Multifocal lens designs with intermediate optical powers

A multifocus, concentric annular ring lens wherein one of the front and back surfaces of the lens defines a central area comprising a circular disc having a spherical surface corresponding to a basic prescription Rx spherical distance optical power. A plurality of annular rings surround the central area and have alternating spherical near and distance optical powers, and at least one intermediate optical power annular ring. The immediate optical power annular ring is located in the middle or outer region of the lens optic zone, and its optical power is intermediate to the distance and near optical powers, to provide visual acuity at intermediate distances. The intermediate optical power annular ring can be placed anywhere in the middle or outer region of the lens optic zone, and can be the second annular ring from the outer edge of the lens optic zone, or can be the outermost annular ring which defines the outer circumference of the lens optic zone. The lens can be a contact lens to be worn on the cornea of the eye, such as a soft hydrogel contact lens, or can be an intraocular lens.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to multifocal lens designs with 
intermediate optical powers, and more particularly pertains to multifocal 
lens designs with intermediate optical powers which provide for visual 
acuity at intermediate distances by adding one or more intermediate 
optical power annular rings to a multifocal concentric annular ring lens. 
2. Discussion of the Prior Art 
The present invention pertains to ophthalmic lenses, and in particular to 
contact lenses such as soft hydrogel contact lenses, and intraocular 
lenses, having more than one optical power or focal length. 
It is well known that as an individual ages, the eye is less able to 
accommodate, i.e., bend the natural lens in the eye in order to focus on 
objects that are relatively near to the observer. This condition is 
referred to as presbyopia, and presbyopes have in the past relied upon 
spectacles or other lenses having a number of different regions with 
different optical powers to which the wearer can shift his vision in order 
to find the appropriate optical power for the object or objects upon which 
the observer wishes to focus. 
With spectacles the process involves shifting one's field of vision from 
typically an upper lens portion far power to a lower lens portion near 
power. With soft or hydrogel contact lenses, however, this approach has 
been less than satisfactory. The contact lens, working in conjunction with 
the natural lens, forms an image on the retina of the eye by focusing 
light incident on each part of the cornea from different field angles onto 
each part of the retina in order to form an image. This is demonstrated by 
the fact that as the pupil contracts in response to brighter light, the 
image on the retina does not shrink, but rather, light comes through a 
smaller area of the lens to form the entire image. 
Similarly, for a person that has had the natural lens of the eye removed 
because of a cataract condition and an intraocular lens inserted as a 
replacement, the ability to adjust the lens (accommodate) to the distance 
of the object being viewed is totally absent. In this case, the lens 
provided is usually set at a single infinite distance focal power, and 
spectacles are worn to provide the additional positive optical power 
needed for in-focus closer vision. For such a patient, a functional 
multifocal lens would be particularly useful. 
It is also known in the art that under certain circumstances the brain can 
discriminate between separate competing images by accepting an in-focus 
image and rejecting an out-of-focus image. 
One example of this type of lens used for the correction of presbyopia by 
providing simultaneous near and far vision is described in U.S. Pat. No. 
4,923,296 to Erickson. This patent discloses a lens system which comprises 
a pair of contact lenses, each having equal areas of near and distant 
optical power, with the lens for one eye having a near upper half and a 
distant lower half and the lens for the other eye having a distant upper 
half and near lower half. Together they provide at least partial clear 
images in both eyes, and through suppression by the brain of the blurred 
images, allow alignment of the clear images to produce an in-focus image. 
U.S. Pat. No. 4,890,913 to de Carle describes a bifocal contact lens 
comprising a number of annular zones having different optical powers. The 
object in the design of this lens is to maintain, at all times regardless 
of pupil diameter, an approximately equal division between near and 
distant powers, which requires between six and twelve total zones on the 
lens. 
Another attempt at providing a bifocal contact lens is described in U.S. 
Pat. No. 4,704,016 to de Carle. Again, this lens attempts to maintain, at 
all times regardless of pupil diameter, an approximately equal division 
between near and distant powers. 
U.S. Pat. No. 5,448,312 entitled PUPIL TUNED MULTIFOCAL OPHTHALMIC LENS, 
discloses a multifocal concentric ophthalmic lens for presbyopic patients 
constructed with three general annular lens portions in a multifocal 
design. A central circular portion of the lens has only the patient's 
distance corrective power, and is surrounded by a first inner annular 
portion, which can consist of multiple annular rings having an inner 
radial portion which enhances the patient's near focal power encircled by 
radial portions of substantially equal cumulative amounts of distance and 
near optical power focal correction for the patient. This is surrounded by 
a second outer annular portion, which can also consist on one or more 
annular rings having additional distance focal power near the periphery of 
the optical surface area of the ophthalmic lens. Each annular ring has 
either a near or distance optical power and works in combination with 
other lens portions to yield the desired focal ratio in that portion of 
the lens. 
Trifocal spectacles are also well known in the prior art in which an upper 
spectacle lens portion has a prescription for far vision, a lower 
spectacle lens portion has a prescription for near vision, and an 
intermediate spectacle lens portion, positioned between the upper and 
lower lens portions, has a prescription for intermediate vision. Moreover, 
blended trifocal and multifocal spectacles are also known in which an 
upper lens portion has a prescription for far vision, and a lower lens 
portion has a prescription for near vision, and an intermediate lens 
portion has a blended prescription which changes gradually from the 
optical power for the upper portion to the optical power for the lower 
lens portion. 
However, these concepts are not readily extendible to contact or 
intraocular lenses, as a wearer cannot shift his vision through different 
upper and lower areas of a contact or intraocular lens. The only change 
that the eye makes with respect to a contact or intraocular lens is an 
involuntary control over the diameter of the pupil, which decreases in 
bright light and increases in dim light. 
SUMMARY OF THE INVENTION 
It is an object, therefore, of the present invention to provide an 
ophthalmic lens for a presbyope that yields improved visual acuity in 
general, and in particular, matches the focal requirements of intermediate 
distance conditions. 
The present invention provides a contact or intraocular lens which matches 
the distribution of near, intermediate and distance focal vision 
corrections to the type of human activity typically undertaken in various 
illumination conditions. The present invention also matches the particular 
dimensions of a contact lens to suit the size of the pupil of the wearer 
as a function of illumination intensity. The ophthalmic lens is designed 
to provide predominantly distance correction under high illumination, 
nearly evenly divided distance and near corrections under moderate 
illumination, and provide intermediate vision correction under low to 
moderate illumination levels. The lens is also specifically designed to 
match the wearer's pupil size as a function of illumination level, and in 
preferred embodiments by also applying pupil size parameters as a function 
of the age of the wearer. 
Accordingly, it is a primary object of the present invention to provide 
multifocal lens designs with intermediate powers which address the problem 
of intermediate optical distance vision by adding one or more intermediate 
optical power annular rings to a multifocal concentric annular ring lens. 
A preferred intermediate optical power is substantially 50% of the add 
difference between the distance power and the near power, but could be 
chosen to be any optical power between the distance and near optical 
powers. 
In accordance with the teachings herein, the present invention provides a 
multifocus, concentric annular ring lens wherein one of the front and rear 
surfaces of the lens defines a central area comprising a circular disc 
having a spherical surface corresponding to a basic prescription spherical 
distance optical power. A plurality of annular rings surround the central 
area and have alternating spherical near optical powers and spherical 
distance optical powers, and at least one intermediate optical power 
annular ring. The intermediate optical power annular ring may be located 
in the outer region of the lens optic zone, and its optical power is 
intermediate to the distance and near optical powers, to provide visual 
acuity at intermediate distances. 
In greater detail, the intermediate optical power annular ring or rings can 
be placed in the outer radial portion of the optic zone, where it can be 
an annular ring in that portion, or it may consist of the entire outer 
radial portion, or it can be placed in the middle radial portion, where it 
is preferably placed in the outer edge thereof, or it may be placed 
anywhere in that portion. The lens can be a contact lens to be worn on the 
cornea of the eye, such as a soft hydrogel contact lens, or can be an 
intraocular lens. The central area and the plurality of annular rings are 
preferably formed on the back surface of a contact lens to minimize flare 
and glare problems. Moreover, the widths of the individual annular rings 
can be different to generate a power profile which varies to generate 
different ratios of distance optical power to intermediate and near 
optical power.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring to the drawings in detail, FIG. 1 illustrates a preferred type of 
embodiment of a lens 10 designed pursuant to the teachings of the present 
invention wherein a central area 12 is a circular disc containing the 
basic prescribed Rx spherical distance power, and is surrounded by a 
plurality of alternating spherical near power and spherical distance power 
annular rings 14, 16, 18 and 20. In the first embodiment of FIG. 1, an 
intermediate optical power annular ring 22, having an optical power 
intermediate to the distance and near optical powers, is added as the 
second outermost annular ring. The intermediate optical power annular ring 
22 is encompassed by an outermost distance optical power annular ring 24. 
A preferred intermediate optical power is 50% of the difference between the 
distance and near optical powers, but could be chosen to be any optical 
power between the distance and near optical powers. A preferred position 
for the intermediate optical power annular ring is in the outer region of 
the lens optic zone 26, preferably the second outermost annular ring 22 
from the outer edge of the lens optic zone 26. The totality of the area 
encompassed by the outer circumference of the outermost ring 24 defines 
the optic zone 26 of the lens 10, which includes the areas of 12, 14, 16, 
18, 20, 22 and 24. The optic zone 26 is surrounded by a peripheral zone 
28, which is a nonoptical area of the lens, which is beveled at 30 to the 
outer circumference 32 of the lens. 
In greater detail, in one exemplary designed embodiment, the center disc 12 
and the annular rings 16, 20 and 24 have a distance radius of 8.4 mm, 
while annular rings 14 and 18 have a near radius of 8.69443 mm, annular 
ring 22 has an intermediate curve radius of 8.3803 mm, and the peripheral 
curve radius is 9.832 mm. 
The center toric disc 12 has a diameter of 2.15 mm, annular ring 14 has a 
diameter of 3.30 mm, annular ring 16 has a diameter of 3.60 mm, annular 
ring 18 has a diameter of 4.30 mm, annular ring 20 has a diameter of 4.80 
mm, annular ring 22 has a diameter of 5.35 mm, annular ring 24 has a 
diameter of 8.00 mm, the lenticular annular area 28 has a diameter of 13.0 
mm to the start of beveled area 30, and the outer circumference of the 
lens has a diameter of 14.0 mm. 
FIG. 2 is a plan view of a second embodiment of a multifocal lens design 
having an intermediate optical power wherein the intermediate optical 
power annular ring 44 is the outermost annular ring 44 in the optical zone 
46 of the lens. Similar to the first embodiment, a central area 33 is a 
circular disc containing the basic prescribed spherical distance power, 
and is surrounded by a plurality of alternating spherical near power and 
spherical distance power annular rings 34, 36, 38, 40 and 42. The 
intermediate optical power annular ring is the outermost annular ring 44 
within the lens optic zone 46. The combined areas of the central spherical 
disk 33 and the surrounding annular rings 34 through 44 comprise the 
active optical area 46 of the lens, which is surrounded by a peripheral 
(nonoptical) area 48 which is beveled at its outer circumference at 50 to 
an outer circumferential edge 52. 
The area of the intermediate power portion preferably should not exceed 25% 
of the total area of the full optic zone. It should be noted that the 
intermediate power is distinct and different from the intermediate 
peripheral curve and is preferably a sphere. 
By varying the widths of the individual annular rings, a power profile can 
be created which generates different ratios of distance optical power to 
near and intermediate optical powers with increasing distance from the 
center of the lens. 
A person's pupil size is a function which is dependent upon light 
intensity, and is an important parameter in the design of ophthalmic 
lenses, particularly contact lenses and intraocular lenses. 
Reliable data was obtained from people in four different age groups. Those 
less than 20 years of age, those between 20 and 40 years of age, those 
between 40 and 60 years of age, and those over 60 years of age. These 
pupil measurements were made on test subjects at three different luminance 
levels, 250, 50 and 2.5 candellas per square meter (cd/m.sup.2). 
The 250 cd/m.sup.2 level corresponds to extremely bright illumination 
typically outdoors in bright sunlight. The 50 cd/m.sup.2 is a mixed level 
which is found in both indoors and outdoors. Finally, the 2.5 cd/m.sup.2 
level is most typically found outdoors at night, usually in an uneven 
illumination situation such as night driving. 
The results of these studies are given in the following Table I, which 
includes in addition to the average pupil diameter at three different 
illumination levels, the standard deviation in the diameter and the range 
associated therewith. 
TABLE I 
______________________________________ 
HORIZONTAL PUPIL SIZE 
Illumination Average Pupil 
Standard 
(candellas/m.sup.2) 
Diameter (mm) 
Deviation (1.SIGMA.) 
______________________________________ 
LESS THAN 20 YEARS OF AGE 
2.5 6.5962 0.9450 
50 4.3499 0.5504 
250 3.4414 0.3159 
20 to 40 YEARS OF AGE 
2.5 6.4486 0.8259 
50 4.4843 0.6342 
250 3.5040 0.4217 
40 to 60 YEARS OF AGE 
2.5 5.4481 0.9787 
50 3.6512 0.5692 
250 3.0368 0.4304 
GREATER THAN 60 YEARS OF AGE 
2.5 4.7724 0.6675 
50 3.4501 0.5106 
250 2.8260 0.3435 
______________________________________ 
Taken in combination with this data are the determinations that have been 
made regarding real world human activity typically encountered under 
different illumination levels. At very high illumination levels, such as 
that represented by 250 cd/m.sup.2, human activity is typically taking 
place outdoors in bright sunlight and requires distant vision tasks. 
At a 50 cd/m.sup.2 illumination level, activity usually occurs both indoors 
and out, and typical human activity is represented by both near and far 
visual tasks. 
Finally, at low illumination levels represented by the 2.5 cm/m.sup.2, the 
activity that takes place is typically outdoors at night and usually 
involves distant vision tasks, such as driving an automobile. 
The corrective powers as a function of the distance from the center of the 
lens must be a function of the patient's specifically measured pupil 
diameter at varying illumination levels, or it can be readily determined 
from the above information based upon the age of the patient. 
Moreover, ocular in vivo image quality measurement devices can be used to 
optimize the ocular image quality in the concentric annular ring designs 
to produce even more improved designs. This is accomplished by using an in 
vivo image quality measurement device, such as an aberroscope or MTF point 
spread measuring device, to measure and decrease the sum of the 
aberrations of the combination of the lens and the eye system. 
Obviously, many different embodiments of the present invention are 
possible, with alterations of the number of annular rings, the widths and 
arrangement of the annular rings, and the optical powers assigned to each 
of the annular rings. 
While several embodiments and variations of the present invention for 
multifocal lens designs with intermediate powers are described in detail 
herein, it should be apparent that the disclosure and teachings of the 
present invention will suggest many alternative designs to those skilled 
in the art.