Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ Background of the Invention 133277~
-~ This invention relates generally to post-cataract
patient care and vis-ion improvement and, more particularly, to an
intra-ocular bifocal lens implantable in a human eye to replace
the natural lens, having been removed, for instance, in a cataract
operation. Commonly, thick glasses have been used for correcting
the vision of post-cataract patients. However, the glasses have
- obvious disadvantages associated with the size and weight of the
glasses. The present invention circumvents the need for heavy
glasses by creating a pseudophakia or an eye in which a plastic
- lenticulus is substituted for the extracted cataract,
- The concept of creating a concentric bifocal lens has
been shown for contact lenses. U.S. Patent No. 3,726,587 is an
example. Contact lenses have a converging meniscus shape in order
to conform to the rounded shape of the cornea. Such a shape could
not apply in an intra-ocular implantation. Other types of multiple
focus contact lenses are well known. Patent No. 3794,414 shows a
lens having a light-transmitting area interrupted by spaced-apart,
opaque portions. ~atent ~lo, 3,962,505 shows a nearly concentric
portion of a contact lens for bifocal vision.
Most of the prior art related to intra-ocular lenses
deals with fixa-tion means for sec~ring the lens in either the
posterior or anterior chamber of the eye. Patent No. 4,010,496
shows an intra-ocular lens having upper and lower refractive seg-
ments for near and far vision.
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~ ~ Summary of the Invention 13 3 2 7 7 8
Pseudopha~ic eyes generally are such that the pupils
~--~ rarely exceed 4 mm in diameter in photopic conditions, nor do
the pupils generally constrict to less than 2 mm in diameter. It
is also well known that slight pupillary constriction occurs t~hen
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the eye attempts to focus at near vision. The eye functions not
only as a seeing mechanism but, also, as a light collecting
mechanism. At any given pupil diameter, light enters the eye and
is focused on the retina. By changing the path of a portion of
the light, it is possible to achieve bi-vision. For example, if
a 3 mm pupil in 2~0 foot candles of illumination (approximately
that found in modern offices~ is juxtaposed to a centrally placed
2,12 mm diameter optic powered for near, the optic being surrounded
concentrically by a far vision optic, multiple focus can be
achieved. In the example, one half of the pupillary area is
powered for near vision while the balance is powered for far vision.
Focusing at near the central lens portion puts the
image on the retina, and mild pupillary constriction aids in
focusing. Although pupillary constriction is helpful, it is not
necessary for the concentric lens. When the eye looks up to far
objects, the near focal power is automatically out of focus while
the concentric distant power takes over to provide clarity for the
far vision. This occurs because of the large light collecting
area of the concentric distant portion of the lens. Even when
extremely bright objects at a distance stimulate increased pupillary
constriction, the increase in depth of focus counters any blurring
from the centrally located near optic.
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~; Should sunglasses be used to eliminate irritating 1332778
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~ brightness in far vision so that the pupil relaxes, the light
- collected by the concentric dlstance lens portion increases to
offset the reduction in depth of focus. Hence, sharp far
vision occurs even in diminished light.
Since the difference in the effective power between
far and near vision is approximately +2.50 diopters in the
- average patient, sufficient distinction in focus is realized
to provide rapid neuro-transfer of far to near vision. This
phenomenon, plus the appropriate light collecting area for a
given pupil area, provides the efficacy of the present intra-ocular
optic design. To maintain the effectiveness of the design, the
range of powers in the far vision portion of the lens is limited
to a range of from +lO.00 diopters to +30.00 diopters effective
power, while the near optic power range is limited to from +10.00
diopters to +40.00 diopters effective power.
While lens diameter may vary with need, 6 mm is average.
The central near optic can vary in diameter relative to need, but
2.12 mm is average for a 3.0 mm pupil stimulated by approximately
2~0 foot candles of illumination.
The lens can have a plano-convex or bi-convex shape
and can be fabricated by lathe cutting, compression or injection
molding or electro-forming. The near optic may be placed on
either surface with the power corrected accordingly.
An object of the invention is, therefore, to provide
an intra-ocular bifocal lens for post-cataract patients which
eliminates the need for heavy, uncomfortable glasses.
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1332778
Another object of the invention is to provide the
post-cataract patient with an intra-ocular bifocal lens which
enables the patient to achieve both near and far vision with
clarity.
Another object of the invention is to provide an
intra-ocular lens of one-piece construction.
Still another object of the inventlon is to provide
simultaneous vision for near and far in the absence of the natural
crystalline lens.
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Brief Description of the Drawings
Figure 1 is a plane view of the intra-ocular bifocal
lens.
Figure 2 shows a sectional view of the intra-ocular
lens having a plano-convex shape.
Figure 3 is a sectional view of the intra-ocular
bifocal lens having a bi-convex shape.
Figure 4 shows a sectional view of a human eye with
the intra-ocular bifocal lens implanted in the anterior chamber.
Figure 5 shows a sectional view of a human eye with
the intra-ocular lens implanted in the posterior chamber.
f~ 1332778
Detailed Description of the Invention
Referring to Figure 1, the intra-ocular bifocal lens
is indicated generally by the number 1. The one-piece body
has a centrally located optically powered portion for near vision,
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` - ~ designated as number 3, which is surrounded by a far vision
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optically powered portion 2, the two portions being concentric and
coaxial. While the body is divided into two distinct portions,
each portion being optically powered, the body itself has a one-
piece construction. The body, in cross section, can be either
plano-convex, as shown in Figure 2, or bi-convex, as shown in
Figure 3.
After a cataract operation in which a natural crystalline
lens is removed from a human eye, the intra-ocular bifocal lens
can be implanted in either the anterior or posterior cham~er of
the eye.
Figure 4 shows a human eye with the lens implanted in
the anterior chamber, while Figure ; shows implantation in the
posterior chamber. In either chamber, the lens is fixed in place.
It can be done so using a variety of methods. ~Sultiple suspensory
or fixation methods currently exist in a generic form that may be
applied to the present invention.
Referring now to Figure 4, the eye is shown generally
by the reference numeral 10. The anterior chamber 8 is defined by
the interior wall of the cornea 7 and iris 11. The pupillary
aperture 9 extends from the anterior chamber 8 to the posterior
chamber 9. The retina is shown generally as number 6. The central
portion or near vision portion of the lens is axially aligned with
the pupillary aperture 9. The central portion is aligned with the
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` pupillary aperture when the lens is positioned in the posterior
~ chamber, as shown in Figure 5. Under normal lighting conditions,
; the pupillary aperture 9 has a diameter slightly larger than the
central near vision portion of the lens. In either Figure
4 or 5, light passes through the pupillary aperture 9 and is
- focused on the retina 6. By changing the path of a portion of
that light, the concentric bifocal intra-ocular lens will create
bi-vision. Optimally, if the pupillary aperture is 3 mm in
diameter, a bifocal intra-ocular lens will have a central near
vision portion having a 2.12 mm diameter, Half of the pupillary
area will be powered for near vision while the other half will
be powered for far vision,
Focusing at near the central portion puts the image on
the retina 6. Some pupillary constriction may clarify the image,
but it is not required, When the eye lQ looks up to far objects,
the near vision portion is automatically out of focus while the
far vision portion becomes effectlve to provide clarity for far
vision. This occurs because of the large light collecting area
of the far vision portion of the lens.
Embodiments shown and descrihed herein provide examples
of the invention with the understandins that modifications may
be made.
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