Progressive lenses for glasses, also called progressive lenses (PAL), progressive lenses, prescription lenses graduated, and variable focal length lenses or multifocal, are corrective lenses used in eyeglasses to correct presbyopia and other disorders accommodation. They are characterized by a gradient of increasing lens power, added to the correction of the company of other refractive errors. The gradient starts with the distance of the holder at the top of the lens and reaches a maximum power of more than, or the addition of the complete reading at the bottom of the lens. The length of the slope of the progressive power surface of the lens depends on the refractive index of the lens, with a final addition power between 0.75 to 3.50 diopters for most carriers. The added value depends on the level prescribed for presbyopia of the patient and is closely related to age and to a lesser extent, the existing order.
“Progressive” or variable-focus glasses (eg Varilux ®, Panamic ®), (also known as seamless trifocal, etc.) sounds like the answer to a prayer of people who face a girl need luck to pass a vision two common focal distance vision glasses. These progressive hi-tech glasses mixed with three priority areas in the field as part of each objective, so that the top of the viewing distance of focus, and the center of the center (for example, reading the labels on the shelves of supermarkets) , and the lower part focuses on reading and the computer screen. At least it’s a requirement.
It ‘true that many users of bifocal progressive transition is an exciting experience – almost like a do not need glasses anymore. (And the same pleasant shock to move data.) But the real worlds are often synonymous with a lack of theoretical perfection. Let’s look at where the multi-focal glasses are needed at all, and then look at how well they really work.
Egg eye adjusts to focus on changing its round shape. Stabilizes a bit ‘to focus on near and far to see bulges slightly. People who are “short sighted” (see very close) are those whose eyeballs bulge less than necessary to optimize their vision of nearby objects.
Young people have more elastic eyes, and are easier to compress and stretch your way to be able to adjust the focus or indirectly. As we age, we lose elasticity, the eyeball and moved to a remote care. (Therefore, the vision correction eye surgery (“Lasik”) in most people over 40 years will be able to correct both eyes for a single distance. However, you must reading glasses. O you can have one eye corrected for near vision and the other for distance. Many women do. But all this could mean you do not need glasses, can not also be able to see if both eyes are synchronized.)
For the production of optical glasses with a variable center of gravity is complex. Consequently, the goal does not provide a uniform change in focus from top to bottom, that is close to that. Because the eyeball is also repair some of the turn from left to right display (not just straight ahead), the appearance of the progress of change in focal length is shaped like an hourglass, with the top mobile-display area is the most large, medium range is narrow, and a reading area wider than the central region. This hourglass shape is also tilted at a lower reading area closest to the nose. (As we focus on nearby objects, looking inward to converge near the object.)