Copyright Indizen Optical Technologies

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Shana Webb
5 years ago
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2 DEFINITION OF FREEFORM Free form is a manufacturing technology that allows cutting and polishing arbitrary surfaces A lens is free-form if at least one of its surfaces is made with free form technology and that surface is not spherical neither torical* *Free-form machines may cut standard surfaces, but as they can also be cut with standard methods, the corresponding lenses should not be named free-form lenses. THE CLAIMED BENEFITS OF FREE-FORM FORM The benefits that follow from advance in lens manufacturing. Freeform lenses have attributes that are not possible to incorporate in traditional lenses. Production accuracy:. D by means of well tuned process with tools, soft pads and slurries not worn out, guarantees better precision than traditional/standard milling and polishing methods. Better optical quality. Free-form technology will allow you to get better optics, as far as you use good optical design tools. Free form is a manufacturing process, not a design method, neither an optical design software. Ophthalmic industry is no longer tied to base-curve restrictions. With standard base curves, a sophisticated lens must be made with a few complex surfaces (semi-finished blanks) and spheres or torus. With free form, each sophisticated lens may have its own sophisticated surface. Optimum compensation of side effects: In Optics, asphericity is the way to correct for aberrations when you cannot use many lens elements. In ophthalmic optics, compensation must be made by just one lens per eye. Each Rx, each lens position, each object position, requires a particular asphericity to get the best possible correction. Standard lenses use the same asphericity for thousands of different situations, thus rendering asphericity useless. A different surface for each lens will allow a different asphericity for each lens = optimum compensation of side effects (aberrations). Optimised lenses: Optimise the lens for the power that the user perceives, not the power measured in the vertometer (which is ok for quality control, but is not the power perceived by the user); Optimise the lens for any position of use (tilts, distance to the eye, etc ); Optimise the lens for any base curve (the spherical base curves used with FF lenses); Better control of lens thickness and Off-centering without losing optical quality (wrap designs).

3 WHAT FREE-FORM FORM CANNOT DO Free-form is a great improvement on traditional lenses. However, freeform is not magic - it cannot right all wrongs in ophthalmic optics. Progressive lenses that violates Minkwitz s theorem (progressives with wider corridors for the same corridor length.) If a corridor is increased in width, some other benefit would have to be compromised the advent of free-form does not mean that Minkwitz s theorem is not valid anymore. Keep this in mind when you are confronted with claims of % plus increase in progressive zones. Lenses without aberrations the distorted areas would now be less distorted. Progressives without an adaptation period adaptation with the new products simply becomes easier. Short progressives with intermediate wide enough for computer displays. In any case, the best lens for computer work is an office lens. The progressives that we prescribe are mainly multi-purpose lenses. BACK SIDE OR FRONT SIDE PROGRESSIVE? Initially the hype about free-from was based on the fact that the progressive surface was located on the back surface of a lens, the so-called internal design. The position of the progressive surface (even if there are two progressive surfaces) is not that important. The important thing is the progressive surface (or both) being free-form and computed with good software, not the position. The performance of any front side progressive can be reproduced in a back side progressive. The opposite is also true. The freeform progressive field of vision is wider because the surface is nearer to the eye. Indeed the back surface is a little bit nearer, but also there is less room for progression on the back, so there is not net improvement. Magnification is more stable because front refractive power is constant. That s true, but the effect is so small. Magnification is mainly due to power. As power increases in a progressive, so does magnification. Back side progressives produce less distortion. False. Distortion depends on the power variation. The faster the variation, the larger the distortion. This is a characteristic of the design, whether it is back of front. In positive lenses, ideal FF surface should be the front surface. In negative lenses, ideal FF surface should be the back surface, but manufacturing currently requires to have the FF surface at the same side > back surface. Classical lens Stratemeyer lens Classical Progressive (5-6 surfaces optimized for each addition) Sphere or torus (non-optimized but different for each addition) Spherical (5-6 curves) FF surface (thousands, each optimized for each prescription)

4 USER PERCEIVED POWER Customisation with free-form only makes real sense if the lens is optimised for user power. If a lens is optimised for user power, vertometer readings does not fully coincide with Rx. And correct addition in user power reads considerably smaller in a vertometer! Lenses made with Free-form Designer, IOT s design software, are calculated to optimise user power. It is important to understand this concept, and the difference with power measured on the lens. User Power is the power that the patient really sees when looking through each point of the lens. User power depends on the shape of each surface of the lens at each point, and also on the lens position and orientation with respect to the eye. User power is important because the final satisfaction of the patient depends on it. For progressives, when looking through the far region of the lens, user power should be equal to the user Rx, and when looking through the near part of the lens, user power should be equal to the Rx plus the addition. IOT lenses are calculated to yield the correct user power, and therefore the maximum user satisfaction. Measured Power is the power calculated by a vertometer or a mapper. When we measure the power on a lens point with a vertometer, or when we see the power map of a lens with a lens mapper device, we observe an approximation to user power, but not the exact value. The vertometer or the lens mapper are based on an optical system that is not equal to the eye, and that is why there are differences between the power observed on an instrument and the real user power. These differences are bigger for points of the lens that are far from the centre, due to the bigger obliquity of the rays. These differences depend on the Rx, the addition, the base curve, the material, and the pantoscopic and wrapping angles. For progressive lenses, these differences will be significant in the near region, and there can be differences as high as.5d between measured power and user power. Rx power is the power read by a vertometer at the center of the lens, with no tilts. When the eye aims off-axis (oblique gaze), the lens does not provide the Rx power. Pay attention to the plane formed by the optical axis and the gaze direction: it is named tangential plane. Oblique gaze Tangential plane

5 [-6.,. 9º] [-6.,. 8º] φ mm -6. SPH [-6.,. 9º] [-6.,. 8º] [-6.,. 5º] For this spherical lens, the axis of the cylinder has radial orientation. When the user aims up or down, the axis is 9º. When the user aims at right or left, the axis is 8º. When the user aims down and right, at a point 5 mm aside from the lens center, the cylinder axis is 5º. In general, the axis of the cylinder error has the orientation of the tangential plane, shown on the first diagram. In a more complex lens, the result is similar: the obliquity produces an error in sphere and also a new cylinder component, the axis of this new component laying most probably on the tangential plane (radial direction in spherical lenses, other directions in more complex lenses). When the lens Rx contains cylinder, the final power perceived by the user results from the combination of the Rx cylinder, and the cylinder produced by the obliquity of rays. This is the physical explanation of the change in power. Unfortunately, this combination cannot be used for accurate computation of the user perceived power, and exact ray-tracing must be employed. Finally the composition of the two astigmatic powers (Rxs and obliquity) gives rise to a new final astigmatism which is changed in value and axis with respect to the Rx. Prescription (same axis everywhere) The axis of the final (user power) astigmatism only would be the same than the axis of the Rx if this Rx axis and the tangential plane had the same orientation. cylinder due to oblicuity (axis mainly in the tangential plane) When the astigmatic component due to obliquity is small and the Rx astigmatism is large, the Rx axis is changed very little. If the Rx astigmatism is small, its axis is very sensitive to the combination with the astigmatism from obliquity. About IOT Indizen Optical Technologies (IOT) is a joint-venture formed by the Applied Optics Complutense Group at Complutense University of Madrid and the consulting firm Indizen Technologies. The team consists of both specialists in optical technology and information technology professionals with vast experience. This combined expertise makes it possible for us to offer complete solutions: design of optical systems, management and processing software, integration of the system with the management process of the customer s business, access to data management... Our objective is twofold. First, we develop leading technology products in the field of optical metrology and vision. Secondly, we develop cutting-edge metrological and quality control technology. IOT is currently focused on two business lines: *IOT-vision, focused on the development of technology and products for vision and *IOT-measure, focused on the development of technologies, products and applications for optical metrology.

6 COMPARISONS The next examples are real-life computations, made with ray tracing techniques on a classical, non-ff, front side PAL (Shamir Genesis), and a FF optimized back side progressive (Free-Form Designer Progressives). Maps are real. There is no touching-up to exaggerate the comparison. Both lenses have addition = D. Color bands are.5 D. A classical lens may have a nice cylinder map when we obtain it from surface optimization, but then ray-tracing shows that real lens performance is not so good User power of the classical lens Some marketing information shows touched up maps, in which the FF lens map is exactly the same whatever the tilt, lens position and Rx. That s not true, and if the design is good, it is not necessary to exaggerate, as the FF lens really improves on classical performance. -.5 Free-Form Designer user power optimised

7 COMPARISONS The example below demonstrates how optimisation provides superior optics in a wrapped lens, even if the panoramic angle is increased. This is not possible with traditional lenses..5 Gets worse at.5 more astigmatism more astigmatism at Classical with wrapped angle = º Classical with wrapped angle = º.5.5 Almost no variation! Free-Form Designer user power optimised Wrapping angle = º Free-Form Designer user power optimised Wrapping angle = º

-6.. FREE-FORM FORM SINGLE VISION LENSES The example below demonstrates how optimisation provides superior optics in a single vision lens, both classic and wrapped designs. 5-6. -6. -6.5-6. 5.8.

8 -6.. FREE-FORM FORM SINGLE VISION LENSES The example below demonstrates how optimisation provides superior optics in a single vision lens, both classic and wrapped designs y (mm) x (mm) y (mm) x (mm) This is an example of a -6 sphere traditional lens. At left, we have a map of the real sphere perceived by the user. At right we have the map of perceived cylinder. As expected, at the center of the lens there is no error in sphere, neither there is any cylinder. But when the eye rotates and aims through a point located at 5 mm from the optical center, the perceived sphere changes to -6. D, and there appears to be cylinder power of D. Perceived power in a traditional wrap lens Perceived power in a freeform wrap lens Perceived power in a traditional lens Perceived power in a freeform lens

3/31/2016. Presented by: Bob Alexander, ABOM/NCLE-AC Lens Consultant Vision Ease. Everywhere and Sportwrap; Understanding Digital Technology

3/31/2016. Presented by: Bob Alexander, ABOM/NCLE-AC Lens Consultant Vision Ease. Everywhere and Sportwrap; Understanding Digital Technology Everywhere and Sportwrap; Understanding Digital Technology Presented by: Bob Alexander, ABOM/NCLE-AC Lens Consultant Vision Ease Digital - Design and Surfacing VE Digital Designs Optimization Compensation