What Are Progressive Lenses?
Bifocals have improved greatly since Benjamin Franklin first glued two different lenses together in 1784 to help his failing vision. One was for reading and one was for distance. Today’s lenses have evolved to line free progressive lenses. So what are progressive lenses? In today’s progressive lenses there is no line demarcating the distance and near focusing areas on the lens, so you don’t have to worry about other people knowing you are now past the 40 year old mark. While using the newer updated line-free multifocal lenses may mark you as progressive, the term means something entirely different in terms of lens technology.
How Long Have Progressive Lenses Been Around?
The first person to ask what are progressive lenses was Owen Aves who patented the initial idea in 1907. The first progressive lens widely produced commercially was the Varilux Lens in 1959. Prior to the Varilux, bifocal lenses all had two zones, separated by lines, one region for near and one for distance. As we age past 40 we need more correction for near vision every year or so until our eyesight stabilizes in our 50’s. At some point intermediate vision starts to be affected, and three separate zones of lens powers are often needed. Trifocal lenses are composed of three different sections, two lines, and a little confusion about where to look. Varilux offered a wonderful new solution.
Why Do We Call Line Free Bifocals Progressive Lenses?
Progressive lenses (also referred to as PAL’s) are so named due to the gradual progression of power that runs from the distance area at the top of the lens to the near area at the bottom. This gradual ramp of increasing power results in a lens power for every distance, without the unnatural jumps in power used in the old style bifocal and trifocal lenses. Progressive lenses are very complicated designs and have some compromises in optics to achieve the gradual ramp. Optically the clear zones resemble something like an hourglass, wider at the top and bottom with a narrower zone of intermediate vision connecting the two. In the periphery outside of the hourglass, the prescription is not quite accurate. Fortunately, almost everyone turns their head when they look in the periphery, and today’s lens designs minimize these types of issues.
What Are Progressive Lenses Today?
Recent changes in lens manufacturing technology and design have greatly altered the quality of progressive lenses. You may hear a number of new buzz words from your optometrist’s office that refer to this new era of lens technology. – Older design progressive lenses are made by molding the progressive part of the lens on the front surface and grinding the prescription onto the back of the lens. Around the dawn of the 21st century, the process of lens manufacturing took a quantum leap. Freeform Technology Lenses can now have the prescription ground on the surface point by point utilizing computer software. We often refer to these resultant lenses as “Digital Lenses”. This allows over a tenfold increase in accuracy just for starters. The progressive part of the prescription can now be ground on the back of the lens and is no longer restricted to the characteristics of a limited number of molds. It allows the lens designers to decrease the number of aberrations, and yields clearer optics. Taken a step farther, we can now customize lenses individually by incorporating your prescription with the characteristics of how the frame is designed. Sometimes this is referred to as a “HD or high definition lens”. Often the terms “freeform, digital lenses and hi def lenses“ are used interchangeably in reference to lenses made with the latest technology.
Just to add a little more confusion to an already blurry picture-
We have an ever increasing number of close range tasks that cannot be addressed by a single lens design. Occupational and Sports lenses are increasingly being used for specific tasks. Computers are a prime example. With a normal progressive lens, you need to look down in the lens part way to be in the area with an appropriate strength. Most monitors are straight ahead or down 15-20 degrees. Normally you will have to lift your chin to view the computer, which can be a pain in the neck! Computer lens designs help eliminate this problem, and give you a wider area of focus in the intermediate zone. The top part of the lens is no longer your full distance correction but still allows you to move around in an indoor office environment. Other designs can help with people who spend hours on cell phones or tablets, or help with the visual demands of golf and other sports. One other area of lenses that can now be customized is the length of the progression zone. Some tasks require you to need a shorter distance between the distance and near zones. If you spend the day alternating between distance and near fine print you might benefit from a short corridor lens. On the other hand, if you drive a truck for a living and use the near part less frequently you will probably find the wider distance area of a longer corridor lens much more appealing. Lens technology is rapidly evolving and can be expected to continue to improve and become more individualized over the near future. Make sure your eye doctor can provide you with the current technology and don’t expect a one size fits all lens design if you want to see your best!