EP1171794A1

EP1171794A1 - Non-correcting eyepiece with prismatic compensation and spectacles equipped with same

Info

Publication number: EP1171794A1
Application number: EP01907880A
Authority: EP
Inventors: Etienne Billard; Alain Ravier
Original assignee: Christian Dalloz Sunoptics
Current assignee: Dalloz Creations SAS
Priority date: 2000-02-22
Filing date: 2001-02-22
Publication date: 2002-01-16
Also published as: FR2805353A1; AU3574801A; FR2805353B1; WO2001063343A1

Abstract

The invention concerns a lens mounted in a frame comprising two bows and consisting of two spherical diopters (6, 8) and an optical centre. When worn in normal position, wherein a horizontal line links the centre of the eye pupil and an ear zone whereon the frame bow rests, the optical axis defined by the straight line passing through the two centres of the spherical diopters forms an angle of at least 10 DEG with a horizontal axis. The invention is characterised in that the optical axis (10), in mounted and borne position, is inclined downwards relative to a horizontal axis (14) corresponding to a straight line passing through the pupil of the eye (12) of the person wearing the spectacles and the ear zone whereon the corresponding bow of the frame is supported.

Description

NON-CORRECTING EYEPIECE WITH PRISM COMPENSATION AND EYEGLASS EQUIPPED WITH SUCH EYEPIECE

The present invention relates to a non-corrective spectacle lens and to a pair of spectacles equipped with such a lens. A non-corrective spectacle lens generally has an outer diopter and an inner diopter which are both a portion of a sphere. These two spheres have different radii and separate centers. Gullstrand's law makes it possible to calculate the power of such a lens as a function of the radii of the spheres, of the position of the centers of these spheres as well as of the index of the material used to make the spectacle lens. For a non-corrective lens, a zero power is chosen and a relationship is thus obtained between the radii of curvature of the diopters, the position of the centers of the spheres corresponding to these diopters as well as the index of the material used. Current technological means make it possible to perfectly control the power of an eyepiece and to produce products with tolerances, from a power point of view, of the order of

1/100 diopter.

A permanent concern in the production of non-corrective lenses is to limit prism faults as much as possible. These defects are greater when the spectacle lens has a significant curvature. The present invention relates to such glasses. For glasses whose radius of curvature of the outer diopter is at most equal to about 90 mm, the problems of prism defect are more important and the invention therefore relates more particularly, but not exclusively, to these glasses.

Document US-1,741,536 describes the need for eccentricity of the optical center relative to the visual center of a mounted eyepiece in order to avoid prism defects. The basic idea is that the optical axis of the lens must always be parallel to the main viewing axis. This American patent describes more particularly the application of this principle to glasses having a large face angle and requiring eccentricity on the horizontal plane.

US Pat. Nos. 5,648,832 and US Pat. We can define the pantoscopic angle as the angle formed by a vertical plane and a plane on which the edge of the spectacle lens would rest, the spectacle lens being in position on a user. These two patents teach to realize an upward offset of the glass. The use of the vertical eccentricity upwards of the optical center of a lens makes it possible to optimize, even to cancel, the defect of prism in the visual center. The vertical offset or positioning of the optical center towards the top of the lens aims to best meet the various international standards which consider only the main line of vision as the measurement axis to assess the quality of a telescope fitted with non-corrective lenses . Document WO99 / 52480 describes a lens whose optical axis is inclined upward relative to the main axis of vision. This upward inclination also makes it possible to cancel the defect in the prism in the visual center. However, this optimization creates a significant prism defect at the bottom of the glass. Thus, if the wearer of such glasses observes for example his feet by lowering his gaze and not the head, the prism presented by the glass in his lower zone gives him the impression that the ground is hiding under his feet. This phenomenon is all the more marked as the curvature of the glass is more pronounced. The object of the present invention is therefore to correct this defect and to provide a spectacle lens which makes it possible to reduce the prismatic deviation observed at the bottom of the glass without this prismatic deviation becoming significant at another place in the glass.

To this end, it offers a non-corrective spectacle lens intended to be mounted in a frame comprising two branches and composed of two spherical dioptres as well as an optical center.

According to the invention, in the normal wearing position, in which a horizontal line connects the center of the pupil of the eye and an area of the ear on which a branch of the frame rests, the optical axis defined by the straight line passing through the two centers of the spherical diopters makes an angle of at least 10 ° with a horizontal axis. In addition, according to the invention, the optical axis of the lens, in the mounted and carried position, is preferably inclined downward relative to a horizontal axis corresponding to a straight line passing through the pupil of the eye of the wearer of glasses and the area of the ear on which the corresponding branch of the frame rests. This goes against the teachings of the aforementioned patents in which the axis optic is chosen substantially parallel to the horizontal axis defined above, or inclined upwards as in document WO99 / 52480.

Such a spectacle lens then has a slight prism value along the main line of vision. This low value remains within the tolerances accepted by the standards to which reference is made throughout the profession and does not cause any discomfort to the wearer of the glasses. On the other hand, the prismatic deviation inflicted by the glass on a light ray passing through it in its low peripheral zone is reduced: the wearer of glasses who looks down, for example to look at his feet, does not have the feeling that the ground hides beneath him.

This result is particularly true for a glass which has a strong curvature corresponding to a radius of curvature at most equal to about 90 mm.

To perfect this result, the glass according to the invention advantageously has a negative power of between -0.1 12 and -0.04 diopters. This power of the glass is preferably between -0.06 and -0.04 diopters. This low power is not perceptible for the wearer of glasses but already makes a good contribution to the reduction of the prismatic defect in the bottom of the glass. The thickness of the glass at the optical center is preferably between 1 and 3 mm to have thin glasses.

The invention also relates to glasses comprising a frame with two arms and two lenses according to the invention.

In any case, the invention will be better understood with the aid of the description which follows, with reference to the appended diagrammatic drawing representing by way of nonlimiting example an embodiment of a spectacle lens according to the invention.

Figure 1 shows a pair of perspective glasses. Figure 2 is a sectional view along the line II-II in Figure 1. Figure 3 shows in front view a circular blank for making a glass according to the invention.

FIG. 4 shows a non-circular blank for making a glass according to the invention, and

Figure 5 shows a head on which glasses according to the invention are positioned. FIG. 1 represents a pair of glasses comprising a frame 2 and two lenses 4 produced in accordance with the invention. These lenses are non-corrective lenses and it is for example a pair of sunglasses. Of course, the shape of the frame and the lenses is given solely by way of illustrative example and cannot limit the scope of the patent application.

Each glass 4 has a concave inner face 6 and a convex outer face 8. The inner and outer faces each have a spherical shape. The outer face 8 corresponds to a sphere of center C 1 and of radius R 1 while the inner face 6 corresponds to a sphere of radius R2 and of center C2. The centers C1 and C2 are offset and define a straight line 1 0 conventionally called the optical axis. At the intersection of the optical axis 10 with the glass 4, the latter has a maximum thickness e. This thickness will gradually decrease as we approach the edge of the glass.

The radius R1 is chosen according to the shape that one wishes to give to the glass 4. For a basic glass 6, this radius will for example be

88 mm. The radius R2 and the distance separating the center C 1 from the center C2 are determined by Gullstrand's law. In the present case, these values will for example be chosen to obtain a power of -0.05 diopters.

2 shows a glass 4 in position in front of an eye 12 of a wearer of the glasses. This figure represents a horizontal axis 14 which corresponds to the vision axis when the eye looks endlessly, the head of the wearer of the glasses being straight. The horizontal axis is for example defined by a straight line which would pass through the pupil of the eye and through the area of the ear on which a branch 1 6 of the frame 2 would rest. FIG. 2 shows an angle α between l optical axis and the horizontal plane.

It is necessary to use a repository here.

A reference system may be the one used in certain standards. For example the ANSI Z87 standard. 1 -1 989 retains the head ALDERSON

"5C ^h percentile" as a reference for the position when wearing a telescope. European standard EN 1 68 also refers to a standard head

"5σ ^h percentile" developed by "UK HEAL TH and SAFETY EXECUTIVE".

As a first approximation, we assume that for these heads, a horizontal line connects the center of the pupil of the eye, and the area of the ear on which the branch 1 6 of the telescope rests. This line is commonly called "main line of vision". It is generally described in these standards that it is along this axis that the optical measurements are carried out. FIG. 5 shows the frame 2 in the wearing position as defined by the above-mentioned ANSI standard. To determine the angle α mentioned above, for example, we can first of all mark the position of the optical center 1 8 of the lens 4. Then, in a vertical plane containing this optical center 1 8, we determine a vertical line 30 tangent to the outer diopter 8, as well as the point 32 of contact between the outer diopter 8 and the vertical line 30. If the vertical plane passing through both the center of the outer diopter and the optical center 18 is chosen, the contact point 32 corresponds to the intersection of the outer diopter 8 with a horizontal straight line, for example the straight line 1 4, which passes through the center of the outer diopter 8.

The point of tangency 32 and the optical center 18 being determined, it is then necessary to measure the distance d separating them. The angle α is then obtained by the formula α = 2 arcsin (d / 2R).

The optical center 1 8 of the glass 4 is located towards the bottom of the glass. In the embodiment of Figure 2, the optical center 1 8 is located substantially in the lower quarter of the glass 4. According to the invention, the optical center is generally located in the lower half of the glass; the angle α formed by the optical axis and the horizontal has a value of at least 10 degrees.

In addition, as can be seen in FIG. 2, the glass 4 is inclined relative to the vertical and has a pantoscopic angle greater than 5 degrees. This pantoscopic angle is the angle formed by the vertical line 20 and a plane on which would rest the inner face 6 of the glass. This angle p is shown in Figure 2

Thus, when the person wearing glasses looks straight ahead, the light rays arriving at the eye 1 2 are slightly deflected This deviation is small and does not interfere with vision Compared to documents of the prior art, such a glass allows Significantly improve vision when the wearer of the glasses is looking down The lower part of the glass is HERE preferred because it is also the part of the glass that is most stressed. Indeed, the eyes generally look straight ahead or downward. This is explained morphologically The precise observation or long of an object in height is accompanied by a movement of the head upwards so that the object to be observed is placed in the main line of vision of the glass which corresponds in Figure 2 to the axis 1 4. When observing an object downwards, the head moves but the lower zone of the glass is more stressed. So, for example to read, a spectacle wearer often looks through the lower part of his spectacle lenses.

The four tables below indicate the prismatic deviation for glasses using base 6 and base 8 lenses and whether or not having a negative power of -0.05 diopters.

TABLE 1 BASE GLASS 6 POWER 0 DIOPTRIE

TABLE 2 BASE GLASS 6 POWER -0.05 DIOPTRY

TABLE 3 BASE GLASS 8 POWER 0 DIOPTRIE TABLE 4 BASE GLASS 8 POWER -0.05 DIOPTRY

These tables clearly show that the value of the prism for a beam passing through the bottom of the glass is improved by an offset of the optical axis (increase in the angle α), by the choice of a power of -0.05 diopters. , and of course by the combination of these two parameters. The two tables below indicate the prismatic deviation for glasses using glasses having a negative power of -0.05 diopters with base 6 and base 8 glasses. These calculations were made according to a given assumption of position of l eye relative to glass and glass height. They are mentioned as an indication in order to show the improvement brought by the proposed invention. The values mentioned will be different if we take other hypotheses of refractive index of the material, thickness and height of glass, pantoscopic angle.

The first table considers the light beam passing through the visual axis while the second table concerns the light beam passing through the bottom of the glass. For each table, we consider three positions of the optical axis:

- the optical axis is horizontal;

- the optical axis passes through the middle of the glass. In this case the angle formed by the optical axis 1 0 and the horizontal viewing axis 1 4 is 6.525 ° for a base lens 6 and 9.180 ° for a base lens 8;

- the optical axis passes to the lower quarter of the glass. The angle between the optical axis 10 and the horizontal visual axis 1 4 is 1 2.96 ° for a base lens 6 and 1 7, 67 ° for a base lens 8. TABLE 5 LIGHT BEAM PASSING THROUGH THE VISUAL AXIS

TABLE 6 LIGHT BEAM THROUGH THE BOTTOM OF THE GLASS

It can be seen in these tables that the prismatic deviation at the bottom of the glass is significantly improved when the optical axis tilts down. This improvement finds its counterpart in the degradation of the value of the prism along the visual axis; the invention achieves a compromise between the prism values perceived in different places of the glass. The values given above have been calculated for polycarbonate lenses.

The glasses according to the invention will have an optical axis inclined by 10 degrees and more relative to the horizontal. According to the drawing retained for the frame, it will be noted that the intersection between the optical axis and the outer diopter of the lens is located in the lower half of the latter (see FIG. 3). The upper limit which will be observed for the angle α is that which corresponds to an excessive prismatic deviation value along the visual axis. It can be seen, for example, that for a basic lens 6, the optical center can be placed entirely at the lower edge of the lens without inflicting excessive deviation along the visual axis (see tables 1 and 2).

The glasses according to the invention are for example obtained from a blank 22 in the form of a circular cap. Such a blank 22 has two spherical dioptres and is delimited by an edge peripheral. The spherical dioptres correspond to the inner 6 and outer 8 faces of the glasses 4. In FIG. 3, a clipping line 24 is shown. This line has an upper edge and a lower edge and the distance vertically between these edges is called H. It corresponds to the geometric height of the glass 4. The optical center 1 8 of the glass is placed in turn to the geometric center of the blank 22. Geometrically, it is located in the lower half of the glass 4. The optical center is placed here at a distance h from the lower edge of the clipping line 24. The height h is substantially equal in the case of FIG. 3 to third of the total height H of the glass 4.

The spectacle lens 4 can also be obtained from a blank 23 such as that described in document FR-2 740 231. The optical center 18 is here offset relative to the geometric center 26 of the blank. The latter is not circular. It has two opposite rectilinear edges as well as two opposite edges in the shape of an arc of a circle. Marks 28 make it possible to locate the optical center 1 8 on the blank 23. This figure shows the clipping line 24 of the glass which is arranged relative to the optical center 1 8 in the same way as for the blank 22 of FIG. 3. Once a right lens and a left lens are trimmed, these are put in place in the frame 2 shown in FIG. 1. The optical centers of the two glasses 4 are then separated by a distance Δ. This distance Δ is for example chosen to be less than the distance separating the two pupils of the wearer of the glasses. The principle described in the document US-1,741,536 cited in the preamble to the present patent application is then used in order to limit defects in the prism towards the lateral edges of the glass.

It goes without saying that the invention is not limited to the embodiments described above by way of nonlimiting examples; on the contrary, it embraces all of the variant embodiments thereof within the scope of the claims below.

Thus, for example, the power of the glasses can be chosen to be different from -0.05 diopters. One can choose for the glass another angle than the pantoscopic angle indicated by way of example in the description.

Claims

1. Non-corrective spectacle lens (4) intended to be mounted in a frame comprising two branches and composed of two spherical dioptres (6, 8} as well as an optical center, so that in the normalized wearing position, in which a horizontal line connects the center of the pupil of the eye and an area of the ear on which a branch of the frame rests, the optical axis (1 0) defined by the straight line passing through the two centers of the diopters spherical makes an angle of at least 10 ° with a horizontal axis, characterized in that its optical axis (1 0), in the mounted and carried position, is inclined downward relative to a horizontal axis (14) corresponding to a right passing through the pupil of the eye (1 2) of the wearer of glasses and the area of the ear on which the corresponding branch of the frame rests.

2. Non-corrective spectacle lens (4) according to claim 1, characterized in that it has a strong curvature corresponding to a radius of curvature (R 1) at most equal to approximately 90 mm.

3. Spectacle glass according to one of claims 1 or 2, characterized in that this glass (4) has a negative power between -0, 1 2 and -0.04 diopter.

4. Spectacle glass according to claim 3, characterized in that the power of the glass (4) is between -0.06 and -0.04 diopters.

5. Spectacle glass according to one of claims 1 to 4, characterized in that the thickness of the glass at the optical center (1 8) is between 1 and 3 mm.

6. Spectacles comprising a frame (2) with two arms (1 6) and two lenses (4), characterized in that the lenses (4) are non-corrective lenses according to one of claims 1 to 5.