DE3821079A1 - Spectacle lens having a variable refractive index - Google Patents

Abstract

A spectacle lens is described which has a variable refractive index and in which the surface which is more strongly curved is selected such that the critical thickness of the spectacle lens does not exceed a predetermined value and the variable refractive index contributes to correcting the aberration (imaging error). The spectacle lens according to the invention is characterised in that the refractive index n is simply a function of the coordinate z running in the direction of the optical axis and in that the change in the refractive index for z >/= 0 serves to correct the aberration, z = 0 being the apex (S2) of the surface (2) on the side of the eyes.

Description

The invention relates to a (single vision) glasses glass with a changing refractive index where the more curved surface is chosen such that the kri table thickness of the lens a predetermined value does not exceed, and the changing refractive index to Correction of aberrations contributes.

Eyeglass lenses with a changing refractive index are have been discussed several times in the literature. This will for example on the overview article "Gradient Index Optics "by W.N. Charman (The Ophthalmic Optician, 1981, Pp. 73-84) as well as the literature given there or on the DE-OS 27 07 601 referenced.

While in this literature essentially the replacement of aspherical surfaces by an "index gradient" or the additional improvement of the imaging properties for glasses with aspherical surfaces by a Index gradient is discussed in DE-OS 36 16 888 was first suggested through use of a changing refractive index the critical thickness, to reduce much more than this alone the use of aspherical surfaces is possible. (The the critical thickness is the center thickness for spectacle lenses with positive effect or the edge thickness of eyeglass lenses with a negative effect.)

In DE-OS 36 16 888 are general to optical Axis of rotationally symmetrical refractive indices in Considered. The in the embodiments of  DE-OS 36 16 888 gradient used in particular radial dependence is comparatively expensive dig, for example by "twisting" and subsequent Heat treatment of a series of concentric cylinders or hollow cylinders with different refractive index, producible.

On the other hand, refractive index variations can be compared simply using an ion exchange bath be put into a glass or plastic block is diving. The ion exchange in the bath leads to Development of a so-called "surface normal" gradient. Refractive index gradients with a radial course can be thus theoretically through "ion exchange" via the cylindrical surface of an "infinite" i.e. very long against glass cylinders, but in practice this is for glasses because of the usually very low Penetration depth of the ion exchange effect only in a few Glass types possible.

The invention has for its object a spectacle lens with a changing refractive index form that a comparatively easy to implement Refractive index gradient can be used.

An inventive solution to this problem is with their Developments characterized in the claims.

According to the invention it has been recognized that a surface normal gradient, i.e. the gradient course, which typically results in ion exchange processes the penetration depths characteristic of these processes only a little influence on the correction of the image error.  

In particular, it is not possible with a spectacle lens its more curved surface regardless of the Correction of aberrations has been chosen - how this is proposed, for example, in DE-OS 36 16 888 has been - the aberrations through a gradient to correct the perpendicular to the eye-side surface and / or the front surface of the spectacle lens.

On the other hand, as has also been recognized according to the invention, an axial gradient, ie a refractive index variation, which only depends on the coordinate z in the direction of the optical axis and which is only provided in the part of the spectacle material which is in the beam Direction "behind" the vertex of the eye-side surface, the correction of the aberrations and the minimization of the critical thickness are very favorably. The following case distinctions result:

• 1. The reduction in the critical thickness takes place in that the more curved surface is bent in a significantly different manner from the Tscherning rule and / or is designed as a rotationally symmetrical aspherical surface (claim 4) with an outwardly "decreasing curvature". For the minus area, the aspherical surface is the back surface (eye-side surface - claim 6), for the plus area, however, the front surface (claim 5).
• The peripheral imaging errors are corrected through the appropriate profiling of the index gradient of the material from one level (on the eye side) through the rear glass crest on the optical axis is vertical.  
• 2. The critical thickness is reduced by a Index gradients "between the tops of the glass". The Gra serves is oriented so that on the glasses glass side, which has the more curved surface, the refractive index has its highest value (claim 3).
• The index variation in the glass material on the eye side going through the rear glass top and to the opti axis perpendicular to the axis in turn serves for the cor rectification of peripheral aberrations. The back surface forms the base curve.
• This solution is preferably available for Plus glasses on.
• 3. Of course it is possible that both the Index variation as well as the design of the stronger ge curved surface and in particular its aspherical Training to reduce the critical thickness and / or to correct peripheral aberrations wear.
• This solution with an as aspherical Surface formed rear surface results in minus glasses much smaller edge thickness and much better Correction than with conventional minus glasses.

An axial gradient can - as in claim 11 bean speaks - easily produce by first one "plane-parallel plate" for example an ion exchange (Claim 12) is subjected, and only after Introduce the refractive index variation to the limit  surfaces of the lens worked out of the block will.

Such an axial gradient has a number of very advantageous properties:

If the two surfaces of a normal spectacle lens like this be chosen to have a small critical thickness results, i.e. the lens under the cosmetic face points are appealing, in general the illustrations are properties of the lens are not acceptable. So exceed already with little effect (refractive index) of the Eyeglass lenses of refractive errors and astigmatism even with comparatively small viewing angles of approx. 25 ° values of 1 dpt.

For the correction of such a spectacle lens resulting aberrations (refractive errors and branching matism) of typically up to several diopters only refractive index variations are required for which the refractive index over a range of a few mm Varies by 0.1 to 0.3 units, for example at a minus glass increases from 1.5 to 1.7. It is particularly preferred if the area over which the bre index varies approximately equal to the apex depth of the eye-side surface is (claim 6). Of course it is also possible that the refractive index over a smaller area (in the direction of the optical axis) as the apex depth changes so that the "correction we kung "only at a certain distance from the optical Axis "starts" or at a certain distance " hears "so that the refractive index is constant from this distance is.  

These ranges of variation are on the order of a few Millimeters typically result from Io exchange procedure.

Surprisingly, it has been found that if the error to be corrected (astigmatism and / or re fraction error) with a lens with the same area design and constant refractive index (refractive index) positive values are too large, the refractive index behind the rear vertex must increase. Conversely, the Refractive index decrease when astigmatism and / or the refractive error in a glass with the same areas design and homogeneous material too large negative values has (claim 2). This teaching according to the invention applies independently depending on whether the glasses are glasses lenglas with a minus or plus effect.

By varying the refractive index " the vertex on the face "almost any Correction conditions are met. For example it is possible to have a great view of astigmatism to keep the angular range practically at zero. Furthermore, it is also possible, one from a physiological point of view optimal ratio between the size of astigmatism and the refractive error. For example there is a high visual acuity if the absolute values of this assume the ratio 1: 2 of both sizes.

Since the calculation of the variation in the refractive index at predefined surface course or the selection of an eye side surface at one by the manufacturing process given course of the index change one on the one relevant area through the above Teaching is readily possible, is meant to be accurate  Description at this point.

In any case, it is particularly advantageous that the commonly used "concave" surfaces on the eye side the thickness of the layer in which the refractive index changes, increases towards the edge; this means that the effects achieved by varying the refractive index increase towards the edge, on the other hand also the fig error caused by the refractive index gradient to be rigged, larger towards the edge, so that a "same course" of the effect of the refraction index gradients and the quantities to be corrected!

Even more surprising is another characteristic of the he axial gradients selected according to the invention:

From an economic point of view, it is not ver pedal, a separate pair of glasses for each special effect to have to manufacture lenglas at which the refractive index with a specially tailored for this effect Profile "varies.

Rather, it is necessary for economical production Lich, a certain area of activity with a so-called basic cure to cover ven. This means that initially semi-finished Eyeglass lenses (blanks) are made where single Lich an area, usually the more complex to produce surface, for example an aspherical surface, is finished. To a certain scope to be completely covered by typically a few diopters ken, then the second area is according to the ordinance made effect.

For spherical surfaces, typically 6 to 8  Base curves needed to cover the area of effect of +8 D. to cover up to -8 dpt.

The proposed axial variation of the Refractive index now has such a basis kurven-Systems has a number of unexpected advantages:

By the correction of the imaging error according to the invention ler in the part of the glass material "behind" the eye side The refractive index, which varies according to the surface vertex, depends on Correction of the glasses practically not from the to Achievement of a certain recipe value selected front Area from. This means that with a variation of the Front surface, as is typically required to in the desired gradation, the different recipe values to be able to manufacture the aberrations of the lens with a given eye area and a fixed index pro keep fil below a certain limit in any case to let.

Even more surprising is the fact that too a given course of the axial gradient one "plane parallel plate" always a series of surfaces and especially of aspherical surfaces for a base curve System can be found for both the requirement for less critical thickness as well as the requirement for a good correction of the aberrations can be fulfilled.

This has the consequence that to manufacture neighboring base curve the same "plane-parallel plates", i.e. in a and the same ion exchange bath under the same conditions material blocks can be used nen.  

The course of the Refractive index a rational manufacture of glasses over a large area of effectiveness.

The invention is illustrated below with reference to embodiments play described with reference to the drawing ben, in which show:

FIG. 1a is a cross section through a lens having positive effect

FIG. 1b schematically the associated index profile of the refraction,

Fig. 2a shows a cross section through a lens with minus effect,

Fig. 2b schematically the associated index profile of the refraction,

Fig. 3 shows the aberrations of a conventional spectacle lens with a positive effect in which the refractive index does not vary,

FIG. 4a shows the aberrations of a spectacle lens with the same effect and the same Flächengestal processing as in the glass of FIG. 3, in which the refractive index is varied in accordance with the invention,

FIG. 4b shows the associated profile of the refractive index,

Fig. 5 shows the aberrations of a spectacle lens with kon stantem refractive index and with a from the viewpoint of minimizing the selected center thickness of the front surface,

FIG. 6a, the aberrations of a spectacle lens with the same surface configuration as shown in Fig. Spectacle lens shown in Figure 5, but in which vari iiert the refractive index in the inventive manner,

Fig. 6b shows the associated profile of the refractive index,

Fig. 7a shows the aberrations of a spectacle lens in which the refractive index variation serves both to the Cor rection of aberrations as well tion to Reduzie the critical thickness,

FIG. 7b, the corresponding index of refraction,

Fig. 8 shows the aberrations of a conventional lens with a negative effect in which the refractive index does not vary,

Fig. 9 shows the aberrations of a spectacle lens with kon stantem refractive index and with a from the viewpoint of minimizing the edge thickness selected aspherical eye-side surface,

FIG. 10a aberrations but vari iiert a spectacle lens with the same surface configuration as shown in Fig. Spectacle lens illustrated 9, in which the refractive index in the inventive manner, and

Fig. 10b the corresponding profile of the refractive index.

Fig. 1a shows a cross section of an ophthalmic lens with positive effect. The coordinate system x , y , z used in the following is entered: The z axis of the coordinate system lies in the optical axis of the spectacle lens, the x axis, not shown, is perpendicular to the plane of the drawing. The zero point 0 of the coordinate system lies at the apex S _{2 of} the surface 2 on the eye side.

The distance of the apex S _{1 of} the front surface 1 from the surface S _{2 of} the eye-side surface (rear surface) 2 is the so-called center thickness d _m , which is the critical thickness for glasses with a positive effect.

The edge thickness d _r and the so-called apex depth d _{s are also} shown in FIG. 1a.

Fig. 1b shows schematically the associated fictional index n according to the invention. The refractive index is a function of the coordinate e.g. If the variation of the refractive index is only intended to correct peripheral aberrations, then the refractive index n between the vertices S ₁ and S _{2 of} the glass, ie constant for z <0, has the value n _o . According to the invention, the refractive index then varies only in the material (in the beam direction) behind the x / y plane lying through the glass apex S _{2 on} the eye side; in the schematic example, the refractive index n for values of z 0 decreases from the value n ₀ to the value n (d _s ). This is indicated by a corresponding hatching.

Fig. 2a shows a cross section of an ophthalmic lens with a negative effect. The same sizes as in Fig. 1a are provided with the same reference numerals, so that a detailed description can be omitted.

Unlike glasses with positive effect is the case of glasses with minus effect is not the center thickness d _m, but the edge thickness d _r, the critical thickness.

FIG. 2b shows schematically the associated erfindungsge MAESSEN course of the refractive index n. The refractive index is in turn only a function of the coordinate z . If the correction of peripheral aberrations is to take place by varying the refractive index, the refractive index n between the vertices S ₁ and S _{2 of} the glass, ie constant for z <0, has the value n ₀ . According to the invention, the refractive index then only varies in the (behind) the x / y plane lying behind the glass apex S ₂ going in the beam direction; in Fig. 2b, the refractive index n takes on values of z 0 of the value of n ₀ to the value n (d _s) to. This is indicated by a corresponding hatching.

In the following, various numerical examples for spectacle lenses according to the invention will be explained and compared with spectacle glasses with a constant refractive index. In this case, 3 to 7 glasses having a positive effect and in FIGS. 8 to 10 glasses are shown with a negative effect in FIGS..

In all of the figures and sub-figures a discussed below, the astigmatism with solid lines and the so-called refractive error, ie the deviation of the mean refractive index at one point from the so-called recipe value, are plotted with broken lines as a function of the viewing angle σ . The astigmatism Δ S and the refractive error Δ R are defined by:

Δ S = T - S
Δ R = (T + S) / 2 - S ′ ₀;

here are:

T tangential refractive index,
S sagittal refractive index,
S ′ ₀ the recipe value.

In the sub-figures b, the refractive index (refractive index) n is plotted as a function of the coordinate z defined in FIGS. 1 and 2.

All glasses with a positive effect have the same overall effect S ′ = 8.00 D, the same curvature C ₂ = 1 / R ₂ = 5.71 D of the (spherical) surface 2 on the eye ( R : radius of curvature in the vertex of the surface) and the same diameter d of 66 mm. In the examples shown in FIGS . 3, 4 and 7, the front surface 1 is a spherical surface, in the case of the case shown in FIGS . 5 and 6, on the other hand, an aspherical surface. The aspherical rotationally symmetrical surface is a conical section surface without restricting the general inventive concept.

The arrow height Δ z of a point (= distance of this point from the surface vertex S ₁ in the direction of the optical axis z ) is then given by:

Δ z = Cr ² / (1 + (1 - ( K + 1) C ² r ²) ⁻ ^1/2 )

With

r : distance of the point from the optical axis z ,
C = 1 / R with R : radius of curvature of the surface in the apex S ₁,
K : Conic section coefficient.

The following Table 1 are for the different Examples of the individual sizes given numerically:  

Table 1

Fig. 3 shows the aberrations in dpt. a conventional spectacle lens with an effect S 'of 8 dpt. With such a spectacle lens, the deflection of the front surface 1 and the rear surface 2 is a compromise between the deflection which is optimal from the point of view of the imaging quality and the "flatter" surface deflection desired from the cosmetic point of view. Both astigmatism as it takes Fig. 3 and the Refrak tion error positive. A positive refractive error is actually not desirable since it cannot be compensated for by accommodation.

FIG. 4a shows the course of the astigmatism and the refraction error as a function of the viewing angle for a spectacle lens with the same surface design as for the spectacle lens according to FIG. 3. In the spectacle lens shown in FIG. 4a, however, the refractive index n varies as a function of z in the way shown in Fig. 4b. The refractive index is constant "between" the surface vertices S ₁ and S ₂ and has the value 1.525 and increases "towards" the x / y plane in the manner shown in FIG. 4b to correct the image errors. The increase is a result of the fact that the image error (astigmatism) to be corrected primarily has positive values that are too large over the viewing angle range.

In the selection of the refractive index variation, no value was deliberately placed on reducing the critical thickness, that is to say the center thickness in the case of plus glasses, but rather a more extensive correction of the aberrations was aimed at. As you can see, the astigmatism can be practically reduced to 0 D up to a value of the viewing angle σ of 40 °. hold. The refractive error takes on the comparatively low value of approx. -0.7 D to larger viewing angles. The negative refraction error can - at least in the case of non-full presbyopens - be compensated for by accommodating. It is particularly advantageous that - although only one variable is available for correcting two image errors - there is a physiologically favorable course of the image error (refraction error) which is not primarily corrected.

FIG. 5 shows the course of the aberrations for an eyeglass lens in which the front surface is designed aspherical. The front surface is a conic section, the characteristic sizes of which are given in Table 1. The course of the aspherical surface design is selected only from the point of view of reducing the central thickness d _m , but not from the point of view of correction. As can easily be seen in FIG. 5, with a "constant refractive index", unacceptable image errors arise even at a comparatively low viewing angle σ of 30 °: the refractive error (dashed line) and the astigmatism (solid line) are each greater than approx. 3.0 dpt.

FIG. 6a shows the course of the image defects for a spectacle lens with the same surface design as for the spectacle lens shown in FIG. 5, but the refractive index varies in the manner shown in FIG. 6b. The decrease in the refractive index is a consequence of the fact that the image errors to be corrected (refractive errors and astigmatism) have negative values that are much too large.

As can be seen, by varying the refractive index, both image errors can be corrected so that the astigmatism practically 0 D over the entire viewing angle range. is, while the refractive error even at a viewing angle σ of 40 ° is less than -1.0 dpt. is. It should again be noted that negative values of the refraction error can easily be compensated for by accommodating.

Fig. 7a shows the course of the image defects for a spectacle lens, the boundary surfaces of which are spherical surfaces. To reduce the center thickness d _m , both by bending the surfaces "more deviating" from Tscher ning's rule than in the glasses lenglass shown in Fig. 3, as well as additionally a variation of the refractive index "between the glass tops S ₁ and S ₂ "introduced. The refractive index varies - as shown in Fig. 7b - not only "behind the surface on the eye side", but also in such a way that it unites in the area of the surface which contributes more to the refractive index, ie in the area of the front surface of a glass with a plus effect greater value than in the base material.

With a total effect of the lens of 8.0 dpt. and an initial refractive index of 1.525, the center thickness can be reduced by 25% compared to conventional spectacle lenses according to FIG. 3. Nevertheless, it is possible to adhere to certain correction conditions; In the embodiment shown, the correction condition used was that the astigmatism is practically zero over the entire viewing angle range.

Below are glasses with a minus effect as further Exemplary embodiments are explained.

All glasses with a minus effect have the same overall effect S ′ = -10.00 D, the same curvature C ₁ = 1 / R ₁ = 3.81 D of the (spherical) front surface 1 and the same diameter d of 66 mm. In the example shown in FIG. 8, the rear surface 1 is a spherical surface, whereas in the examples shown in FIGS. 9 and 10 it is an aspherical surface. The aspherical rotationally symmetrical surface is, without limitation of the general inventions, a conic section surface, the arrow height Δ z of which is given by the cone equation given above. The conical internal forces C = 1 / R ₂ and K naturally relate to the surface 2 on the eye side; R ₂ is the radius of curvature of the back surface in the apex S ₂ .

The following table 2 are for the different Examples of the individual sizes given numerically:  

Table 2

Fig. 8 shows a conventional spectacle lens with a constant refractive index, in which the deflection of the front surface 1 and the eye-side surface 2 is chosen as a compromise between the deflection which is optimal from the point of view of the aberrations and that which is desired from a cosmetic point of view. As you can see, the image defects are comparatively small, but the edge thickness d _R is very large at 13.95 mm, so that the glass can hardly be cut into fashionable eyeglass frames and is also very heavy.

FIG. 9 shows an example of a glass with a minus effect, in which the eye-side surface 2 is designed as an aspherical surface in order to reduce the edge thickness. The surface 2 on the outside is, without restriction of the generality, a conical section surface, the characteristic sizes of which are given in Table 2. By using this aspherical surface, the edge thickness d _{r can be} considerably reduced to 6.98 mm, but the image errors, the refraction errors and the astigmatism reach unacceptable values of 2.5 dpt and larger even at image angles of less than 20 ° .

FIG. 10a shows the effect of refractive index variation "behind the eye-side apex of the surface S _2" on the aberrations. The surface design of the glass and thus also the center and edge thickness correspond to the glass shown in FIG. 9. In particular, the individual size of the conical section of Table 2 can be found.

By varying the refractive index, the imaging errors shown in FIG. 9, caused by the surface design, can be corrected to very small values. In particular, the correction condition "astigmatism over the viewing angle range practically = 0" is again met in the exemplary embodiment shown in FIG. 10 been.

Since both the refractive error and the astigmatism have assumed positive values in the "homogeneous case", an increase in the refractive index behind the eye-side surface vertex ( z = 0) is necessary, as shown in FIG. 10b. Above, the invention has been described with reference to examples of execution without limiting the general inventions.

In particular, the general inventive idea set out in claim 1 can be applied to glasses made of any materials and with any surface design. It is not necessary for the "output" refractive index to be 1.525. Depending on the starting material, the refractive index can of course be lower - for example 1.5 for plastic materials - or higher and, for example, have values of 1.6 or 1.7 (typical values of high-index glasses). It is also not required that a conical surface is used as the aspherical surface. Of course, more complicated aspherical surfaces can also be used, which in particular already contribute to the correction of the image errors by the surface design. Furthermore, both surfaces can also be designed as aspherical surfaces and / or the front surface can have a cylindrical effect.

Furthermore, it is of course not necessary that always the correction condition "astigmatism over the Viewing angle range approximated = 0 "is observed other Cor rectification conditions, for example the condition "Absolute value of the refractive error / absolute value of astigmatism 2: 1 "are observed.

In any case, however, the teaching of the invention applies that the refractive index must increase if the one to be corrected Error has positive values that are too large, or has to decrease, if the error to be corrected (astigmatism or re fraction error) has "too large" negative values.

Claims (12)

1. spectacle lens with a changing refractive index, in which the more curved surface is selected such that the critical thickness of the spectacle lens does not exceed a predetermined value, and the changing refractive index contributes to the correction of the aberrations, characterized by the following features:

• the refractive index n is only a function of the coordinate z extending in the direction of the optical axis,
• - The correction of the aberration serves to change the refractive index for z 0, where z = 0 is the vertex ( S ₂ ) of the eye-side surface ( 2 ).

2. Spectacle lens according to claim 1, characterized in that to correct the astigmatism and / or the refractive error, the refractive index for z 0 increases when the astigmatism or refractive error values are positive with the same area design and constant refractive index, and decreases when the Astigmatism or refractive error values are negative. 3. Spectacle lens according to claim 1 or 2, characterized in that to reduce the critical thickness of the spectacle lens, the refractive index between the apex S ₁ ( z = - d _m ) of the front surface and the apex S ₂ ( z = 0) changes the surface on the eye side such that it has its greatest value on the side of the more curved surface. 4. spectacle lens according to one of claims 1 to 3, characterized in that at least one surface a is aspherical surface. 5. spectacle lens with plus effect according to claim 4, characterized in that the aspherical surface Front surface is. 6. spectacle lens with minus effect according to claim 4, characterized in that the aspherical surface surface on the eye side. 7. spectacle lens according to one of claims 1 to 6, characterized in that the refractive index to Correction of aberrations over an area changes which is approximately equal to the apex depth of the eye side Area is.   8. spectacle lens according to claim 7, characterized in that the refractive index in this range for glasses with a positive effect of around 0.1-0.2 Units and for glasses with a minus effect of around 0.2-0.5 Units changes. 9. Spectacle lens series, in which a surface for covering a certain effective range is available in a certain number of so-called basic curves with a graded refractive index, and the second surface is selected in order to achieve the so-called prescription effect in a certain refractive index range, after one of claims 1 to 8, characterized in that the refractive index function n (z) is independent of the refractive index of the second surface over a certain effective range. 10. Spectacle lens series according to claim 9, characterized in that the refractive index function n (z) is the same for at least some of the base curves. 11. Process for the manufacture of spectacle lenses one of claims 1 to 10, characterized in that initially a plane parallel Plate is made that perpendicular to at least one of the two boundary surface of the plate a variation of the refractive index is produced, and then the curved limbs tion surfaces of the lens can be produced. 12. The method according to claim 11, characterized in that the variation of the refractive index dex by immersing the plane-parallel plate in one Ion exchange bath is generated.