Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
1998-12-21
2001-05-22
Epps, Georgia (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C264S002200
Reexamination Certificate
active
06234629
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a differential thickness contact lens which is compensated for differential shrinkage, as well as a method of manufacturing such lens.
BACKGROUND OF THE INVENTION
Contact lenses are generally used to correct various types of vision problems. See, for example, U.S. Pat. Nos. 4,573,774; 5,650,837; and 5,652,638, which are incorporated herein in their entireties by reference. Also, various texts discuss the principles of contact lens design and manufacturing: Ruben et al., Contact Lens Practice (Chapman & Hall, London); Stein, Slatt & Stein, Opthalmic Terminology (C.V. Mosby Company, St. Louis, 1987), which are also incorporated herein by reference.
Astigmatism occurs when a portion of the eye focuses light at a different focal point than the rest of the eye, i.e., it is a refractive error of the eye in which the rays of light do not come to a single point focus on the retina. Toric lenses, or lenses with cylinder power typically are used to correct for astigmatism. For toric lenses, the cylinder power is along the cylinder radius, which is orthogonal to the cylinder axis. The cylinder power of the toric lens results in the eye focusing light rays at a common focal point.
As indicated above, toricity is used to correct astigmatism so that it focuses light rays at a common point. However, the common focal point may be located at an incorrect position with respect to the retina. This condition is referred to as either “myopia” or “hyperopia”. Myopia typically results from a steep cornea that causes light rays to focus at a focal point that is short of the retina. Conversely, hyperopia is a case in which a flat cornea causes light rays to focus at a focal point that is behind the retina. Sphere power is included in a lens to cause light to properly focus on the retina.
Contact lenses may include either or both spherical correction or cylinder correction depending on the particular circumstances of the lens user's eyes. Lenses that have only spherical correction are spherically symmetric and, thus, any rotation of the contact lens inside the eye is irrelevant and does not disturb the intended vision correction. Toric contact lenses, or other rotationally stabilized lenses, on the other hand are typically designed to include areas of different thickness, resulting in a spherically asymmetric lens. As a result, toric contact lenses need to be rotationally stabilized on the eye to insure that the lens is properly oriented with respect to the eye in order to carry out its function of correcting the vision of particular areas of the eye. Additionally, lenses may also need to be stabilized in the eye for comfort reasons.
Rotational stability may be achieved using a number of designs including inferior truncation, double truncation, thin zones (also called “double slab-off”), back surface toricity and prism wedge profile. These rotation stabilizing designs may be used individually or in combination. One common feature of these rotation stabilizing designs is the use of different thickness areas in the lens to achieve rotational stability. For example, in the case of a “slab off” design, the top and bottom portions of the lens orient beneath the eyelids. At the same time, the thicker portions of the lens are positioned in between the eyelids.
The process for manufacturing differential thickness lenses typically includes a curing step, which may involve UV, heat, or other similar curing process. However, as a result of the curing step, the material of the lens shrinks at different rates due to the differential thicknesses. This differential shrinkage results in an induced, undesired toricity in the lens.
SUMMARY OF THE INVENTION
The present invention is for a differential thickness contact lens which is compensated for differential shrinkage during the manufacturing process. The present invention is also for a method of manufacturing and compensating a differential thickness lens for differential shrinkage during the manufacturing process. The unwanted toricity induced by the differential shrinkage caused by a particular manufacturing process is experimentally determined, both in terms of angular position and power. The lens compensation is achieved by providing an equal and opposite power to the unwanted toricity induced by the manufacturing process. The lens compensation may be used in conjunction with intended toricity, i.e., the lens compensation is used to provide a baseline lens, which is then designed to include a particular, desired toricity. The lens compensation is implemented by adjusting the lens geometry so that upon curing, the lens corresponds to the desired, prescribed lens, without any unwanted toricity.
The present invention is for a method of producing a compensated contact lens, and also a compensated contact lens, which is produced using the following steps:
designing a lens to have first and second areas of different thickness;
determining any differential shrinkage which will occur during the curing of the lens having first and second areas of different thickness; and
modifying the lens to include geometrical features to compensate for the differential shrinkage.
REFERENCES:
patent: 3248460 (1966-04-01), Naujokas
patent: 4153349 (1979-05-01), Wichterle
patent: 4208364 (1980-06-01), Shepherd
patent: 4565348 (1986-01-01), Larsen
patent: 4573774 (1986-03-01), Sitterle
patent: 4573903 (1986-03-01), Boudet et al.
patent: 5219497 (1993-06-01), Blum
patent: 5366668 (1994-11-01), Cuthbertson et al.
patent: 5466147 (1995-11-01), Appleton et al.
patent: 5650837 (1997-07-01), Roffman et al.
patent: 5652638 (1997-07-01), Roffman et al.
patent: 5962548 (1999-10-01), Vanderlaan et al.
patent: 5988813 (1999-11-01), Neadle et al.
patent: 0 051 027 (1982-05-01), None
patent: 0 561 481 (1993-09-01), None
Clutterbuck Timothy
Neadle Susan
Epps Georgia
Johnson & Johnson Vision Care Inc.
Schwartz Jordan M.
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