Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2001-12-04
2003-02-18
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
Reexamination Certificate
active
06520637
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally pertains to an ophthalmic lens. More particularly, the present invention relates to a contact lens, and even more particularly relates to a rigid gas-permeable contact lens.
When contact lenses were first commercialized, they were made of a rigid material, such as polymethylmethacrylate (PMMA). As shown in
FIG. 1
, such contact lenses had a posterior surface
10
including a central optical zone
12
and one or more peripheral zones
14
,
16
. Optical zone
12
on posterior surface
10
was defined by a generally spherical surface having a radius of curvature corresponding to a measured base curve of the cornea upon which the contact lens was to be worn. The peripheral zones (
14
,
16
) were also defined by spherical curves and were typically flatter than the curve defining central optical zone
12
. The peripheral zones were dimensioned to closely fit the outer area of the cornea. The anterior surface
20
of these early contact lenses typically had one to three zones, including a front central optical correction zone
22
, an optional intermediate zone
24
and an optional peripheral lenticular zone
26
. Both of these anterior surface zones were defined by spherical curves, with the radius of curvature of anterior central optical zone
22
being selected so as to provide the appropriate optical power for correction of the patient's hyperopic, myopic, and/or astigmatic condition. The radius of peripheral lenticular zone
26
on anterior surface
20
was selected so as to provide a transition from central optical zone
22
to an edge
17
of the contact lens, which typically had a thickness of, for example, 0.125 mm. The transitions
25
between zones on anterior surface
20
generally aligned with transitions (
18
,
28
) between zones on posterior surface
10
.
In the late 1960's, contact lenses were modified somewhat by removing the discrete junctions (
18
) between the zones by joining the spherical curves with tangential transitions (
28
). Subsequently, the posterior surfaces of the contact lens were made aspheric so as to more closely fit the anterior surface of the cornea, which is also aspheric.
While soft contact lenses were developed subsequent to rigid lenses and are currently in wide use, such soft contact lenses cannot be used as effectively to correct the vision of individuals having more severe optical impairment. Thus, there remains a large market for rigid and rigid gas-permeable (RGP) lenses.
Individuals who wear rigid lenses may experience discomfort, which is typically caused by the sensation of having a rigid foreign object with a significant amount of mass on the individual's eye. While consideration has been given to reducing the thickness of the rigid contact lenses so as to reduce their mass and increase oxygen permeability, thin rigid contact lenses have not been commercially feasible due to the weakening of the contact lens structure and the resultant increased likelihood of breakage, warpage, and flexure. Flexure in a rigid contact lens is undesirable because the lens flexes each time the patient blinks thereby resulting in variable vision correction.
Thin lens designs gained worldwide popularity with the introduction of Syntex's Polycon I material in 1979. That material, now coined a silicon/acrylate, had an oxygen permeability (DK) of 5×10
−11
. The lenses were available in inventory designs of 9.5/8.4, 9.0/7.8, and 8.5/7.3 (outer diameter/optical zone). The 9.5−mm diameter lens incorporated a specific anterior lenticular design and a standard spherical tri-curve posterior design. The lens was fitted approximately 1.00 to 1.50 D flatter than “K” to permit lid/lens attachment in unobstructed upward lens movement. “K” is considered to be the flattest central curve of the cornea.
The Polycon I lens was eventually phased out and replaced with the Polycon II material, which has a DK=12×10
−11
. Past attempts to produce thin RGP lens designs in moderate to high DK materials have met with only limited success. Material brittleness, warpage, and base curve instability as well as visual interference caused by flexure have prevented the designs from enjoying the success of the low DK Polycon II.
Therefore, a need has existed in the rigid contact lens market for a contact lens having a lower mass while retaining structural rigidity and strength.
SUMMARY OF THE INVENTION
Accordingly, it is an aspect of the present invention to solve the above problems by providing a low-mass rigid contact lens that has the same overall rigidity and strength as a conventional rigid contact lens. It is another aspect of the present invention to provide a rigid contact lens having approximately 50 percent less mass than a conventional rigid contact lens. It is an additional aspect of the present invention to provide a rigid contact lens that is much thinner than the conventional rigid contact lens and thereby provides for additional oxygen transmission through the lens. To achieve these and other aspects and advantages, an ophthalmic lens according to the present invention comprises a posterior surface and an anterior surface, where the anterior surface has a spherical central optical correction zone, an aspheric intermediate zone, and an aspheric peripheral zone. The aspheric intermediate and peripheral zones are not used for optical correction, while the central optical correction zone is used for providing correction at a single focal length.
These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.
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patent: 4640595 (1987-02-01), Volk
patent: 4909621 (1990-03-01), Evans
patent: 5125729 (1992-06-01), Mercure
patent: 5517260 (1996-05-01), Glady et al.
patent: 5526071 (1996-06-01), Seidner et al.
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patent: 5623323 (1997-04-01), Johnson et al.
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patent: 5790231 (1998-08-01), Mercier
patent: 6325509 (2001-12-01), Hodur et al.
Caroline Patrick J.
Hodur Neil R.
Art Optical Contact Lens, Inc.
Price Heneveld Cooper DeWitt & Litton
Sugarman Scott J.
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