Bifocal Contact Lenses provide both near and distance vision
Colored Contact Lenses give your eyes a subtle or dramatic change
Disposable Contact Lenses enable a healthier wearing experience
Extended Wear Contact Lenses for safe overnight wear
Gas Permeable (GP) Contact Lenses for the ultimate in crisp vision
Monovision is an alternative to bifocals for presbyopia
Orthokeratology Lenses for overnight corneal reshaping
Prosthetic Contact Lenses mask eye injury or disfigurements
Silicone Hydrogel Contacts transmit more oxygen to your eyes
Special-Effect Contact Lenses let you become a leopard or cheetah
Specialty Lenses for the "hard-to-fit" patient
Toric Contact Lenses provide good vision if you have astigmatism
Sunday, June 29, 2008
About Contact Lenses
Modern contact lenses fall into two categories: soft lenses that are made from water-containing plastics, and GP or "oxygen permeable" rigid contact lenses.
Contact lenses may also be classified by wearing schedule. Daily wear lenses must be removed, cleaned and stored each night, while extended wear contact lenses are made from materials which are safe to be worn during sleep. You may also have heard of "continuous wear" contact lenses, a type of extended wear that can be worn for up to 30 days.
Various lens designs are available for different vision problems. Spherical contact lenses correct nearsightedness or farsightedness and are indicated by a minus or plus in your prescription, respectively. Bifocal contact lenses are similar to multifocal eyeglasses in that they use different optical zones to correct presbyopia (the decreased ability see at both near and far distances). Toric contact lenses correct astigmatism, which can accompany either nearsightedness or farsightedness.
All of the contact lenses mentioned above can be custom fabricated for unusual prescriptions, and many other contact lens designs are available as well, including designs for conditions like keratoconus.
Many lens designs come in colors that can enhance or change your natural eye color. Special-effect contact lenses are also available for novelty use and are used extensively in theatrical and filmed productions. Prosthetic lenses are colored contact lenses that can cosmetically mask eye disfigurement. Many contact lenses also come with an embedded UV inhibitor.
Which is the right contact lens for you? First and foremost, your contact lenses must correct your vision problem. Second, each lens must properly fit your cornea, so contact lenses come in tens of thousands of parameters, meaning the combination of size, shape and power.
Your eye care practitioner will evaluate your eyes to determine which lens is right for you, and will take into account your special needs such as dry eyes, a desire for color change or the need for overnight wear.
Contact lenses may also be classified by wearing schedule. Daily wear lenses must be removed, cleaned and stored each night, while extended wear contact lenses are made from materials which are safe to be worn during sleep. You may also have heard of "continuous wear" contact lenses, a type of extended wear that can be worn for up to 30 days.
Various lens designs are available for different vision problems. Spherical contact lenses correct nearsightedness or farsightedness and are indicated by a minus or plus in your prescription, respectively. Bifocal contact lenses are similar to multifocal eyeglasses in that they use different optical zones to correct presbyopia (the decreased ability see at both near and far distances). Toric contact lenses correct astigmatism, which can accompany either nearsightedness or farsightedness.
All of the contact lenses mentioned above can be custom fabricated for unusual prescriptions, and many other contact lens designs are available as well, including designs for conditions like keratoconus.
Many lens designs come in colors that can enhance or change your natural eye color. Special-effect contact lenses are also available for novelty use and are used extensively in theatrical and filmed productions. Prosthetic lenses are colored contact lenses that can cosmetically mask eye disfigurement. Many contact lenses also come with an embedded UV inhibitor.
Which is the right contact lens for you? First and foremost, your contact lenses must correct your vision problem. Second, each lens must properly fit your cornea, so contact lenses come in tens of thousands of parameters, meaning the combination of size, shape and power.
Your eye care practitioner will evaluate your eyes to determine which lens is right for you, and will take into account your special needs such as dry eyes, a desire for color change or the need for overnight wear.
Thursday, June 26, 2008
History of Contact lens
In 1887, Adolf Fick was apparently the first to successfully fit contact lenses, which were made from blown glass
Leonardo da Vinci is frequently credited with introducing the general principle of contact lenses in his 1508 Codex of the eye, Manual D, where he described a method of directly altering corneal power by submerging the eye in a bowl of water. Leonardo, however, did not suggest his idea be used for correcting vision—he was more interested in learning about the mechanisms of accommodation of the eye.[6]
René Descartes proposed another idea in 1636, in which a glass tube filled with liquid is placed in direct contact with the cornea. The protruding end was to be composed of clear glass, shaped to correct vision; however the idea was impracticable, since it would make blinking impossible.
In 1801, while conducting experiments concerning the mechanisms of accommodation, scientist Thomas Young constructed a liquid-filled "eyecup" which could be considered a predecessor to the contact lens. On the eyecup's base, Young fitted a microscope eyepiece. However, like Leonardo's, Young's device was not intended to correct refraction errors.
Sir John Herschel, in a footnote of the 1845 edition of the Encyclopedia Metropolitana, posed two ideas for the visual correction: the first "a spherical capsule of glass filled with animal jelly", and "a mould of the cornea" which could be impressed on "some sort of transparent medium".[7] Though Herschel reportedly never tested these ideas, they were both later advanced by several independent inventors such as Hungarian Dr. Dallos (1929), who perfected a method of making molds from living eyes. This enabled the manufacture of lenses that, for the first time, conformed to the actual shape of the eye.
It was not until 1887 that a German glassblower, F.E. Muller, produced the first eye covering to be seen through and tolerated.[8] In the next year, the German physiologist Adolf Eugen Fick constructed and fitted the first successful contact lens. While working in Zürich, he described fabricating afocal scleral contact shells, which rested on the less sensitive rim of tissue around the cornea, and experimentally fitting them: initially on rabbits, then on himself, and lastly on a small group of volunteers. These lenses were made from heavy brown glass and were 18–21mm in diameter. Fick filled the empty space between cornea/callosity and glass with a dextrose solution. He published his work, "Contactbrille", in the journal Archiv für Augenheilkunde in March 1888.
Fick's lens was large, unwieldy, and could only be worn for a few hours at a time. August Müller in Kiel, Germany, corrected his own severe myopia with a more convenient glass-blown scleral contact lens of his own manufacture in 1888.[9]
Also in 1887, Louis J. Girard invented a similar scleral form of contact lens.[10]
Glass-blown scleral lenses remained the only form of contact lens until the 1930s when polymethyl methacrylate (PMMA or Perspex/Plexiglas) was developed, allowing plastic scleral lenses to be manufactured for the first time. In 1936, optometrist William Feinbloom introduced plastic lenses, making them lighter and more convenient.[11] These lenses were a combination of glass and plastic.
In 1949, the first "corneal" lenses were developed.[12][13][14][15] These were much smaller than the original scleral lenses, as they sat only on the cornea rather than across all of the visible ocular surface, and could be worn up to sixteen hours per day. PMMA corneal lenses became the first contact lenses to have mass appeal through the 1960s, as lens designs became more sophisticated with improving manufacturing (lathe) technology.
One important disadvantage of PMMA lenses is that no oxygen is transmitted through the lens to the conjunctiva and cornea, which can cause a number of adverse clinical effects. By the end of the 1970s, and through the 1980s and 1990s, a range of oxygen-permeable but rigid materials were developed to overcome this problem. Collectively, these polymers are referred to as "rigid gas permeable" or "RGP" materials or lenses. Although all the above lens types—sclerals, PMMA lenses and RGPs—could be correctly referred to as being "hard" or "rigid", the term hard is now used to refer to the original PMMA lenses which are still occasionally fitted and worn, whereas rigid is a generic term which can be used for all these lens types. That is, hard lenses (PMMA lenses) are a sub-set of rigid lenses. Occasionally, the term "gas permeable" is used to describe RGP lenses, but this is potentially misleading, as soft lenses are also gas permeable in that they allow oxygen to move through the lens to the ocular surface.
The principal breakthrough in soft lenses was made by the Czech chemist Otto Wichterle who published his work "Hydrophilic gels for biological use" in the journal Nature in 1959.[16] This led to the launch of the first soft (hydrogel) lenses in some countries in the 1960s and the first approval of the "Soflens" material by the United States Food and Drug Administration (FDA) in 1971. These lenses were soon prescribed more often than rigid lenses, mainly due to the immediate comfort of soft lenses; by comparison, rigid lenses require a period of adaptation before full comfort is achieved. The polymers from which soft lenses are manufactured improved over the next 25 years, primarily in terms of increasing the oxygen permeability by varying the ingredients making up the polymers.
In 1999, an important development was the launch of the first silicone hydrogels onto the market. These new materials encapsulated the benefits of silicone—which has extremely high oxygen permeability—with the comfort and clinical performance of the conventional hydrogels which had been used for the previous 30 years. These lenses were initially advocated primarily for extended (overnight) wear although more recently, daily (no overnight) wear silicone hydrogels have been launched.
Article source From Wikipedia, the free encyclopedia
Leonardo da Vinci is frequently credited with introducing the general principle of contact lenses in his 1508 Codex of the eye, Manual D, where he described a method of directly altering corneal power by submerging the eye in a bowl of water. Leonardo, however, did not suggest his idea be used for correcting vision—he was more interested in learning about the mechanisms of accommodation of the eye.[6]
René Descartes proposed another idea in 1636, in which a glass tube filled with liquid is placed in direct contact with the cornea. The protruding end was to be composed of clear glass, shaped to correct vision; however the idea was impracticable, since it would make blinking impossible.
In 1801, while conducting experiments concerning the mechanisms of accommodation, scientist Thomas Young constructed a liquid-filled "eyecup" which could be considered a predecessor to the contact lens. On the eyecup's base, Young fitted a microscope eyepiece. However, like Leonardo's, Young's device was not intended to correct refraction errors.
Sir John Herschel, in a footnote of the 1845 edition of the Encyclopedia Metropolitana, posed two ideas for the visual correction: the first "a spherical capsule of glass filled with animal jelly", and "a mould of the cornea" which could be impressed on "some sort of transparent medium".[7] Though Herschel reportedly never tested these ideas, they were both later advanced by several independent inventors such as Hungarian Dr. Dallos (1929), who perfected a method of making molds from living eyes. This enabled the manufacture of lenses that, for the first time, conformed to the actual shape of the eye.
It was not until 1887 that a German glassblower, F.E. Muller, produced the first eye covering to be seen through and tolerated.[8] In the next year, the German physiologist Adolf Eugen Fick constructed and fitted the first successful contact lens. While working in Zürich, he described fabricating afocal scleral contact shells, which rested on the less sensitive rim of tissue around the cornea, and experimentally fitting them: initially on rabbits, then on himself, and lastly on a small group of volunteers. These lenses were made from heavy brown glass and were 18–21mm in diameter. Fick filled the empty space between cornea/callosity and glass with a dextrose solution. He published his work, "Contactbrille", in the journal Archiv für Augenheilkunde in March 1888.
Fick's lens was large, unwieldy, and could only be worn for a few hours at a time. August Müller in Kiel, Germany, corrected his own severe myopia with a more convenient glass-blown scleral contact lens of his own manufacture in 1888.[9]
Also in 1887, Louis J. Girard invented a similar scleral form of contact lens.[10]
Glass-blown scleral lenses remained the only form of contact lens until the 1930s when polymethyl methacrylate (PMMA or Perspex/Plexiglas) was developed, allowing plastic scleral lenses to be manufactured for the first time. In 1936, optometrist William Feinbloom introduced plastic lenses, making them lighter and more convenient.[11] These lenses were a combination of glass and plastic.
In 1949, the first "corneal" lenses were developed.[12][13][14][15] These were much smaller than the original scleral lenses, as they sat only on the cornea rather than across all of the visible ocular surface, and could be worn up to sixteen hours per day. PMMA corneal lenses became the first contact lenses to have mass appeal through the 1960s, as lens designs became more sophisticated with improving manufacturing (lathe) technology.
One important disadvantage of PMMA lenses is that no oxygen is transmitted through the lens to the conjunctiva and cornea, which can cause a number of adverse clinical effects. By the end of the 1970s, and through the 1980s and 1990s, a range of oxygen-permeable but rigid materials were developed to overcome this problem. Collectively, these polymers are referred to as "rigid gas permeable" or "RGP" materials or lenses. Although all the above lens types—sclerals, PMMA lenses and RGPs—could be correctly referred to as being "hard" or "rigid", the term hard is now used to refer to the original PMMA lenses which are still occasionally fitted and worn, whereas rigid is a generic term which can be used for all these lens types. That is, hard lenses (PMMA lenses) are a sub-set of rigid lenses. Occasionally, the term "gas permeable" is used to describe RGP lenses, but this is potentially misleading, as soft lenses are also gas permeable in that they allow oxygen to move through the lens to the ocular surface.
The principal breakthrough in soft lenses was made by the Czech chemist Otto Wichterle who published his work "Hydrophilic gels for biological use" in the journal Nature in 1959.[16] This led to the launch of the first soft (hydrogel) lenses in some countries in the 1960s and the first approval of the "Soflens" material by the United States Food and Drug Administration (FDA) in 1971. These lenses were soon prescribed more often than rigid lenses, mainly due to the immediate comfort of soft lenses; by comparison, rigid lenses require a period of adaptation before full comfort is achieved. The polymers from which soft lenses are manufactured improved over the next 25 years, primarily in terms of increasing the oxygen permeability by varying the ingredients making up the polymers.
In 1999, an important development was the launch of the first silicone hydrogels onto the market. These new materials encapsulated the benefits of silicone—which has extremely high oxygen permeability—with the comfort and clinical performance of the conventional hydrogels which had been used for the previous 30 years. These lenses were initially advocated primarily for extended (overnight) wear although more recently, daily (no overnight) wear silicone hydrogels have been launched.
Article source From Wikipedia, the free encyclopedia
What's Contact lens
A contact lens (also known simply as a contact) is a corrective, cosmetic, or therapeutic lens usually placed on the cornea of the eye. Modern soft contact lenses were invented by the Czech chemist Otto Wichterle, who also invented the first gel used for their production.
Contact lenses usually serve the same corrective purpose as conventional glasses, but are lightweight and virtually invisible—many commercial lenses are tinted a faint blue to make them more visible when immersed in cleaning and storage solutions. Some cosmetic lenses are deliberately colored to alter the appearance of the eye.
It has been estimated that 125 million people use contact lenses worldwide (2%),[1] including 28 to 38 million in the United States[1][2] and 13 million in Japan.[3] The types of lenses used and prescribed vary markedly between countries, with rigid lenses accounting for over 20% of currently-prescribed lenses in Japan, Netherlands and Germany but less than 5% in Scandinavia.[1]
People choose to wear contact lenses for various reasons.[4] Some people may consider their appearance to be more attractive with contact lenses than with glasses. Contact lenses are less affected by wet weather, do not steam up, and provide a wider field of vision. They are more suitable for a number of sporting activities.[5] Additionally, ophthalmological conditions such as keratoconus and aniseikonia may not be accurately corrected with glasses.
article source From Wikipedia, the free encyclopedia
Contact lenses usually serve the same corrective purpose as conventional glasses, but are lightweight and virtually invisible—many commercial lenses are tinted a faint blue to make them more visible when immersed in cleaning and storage solutions. Some cosmetic lenses are deliberately colored to alter the appearance of the eye.
It has been estimated that 125 million people use contact lenses worldwide (2%),[1] including 28 to 38 million in the United States[1][2] and 13 million in Japan.[3] The types of lenses used and prescribed vary markedly between countries, with rigid lenses accounting for over 20% of currently-prescribed lenses in Japan, Netherlands and Germany but less than 5% in Scandinavia.[1]
People choose to wear contact lenses for various reasons.[4] Some people may consider their appearance to be more attractive with contact lenses than with glasses. Contact lenses are less affected by wet weather, do not steam up, and provide a wider field of vision. They are more suitable for a number of sporting activities.[5] Additionally, ophthalmological conditions such as keratoconus and aniseikonia may not be accurately corrected with glasses.
article source From Wikipedia, the free encyclopedia
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