WO2001095842A1

WO2001095842A1 - Aspheric iridectomy/iridotomy treatment lens

Info

Publication number: WO2001095842A1
Application number: PCT/US2001/019445
Authority: WO
Inventors: Richard M. Mueller
Original assignee: Volk Optical, Inc.
Priority date: 2000-06-16
Filing date: 2001-06-18
Publication date: 2001-12-20
Also published as: AU2001271325A1

Abstract

The invention relates to a direct ophthalmoscopy lens device, of the contact type, for diagnosis and laser treatment of the iris of a patient's eye in conjunction with a slit-lamp or other biomicroscope. The contact type invention consists of a concave contact surface (1) with a large aspheric convex surface (3) located off-center axis that provides superior optics and laser beam convergence due to the use of aspheric surfaces.

Description

ASPHERIC IRIDECTOMY/IRIDOTOMY TREATMENT LENS

BACKGROUND OF THE INVENTION

The invention relates to a direct ophthalmoscopy lens device, of the contact type, and specifically a contact iridectomy/iridotomy lens for diagnosis and laser treatment of the iris of a patient's eye in conjunction with a slit-lamp or other biomicroscope.

Known iridectomy/iridotomy lenses have been used for the treatment of the eye disease glaucoma by creating iridian drainage holes. The ciliary process of the eye produces the aqueous humor, which flows up tlirough the pupil into the anterior chamber. From there, the aqueous humor drains into the trabecular meshwork, into the Canal of Schlem then into the veneous drainage system of the body. Eye diseases such as glaucoma inhibit the free circulation of aqueous humor to the anterior chamber of the eye. When the trabecular meshwork becomes clogged, it does not allow the aqueous humor to drain. This causes the entire eye to experience pressure on the sensitive retina and optic nerve, damaging the nerve fiber. This is called open-angle glaucoma and, if not treated, can cause total blindness. A second type of glaucoma is called acute angle-closure glaucoma. Sometimes the lens of the eye becomes too concave on both surfaces and blocks the drainage angle in the anterior chamber. This effect is a true emergency and, while medicines can lower the eye pressure, treatment must occur.

One method of treating glaucoma is to make a small precise hole in the iris to allow the aqueous humor to drain from the anterior chamber, even when the pupil rests against the lens which ultimately reduces the pressure of the eye. Iridectomy/iridotomy lenses are used for this treatment. The known Abraham Iridectomy Lens, for example, uses an 8.0 mm diameter, 66 diopter glass button cemented to a piano surface. Although this lens performs adequately in its purpose of imaging and converging the laser on the iris, it has a limited field of view.

Another such iridectomy style lens is disclosed, for example, in U.S. Patent No. 4,750,829 to James B. Wise, incorporated herein by reference. This device utilizes an off center axis 103 diopter button to increase the energy density. This device create a 2.65x image magnification, and the power density created by the laser beam convergence on the iris from this device is extremely powerful for creating iridian drainage holes. However, this device utilizes spherical optics and has limited image quality.

There is thus a need for an iridectomy/iridotomy lens with a wider field of view and improved image quality for exacting laser spot placement.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a direct ophthalmoscopy lens device, of the contact type, with improved image resolution, stereopsis, laser beam energy convergence, increased field of view and ease of use for diagnosis and laser treatment of the iris of a patient's eye in conjunction with a slit-lamp or other biomicroscope.

The above and other objects are accomplished in accordance with the invention by the provision of an iridectomy/iridotomy lens system for at least one of observing and treating an eye, comprising: an integral, one-piece contact lens body having a concave posterior surface and a convex anterior surface, wherein the posterior concave surface has a curvature corresponding to a curvature of an average cornea and a central axis that is substantially coincident with the central optical axis of the eye when centrally located on the cornea of the eye, and the convex anterior surface is less steeply curved than the concave posterior surface and has a central axis that is offset from the central axis of the concave posterior surface by a sufficient distance for creating a focal point on the iris of the eye. In accordance with the invention, the above construction of the lens body creates a magnified virtual image behind the iris inside the patient's eye. Further, because the convex anterior surface is less steeply curved than the concave posterior surface, the edge- to-edge diameter of the convex surface can be significantly larger than the anterior button lens of the known iridectomy lenses. The invention enables a larger field of view as compared to the known iridectomy lenses where, in order for the convex surface of the offset and steeply curved surface of the attached button lens to be contained with the same region as the posterior concave surface, the edge-to edge diameter of the button lens must be significantly less than the diameter of the concave posterior surface.

According to a further aspect of the invention, at least the convex anterior surface is aspheric for improved optical properties of the lens, such as improved resolution, imaging, laser convergence, stereopsis and decreased aberrations. Preferably the concave posterior surface also is aspheric. The applicant herein has discovered that by using an aspheric concave posterior surface and a larger diameter aspheric convex anterior surface with a determined lens center thickness and correspondingly chosen conic constants for the aspheric surfaces, it is possible to provide a large field of view together with a highly detailed image magnification, resolution, and laser energy convergence for creating iridian holes.

The conic constants are determined by the thickness of the lens between the posterior concave and anterior convex surfaces. This invention comprehends a series of lenses having a range of center thickness and, as a result, a corresponding range of conic constants, image magnifications, laser spot sizes, and lens powers.

As compared to the 8.0 mm diameter, 66 diopter Abraham Iridectomy Lens which uses spherical optics, the field of view, detailed imaging, and laser convergence or spot creation provided by the present invention are greatly enhanced. The use of aspheric optics in the present invention improve image quality, stereopsis, resolution, and correction for aberrations to an extent not possible with the spherical optics of the known iridectomy/iridotomy lenses.

Through research and testing, the new invention, utilizing aspheric optics, provides superior imaging optics, stereopsis, resolution, and laser beam convergence as well as a larger field of view. As an example, in one implementation of the iridectomy lens of the present invention, the concave surface has an apical radius of 7.65, conic constant -0.18, and diameter (edge-to-edge) of 12.7 mm while the convex surface has an off-set diameter (edge- to-edge) of 11.6 mm, a apical radius of 7.91 mm, conic constant of -0.18, and a center thickness of 6.86 mm, with the center axis of the convex anterior surface being off-set by 2.5 mm from the center axis of the concave posterior surface. This lens design produces a power of 38.97 diopters, an iridian image magnification of 1.70x and a 0.66x laser spot magnification factor at the iris.

By varying the center thickness and conic constants, the image magnification, laser spot, and lens diopter power changes accordingly. Preferably, image magnification will range between about 1.47 and 2.20 and laser spot size reduced to between about 0.53x and 0.779x and a diopter power range between 31.0 and 46.0. h exemplary implementations, the concave surface has an apical radius of between about 7.55 mm and 7.75 mm; a conic constant of between about -0.01 and -0.20 and a diameter (edge-to-edge) between about 12.0 mm and 13.0 mm. The convex surface has an apical radius between about 7.0 mm and 8.0 mm; a conic constant between about -0.020 and 0.226 and a diameter (edge-to-edge) between about 10.0 mm and 12.0 mm. Further, the center thickness will be in a range between about 4.5 mm and 9.5 mm and the off-set distance between the center axes of the posterior and anterior curved surfaces will be in a range between about 2.0 mm and 3.0 mm. Other features, advantages and benefits of the invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross section of a direct, contact ophthalmoscopy lens device according to the invention with an overlaid ray.

FIG. 2 shows a plan lens view of the embodiment of Fig. 1 and shows, in dotted lines, by comparison, a standard 8.0 mm diameter button lens of an Abraham Iridectomy Lens.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a lens layout of one embodiment of a direct, contact ophthalmoscopy lens device according to the invention that includes an integral, one piece lens body L with a posterior concave surface 1, an anterior piano portion 2 and an anterior convex surface 3. In practice, the lens L can be fixed in a common shaped frame or housing (not shown) as known in the art.

Posterior lens surface 1 has a concave surface that has a curvature generally corresponding to the curvature of an average cornea for placement in contact with a patient's eye. Concave posterior surface 1 has a central axis Ai that corresponds with the central axis CL of a patient's eye when centrally located thereon. Convex anterior surface 3 is less steeply curved than concave posterior surface 1. Anterior surface 3 has an optical axis A₂ offset from the central optical axis Ai of concave posterior surface 1. Piano anterior portion 2 results from the offset of optical axes Ai and A₂. The lens body may be made of PMMA (polymethyhnethacrylate) acrylic which has an index of refraction of 1.491. However, preferred embodiments are not limited to any particular optical material or refractive index.

The following Table summarizes characteristics of the lens surfaces and their relative spacing according to exemplary implementations of the invention. The "Radius" in the table and as used throughout is the apical radius of curvature. A radius of "Infinity" represents a flat surface. The "Distance from Corneal Apex" is the distance from a surface or, in the case of a curved surface, the distance from the apex of that curved surface to the corneal apex. The distance is measured along a line perpendicular to the tanget of the corneal apex. The distance from the posterior concave surface to the corneal apex is understood to be 0, since, when the lens is in place on an eye this distance is 0 or close thereto. A "Conic Constant" of 0 indicates a spherical surface and a non-zero conic constant indicates an aspheric conoid. The "Diameter" is the distance between the outer edges of the respective lens surface.

The "Design Number" relates to the specific design where surface 1 and 2 remain constant and the surface 3 center thickness and conic constant is varied, per the design number, resulting in specific lens attributes. The "Image Distance From Corneal Apex" is the distance the image is produced from the corneal apex or, equivalently, the apex of the posterior concave surface under conditions where the two apexes are essentially coincident. A negative sign for this distance means the image is behind the cornea inside the eye. The resulting "hnage magnification," "Diopter Power," "Laser Spot Size," and "Image Distance From Corneal Apex" are the lens design attributes produced by surface 3 having a specific radius and conic constant and located at the respectively indicated distances from surface 1. TABLE I

In use, light rays, which originate at the patient's iris, pass through the cornea, exit the eye and pass through the lens device in accordance with the ray tracing which overlays the lens layout in FIG. 1. The iris location in air is represented in FIG. 1 as the line labeled "Iris." As illustrated, light rays exiting the eye will be refracted at surfaces 1 and 3 and to form a virtual image at plane I behind the iris. Lenses made according to the respective Design Numbers 1-12 in the above Table will produce a virtual image at a location 1.62 to 4.19 mm behind the corneal apex.

Figure 2 shows a top view of the lens in Figure 1. Figure 2 additionally shows in dashed line the approximate optical viewing area that would be available with the known iridectomy/iridotomy lens employing a steeply curved, smaller diameter anterior button lens 4. The cross-hatched region represents the increased optical viewing area that is provided by the iridectomy/iridotomy lens of the invention compared to prior art iridectomy/iridotomy lenses. As can be seen, the present invention provides approximately twice the viewing area provided by the known iridectomy/iridotomy lenses, and a correspondingly larger field of view.

The invention has been described in detail with respect to a preferred embodiment, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and the invention, therefore, as defined in the appended claims is intended to cover all such changes and modifications as fall within the true spirit of the invention.

Claims

What is claimed is:

1. An iridectomy/iridotomy lens system for at least one of observing and treating an eye, comprising: an integral, one-piece contact lens body having a concave posterior surface and a convex anterior surface, the concave posterior surface having a curvature corresponding to a curvature of an average cornea and a central axis that is substantially coincident with the central optical axis of the eye when centrally located on the cornea of the eye; the convex anterior surface being less steeply curved than the concave posterior surface and having an central axis that is offset from the central axis of the concave posterior surface by a sufficient distance for creating a focal point on the iris of the eye.

2. The iridectomy/iridotomy lens according to Claim 1, wherein the convex anterior surface is aspheric.

3. The iridectomy/iridotomy lens according to Claim 1, wherein the convex anterior surface has a conic constant in a range from about -0.02 to about 0.226.

4. The iridectomy/iridotomy lens according to Claim 1 , wherein the concave posterior surface is aspheric.

5. The iridectomy/iridotomy lens according to Claim 1, wherein the concave posterior surface has a conic constant in a range from about -0.01 to about -0.20.

6. The iridectomy/iridotomy lens according to Claim 1, wherein the convex anterior surface has a central axis that is offset by at least 2.0 mm from the central axis of the concave posterior surface.

7. The iridectomy/iridotomy lens according to Claim 6, wherein the central axis of the convex anterior surface is offset from the central axis of the concave posterior surface by about 2.5 mm.

8. The iridectomy/iridotomy lens according to Claim 1, wherein the lens body has a center thickness in a range from about 4.5 mm to about 9.5 mm.

9. The iridectomy/iridotomy lens according to Claim 1, wherein the concave posterior surface has a diameter of at least about 12.0 mm.

10. The iridectomy/iridotomy lens according to Claim 1, wherein the convex anterior surface has a diameter of at least about 10.0 mm.

11. The iridectomy/iridotomy lens according to Claim 1, wherein the convex anterior surface has an apical radius in a range from about 7.0 mm to about 8.0 mm.

12. The iridectomy/iridotomy lens according to Claim 1, wherein the lens body includes a planar ring surrounding the convex anterior surface.

13. The iridectomy/iridotomy lens according to Claim 1, wherein the lens comprises polymethylmethacrylate (PMMA).

14. The iridectomy/iridotomy lens according to Claim 1, wherein the lens has a refractive index of about 1.49.

15. the iridectomy/iridotomy lens according to claim 1, wherein the lens has a diopter power between 31.0 and 46.0.