VisionPlus India

addition lenses may be designed with distance to intermediate or intermediate to near prescriptions specifically for use as an occupational lens, or to offer enlarged near and intermediate view areas. The traditional progressive lens is produced from a so-called semi-finished lens. The semi-finished lens is molded with an asymmetrical power pattern on the front. On the back side a custom surfacing is made to adjust the power for each patient. This method is however problematic, especially for astigmatic prescriptions. The reason being that the semi-finished front pattern is designed for a spherical prescription. Freeform designs are tailored to each prescription and do not have this problem. Since the 1980s, manufacturers have been able to minimize unwanted aberrations by: • Improvements in mathematical modeling of surfaces, • Allowing greater design control; • Extensive wearer trials; and • Improved lens manufacturing and measurement technology. FREEFORM IN THE PRESENT Today the complex surfaces of a progressive lens can be cut and polished on computer-controlled machines, allowing 'freeform surfacing', as opposed to the earlier casting process, thus explaining the difference in price. In short, the price is based on the technology used and the year the lens came to market. FREEFORM PROCESS, PERSONALIZATION AND SUPERIOR DESIGNS Lenses, made by freeform technology can produce superior designs, but that does not mean that all such lenses are perfect. The Freeform process creates potential for perfection, but the lens is as good as its design, the software calculations and the measurements taken. TODAY THE COMPLEX SURFACES OF A PROGRESSIVE LENS CAN BE CUT AND POLISHED ON COMPUTER- CONTROLLED MACHINES... viewing to reading. The point of reading is about 14 mm below and 2 mm to the nasal side in comparison to distance viewing. By tilting the reading power towards the nasal side in perfect symmetry, appropriate reading power was given to the wearer. The symmetric design, however, was difficult to accept and adapt for patients, because the eyes, in general, work asymmetrically. When you look to your right, your right eye views distal (i.e. looking through the lens near to the arm of the spectacles) while your left eye views nasal (i.e. looking through the lens near to the bridge). Modern sophisticated progressive lenses are designed asymmetrically for greater patient acceptance and include special designs to cater to many separate types of wearer application: for example progressive 48 VISION PLUS INDIA EDITION