JPH0239769B2 - RUISHINTASHOTENRENZU - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a progressive multifocal lens having a prescription for myopia correction in the distance region.

An object of the present invention is to improve chromatic aberration in the near vision region of a progressive multifocal lens. Another objective is to make the lens thinner and lighter.

Nowadays, glasses have become an indispensable part of our daily life. Even if you don't need it now,
Eventually, when you get older, you will develop presbyopia and will need reading glasses. In this way, eyeglasses have a deep connection to our lives, and the first requirement for the lenses of these glasses is that they provide good visibility when worn, and they also need to be thin, light, and fashionable. Examples include being rich in things, being hard to get hurt, etc. From this point of view, various lens materials have been developed and are now on the market as products. However, there is currently no product that satisfies all of the above conditions. This is because in order to satisfy the condition of thinness, the material must have a high refractive index, but materials with a high refractive index generally have a small Atbe's number, making it difficult for the lens to be made. This is due to so-called chromatic aberration, which causes the outline of an object to appear blurred and colored when viewed from the periphery. This chromatic aberration is not a very important problem in single-focal lenses that correct general nearsightedness or farsightedness.
This is because when we normally wear glasses, we hardly use the peripheral parts of the lenses, but instead use the parts near the center. However, in the case of progressive multifocal lenses, chromatic aberration becomes an important problem. This is because a progressive multifocal lens has an area for seeing far away (distance area), an area for seeing up close (near area), and an area for seeing intermediate distances (intermediate area). This is because the near vision area is located 15 to 25 mm below the center of the lens, and chromatic aberration appears significantly in that area. For this reason, materials with high refractive index have rarely been used in progressive multifocal lenses. The present invention improves the chromatic aberration in the near vision area of such progressive multifocal lenses, which makes it possible to use materials with high refractive index that could not be used in the past, making it possible to create thinner and lighter lenses. .

The present invention will be explained in detail below.

FIG. 1 shows a vertical cross-sectional shape of a conventional progressive multifocal lens having a myopia correcting prescription in the distance region. Triangles in the figure indicate prisms at each position, the size indicates the amount of prism, and the direction indicates the base direction. FIG. 2 shows the prism in more detail. The vertical axis of the figure is the position on the vertical cross section of the lens, O is the fitting point (position in front of the eye), and A and B are the upper and lower ends of the lens used as eyeglasses, respectively. Symbols are the same as in Figure 1. The part from O to upper A is in the distance region, the part to lower C is in the intermediate region, and then C
The lower part B is within the near vision region. The horizontal axis indicates a prism, and the right direction of the vertical axis indicates the prism amount Pup with a base direction of 90°, and the left direction indicates the prism amount Pdn with a base direction of 270°. In the case of a single focus lens, the amount of prism P at each position on the lens can be approximately determined by the following equation (1).

P=PW×h...(1) Here, PW is the power of the lens (in diopters), and h is the distance (in cm) from the optical center (normally, the optical center almost coincides with the fitting point). be. In the case of a progressive multifocal lens, as shown in the figure, the entire distance region is approximately the lens prescription power PW, so the prism can be approximated by equation (1), but in the intermediate region In the near vision region, the power gradually increases from intermediate region O to C, and in the near vision region, the power increases by the addition power (ADD) and becomes almost constant (PW + ADD), so the prism
The distribution gradually approaches the straight line of (PW + ADD) × h from the straight line of PW × h.

Now, the magnitude I of the chromatic aberration of a lens can be expressed by the Abbe number ν of the lens material and the prism amount P, as shown in equation (2).

I=P/ν...(2) It is known that chromatic aberration is generally perceived when I=P/ν>0.2...(3). Conversely, the condition for a lens to be used as a spectacle lens without the influence of chromatic aberration is that the chromatic aberration in the range of use of the lens as a spectacle lens satisfies the relationship I=P/ν<0.2...(4) be.

In a progressive multifocal lens, the maximum amount of prism is the prism Pa at the upper end A of the lens in the distance region, and the prism Pb at the lower end B of the lens in the near vision region. As can be seen, the lower end B is nearly twice as far from the optical center as the upper end A, so there is a relationship of Pb>Pa. Therefore, in materials with a small Abbe number, chromatic aberration first occurs in the near vision area. In other words, if the limit amount of prism at which chromatic aberration is perceived is Pg, then Pg is calculated as Pg=0.2×ν...(5), and when ν is small to some extent as in the case of high refractive index materials, as shown in Figure 2. D in the near vision area
During B, the amount of prism exceeds the limit value Pg (in the far vision region, it is below Pg), and chromatic aberration is perceived between D and B in the near vision region.

Next, examples of the present invention will be shown. FIG. 3 is a vertical cross-section of a progressive multifocal lens with a myopia correcting prescription according to the present invention. The representation method in the figure is the same as that in FIG. 1, but for comparison, the conventional example shown in FIG. 1 is shown by broken lines. A feature of the present invention is that, as shown in the figure, the prism prescription is 90° in the base direction, and this prism prescription is not intended for strabismus correction, but is applied equally to the left and right lenses of eyeglasses. FIG. 4 shows the prism in this embodiment in more detail, and the method of representation is the same as that in FIG. 2. The broken line in the figure is that of the conventional example shown in FIG. 2, which is included for comparison. As shown in the figure, by inserting a prism Pt with a 90° angle toward the base, the number of prisms increases by that amount in the distance vision region, and decreases by that amount in the near vision region. This increase or decrease in the prism directly means an increase or decrease in chromatic aberration, so chromatic aberration increases in the distance vision area and decreases in the near vision area. In this example, Pt is determined so that the prism amount Pb at the lower end B of use in the near vision area is equal to the prism amount Pg at the limit where chromatic aberration is perceived. Chromatic aberration is not perceived and a good field of view is obtained. What should be noted at this time is chromatic aberration in the distance region. As mentioned earlier, in the distance vision region, the addition of a prism with a base in the 90° direction increases the number of prisms, resulting in worsening of chromatic aberration, but as can be seen from Figure 4, the distance vision region normally Distance to top of use
Since OA is not very long (10-15mm),
The prism Pa at the upper end A almost never exceeds the limit value Pg due to an increase in prisms. Therefore, no chromatic aberration is perceived even in the far vision region, and a good visual field can be obtained.

As explained above, the purpose of the present invention is to improve chromatic aberration in the near vision region by applying a prism oriented at 90 degrees in the base direction, and the amount of prism to be applied is determined as follows.

The size of the prism at the lower end B of the near vision area is Pb
is approximately given by the following equation.

Pb=-(PW×ADD)×Here, the distance between O and B (cm).If we add a prism Pt with a base direction of 90 degrees to this, the prism at point B becomes Pb-Pt, which is because there is no chromatic aberration. Substituting into conditional expression (4) and transforming it, Pt>Pb−0.2×ν=−(PW+ADD)×−
0.2×ν When further transformed, Pt＞−K×(PW+ADD)−0.2×ν ……(5) Here, K==1.5~2.5 The coefficient K represents the distance, and it depends on the design of the lens and the user's lens. The range of use is as shown above, depending on individual differences.

If Pt determined by equation (5) is too large and causes visual impairment or large chromatic aberration in the distance region, set Pt smaller than that of equation (5) and adjust the lens. A lens with good chromatic aberration can be obtained by coloring the lens in yellow, brown, or blue. This is because what humans perceive as chromatic aberration is a blur of yellow and blue that appears on the outline of objects...and this chromatic aberration, which cannot be erased by adding a prism Pt, can be removed by using a yellow, brown, or blue lens. This is because the coloring makes it difficult to perceive.

In addition to the above-mentioned effects on the chromatic aberration surface, the present invention has the effect of making the lens thinner and lighter. As is clear from the comparison of the cross sections of the conventional lens and the lens according to the present invention in FIG. 3, the addition of the 90° prism in the base direction makes the lens thicker on the distance vision side.
The lens becomes thinner on the near vision side. Therefore, as a lens, the increase in the distance vision region and the decrease in the near vision region cancel each other out, so there is no effect of thinning and weight reduction. However, when placed in a spectacle frame, the area ratio of the distance region, intermediate region, and near vision region is approximately 1:2, so when used as eyeglasses, the lens is thin and light as a whole.

As described above, according to the present invention, in a progressive multifocal lens, especially a progressive multifocal lens using a high refractive index material with a small Atbe's number, chromatic aberration in the near vision region is improved, and the thickness is reduced. Weight reduction can be achieved.

Note that the effects of the present invention can be obtained even if the base direction of the prism is slightly deviated from 90 degrees, and this does not go beyond the scope of the present invention.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a progressive multifocal lens having a conventional myopia correction prescription. FIG. 2 is a diagram showing the prism distribution of the lens in FIG. 1. FIG. 3 is a cross-sectional view of a progressive multifocal lens having a myopia correcting prescription according to the present invention. FIG. 4 is a diagram showing the prism distribution of the lens in FIG. 3. Explanation of symbols, O...Fitting point,
A... Upper end position of the lens, B... Lower end position of the lens, C... Boundary between intermediate region and near vision region, Pup... Prism at 90° in the basal direction, Pdn... 270° in the basal direction Prism, Pg...The limit amount of prism that causes chromatic aberration.

Claims (1)

[Scope of Claims] 1. A progressive multifocal lens having a prescription for myopia correction in the distance region, characterized in that a prism of 90 degrees in the basal direction, which is not intended for strabismus correction, is added to the prescription. focal lens. 2 Preferably, the size Pt of the prism is such that, where ν is the Atsube number of the lens material, PW is the myopia correction prescription for the distance region, and ADD is the addition power, Pt>−K×(PW+ADD)− The progressive multifocal lens according to claim 1, which satisfies the following relationship: 0.2×ν 1.5≦K≦2.5. 3. Claims 1 or 2 characterized by being colored yellow, brown, or blue.
The progressive multifocal lens described in section.