Patent ID: 12197045

InFIG.1, a progression curve is illustrated that describes the optical strength of the lens as a function of the angle at which the user looks at the lens. This angle is illustrated in more detail inFIG.3.

FIG.2illustrates an eyeglass lens1in accordance with the present invention. A line20extends vertically through lens1. Here, line20extends through the highest points on the lens and is generally referred to as vertex line.

FIG.3illustrates the construction of eyeglass1in accordance with the present invention. This construction is performed based on the progression curve shown inFIG.1.

InFIG.3, an eye is represented by a point6. A first axis of rotation R1is drawn from point6. At a given distance from point6, the construction of a rear vertex line2and a front vertex line4starts. Here, front vertex line4is assumed known as this line corresponds to a predefined spherical shape of a blank from which eyeglass1will be manufactured.

Rear vertex line2is segmented in a plurality of line segments2A-2G. Similar segments4A-4G can be identified for front vertex line4. A pair of front and rear line segments, e.g.2A and4A, corresponds to a segment of lens1. Such segment of lens1has a given angular position relative to point6. This angular position is indicated by angle α. For example, at an angle α1a start point S1of rear vertex line2and a start point S2of front vertex line4can be identified. It should be noted that rear vertex line2at least partially forms vertex line20as will be explained later.

Front vertex line segment4A and rear vertex line segment2A are perpendicular to axis of rotation R1. Rear vertex line segment2A is formed using a Cartesian oval that is characterized by a focal point A2located to the left of rear vertex line segment2A and a focal point C2located to the right of rear vertex line segment2A. Similarly, front vertex line segment4A is formed using a Cartesian oval that is characterized by a focal point A1located to the right of front vertex line segment4A and a focal point C1located to the left of front vertex line segment2A. As front vertex line4is spherical, both A1and C1are completely determined as a circle is a particular example of a Cartesian oval.

It should be noted that the optical properties of the lens segment corresponding to rear vertex line segment2A and front vertex line segment4A also depend on the refraction index of the final lens material and the distance between line segments2A,4A. These two parameters are fixed during optimization so that the Cartesian ovals are fully specified by the parameters A1, C1or by A2, C2.

Focal points A2and C2need to be calculated by means of optimization. This is achieved using ray tracing techniques. More in particular, focal point C2is the parameter that most strongly determines the optical strength associated with rear vertex line segment2A. This optical strength should, together with the optical strength of front vertex line segment4A, give the desired optical strength of the lens segment corresponding to line segments2A,4A. This latter desired optical strength can be derived from the progression curve inFIG.1, wherein the optical strength associated with front line segment4A, as well as the other front line segments, is fixed.

Parameters A2and C2are found such that rear vertex line2A has the desired optical strength and such that a desired imaging quality is achieved. For example, a size of a region of least confusion can be calculated using ray tracing techniques. When applying these techniques, a model of an eye can be used that describes the optical properties of the eye of the intended user. The retina of this model could for example be moved between the sagittal focal plane and the meridional focal plane of the segment lens corresponding to rear vertex line segment2A to find the region of least confusion. The size of this region should be minimized while at the same time the desired optical strength should be achieved. During this optimization it may be useful to use bounds for moving the retina, i.e. to move within a given range back and forth towards the lens segment, and to use a desired optical strength range, for example +/− 5% of the desired optical strength as dictated by the progression curve. Typically, A2and C2are determined such that an at least local minimum if found for the size of the region of least confusion while the optical strength is within the abovementioned desired optical strength range. Furthermore, as a starting condition, A2may be set equal to A1. It should be noted that the optical strength may be predominantly determined by C2. Nevertheless, when changing A1, its affect on the optical strength must be accounted for by also varying C2.

For the next rear vertex line segment2B, parameter A2can be taken equal to the optimized value of A2for rear vertex line segment2A.

By repeating the procedure above, rear vertex line2can be specified completely. In some cases, it may be advantageous to deviate slightly from the progression curve according to the progression curve and to perform one or more re-iteration steps.

As shown inFIG.3, constructed rear vertex line2comprises multiple segments that are now characterized by known Cartesian ovals. This means that these line segments are shaped as small sections of these ovals. Furthermore, rear vertex line2extends between start point S1and an end point S3, whereas front vertex line4extends between start point S2and an end point S4.

As a next step, both rear vertex line2and front vertex line4are rotated about axis of rotation R1, preferably by 360 degrees, for forming a main rear surface and a main front surface, respectively. This is illustrated inFIG.3using lines2′ and4′, respectively, where it is noted thatFIG.3is a cross sectional view.

Main front surface is a spherical surface whereas main rear surface is not. Moreover, start points S1and S2represent umbilical points as the respective main surfaces are locally spherical at these points.

Next, a cut-out region5is defined on this surface. Cut-region5defines the lens to be manufactured. More in particular, the cut-out regions of the main front surface and the main rear surface are used for controlling the machines that manufacture the eyeglass lens such that the rear surface of that lens corresponds to the cut-out region of the main rear surface and that the front surface of that lens corresponds to the cut-out region of the main front surface.

In some cases, a large thickness variation may occur in the lens. To solve this issue, the main front surface may be rotated about a third axis of rotation R2such that the thickness variation is reduced. This latter rotation is a well known procedure to adapt the lens thickness. Additionally or alternatively, the separation between the main rear surface and the main front surface can be changed.

FIG.4shows the optical power profile of a rotationally symmetric varifocal eyeglass. The addition (optical power difference from top to bottom) for this lens is 2.5 D. The rotation axis of the rear surface is located at the common center of the radial arcs above the lens.

FIG.5shows the astigmatism profile of the rotationally symmetric varifocal eyeglass ofFIG.4. The rotation axis of the rear surface is located at the common center of the radial arcs above the lens. The astigmatism increases from 0 D at the top to about 1.0 D at the bottom.

FIG.6shows the optical power profile of the varifocal eyeglass ofFIG.4when torically deformed. It clearly shows that by using differential toric deformation, the power contour lines can be made to approximate horizontal lines, meaning that the perceived optical power remains more constant from left to right at the same viewing height or viewing angle respectively. Differential torical deformation means that the torical deformation increases or decreases from the top of an initially rotationally symmetric varifocal lens to the bottom of said lens. The addition (optical power difference from top to bottom) for this lens is 2.5 D.

FIG.7shows the astigmatism profile corresponding to the torically deformed varifocal eyeglass of which the optical power profile was shown inFIG.6. The astigmatism increases from 0 D at the top to about 0.2 D at the bottom along the central vertex line. From the center to either the left or the right side of the glass the astigmatism increases by about 0.5 D. It clearly shows that by using differential toric deformation, the increase of astigmatism to the left and right can be made both smaller and more evenly distributed than in a rotationally varifocal glass according to the present invention. This means that the so called corridor of varifocal eyeglasses according to the present invention can be made both wider and of a more homogeneous width from the top to the bottom of the lens.

For the examples shown inFIGS.4-6, a simple elliptical eyeglass form was used with 20 mm vertical half axis and 25 mm horizontal half axis. Since a commercial base semi-finished spherical blank was used in this case, a full front surface was already defined, which formally can be obtained by rotating a constant-curvature profile around a rotation axis that is essentially positioned in the center of the intended final eyeglass lens.

Using a commercial CNC freeform lens cutting machine, the exact form of the rear surface was machined into the rear surface of the semi-finished blank. As a final step, the resulting lens was given a contour to fit the eyeglass frame chosen, in this case of elliptical form. This procedure, like the polishing of the rear surface and applying anti-reflection and anti-scratch coating, is standard in the optical industry.

In the above, the present invention has been described using detailed embodiments thereof. It should be noted that various modifications can be made without departing from the scope of the invention which is defined by the appended claims and their equivalents.