thus, in one or more embodiments the overall field of view
82 (that is, of the stack of meridians 40 in the aggregate) has a
funnel-like shape. In one or more embodiments, a minimum width of
the funnel 82 at each height along the lens is defined according to
the formula illustrated in FIG. 6, i.e. based on typical object
dimensions L corresponding to a plurality of viewing distances D.
For example:
TABLE-US-00001 Viewing distance D Typical object and L Funnel width
Infinity (>6 m) Entire field of view Width of lens Mid-near (60
cm) Computer screen (50 cm) 17 mm Near (30 cm) Book page (12 cm) 15
mm
Notably, this results in a visual field quite different from the
narrow-waisted hourglass shape that typifies conventional
progressive lenses.
[0034] At the horizontal edges of the funnel 82, particularly
toward the outer edge of the lens, the area of defocus 80 that
widens from top to bottom of the lens enables smooth transitions
between the adjacent meridians 40, without sharp edges or jumps
between the meridians. The widening defocus also enables smooth
power gradients at the ends of the meridians 40, without sharp
edges or image jumps between the meridians and the area of defocus
80. An aspect of the invention is the new understanding that human
vision is more tolerant of defocus than of image jump or
astigmatism, and that attempts to minimize areas of defocus,
according to conventional wisdom of lens design, are
counterproductive at least because such attempts promote large
areas of astigmatism, which many lens wearers find discomforting in
daily vision.
[0035] FIG. 5 depicts experimental results according to an
exemplary embodiment, using a conventional checkerboard pattern to
highlight the different regions of the lens 12. In the areas of
defocus 80 the checkerboard pattern is not significantly distorted,
but is somewhat blurry. In the funnel 82, the checkerboard pattern
is clearly focused and not distorted throughout the length of the
focal length deceleration curve 42. This is by contrast to the
conventional progressive lenses as illustrated by example in FIG.
4. Note that in the image of FIG. 5 the "funnel" 82 is separated
from the areas of defocus 80 by a dashed line that is not present
in the original photograph. This line is provided only for clarity
of understanding.
[0036] Thus, FIG. 1, FIG. 2, FIG. 3, and FIG. 5 together
illustrate: [0037] 1. continuous addition of power across the
height of the lens, rather than any "corridor" as found in
progressive power lenses; [0038] 2. meridians of various additional
plus powers; [0039] 3. a broad field of view; [0040] 4. areas of
defocus rather than any undulating power changes at the edges of
the field of view.
[0041] In one aspect of the invention, a broadview lens for
mitigating presbyopia includes multiple meridians of differing
optical powers. Such a lens provides significant advantages over
progressive power lenses, which employ designs using a relatively
narrow corridor of continuously increasing power; the corridor of a
progressive lens connects an area in the upper part of the lens,
which affords a power intended for viewing objects at far object
distances (i.e., six meters or greater, referred to in the field as
"far" or "distance" vision) with an area in the lower part of the
lens, which affords a power intended for viewing objects at near
object distances (i.e., thirty to forty centimeters, referred to in
the field as "near" vision). While a lens according to an exemplary
embodiment of this disclosure also provides areas for far and near
object distances, these areas incorporate continuously varying
meridians of optical power that reduce distortions at the edges of
the lens.
[0042] At each meridian, the acceleration of optical power with
respect to vertical distance is controlled so as to minimize
undesirable effects that a subject wearer might otherwise perceive,
such as defocus, distortion, or "swim." Furthermore, the shape of
the surface in each meridian is designed in such a way as to be
coordinated with surrounding meridians, in other words with no
perceptible line between meridians, so as to eliminate any
sensation on the part of the subject as his or her eyes transition
from one meridian to the next. However, along each horizontal
meridian 40 within the funnel 82, the lens is constant in optical
power to the extent this is feasible by modern manufacturing
techniques.
[0043] Within each meridian, the width of the field of view (that
is, the area of clear vision or funnel 82) diminishes from the top
to the bottom. The curvature of the surface is adjusted, according
to conventional techniques, to eliminate any abrupt lateral power
change. This introduces the areas of defocus 80 at horizontal ends
of the power meridians, but advantageously reduces or eliminates
the waviness that plagues progressive power lenses.
[0044] In certain embodiments of the present invention, the shape
of the frame into which the lens is to be fitted is taken into
consideration in the designs of the meridians, so that the
uppermost meridian provides a field of view as wide as the frame.
Furthermore, the position of the meridians in the frame is
established to facilitate a sensation of natural vision when
viewing objects at common distances, as shown in FIG. 2. For
example, in one or more embodiments the focal length deceleration
curve 42 is arranged consistent with the natural lateral
convergence of eyes from infinity gaze toward near gaze. This
eliminates any need to measure the height of the patient's pupil in
the frame as normally positioned for wear.
[0045] Other embodiments, having other configurations of meridians,
are possible. For example, having intermediate power meridians at
the top of a lens, distance meridians a little further down, and
intermediate and near meridians toward the bottom, is a useful
configuration for pilots, who must be able to view controls above
their heads as well as the controls below their shoulders and the
distant planes ahead of them.
[0046] Preferably, a design for a lens according to an exemplary
embodiment is produced by a lens design system capable of
processing multiple independent visual fields, e.g., one visual
field for each bundle of meridians or area of the lens.
[0047] Given the foregoing description and in view of the
accompanying drawings, it will be appreciated that one aspect of
the invention provides an ophthalmic lens apparatus 12, which
includes a visual field 82 of a plurality of horizontal meridians
40 each having constant optical power. The optical power of the
visual field 82 continuously varies from a top portion 30 of the
lens to a bottom portion 34 of the lens by the horizontal meridians
being arranged with their midpoints along a generally vertical
focal length deceleration curve 42 that extends across the height
of the visual field and at least some adjacent horizontal meridians
having different optical powers. The focal length deceleration
curve 42 follows a major design backbone of the visual field and is
at least 20 millimeters (mm) long.
[0048] In one or more embodiments, widths of the horizontal
meridians 40 across the lens 12 decrease from a top end of the
focal length deceleration curve 42 toward a bottom end of the focal
length deceleration curve. In one or more embodiments, widths of
the horizontal meridians near a midpoint of the focal length
deceleration curve are no less than 15 mm. In one or more
embodiments, widths of the horizontal meridians at a portion of the
focal length deceleration curve corresponding to a mid-near gaze
are no less than 15 mm.
[0049] In one or more embodiments, the lens surface beyond the
horizontal ends of the meridians 40 provides visual comfort to a
user of the lens by providing smooth gradients of defocus 80
without sharp edges, image jumps, waviness or distortions of
image.
[0050] In one or more embodiments, each meridian 40 proceeding
along the focal length deceleration curve 42 from a top end toward
a bottom end has a shorter focal length than a preceding adjacent
meridian. In one or more embodiments, differences in focal length
between adjacent meridians are greater toward a midpoint of the
focal length deceleration curve than toward either the top end or
the bottom end. In one or more embodiments, a difference in focal
length between meridians along a 1 mm length of the focal length
deceleration curve is no greater than 0.25 Diopter in total. In one
or more embodiments, adjacent meridians are spaced apart along the
focal length deceleration curve by no more than 0.1 mm. In one or
more embodiments, the focal length deceleration curve is about 30
mm long.
[0051] In one or more embodiments, the focal length deceleration
curve extends within about 20.degree. from vertical. In one or more
embodiments, the focal length deceleration curve extends between
about 3.degree. and about 15.degree. from vertical. In one or more
embodiments, the focal length deceleration curve extends between
about 3.degree. and about 5.degree. from vertical. In one or more
embodiments, the focal length deceleration curve proceeds generally
toward an inner edge of the lens from a top end of the focal length
deceleration curve to a bottom end of the focal length deceleration
curve.
[0052] In one or more embodiments, the top end of the focal length
deceleration curve is at least 3 mm below a top edge of the
lens.
[0053] A lens designer will understand, from the foregoing
description, the system and method as described and many of its
attendant advantages. It will be apparent to the ordinary lens
designer that various changes may be made in the form,
construction, and arrangement of the components thereof without
departing from the scope and spirit of the invention or without
sacrificing all of its material advantages. Equivalent elements can
be substituted for the ones set forth above such that they perform
in substantially the same manner in substantially the same way for
achieving substantially the same result. The form herein described
being merely an exemplary and explanatory embodiment of the
invention, the following claims intend to encompass and include all
equivalent variations of this disclosure.
* * * * *