Progressive Ophthalmic Lens

The present invention relates to eyeglass (ophthalmic) lenses with progressive surfaces. A surface of such a lens has an average surface refraction value ##EQU1## which changes continuously in any direction, where n is index of refraction and R.sub.1 and R.sub.2 are main curvature radii. In known lenses of this type according to French Pat. No. 1,544,799; GDR Pat. No. 71,210; French Pat. No. 2,058,499; German Offenlegungsschrift No. 2,439,127; German Auslegeschrift No. 2,044,639; and Austrian Pat. No. 322,238, progressive surfaces are formed by families of circles or conic sections, which intersect the main meridian at right angles. The main meridian is thus preferably, but not necessarily (ref: French Pat. No. 1,509,090) a plane curve, the curvature of which increases continuously from the far-sight field to the near-sight field and in which both main curvatures are of equal magnitude at each point on the progressive surface. This main meridian thus forms a so-called "umbilical line".

The present invention is related to the fact that the determining image properties of the progressive surface of a lens for the eyeglass wearer are determined by the average surface refraction value ##STR1## and the surface astigmatism ##EQU2## where r.sub.1 and r.sub.2 are main curvature radii, at all points on the progressive surface. All of the image properties taken together, such as sharpness of image and refraction accurateness of correction, and all characteristics by wearing, such as static and dynamic distortion and hibituation depend casually on these two values. The surface is thus clearly determined by giving the surface refraction value along an umbilical line and a family of lines of equal average surface refraction value intersecting the umbilical line.

In a desirable progressive surface, the surface refraction value D (on both sides of the umbilical line of average surface refraction value D) should increase from top to bottom not only along the umbilical line, but also uniformly around the periphery, with approximately the same gradient. According to a statement (theorem) by Minkwitz (Optica Acta, 10, 1963, 223), however, next the umbilical line the surface astigmatism .DELTA.D at a right angle to the umbilical line first increases twice, as the surface refraction value along this umbilical line changes. In addition at a greater distance from the umbilical line, the surface astigmatism is dependent on the course of lines of equal average surface refraction value and vice versa. A desirable progressive surface should now have on both sides along the main meridian either no surface astigmatism or only a slight one (e.g.<0.25 diopters). The far sight field, i.e, the section essentially above the horizontal through the so-called optical far reference point B.sub.F, should have a constant average surface reference value and a small surface astigmatism (e.g..ltoreq.1.0 diopters) which is physiologically not troublesome, and which perhaps disappears far in the periphery. Accordingly, the same is true for the near sight section below the horizontal through the so-called optical near reference point B.sub.N.

The known progressive surfaces only fulfill the above requirements very inadequately, or not at all, since they are given either from a purely mathematical viewpoint of a sufficiently simple geometric law of formation (see, e.g. French Pat. Nos. 2,058,499, 1,544,799, German Offenlegungsschrift No. 2,439,127) or by the manufacturing process (see, e.g. French Pat. No. 1,095,375). The necessarily resulting image properties must be taken into account. If lines D=const. are calculated by this surface, sections with irregular such lines (D=const.) are encountered peripherally in the progression zone. This means, in part, that there is a considerable deviation from the refraction accurateness of the glasses in this visual regions. The eyeglass wearer, for example, finds in the progression zone of glasses (according to German OS No. 2,439,127 and French Pat. No. 2,058,499) regions with a more intense negative optical effect than in the far sight region; thus the glass is under-corrected for close vision and also under-corrected for distance vision in the case of hyperopia while over-corrected in the case of myopia. In addition, in a surface in which the lines of intersection are "evolutive conic sections" perpendicular to the main meridian (French Patent 2,058,499), lines of equal average surface refraction value are curved upward and incorporated far into the far sight field. In this way hyperopia is over-corrected and myopia, under-corrected. This sort of erroneous correction causes an image sharpness which, e.g., can have dangerous consequences when the person is in traffic, if a shortsightedness increased by 1 diopter or more through the wide opened pupil remains uncorrected.

Since the distribution of the surface astigmatism over the surface depends on the course of the lines of equal average surface refraction value and on the increase in curvature of the umbilical line, the known embodiments of progressive surfaces have considerable imperfections.

It is an important object of the invention to create the progressive surface from the physiological-optical standpoint so that the image properties and characteristics by wearing given above are improved.

The eyeglass lens as described above is basically characterized in accordance with the invention in that also in the progression zone the lines of equal average surface refraction value intersect the main meridian and extend on both ends to the periphery of the eyeglass lens. In the construction of progressive surfaces with different near sight sections and different far sight sections, according to the invention, one proceeds by determining suitably selected families of lines of the same average surface refraction value, which are combined with the proper main meridians. In this way the surface itself can be derived and shown by calculation (numerical integration of a partial differential equation of the elliptical type).

The lines of equal average surface refraction value extend from the main meridian on both sides continuously to the edge of the glass. Their course is determined from the physiological-optical standpoint such that refraction accurateness consists in the far sight section above a horizontal through the optical far reference point and in the near sight section below a horizontal through the optical near reference point with respect to the average surface refraction values and at the same time, the surface astigmatism is sufficiently small in the entire progression zone.

The eyeglass lens is preferably characterized by the fact that a finite difference exists between the two main curvatures on at least one portion of the main meridian points, which is greater than 0.01/(n-1)100 cm.sup.-1 and smaller than 0.25/(n-1)100 cm.sup.-1, and preferably smaller than or equal to 0.12/(n-1)100 cm.sup.-1.

The main meridian is thus not given as an exact umbilical line. One can thus displace the basically unavoidable surface astigmatism away from the main meridian which impairs lateral vision in the progression zone. Therefore a considerably widened far sight-near sight field transition region which is important for clear vision, is obtained. If an exact umbilical line were provided as the main meridian, then an expansion of the optically useful transition region would not be possible, since the above-given (scientifically correct and inevitable) statement by Minkwitz would be contradicted.

In another embodiment of the invention, the eyeglass lens is preferably characterized by the fact that the curvature change along the main meridian has its maximum value in or near the center of the progression zone--preferably at a position of about 0.5 times the value of the additional (incremental) diopter values from far to near field. This produces astigmatism values which are properly small in the far sight and near sight sections. Therefore the change in curvature runs on both sides of this maximum value, preferably--at least approximately--symmetrically. In this way the astigmatism will be kept very small in the far sight and near sight regions.

In another embodiment of the invention, the eyeglass lens is preferably characterized in that the change in curvature along the main meridian has its maximum value in or next to the lower edge of the progression zone--preferably at a position lying between the 0.5.times. and the 0.9.times. value of the additional (incremental) diopter values. In this way, the maximum values of the surface astigmatism in the near sight region will be deflected to the lower side regions which are not important for close vision.

Lines of equal surface refraction value proceed preferably substantially horizontally--at least approximately--in the progression zone. In this way the surface refraction values in the side regions are approximately the same as those in the main meridian and thus under-corrections will be avoided in these regions.

In addition, lines of the same average surface refraction value proceed preferably substantially horizontally--at least approximately--in the upper and/or lower sections. In this way the refraction accuracy consists in the upper region with respect to the average surface refraction values and the surface astigmatism in this region becomes increasingly smaller and disappears.

In another embodiment of the invention, the lens is characterized in that lines of equal average surface refraction value proceed, curved downward in the lower region with increasing distance from upper margin of the progression zone so as to deflect outward the surface astigmatism values in the near-sight field which are too high and occur in unsymmetrical main meridians.

Lines of equal average surface refraction value can intersect the main meridian at an angle slightly different from 90.degree., if this latter is not an exact umbilical line, or if it is an exact umbilical line, must not proceed at a distance from it in a right angle to it. It suffices if this angle is 90.degree..+-.10.degree.. In this way it is possible to obtain in both eyes the same image quality in the two different positions looking through the eyeglasses for side vision (e.g. nasal in left eye and temporal in right).

Since the axes of the eye converge in close vision, the main meridian does not necessarily proceed vertically, but can proceed under an angle of .+-.10.degree. to the vertical, whereby it comes together preferably converging down toward the nose (rather than converging upwardly).

Other objects, features and advantages of the invention will be apparent from the following detailed description of preferred embodiments, taken with reference to the enclosed drawing in which,

FIG. 1 is a diagram showing the concept employed;

FIGS. 2-3 are optical correction diagrams showing two possibilities for determining lines of equal average refraction value according to preferred embodiments of the invention and the consequences resulting therefrom;

FIGS. 4 and 5 similarly show two possibilities for determining the surface refraction values along the main meridian according to preferred embodiments of the invention.

FIG. 1 shows a progressive lens diagrammatically and illustrates the terms used herein as follows:

H Main meridian=umbilical point line or quasi-umbilical point line

F Far-sight field

P Progression zone

Near-sight field

B.sub.F Optical far reference point=Site for the prescribed far correction

B.sub.N Optical near reference point=Site for the prescribed near correction

D.sub.F Surface refraction value in the far-sight field

D.sub.N Surface refraction value in the near-sight region

D Average surface refraction value

Add Near addition =D.sub.N -D.sub.F

Using FIG. 1 as background, FIGS. 2-3 show polar diagrams with x and y axes (in mm) of two embodiments of lenses wherein there is superimposed in each case on the lefthand side, lines of equal average surface refraction value (in diopters) and on the right side, lines of equal surface astigmatism (in diopters).

In the design according to FIGS. 1-2, the surface refraction value is 6.5 in the far sight field and 9.5 in the near sight field. The surface refraction value gradually increase in progression zones P. Lines of equal surface refraction value run horizontally. In the right half of FIG. 2, it can be seen that the surface astigmatism practically disappears in the far-sight field and in the upper region of the progression zone, while it still increases to high values in the lower right field. Thus, the maximum values of the surface astigmatism lie in a field which is practically not used in close vision. If lines of equal average surface refraction value were curved downward in the near sight section with increasing distance from the upper margin of the progression zone, these high surface astigmatism values would be considerably smaller.

In the design according to FIGS. 1 and 3, lines of equal average surface refraction value are the same as in FIGS. 1-2 but the increase is different from the far sight region to the near sight region. In the upper and lower sections, the surface astigmatism practically disappears; only the surface astigmatism below the central region increases to values up to 3.

The surface refraction value along the main meridian, which is shown in FIG. 4 (with reference to FIG. 1 too), corresponds to the design according to FIGS. 1-2.

The surface refraction value along the main meridian, which is shown in FIG. 5, corresponds to the design according to FIGS. 1, 3.

In the design according to FIG. 4, the maximum K value for change in curvature is 1.8 diopters (0.6.times.3 diopters) and in FIG. 5, 1.5 diopters (0.5.times.3 diopters).

The preferred embodiment examples explained above give possible, yet not optimal solutions for all cases. However, optimal solutions in any particular case according to the principle which forms the basis of the invention can be determined by those skilled in the art without any fundamental difficulties:

(a) One determines the surface refraction values along the main meridian and lines of equal average surface refraction value from the main meridian to the periphery of the eyeglass lens.

(b) Thus, lines of equal average surface astigmatism can be calculated and checked to see whether they conform to desires.

(c) But one will always find that lines with equal average surface astigmatism are more favorable and the surface astigmatism is lower than it is when lines of equal average surface refraction value are determined, which begin at the periphery of the eyeglass lens and also end there, as presently is the case in all known progressive eyeglass lenses due to their different viewpoint of adequate construction.

It is evident that those skilled in the art, once given the benefit of the foregoing disclosure, may now make numerous other uses and modifications of, and departures from the specific embodiments described herein without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in, or possessed by, the apparatus and techniques herein disclosed and limited solely by the scope and spirit of the appended claims.