JP2958189B2 - Toric contact lens, method of manufacturing the lens, and method of designing the lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact lens capable of correcting astigmatism, a method of manufacturing the lens, and a method of manufacturing the lens.
Related to the design method . More specifically, a toric contact lens that can prevent rotation on the eyes when worn and
The present invention relates to a method for manufacturing the lens and a method for designing the lens .

[0002]

The Background of the Invention astigmatism, are parallel rays means a state in which no image on one point, using general glasses or contactor Torre lens in order to correct this astigmatism.

Conventionally, as a contact lens (hereinafter, referred to as CL) for correcting astigmatism, there is a toric contact lens (hereinafter, referred to as TCL). TCL
Is a contact lens in which the rear and / or front curved surfaces have different radii of curvature in two orthogonal radial directions.

[0004] Due to the nature of astigmatism, the CL must always be worn at a fixed position with respect to the human eye. In the case of glasses, since the frame having the lens is fixed by the ear or nose, the position of the lens is always guaranteed, but in the case of normal CL, there is nothing to fix the lens,
It rotates on the eye, making it impossible to perform proper correction.

Therefore, in the case of TCL, various improvements have been conventionally proposed in order to prevent rotation on the eyes.
These improvements can be broadly classified into two types.

[0006] The first type is to prevent the rotation of the lens on the eye (on the cornea) by making the area below the TCL relatively heavy, and is called a ballast type. A bifocal type (bifocal) CL31 (see FIG. 5) belonging to this type of CL has been known for some time (JP-B-37-18531).

The second type corresponds to the shape of a human (wearer) eyeball and prevents the lens from rotating on the cornea. This type can be further divided into two types.
That is, a so-called truncation type in which a notch (hereinafter referred to as a truncation portion) 33 is provided on a part of the outer periphery of the CL 32 (see FIG. 6)
048) and CL34 (see FIG. 7)
5 which is called slab-off type
0-13351).

[0008]

In the case of the ballast type CL, the thickness of the lens is increased in order to shift the center of gravity downward. For this reason, when the lens is worn, the eyes are pressed, resulting in a foreign body sensation or pain. In addition, as the ballast type CL, a so-called prism ballast shape in which the center axis of the inner surface of the CL is shifted from the center axis of the outer surface is adopted, so that the thickness of the lens continuously increases as going downward. There has been proposed a device in which the feeling of wearing is improved. However, when the lens is designed within the standard of the lens (such as power), the thickest part of the lens may have a thickness that cannot be practically used. In addition, as the thickness of the lens increases, the amount of oxygen passing through the lens decreases, and the safety of the cornea may be impaired.

On the other hand, in the case of a truncation type CL, since the peripheral portion in the planar shape of the lens is not smooth, there is a feeling of foreign matter when worn. Further, in order to improve the feeling of wearing, it is necessary to process the truncation portion smoothly, but it requires extremely high processing technology and skill, and the effect may not be exhibited depending on the shape of the eyelid.

Further, in the case of the slab-off type CL, there is no problem with the feeling of wearing, but since the center of gravity of the lens is located at the geometric center, the lens is slightly stable against rotation on the cornea due to blinking. There's a problem.

In order to solve the problems of the ballast type, truncation type and slab-off type, a technique combining a ballast type and a slab-off type has been proposed as follows.

First, US Pat. No. 4,324,461 proposes a technique in which a thin portion (hereinafter, referred to as a slab-off) is provided on an upper portion of a lens to shift a center of gravity downward.

Second, US Pat. No. 5,020,898 proposes a technique in which slab-offs are provided at the upper and lower portions of a lens to shift the center of gravity downward. However, it is difficult to secure the amount of displacement of the center of gravity necessary to prevent the rotation of the lens on the cornea, and there is a case where good and stable visual acuity cannot be obtained.

As still another example, a slab-off is provided at the lower part of the lens and a prism is applied to the lens to make the lower part heavy (US Pat. Nos. 4,508,436 and 4,573,774). However, also in these cases, by providing the slab-off at the lower part, the position of the center of gravity moves upward, and the effect of preventing the rotation of the lens on the eyes decreases.

The present invention can solve the above-mentioned problems, and more reliably prevents rotation on the cornea, and has a good wearing feeling and can be used safely. And a method of manufacturing the lens and the lens.
The purpose of the present invention is to provide a design method of a lens .

[0016]

Means for Solving the Problems Conventionally, when stability of rotation is measured by the shape of a prism ballast, the design and development have been made according to the number of prisms to be provided, that is, the degree of the prism amount (prism frequency). The present inventors consider a new viewpoint, that is, how much a deviation rate is caused by adopting a prism ballast shape, and carry out a design and development to obtain an appropriate ballast effect with a lens thickness as thin as possible. Conversion.

Here, the deviation ratio is the distance (displacement amount) between the center and the center of gravity with respect to the diameter in the frontal shape of the lens.
Means the percentage. That is, for example, diameter 1
If the center of gravity of a 4 mm TCL is shifted by 0.6 mm from its geometric center, the shift rate is 0.6 ÷ 14 × 100 = 4.
3 (%). Note that the shift amount at this time is 0.6 mm.

As a result, specifically, according to our own research, the deviation rate from the geometric center of the lens, which is required to produce the effect of rotation stability in almost all TCL standards, is 2. It has been found that if the amount is set in the range of 5 to 7.5%, sufficient stability against rotation can be obtained.

[0019] That toric contact lenses of the present invention exhibits a prism ballast shape, the position of the center of gravity is a toric contact lens which is decentered downward from the geometric center, the heavy of the toric contact lens
When the deviation rate from the geometric center of the heart is 2.5-7.5%
There, the being slab-off thin area in the peripheral portion is formed with at least top and bottom of the lens, the upper
The central axis of the thin part of the part, the thin part of the lower part, and the front optical part
It is characterized by being formed differently .

[0020]

Further, it is preferable that the front surface of the toric contact lens has a toric surface. Further, the method for producing a toric contact lens of the present invention is a method for producing a toric contact lens having a prism ballast shape, wherein the position of the center of gravity is decentered below the geometric center, and (a) the corneal shape of the wearer (B) setting the curvature of the front surface of the lens that meets the standard of the desired contact lens based on the curvature set in the step; and (c) determining the prism amount of the lens. Setting; (d) setting the minimum thickness of the lens; (e) setting the slab-off width at the upper and lower peripheral portions of the lens to 2.5 mm or less ; and (f) the center of gravity of the lens. And (g) cutting or molding after each step. Furthermore, the method for designing a toric contact lens of the present invention is a method for designing a toric contact lens having a prism ballast shape, and the position of the center of gravity is decentered below the geometric center, and (a) the corneal shape of the wearer (B) designing the curvature of the front surface of the lens that meets the standard of the desired contact lens based on the curvature designed in the step; and (c).
A step of designing the prism amount of the lens, (d) a step of designing the minimum thickness of the lens, (e) a step of designing the slab-off width of the upper and lower peripheral portions of the lens to be 2.5 mm or less, f) a step of designing the position of the center of gravity of the lens.

[0022]

According to the toric contact lens of the present invention, the whole shape is formed in a prism-shaped ballast shape to shift the center of gravity downward, and the slab-off is formed by cutting off the upper peripheral portion of the TCL. The effect of preventing the rotation of is improved. Therefore, as compared with the case where the rotation of the lens is prevented only by the prism ballast shape, the deviation rate can be reduced, and the prism amount (prism power) can be reduced. Therefore, the total thickness including the maximum thickness of the TCL can be reduced, and the feeling of wearing can be improved. Further, the supply amount of oxygen to the cornea can be increased, and damage to the cornea can be prevented.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The contact lens of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view showing an embodiment of the toric contact lens of the present invention, FIG. 2 is a sectional view taken along the line II-II of the contact lens of FIG. 1, and FIG. 3 is another embodiment of the toric contact lens of the present invention. FIG. 4 is a flowchart showing a design procedure of the toric contact lens of the present invention.

The toric contact lens of the present invention (T
1), the entire shape of the TCL 1 is a prism ballast shape. That is, the rear surface 2 and the front surface 3 of the TCL 1 are formed of a spherical surface and a toric surface, respectively, and the central axis B of the front surface 3 is lower than the central axis A of the rear surface 2, and A
It has a shape extending in parallel to. Therefore, the thickness of the TCL 1 is thicker in the lower portion, and the center of gravity is shifted downward (see FIG. 2). Further, spherical cut surfaces (surfaces after the slab-off is formed) 6 and 7 are formed on the slab-offs 4 and 5 on the upper and lower sides of the TCL 1, respectively. In addition, 8 is a boundary line between the front surface 3 and the cut surface 6, and 9 is a boundary line between the front surface 3 and the cut surface 7. Further, a region 10 surrounded by the boundaries 8 and 9 is an optical portion that actually functions as a contact lens.

The front surface 3 is formed with a toric surface. That is, two orthogonal directions are used to correct astigmatism.
The curved surface is formed such that the radius of curvature of the front surface 3 is different in the two radial directions. Therefore, when the toric surface is formed by cutting, it can be manufactured more easily than when it is formed on the rear surface 2.

In the TCL constructed as described above, the whole shape is formed in a prism ballast shape and the center of gravity is shifted downward, so that the rotation can be prevented as well as the ballast type. Since the lower peripheral portion is cut off, the deviation rate of the lens is smaller than that of the prism ballast type. Therefore, the maximum thickness of the TCL1 (the thickness of the lowermost portion of the TCL1 shown in FIG. 2) can be reduced, and at the same time, the overall thickness of the TCL1 can be reduced, and the feeling of wearing can be improved. it can. Further, the supply amount of oxygen to the cornea can be increased, and damage to the cornea can be prevented.

The TCL 11 shown in FIG. 3 has a lower slab-off extending to the upper portion through both sides. That is, the lower cut surface 12 is formed, and then the upper cut surface 13 is formed. The two-dot chain line in the figure is a boundary line of the lower cut surface 12 that disappears with the formation of the upper cut surface 13. is there. This TCL 11 is also T
The same function as CL1 can be performed.

Further, it is preferable that the lens deviation rate is selected from the range of 2.5 to 7.5%. Because 7.5%
This is because if the deviation rate is set to exceed the above range, the lens becomes too thick depending on the standard, while if it is less than 2.5%, a sufficient ballast effect cannot be obtained. In order to more effectively stabilize the rotation of the lens, it is preferable to select the deviation rate from the range of 3.5 to 5.5%.

Further, since the ballast provided in the TCL of the present invention has a prism ballast shape, the surface shape is very smooth unlike a conventional CL which is simply weighted at the lower portion like a CL. Therefore, the feeling of wearing is further improved.

When designing the TCL 1 configured as described above, first, the lens shift rate is set, and the lens shift amount (that is, the geometric center) is set so as to achieve the set lens shift rate. Is calculated, and the prism amount of the lens and the slab-off width are set. Of course, in this design, the amount of lens displacement due to the toric surface is also taken into consideration.

More specifically, as shown in the flow chart of FIG. 4, the following design procedure is performed.

First, the minimum thickness t _min of the TCL 1 for obtaining the required strength is set. The minimum thickness t _min varies depending on the material, and is set in consideration of various conditions. Further, a desired lens displacement H is also set.

Next, the curvature of the rear surface 2, that is, the so-called base curve (BC) is set so as to match the corneal shape of the wearer (step 14).

Next, the front surface 3 is designed so as to conform to a desired CL standard (for example, a spherical power, a cylindrical power, or an astigmatism axis) in consideration of a preset BC (step 15).

Next, the prism amount (prism frequency) is arbitrarily set (step 16).

Next, the thickness of the lens is inspected (step 17). Since the TCL 1 is formed in a prism ballast shape, the geometric centers of the rear surface 2 and the front surface 3 do not coincide. Therefore, the position where the thickness of the lens becomes the minimum appears outside the geometric center or the periphery of the CL,
The minimum thickness is determined by examining the thickness of the lens (at all locations).

As a result, if the minimum value of the lens thickness t is the minimum thickness t _min , the process proceeds to the next step. Otherwise, the process returns to step 16 to set the prism amount (prism power) again. Perform

Next, upper and lower slab-off widths are set (step 18). At this time, if the upper slab-off width (width C shown in FIGS. 1 and 3) is as large as possible, the amount of displacement increases, and the effect of preventing rotation can be improved. 2.5mm). Of course, it is not limited to this value, and can be set to any value.

Next, the position of the center of gravity (the amount of displacement) is calculated (step 19). At this time, if the shift amount is equal to or more than the initially set shift amount H, the prism amount (prism frequency) and the slab-off width obtained in the previous step are determined as formal values. If the deviation is less than H, the flow returns to step 18 and the slab-off width is set again. In this case, in order to secure an effective width of the optical unit 10 of the TCL 1, if the upper slab-off width C is 2.5 mm, the lower slab-off width (the width D shown in FIGS. 1 and 3) is 0.1. ~
Limited to 2.5 mm.

If the desired amount of displacement is not obtained by the operation of step 18, the process returns to step 16 to reset the amount of prism (prism power).

Although not shown in the figure, if there are many TCLs designed according to the above-described design procedure under the same standard, the total thickness (thickness at the center and thickness at the periphery) is selected from among them. The smallest thickness in consideration of
Adopted as the shape of CL1.

When manufacturing the TCL 1 designed according to the above design procedure, the TCL 1 can be easily manufactured by cutting or molding which is well known to those skilled in the art.

In this embodiment, the toric surface is formed on the front surface. However, the present invention is not limited to this, and the toric surface may be formed on the rear surface or both front and rear surfaces.

[0045]

According to the present invention , the rotation of the lens can be effectively prevented, and a good wearing feeling can be obtained. Further, since the supply amount of oxygen to the cornea can be secured, safety is also improved. Further, since the restrictions imposed by the lens standard are substantially extended, the degree of freedom in design is improved. Further, since the amount of prism (prism power) can be reduced as compared with the related art, an adverse optical effect (for example, polarization) can be reduced.

[Brief description of the drawings]

FIG. 1 is a front view showing an embodiment of a toric contact lens according to the present invention.

FIG. 2 shows II-I of the toric contact lens of FIG.
It is an I line sectional view.

FIG. 3 is a front view showing another embodiment of the toric contact lens of the present invention.

FIG. 4 is a flowchart showing a procedure for designing a toric contact lens of the present invention.

FIG. 5 is a cross-sectional view showing an example of a conventional contact lens.

FIG. 6 is a cross-sectional view showing another example of a conventional contact lens.

FIG. 7 is a sectional view showing still another example of a conventional contact lens.

[Explanation of symbols]

 1,11 Toric contact lens 3 Front 4,5 Slab off 6,7,12,13 Cut surface

Continuation of the front page (56) References JP-A-55-50216 (JP, A) JP-A-64-500466 (JP, A) Journal of the Japanese Association of Contact Lenses, Vol. 32, No. 2, pages 88-95 Page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02C 7/04

Claims (5)

(57) [Claims] 1. A toric contact lens having a prism ballast shape, wherein the position of a center of gravity is decentered below a geometric center, wherein the toric contact lens is provided.
The deviation rate from the geometric center of the center of gravity of the
5%, and a slab-off of a thin region is formed at least in a peripheral portion of an upper portion and a lower portion of the lens ;
In the upper thin area, the lower thin area, and the front optical section
A toric contact lens, wherein the axes are formed differently . 2. A toric contact lens of claim 1, wherein said thin region is characterized der Rukoto below 2.5 mm. 3. The toric contact lens according to claim 1, wherein a front surface of the toric contact lens has a toric surface. 4. A method of manufacturing a toric contact lens having a prism ballast shape and a center of gravity decentered below a geometric center, wherein: (a) setting a curvature of a rear surface of the lens to match a corneal shape of a wearer; (B) setting the curvature of the front surface of the lens that conforms to the desired contact lens standard based on the curvature set in the step; (c) setting the prism amount of the lens; (E) setting the minimum thickness of the lens; (e) setting the slab-off width at the upper and lower peripheral portions of the lens to 2.5 mm or less ; and (f) setting the position of the center of gravity of the lens. (G) a method for producing a toric contact lens, comprising: a step of cutting or molding after each step. 5. A method for designing a toric contact lens having a prism ballast shape, wherein the position of the center of gravity is decentered below the geometric center, wherein (a) the curvature of the rear surface of the lens conforming to the wearer's corneal shape is determined. (B) designing the curvature of the front surface of the lens that meets the standard of the desired contact lens based on the curvature designed in the step; (c) designing the prism amount of the lens; d) a step of designing the minimum thickness of the lens; (e) a step of designing the slab-off width at the upper and lower peripheral portions of the lens to 2.5 mm or less ; and (f) a step of designing the position of the center of gravity of the lens. Design method of toric contact lens consisting of