HK1003013B - Soft toric contact lens - Google Patents

Description

The invention relates to a soft toric contact lens for the correction of pure astigmatism and astigmatism associated with spherical misalignment according to the general concept of independent claim.

In contrast to hard contact lenses, which are stable in shape, soft contact lenses are made of a flexible material and stick to the cornea and sclera of the eye when worn.

A well-known and proven method for the manufacture of soft contact lenses is the so-called semimold method (see, e.g. US-PS 4 155 962), a casting method in which only the back surface of the contact lens already acquires its definitive shape, while the front surface is produced by the casting process itself, following the casting process, by the process of removing the spanner.

The toric lens surface required for the correction of corneal stigmatism can be located or formed from the optical point of view, in principle, both on the front face of the contact lens facing the eye and on the back face of the eye. In the case of soft contact lenses, the toric lens surface is usually the front surface. There are also contact lenses with toric back surface, which is formed as negative or complementary to the cornea to be inserted. However, these contact lenses are problematic and after-effective in various respects.

The manufacture of soft toric contact lenses with medium or high negative total refractive power by means of the aforementioned semimold process and the fly-cut process is now well controlled and proven. Difficulties arise, however, with low negative and especially positive total refractive power. If the toric frontal surfaces of such contact lenses are to be produced in the conventional fly-cut process, then lenses so thick that wearing these lenses in practice is not possible are produced. Unpractical lenses are usually avoided by a lenticular design, in which the contact lenses are only rebuilt in their optically effective central region, which are required to maintain their thickness, but in peripheral areas much thinner.

One of the tasks of the present invention is therefore to create a soft toric contact lens in the entire refractive index range, which can be produced rationally even with positive total refractive power and with lenticular construction and also offers the comfort of wearing modern contact lenses with ellipsoidal back surfaces.

According to the most general idea of the invention, the solution to these problems underlying the invention is to shift the correction of corneal stigmatism to the optically effective central area of the contact lens back surface, i.e. to place the toric lens surface in this central area of the contact lens back surface, which generally has an average diameter of about 5 mm to 14 mm. (This optically effective central area of the back surface is an oval area, the smallest and largest dimensions of which are about 5 mm and 14 mm respectively.) By confining the toric surface to the optically effective central area of the contact lens back surface, the peripheral area of the lens back surface can be optimized in terms of its internal comfort and other aspects, such as its elliptical shape (USPS 54692) and its physical shape, which is extremely good in both physical and geometrical terms, and therefore can be used to achieve excellent back-contact with the lens.

The concept of the invention of moving the torus to the central area of the contact lens back surface is based on the surprising finding that the back surface torus or the radius difference of the back surface torus to the corneal torus, due to the softness of the contact lens material, is transferred to the front surface of the contact lens and there at least partially has the same optical effect as an original front surface torus, but without any manufacturing problems and other disadvantages.

The contact lens of the invention, which fulfils the task defined above, is characterized by the characteristics of the independent claim.

The stabilization of the orientation of the contact lens on the eye is preferably achieved in a dynamic way by the eyelash impact, for which the contact lens is provided with a flattened stabilization zone at the front in its upper and/or lower regions (see US-PS 4 095 878).

A major advantage of the contact lens according to the invention is that the front surface is formed purely rotationally symmetrically or, with positive total refractive forces, can have a rotationally symmetrical lenticular structure, which makes the manufacture of the contact lens in any case rational.

It has also been shown that the contact lens of the invention can be adjusted in the simplest way with the help of only two measuring lenses; a special adjustment set is not required, since the basic geometry required for stabilization (edge thickness difference, etc.) is the same for each lens. Due to the use of only two cylinder values (preferably about minus 1 cylinder and minus 1.75 cylinder) for the back surface area, the stock is minimal in a practiced direct delivery, i.e. the number of lenses in a contact lens sales set is kept within rational limits.

The following illustration gives a detailed description of a contact lens according to the invention and shows: Figure 1a partially cut contact lens in perspective,Figure 2a view of the lens in Figure 1,Figure 3a cut according to lines III to III of Figure 2 andFigure 4a cut according to lines IV to IV of Figure 2.

The contact lens, designated as a whole by CL, has a predominantly rotationally symmetrical front surface composed of a rotationally symmetrical optically effective central region 2 and a rotationally symmetrical (spherical or aspherical) lenticular region 1 and two flattened, approximately sickle-shaped stabilization zones 4 and 5 opposite each other at the 12 o'clock and 6 o'clock positions.

The illustrated example of the contact lens according to the invention has a positive total refractive power. Lenses with negative total refractive power have a minus-lenticular structure with the aim of edge rejuvenation.

Stabilization zones 4 and 5 are similar in design and effect to conventional zones of this type, such as those described in US PS 4 095 878.

The material of the soft contact lens of the invention is conventional, for example, the following materials may be used: tefilcon (38%) ((Dk=8), hefilcon A&B (43%) ((Dk=12), xylofilcon A (67%) ((Dk=29), scafilcon A (71%) ((Dk=30), deltafilcon A (43%) ((Dk=10), ocufilcon (44%) ((Dk=16), etafilcon A (58%) ((Dk=20), vifilcon A (55%) ((Dk=16).

According to the main idea of the invention, the toric lens surface required for the correction of corneal stigmatism is located in the central region 7 of the lens back surface. The surrounding peripheral region 8 of the lens back surface is aspherical, preferably ellipsoid shaped with the geometry described, e.g., in USPS 5 069 542.

The optically active toric central region 7 of the lens back surface has an average diameter of about 5 mm to about 14 mm and has an oval surface shape.

A contact lens assembly constructed with the contact lens of the invention covers a wide range of supplies with only a few different cylinder values of the toric central region 7 of the contact lens back surface. It has been shown that in practice two values of about minus 1 dpt cyl and minus 1.75 dpt cyl are sufficient in most cases. In the case of an ellipsoidal design of the peripheral region 8 of the lens back surface according to US-PS 5 069 542, only two geometries are also sufficient, and one for the so-called flat and one for the so-called steep.

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Claims (6)

1. A soft toric contact lens for correcting pure astigmatism or astigmatism combined with spherical sight defects, having a front face (1,2) remote from the eye and a rear face (7,8) facing the eye that has an optically effective central region having toric effect and a peripheral region surrounding that central region, wherein the front face (1,2) of the contact lens (CL) is of substantially rotationally symmetrical shape and wherein the rear face (7,8) of the contact lens is of aspherical, especially ellipsoidal, shape in the peripheral region (8).
2. A contact lens according to claim 1, wherein the front face (1) is provided in an upper and/or lower region with a flattened stabilisation zone (4,5) for dynamic stabilisation of the orientation by blinking.
3. A contact lens according to claim 1 or 2, wherein especially in the case of positive total refractive power the front face (1,2) is divided into an optically effective central region (2) and an adjacent rotationally symmetrical lenticular region (1).
4. A contact lens according to any one of claims 1 to 3, wherein the optically effective central region (7) of the rear face (7, 8) has a mean diameter of from about 5 mm to about 14 mm and is of approximately oval shape.
5. A lens set comprising contact lenses according to any one of the preceding claims, wherein the toric central regions (7) of the contact lens rear faces (7,8) preferably have only two different cylindrical values, especially approximately minus 1 dptcyl and approximately minus 1.75 dptcyl.
6. A lens set according to claim 5, wherein the aspherical, especially ellipsoidal, peripheral regions (8) of the contact lens rear faces (7,8) preferably have only two geometries.