JP3171629B2 - Multifocal ophthalmic lens and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens (hereinafter referred to as an ophthalmic lens) to be worn or buried in an eyeball or an eye such as a contact lens or an intraocular lens. The present invention relates to an observation type multifocal ophthalmic lens and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a multifocal lens has been used as an ophthalmic lens for supplementing visual acuity adjusting power, which has been applied to an eye with poor visual acuity adjusting ability, such as presbyopia, and has a large number of powers in one lens. Ophthalmic lenses have been proposed.

[0003] Such multifocal ophthalmic lenses can be broadly classified into two types. A distance vision correction area and a near vision correction area set for the lens are selectively used as necessary, and are separately used. And the distance vision correction area and the near vision correction area are simultaneously observed, and the observation distance is selected and determined according to the brain of the wearer (observer). However, in the field of ophthalmic lenses, it is difficult to use multiple correction zones properly for observation, so the latter type (simultaneous observation type) that observes each correction zone at the same time. But it is becoming mainstream.

Further, as described in Japanese Patent Application Laid-Open No. 60-91327, this simultaneous observation type ophthalmic lens has a so-called two-focal point having a far vision correction area and a near vision correction area. Bifocal type and
As disclosed in JP-A-208524, there is a so-called multifocal type having a multifocal point whose power continuously changes from a distance vision correction area to a near vision correction area.

However, since the former bifocal type ophthalmic lens has only two focal points, the wearer has
When a point at an intermediate distance between the far point and the near point is visually recognized, a clear image cannot be obtained, making it difficult for the brain to make a judgment, and causing a phenomenon such as ghost or double vision.

On the other hand, in the latter multifocal type ophthalmic lens, although a clear image is obtained even at the intermediate point, the power of the lens changes at a substantially constant rate of change in the radial direction. Since a long distance vision correction area and a near vision correction area are not secured, sufficient visibility is not obtained at a far point and a near point where a clear image is particularly required, and the image is blurred. It could cause inconvenience and was not suitable for practical use.

In order to secure a distance vision correction area or a near vision correction area, some proposals have been made in which a multifocal lens is combined with a single-focus spherical lens, but none of them has been proposed. , Neglecting the focus shift due to the spherical aberration of the spherical lens part, and because the smooth power change was not obtained at the boundary between the spherical lens part and the multifocal lens part, the aforementioned bifocal type eye Like a lens, there is a risk of causing a phenomenon such as ghost or double vision.

In addition, since the conventional multifocal type ophthalmic lens employs an aspherical shape in which the power of the lens changes at a substantially constant change rate in the radial direction, the eye of the wearer's individual eye is used. It is not possible to satisfactorily adjust the clarity between the far point, near point, and intermediate point, which is required according to the degree of refractive power adjustment and living conditions, and the optical effect is limited. The problem was that it was inherent.

[0009]

Here, the present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a clear image at any of a far point, a near point, and an intermediate point. Can be observed, blurred images and ghosts,
A phenomenon such as double vision can be prevented as much as possible, and it is possible to perform optical adjustment of the lens according to each individual wearer, and a multifocal ophthalmic lens that is easy to fit to each individual, It is to provide a manufacturing method thereof.

[0010]

According to the present invention, there is provided a multifocal ophthalmic lens having a plurality of dioptric powers on a concentric circle, wherein a distance vision correction area and a near vision correction area are provided. And an intermediate visual acuity correction area between them is provided concentrically with each other with a predetermined width in the radial direction, while each of the correction areas shows a frequency distribution curve that continuously changes in the radial direction, and each correction area The power distribution curve has a continuous lens surface shape at the boundary between, and the radial power change rate in the distance vision correction area and the near vision correction area is the radial power rate in the intermediate vision correction area. A multifocal ophthalmic lens smaller than the rate of change
This is the gist.

The present invention also relates to such a multifocal ophthalmic lens, wherein the rate of change in the radial direction in the distance vision correction area and the near vision correction area is 1 D (diopter) / mm or less. Is also the gist of this.

Further, in the present invention, when producing the above-mentioned multifocal ophthalmic lens, the power distribution curves in the distance vision correction area, the near vision correction area and the intermediate vision correction area are determined. In addition, after determining the surface shape on one side of the lens, the surface shape on the other side of the lens is determined by a ray tracing method so as to obtain a power corresponding to the power distribution curve. A method of manufacturing a multifocal ophthalmic lens is also the gist of the present invention.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, as a specific form of the multifocal ophthalmic lens according to the present invention, a distance vision correction area is provided at the center of the lens, and a near vision correction area is provided at the outer periphery of the lens. Each is provided, and the intermediate vision correction area is provided between the distance vision correction area and the near vision correction area, and the near vision correction area is located at the center of the lens, and the distance vision correction area is located at the outer periphery of the lens. There are two forms: a case where a visual acuity correction area is provided, and a case where an intermediate visual acuity correction area is provided between the near vision correction area and the distance vision correction area.

In any of these embodiments, the distance vision correction area, the near vision correction area, and the intermediate vision correction area include:
It suffices if they are formed on mutually concentric circles. That is, the center (optical axis) of the concentric circle may be decentered from the center of the lens, or each correction area may not be a perfect circle.
It may be elliptical or the like. In this sense, it should be understood that the radial direction in each visual acuity correction area does not always coincide with the lens radial direction.

When the distance vision correction area is set at the center of the lens and the near vision correction area is set at the outer periphery, the distance vision correction area is equal to or smaller than the pupil diameter under dim conditions. It is preferable to set as follows, specifically, it is preferable to set the diameter to be 2 to 6 mm. More preferably, in addition to the above conditions, the distance vision correction area is 10 to 3 times the area of the entire optical part of the lens.
The near vision correction area is set so as to occupy 20% to 50% of the entire area of the optical unit of the lens.

[0016] This enables observation in the distance vision correction area and the near vision correction area even when the pupil diameter changes,
This is to prevent blurring of the image at each point from the far point to the near point. However, it is also acceptable to set the distance vision correction area to be approximately the same as the pupil diameter under dim conditions because of the fact that far point observation is generally performed under dim conditions.

On the other hand, when setting a near vision correction area at the center of the lens and a far vision correction area at the outer periphery,
The near vision correction area is preferably set to be smaller than the pupil diameter under dim conditions, and more specifically, it is preferable to set the diameter to be 1 to 5 mm. More preferably, in addition to the above conditions, the near vision correction area occupies 5 to 20% of the area of the entire optical unit of the lens, and the far vision correction area is the area of the entire optical unit of the lens. 60-9
Each is set to occupy 0%. This is for the same reason as described above.

The intermediate vision correction area is defined as a transition between the distance vision correction area and the near vision correction area, and the distance vision correction area and the near vision correction area determined as described above are determined. It will be formed over the whole area between the areas.

Each of the distance vision correction area, the near vision correction area, and the intermediate vision correction area is formed to have a shape showing a power distribution curve that continuously changes in the radial direction. In other words, the frequency distribution curve in each of the visual acuity correction areas is set to have a curve shape having one tangent line at any point. The power distribution curve indicates the relationship between the distance of the lens from the optical axis and the power at that distance.

In addition, the lens surface shape is determined so that the power distribution curve in each visual acuity correction area is continuous even at the boundary between the respective visual acuity correction areas. That is, the frequency distribution curve is set to have a curve shape having one tangent line between the respective vision correction areas.

Further, in this case, the radial power change rate in the distance vision correction area and the near vision correction area is set to be smaller than the radial power change rate in the intermediate vision correction area. More preferably, the power rate of change in the radial direction in the distance vision correction area and the near vision correction area is 1D
(Diopter) / mm or less. Thereby, it is possible to more advantageously obtain the sharpness of the image at the time of far point observation and at the time of near point observation.

In short, in the distance vision correction area and the near vision correction area, the power is not constant in the radial direction, but the rate of change is reduced, and the two vision correction areas are connected. An intermediate visual acuity correction area having a relatively large radial power change rate is formed. Thus, the intermediate vision correction area is formed in such a manner as to complement the distance vision correction area and the near vision correction area.

Hereinafter, a preferred method of manufacturing the multifocal ophthalmic lens according to the present invention having the above-described shape will be further described.

In manufacturing the multifocal ophthalmic lens according to the present invention, first, a power distribution (power distribution curve) of a target lens is determined.

First, a required far vision correction power and a required maximum near vision correction power are determined in accordance with the wearer's visual acuity adjusting ability and the like. Then, by adding an additional power to the required maximum distance vision correction power, a power distribution curve is set so that the maximum required near vision correction power at the optical axis center or the outer peripheral portion is obtained. .

Here, the frequency distribution curve can be set by a single or a plurality of linear or quadratic polynomials. In particular, if the frequency distribution curve is set by two or three quadratic polynomials, the setting (calculation) becomes easy, and the difference is much larger than when a more complicated polynomial is used. This is preferable because a lens having no optical characteristics can be obtained.

More specifically, for example, as shown in FIG. 1, in a multifocal ophthalmic lens having a distance vision correction area at the center of the lens, a distance vision correction area,
When the intermediate vision correction area and the near vision correction area are each set by a second-order polynomial, first, the following values are determined according to the wearer's vision adjustment ability and the like.

X ₁ : radius of the distance vision correction area X ₂ : radius of the intermediate vision correction area X ₃ : radius of the near vision correction area Y ₀ : target minimum refractive power (required maximum distance vision correction) Y ₁ : Additional power at the boundary between the distance vision correction area and the intermediate vision correction area Y ₂ : Additional power at the boundary between the intermediate vision correction area and the near vision correction area Y ₃ : Maximum required near vision power Additional power to obtain correction power

First, assuming that a frequency distribution curve in the distance vision correction area is Y = A ₁ · X ² , A ₁ = Y ₁ / X ₁₂ ² (1). ), The power distribution curve in the distance vision correction area is determined.

Next, assuming that a power distribution curve in the intermediate visual acuity correction area is Y = A ₂ · X ² + B ₂ · X + C ₂ , A ₂ · X ₁ ² + B ₂ · X ₁ + C ₂ = Y ₁ · because it is _{·· (1) a 2 · X} 2 2 + B 2 · X 2 + C 2 = Y 2 ··· (2) 3A 1 · X 1 2 = 2A 2 · X 1 + B 2 ··· (3) From these (1), (2), and (3), a power distribution curve in the intermediate vision correction area is determined.

Further, a frequency distribution curve in the near vision correction region, when ^{_{Y = A 3 · X 2 +}} B 3 · X + C 3, 2A 2 · X 2 + B 2 = 2A 3 · X 2 + B 3 ·· is _{· (1) A 3 · X} 2 2 + B 3 · X 2 + C 3 = Y 2 ··· (2) A 3 · X 3 2 + B 3 · X 3 + C 3 = Y 3 ··· (3) Thus, from these (1), (2), and (3), the power distribution curve in the near vision correction area is determined.

Next, after determining the power distribution curve of the target lens as described above, the shape of the lens surface is determined.

First, the surface on either side of the lens is set to a desired shape. In particular, in the case of a contact lens, it is preferable that the inner surface (concave surface) be shaped to match the shape of the eye (cornea) of the wearer in order to ensure ease and goodness of wearing. Therefore, first, such an inner surface must have a suitable spherical surface or aspherical surface (for example,
(An elliptical surface or a combined surface of an elliptical surface and a spherical surface).

Then, the surface shape on the other side of the lens is determined by using the ray tracing method so as to obtain a power corresponding to the power distribution curve determined as described above.

More specifically, for example, as shown in FIG. 2, in the contact lens material 10 in which the concave surface is set to a predetermined shape, an arbitrary point on the convex surface: A
Assuming that the intended refractive power at (X ₁ , Y ₁ ) is P ₁ , a curve passing through the point A is an aspherical parameter: s
It is represented by the following equation using (s <−1).

[0036]

(Equation 1)

Therefore, assuming that the angle between the normal at the point A and the X axis (optical axis) is θ ₁ , this θ ₁ is expressed by the following equation.

[0038]

(Equation 2)

The angle formed by the emitted light at the point A and the normal is θ.
Assuming that ₄ , the following equation holds according to Snell's law. n ′ · sin θ ₄ = n · sin θ ₁ where n: refractive index of air n ′: refractive index of lens material

Further, assuming that the angle formed by the emitted light at the point A with the X axis is θ ₅ , this θ ₅ is expressed by the following equation. θ ₅ = θ ₁ − θ ₄

On the other hand, assuming that a straight line representing the emitted light at the point A is y = c ₁ · x + d ₁ , c ₁ and d ₁ are respectively expressed by the following equations.
expressed. c ₁ = tan θ ₅ d ₁ = Y ₁ −c ₁ · X ₁

If the point at which the emitted light intersects the concave surface is B (X ₁₁ , Y ₁₁ ), the curve representing the concave surface is represented by (X−K ₁₁ ) ² + Y ² = BC ² (BC: concave surface) However, since K ₁₁ = BC + TH (TH: thickness at the center of the lens optical axis), the coordinates (X ₁₁ , Y ₁₁ ) of the point B can be expressed by the following equations, respectively. Is done.

[0043]

(Equation 3)

Therefore, assuming that the angle formed by the normal at the point B and the X axis is θ ₁₁ , this θ ₁₁ is expressed by the following equation. tan θ ₁₁ = Y ₁₁ / (X ₁₁ −K ₁₁ )

Further, the incident light at the point B is the light emitted at the point A, the angular incident light at the point B makes with the X-axis: theta ₁₂ is angle light emitted at the point A makes with the X-axis equal to the theta _5, angular incident light at the point B makes with the normal line:: theta ₁₃ is as shown by the following formula, expressed. θ ₁₃ = θ ₁₁ − θ ₁₂

The angle formed by the emitted light at the point B with the normal is θ.
Assuming ₁₄ , the following equation is established from Snell's law. n · sin θ ₁₄ = n '· sin θ ₁₃

Further, assuming that the angle formed by the light emitted at the point B with respect to the X axis is θ ₁₅ , this θ ₁₅ is expressed by the following equation. θ ₁₅ = θ ₁₁ − θ ₁₄

On the other hand, assuming that a straight line representing the light emitted at the point B is y = c ₁₁ · x + d ₁₁ , c ₁₁ and d ₁₁ are respectively represented by the following equations.
expressed. c ₁₁ = tan θ ₁₅ d ₁₁ = Y ₁₁ −c ₁₁ · X ₁₁

Therefore, the emitted light is reflected at the point X which intersects the X axis.
The coordinates: XP ₀ can be expressed as in the following equation. XP ₀ = −d ₁₁ / c ₁₁

Therefore, calculation is performed by changing the aspherical parameter: s until XP ₀ becomes equal to 1000 / P ₁ . From the coordinates of the point A at the time of convergence, the radius of curvature R of the lens convex surface at that point can be obtained based on the following equation.

[0051]

(Equation 4)

Then, the surface shape of the lens is determined by such a ray tracing method, and based on the result, the lens material is cut by using a numerically controlled cutting device or the like, thereby obtaining the desired object as described above. A multifocal ophthalmic lens will be manufactured.

[0053]

That is, in the multifocal ophthalmic lens according to the present invention, as described above, the power distribution curve is made continuous in the radial direction centered on the optical axis of the lens, thereby changing the power. Blur, ghost, double vision and the like of the observed image due to optical discontinuity at points can be prevented as much as possible.

Since the distance vision correction area having a large power difference and the near vision correction area are continuously and smoothly connected to each other by the intermediate vision correction area, the intermediate vision point is clear. The image can be observed, which facilitates midpoint observation.

In addition, since the power rate of change in the distance vision correction area and the near vision correction area is set to be smaller than that in the intermediate vision correction area, even in various conditions, the distance vision correction area and the near vision correction area can be used for far point observation and near point observation. A clear image can be advantageously obtained, and therefore, a great effect is obtained in that particularly required far-point observation and near-point observation are facilitated without sacrificing the clarity of the image at the intermediate point. You get.

Further, since the intermediate vision correction area is formed with a frequency distribution curve that is continuous with the distance vision correction area and the near vision correction area, by adjusting the power distribution form in the intermediate vision correction area. The image obtained at the time of far-point observation or near-point observation is complemented by the intermediate vision correction area, and it is also possible to make the visual recognition easy, and the adjustment of the intermediate vision correction area according to the wearer becomes possible. The optical characteristics as an excellent multifocal ophthalmic lens can be exhibited.

Further, when the surface shape of the lens is determined by the ray tracing method according to the present invention, a multifocal ophthalmic lens having various arbitrary power distribution curves can be easily designed and manufactured. It is.

[0058]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a contact lens is manufactured according to the present invention will be specifically described below. It should be noted that the present invention is not to be interpreted in a limited manner by the specific description in the above detailed description or the description of the following examples, and various changes and modifications are made based on the knowledge of those skilled in the art. , Improvements, etc.
Further, it goes without saying that any of the embodiments in which such changes and the like are added are included in the scope of the present invention without departing from the spirit of the present invention.

In the present embodiment, a description will be given of a contact lens having a distance vision correction area at the center, a near vision correction area at the outer periphery, and an intermediate vision correction area therebetween. .

First, when manufacturing such a contact lens, the intended maximum distance vision correction power of -6.00 is set.
D, the maximum value of the additional power was determined to be + 1.6D, and it was determined that an aspherical surface with an eccentricity of 0.4 (vertical curvature: 8.00 mm) was used as the concave lens surface.

Further, the radius of the distance vision correction area: X ₁ , the radius of the intermediate vision correction area: X ₂ , the radius of the near vision correction area:
X ₃ , the additional power at the boundary between the distance vision correction area and the intermediate vision correction area: Y ₁ , the additional power at the boundary between the intermediate vision correction area and the near vision correction area: Y ₂ , and the maximum additional power: Y ₃
Was determined as follows, respectively. (X ₁ , Y ₁ ) = (1.5 mm, +0.4 D) (X ₂ , Y ₂ ) = (3.0 mm, +1.4 D) (X ₃ , Y ₃ ) = (4.0 mm, +1.6 D) )

The frequency distribution curves in the radial direction in the distance vision correction area, the intermediate vision correction area, and the near vision correction area are set by quadratic polynomials, respectively. A frequency distribution curve in the correction area was obtained. The obtained frequency distribution curve is
It is shown in FIG.

Next, based on the obtained power distribution curve, the surface shape on the convex side of the contact lens was obtained by the ray tracing method as described above. The results are shown in Table 1 below.

[0064]

[Table 1]

In Table 1, in the central portion (X = 0 to 0.80 mm) of the distance vision correction area, there is no change in the radius of curvature: R within the range shown in the table. ,
As described above, the frequency distribution curve of the distance vision correction area is set by a quadratic polynomial, and the radius of curvature is determined based on the curve.
It should be recognized that there is a continuous frequency change.
Further, in the present embodiment, the reason why the radius of curvature on the convex side is constant at the central portion as described above is that the amount of change in the radius of curvature is within the range of an error due to a significant figure in calculation, or This is considered to be caused by a change in the power of the entire lens due to a change in the radius of curvature in the radial direction on the concave surface side set to the spherical shape.

Then, based on the values obtained in this manner, the lens material was cut using a numerically controlled cutting device to obtain the intended multifocal type contact lens.

The Contact Lens Obtained (Example)
Are shown in Table 2 below together with the clinical results for the simultaneous observation type bifocal type contact lens (Comparative Example).

[0068]

[Table 2]

From these clinical results, it can be seen that the multifocal type contact lens having the structure according to the present invention can provide a wearer with a very clear image in both the far-point observation and the near-point observation. It is clear that it has excellent optical effects.

[Brief description of the drawings]

FIG. 1 is a graph showing a specific example of a frequency distribution curve employed in an ophthalmic lens according to the present invention.

FIG. 2 is an explanatory diagram for explaining an operation for obtaining a lens surface shape having a power corresponding to a target power distribution curve by using a ray tracing method.

FIG. 3 is a graph showing a frequency distribution curve obtained in an example.

[Explanation of symbols]

 10 Contact lens materials

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tadashi Sawano 3-4-15 Sakae, Naka-ku, Nagoya-shi Kagami Sakae Building Inside Menicon Clinical Center (72) Inventor Shingo Hibino 3 Shinsama, Seki City, Gifu Prefecture, Ltd. Inside the Menicon Seki Plant (72) Inventor Hiroshi Iwai 3-12-7 Biwajima, Nishi-ku, Nagoya City Inside Menicon Biwajima Research Laboratories (56) References JP-A-52-46826 (JP, A) JP-A-52-110646 ( JP, A) JP-A-63-253474 (JP, A) JP-A-59-208524 (JP, A) JP-A-2-240625 (JP, A) JP-A-2-500468 (JP, A) JP-A Hei 3-504419 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02C 7/06 A61F 2/16 G02C 7/04

Claims (10)

(57) [Claims] Claims: 1. An implanted or implanted eyeball or eye
A lens, simultaneous there are multiple frequencies on concentric circles
And the observation type multifocal ophthalmic lens, the central portion of the distance vision correction region and the near vision correction region and the intermediate vision correction region therebetween, vision correction area for distal lens
And the near vision correction area is located on the outer peripheral portion.
As described above, concentric with each other with a predetermined width in the radial direction, the diameter of the distance vision correction area is 2 to 6 mm.
While you configured, they each correction zone, with showing the frequency distribution curve that varies continuously in each radial direction, without a lens surface shape frequency distribution curve is continuous at the boundary between the correction area, and A multifocal ophthalmic lens, wherein a radial power change rate in the distance vision correction area and the near vision correction area is smaller than a radial power change rate in the intermediate vision correction area. 2. The optical system according to claim 1, wherein the distance vision correction area is an optical part of a lens.
Occupy 10-30% of the total area,
Eyesight correction area is 20 to 5 times the area of the entire optical part of the lens.
2. The device according to claim 1, wherein the device is configured to occupy 0%.
Multifocal ophthalmic lens. Wherein the rate of power change radial direction in the distance vision correction region and near vision correction region is, according to claim 1 or 2, characterized in that a 1D (diopter) / mm or less
2. The multifocal ophthalmic lens according to item 1. 4. The distance vision correction provided concentrically.
Center, the intermediate vision correction area and the near vision correction area
4. The method according to claim 1, which is eccentric from the center of the noise.
Multifocal ophthalmic lens. 5. The multi-function device according to claim 1, wherein
In producing a focal ophthalmic lens, the power distribution curve in the distance vision correction area, the near vision correction area and the intermediate vision correction area is determined, and the surface shape of one side of the lens is determined. the other side of the surface shape, as the frequency corresponding to the frequency distribution curve is obtained in, characterized in that determined by the ray tracing method
Method of fabricating a multi-focal ophthalmic lens. 6. An implanted or implanted eyeball or eye
A lens that has multiple powers on concentric circles
Observation type multifocal ophthalmic lens, with distance vision correction area, near vision correction area,
The intermediate vision correction area is defined as the near vision correction area in the center of the lens.
And the distance vision correction area is located in the outer peripheral portion.
Concentric with each other with a certain width in the radial direction
Provided, the diameter of the near vision correction area is 1 to 5 mm
While setting each correction area in the radial direction.
In addition to showing a continuously changing frequency distribution curve, each correction area
Lens surface shape with a continuous power distribution curve at the boundary between
And in the distance vision correction area and the near vision correction area.
The radial power change rate in the intermediate vision correction area.
The rate of change in the frequency in the radial direction
Multifocal ophthalmic lens. 7. The optical system according to claim 1, wherein the near vision correction area is an optical unit of a lens.
Occupy 5-20% of the whole area
The eyesight correction area is 60 to 90 of the area of the entire optical part of the lens.
%.
Multifocal ophthalmic lens. 8. The distance vision correction area and near vision correction.
Change rate in the radial direction in the region is 1D (diopter
-) / Mm or less.
2. The multifocal ophthalmic lens according to item 1. 9. The near vision correction provided concentrically.
Center, the intermediate vision correction area and the distance vision correction area
9. The method according to claim 6, which is eccentric from the center of the noise.
Multifocal ophthalmic lens. 10. The method according to claim 6, wherein
When manufacturing a chifocal ophthalmic lens,
The vision correction area, near vision correction area, and intermediate vision correction area
Determine the power distribution curve for
After determining the surface shape on one side, the other side of the lens
Side surface shape, a frequency corresponding to the frequency distribution curve is obtained.
To be determined by the ray tracing method
Method of manufacturing a multifocal ophthalmic lens.