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The Evolution of Bifocals

March 22nd, 2010

What will people do if they have some very serious eye problems, like astigmatism, presbyopia, myopia, etc, especially when they are over forty? They may choose to wear bifocal lenses without any hesitation. It seems that those lenses are very common and sufferers of the above mentioned problems have got used to them. However, unlike common lenses, bifocals have really very short history, but they have evolved radically since their first emergence.

According to the data from bifocal lenses Wiki, the bifocal lenses history is no more than two and a half centuries. It is said that bifocals do not come into being till the 18th century. And there are still some controversies about who is the bifocal lenses inventor. However, the universally recognized inventor is Benjamin Franklin, a well-known US state man in the 18th century.

It matters little who have invented the first bifocals, but it matters much what the first bifocals are looked like. According to some documents, the first bifocals are roughly manufactured and very heavy to wear and inconvenient to use. The reason is each lenses are directly overlapped by two full lenses. Therefore, there are almost four full lenses on each pair of them. And such condition does not change until the 20th century.

The 20th century has witnessed the rapid developments and changes in glasses industry. And bifocals have also gained great rapidity then. Some designers have noticed that conventional bifocals are roughly made and have caused lots of troubles to wearers. Based on all possible scientific data in the industry, designers have combined each lens by two cut lenses. This innovation has greatly enhanced the comfort of wearing. Now that those lenses are combined by two different lenses, there is a division line between them. And there comes bifocal progressive as a result. Here is a contrast- bifocal lenses Vs Progressive.

The first type is called lined lenses and has very evident division line in their middle part, whereas no such line can be found in the latter form. Wearers will endure radical vision change with bifocal lenses, but never with progressive. And many people begin love to wear progressive thereafter.

Bifocals are always in the process of evolution and people will benefit from it. For example, some bifocal lenses for spectacles are available if people want to replace them.

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Progressive lenses with a range of powers

February 1st, 2010

Progressive lenses are corrective lenses used for presbyopia and other eye problems. They are special because of their gradient of increasing lens power. Progressive lenses have several names, such as progressive addition lenses (PAL), progressive power lenses, graduated lenses, no-line bifocals, and varifocal lenses. All of these names can reflect some of the features of progressive lens.

People look down for close reading so that the gradient of progressive lenses starts at the top of the lens, at a minimum power and reaches a maximum addition power at the bottom of the lens. This structure of progressive lenses provides the most comfortable and convenient reading effect. The power gradient length of progressive lens is usually between 15 and 20mm. The power addition gap of progressive lens is between 1.0 to 2.5 which depends on the level of presbyopia of the patient.

Just as the name no-line bifocals suggests, progressive lenses have relationship with bifocal lenses, which have visible lines on the lenses. Progressive lens just eliminates the lines on bifocals and trifocals, so that others will not find that you need reading glasses. This is one advantage of progressive lenses.

Bifocal lenses and trifocal lenses provide two or three lens power on the lens, while progressive lenses provide a seamless progression of many lens power. Progressive lens performs well in more situations, including intermediate zone computer reading. In contrast to several lens power, progressive lenses just provide a more natural correction.

Progressive lens is not perfect. As the lenses combine a range of powers in a single surface, geometric distortions may be caused to visual field, which in turn bring visual discomfort.

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What are bifocals and bifocal contacts?

December 5th, 2009

Though bifocals are not the earliest members in the glasses family, they have made great success since the day they are invented. It is said that the great Benjamin Franklin has created the first bifocals. Despite there are no evidences that can exactly tell who is the inventors; the world has unanimously agreed that Franklin is the inventor of bifocals.

The earliest function of bifocals is for vision correction. Some people in then time accidentally found that bifocals can improve their eyesight. The earliest bifocals are comprised of two pieces of convex glasses, and they can help people look objects much clearer.

The first bifocals are very different from that of nowadays. With time goes by, bifocals have got their modern forms since the beginning of 20th century. Nowadays people can notice that the different forms of bifocals are available in modern society.

Among various forms of bifocals, bifocal contacts are very special and popular. Regular wearers have come into recognition that bifocal contacts are not limited to improve their vision. Generally speaking, bifocal contacts can always make their wearers comfortable. When wearing a pair of bifocal contacts, people feel that their eyes are in ease all the time. With the usage of high technologies in bifocals, bifocal contacts are easily to take off or wear. And almost all bifocal contacts are UV-resistible.

As for many wearers, bifocal contacts are essential for their lives. Some people, especially these old people, are very satisfied with bifocal contacts, for in their past several decades, these vision correction aids have made their life colorful.

Addition to bifocal contacts, there are still many other forms of bifocals at the market. However changeable are their forms, bifocals will serve for the people all long.

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Innovative bifocal glasses

December 2nd, 2009

Bifocal glasses are not a recent invention. As the story says, Benjamin Franklin had two sets of glasses, one for faraway objects and the other for close reading. He reluctantly shifted from the two separate glasses, which is very inconvenient. After quite a period of this bother, the great forerunner designed a pair of bifocal glasses that allow him to see both distant and near things clearly. This was the initial form of bifocal reading glasses. He just cut the two pairs of glasses in half and used half of each lens for each eye so that the bifocal glasses were invented.

Science and technology always advance at a rapid pace, but the basic principle of bifocal reading glasses has remained the same since its invention. The lens of modern bifocal glasses has two parts: the lower part for close reading and the upper for distant vision. This design principle of bifocal reading glasses is based on the common sense that people generally use bifocal glasses in certain ways. They look downwards the bifocal reading glasses when reading or looking at close objects and look up when looking at distant things.

Bifocal glasses are truly useful for a large population that develops prysbiopia on earth. In the US alone, almost 4 million people suffer from it each year, most of which are between thirty to fifty years of age. Bifocal glasses have become a necessary part of their lives. Bifocal reading glasses eliminate the switch between separate glasses.

Bifocal glasses also perform as the pioneer of multifocals, followed by trifocals and progressive glasses. After the invention of bifocal reading glasses, multifocal glasses are natural.

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Differences between Trifocals and Bifocals

November 21st, 2009

Trifocals are a new group of special reading glasses which have three divisions on the lenses for correcting vision. It is different from traditional bifocals which have only two such divisions. The lower sections of the lens of trifocals are demarcated by a thin line which is a semi circular arc. One area is for near and the other for intermediate vision correction. And the part for intermediate rectification lies above the nearsighted correction area which is near the bottom of the lens. For those who used to wear bifocals may think it is strange to reading with glasses having three lines etched on it. As trifocals are new to most of people, it actually did need time for patient who uses this type of glasses to adjust to them. However, once you used to wear them, you will find it pretty easy to use and it is more convenient than bifocals.

After eye exam by the eye doctor, those people with extreme presbyopia, which means their net optical power with a special unit of diopter is very high, will be recommended to use trifocals. Because, unlike bifocals, trifocals can correct all ranges of vision, from nearby, intermediary to far distance, when bifocals can correct only two of them, either near vision or distance vision. Since trifocals can offer three levels of correction, it can give you a better vision. So, if you are one of the extreme presbyopia, you will get the better and more clarified vision when you use trifocals.

Trifocals are not only for those who have extreme presbyopia, it can also correct intermediate distance which can’t be provided by bifocals. For example, if your have a vision of -4 diopters, usually you will be recommended to use a glasses with a correction of 3 units, which means you vision is -1 diopter when you wear your reading glasses. The intermediate correction for such situation may be end up with a power of -2.5, which may take patients a little time to get used to it.

So with a single pair of trifocals, you can solve all problems that are related to presbyopia.

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What Do You Know About Trifocals?

November 10th, 2009

People over 40 mostly find their eyes lose their capacity to adjust and focus on different things. This is a common biological change. As body ages, our eyes age as well, resulting in presbyopia, a term derived from Latin with the meaning of ‘ageing eyes’. This is different from myopia and hyperopia which are caused by deficiency of eyes and can not be cured by corrective glasses, refractive surgery or contact lenses. People with presbyopia usually use trifocals.

Trifocals are glasses where the lenses have 3 regions to correct for distance, intermediate (arm’s length), and near vision. They most used by people with advanced presbyopia who have been prescribed 2 diopters or more of reading addition. Compared with bifocals, trifocals provide more clear vision to the wearer although, in some degree, they sound to be tougher to see through.

Those who have ever worn bifocal glasses may know that at the very first time when they wear them, they often feel hard to get used to bifocals. They frequently feel dizzy. The insertion of the intermediate addition of trifocals which steps between the distant and reading distance make things easier for a person to progress one step to another. The intermediate addition is normally half of the reading addition and half of the long addition. So for someone with a distance prescription of -4 diopters and a reading addition of +3 diopters, the reading portion of their trifocals would have a net power of -1, and the intermediate segment would be -2.5 diopters. Thus, those wearing trifocals obtain clearer vision and experience less strain on the eye than those wearing bifocals.

Therefore, we can see, based on the same principle, trifocals, only differing from bifocals in vision of divisions, are equipped with three additions rather than two. Trifocal is a type of glasses belong to multifocal glasses.

Just like bifocals, trifocals are also equipped with the semi-circular area with each the reading addition and distance addition. Meanwhile the mid-range of trifocals are equipped with a narrow band, for people seeing things that are not very far but further than the reading distance. If you frequently spend your time before a computer, trifocals will provide you with great comfort.

Trifocals offer the wearer the benefits of three corrective prescriptions without the need for three separate pairs of glasses. For those who want the benefit of trifocals without telltale lines, there are progressive lenses, which may also be called progressive addition lenses or PALs, progressive power lenses, graduated lenses and varifocal lenses. These terms may be used to describe ‘no-line’ bifocals as well.

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