A contact lens (also known simply as a contact) is a corrective, cosmetic, or therapeutic lens usually placed on the cornea of the eye. A corrective lens is a lens worn in front of the Eye, mainly used to treat Myopia, Hyperopia, astigmatism, and adjustable focus A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain Modern soft contact lenses were invented by the Czech chemist Otto Wichterle, who also invented the first gel used for their production. The Czech Republic ( ˈt͡ʃɛskaː ˈrɛpuˌblɪka short form in Česko ˈt͡ʃɛskɔ also called Czechia, A chemist is a Scientist trained in the Science of Chemistry. Otto Wichterle ( 27 October, 1913 in Prostějov in Austria-Hungary, now in the Czech Republic &ndash 18 August, 1998 A gel (from the lat gelu &mdashfreezing cold ice or gelatus &mdashfrozen immobile is an apparently solid jelly-like material formed from a
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. Glasses, also called eyeglasses or spectacles, are frames bearing lenses worn in front of the Eyes normally for vision correction, 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%), including 28 to 38 million in the United States and 13 million in Japan.  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. For a topic outline on this subject see List of basic Japan topics. The Netherlands ( Dutch:, ˈnedərlɑnt is the European part of the Kingdom of the Netherlands, which consists of the Netherlands the Netherlands Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. Terminology and usage As a cultural term "Scandinavia" has no official definition and is subject to usage by those who identify with the culture in question as well 
People choose to wear contact lenses for various reasons.  Many 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.  Additionally, ophthalmological conditions such as keratoconus and aniseikonia may not be accurately corrected with glasses. Ophthalmology is the branch of Medicine which deals with the diseases and surgery of the visual pathways including the Eye, Brain Keratoconus (from Greek: kerato- horn cornea and konos cone is a degenerative disorder of the Aniseikonia (sometimes misspelled as aneisokonia, and spelled anisoeikonia in British English is an ophthalmological condition where there is a significant
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 di ser Piero da Vinci ( April 15 1452 – May 2 1519 was an Italian Polymath, having been a scientist Mathematician, Engineer The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. 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. Accommodation is the process by which the:eye increases Optical power to maintain a clear image ( focus) on an object as it draws near the eye 
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. Thomas Young (13 June 1773 &ndash 10 May 1829 was an English Polymath who contributed to the scientific understanding of vision, Light 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". Sir John Frederick William Herschel 1st Baronet KH, FRS ( March 7, 1792 &ndash May 11, 1871)was an The Encyclopaedia Metropolitana was published in London from 1817 to 1845 Quarto, 30 vols Gelatin (also gelatine, from French gélatine) is a translucent colourless brittle nearly tasteless solid substance, extracted from the  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.  In the next year, the German physiologist Adolf Eugen Fick constructed and fitted the first successful contact lens. Adolf Eugen Fick (1 April 1829 in Kassel Germany – 21 August 1901 in Blankenberge Flanders) was a German physiologist usually credited 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. Zürich (, Zürich German: Züri, Zurich, Zurigo; in English generally Zurich) is the largest city in Switzerland and capital of the A scleral lens is a large type of Contact lens that rests on the Sclera and creates a tear -filled vault over the Cornea. 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. For a broader class of publications which include scientific journals see Academic journal.
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. August Müller (1864 &ndash 1949 born in Mönchengladbach, was a medical student at the University of Kiel, Germany, and a pioneer in the manufacture For the city in the United States, see Kiel Wisconsin. For the name see Kiel (name. 
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. Poly(methyl methacrylate ( PMMA) or poly(methyl 2-methylpropenoate is a Thermoplastic and transparent Plastic. In 1936, optometrist William Feinbloom introduced plastic lenses, making them lighter and more convenient. William Feinbloom ( Brooklyn 1904-1985 was an American Optometrist considered to be a pioneer in the field of low vision Visual rehabilitation, and the  These lenses were a combination of glass and plastic.
In 1949, the first "corneal" lenses were developed.  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. The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. 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. Oxygen permeability (abbreviated Dk) is a parameter of a Contact lens. Collectively, these polymers are referred to as "rigid gas permeable" or "RGP" materials or lenses. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds 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. Czechoslovakia may also refer to what is now the Czech Republic and Slovakia. Otto Wichterle ( 27 October, 1913 in Prostějov in Austria-Hungary, now in the Czech Republic &ndash 18 August, 1998  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. Oxygen permeability (abbreviated Dk) is a parameter of a Contact lens.
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. Oxygen permeability (abbreviated Dk) is a parameter of a Contact lens. These lenses were initially advocated primarily for extended (overnight) wear although more recently, daily (no overnight) wear silicone hydrogels have been launched.
A corrective contact lens is a lens designed to improve vision. In many people, there is a mismatch between the refractive power of the eye and the length of the eye, leading to a refraction error. A refractive error, or refraction error, is an error in the focusing of Light by the Eye and a frequent reason for reduced Visual acuity A contact lens neutralizes this mismatch and allows for correct focusing of light onto the retina. The vertebrate retina is a light sensitive part inside the inner layer of the Eye. Conditions correctable with contact lenses include near (or short) sightedness (myopia), far (or long) sightedness (hypermetropia), astigmatism and presbyopia. Myopia (from Greek: μυωπία myopia "near-sightedness" also called near- or short-sightedness, is a refractive defect Hyperopia, also known as farsightedness or longsightedness, is a Defect of vision caused by an imperfection in the Eye (often when Astigmatism is an optical defect whereby vision is blurred due to the inability of the optics of the eye to focus a point object into a sharp focused image on the retina Presbyopia (Greek word "presbys" (πρέσβυς meaning "old person" describes the condition where the Eye exhibits a progressively diminished ability Contact wearers must usually take their contacts out every night or every few days, depending on the brand and style of the contact. Recently there has been renewed interest in orthokeratology, the correction of myopia by deliberate overnight flattening of the cornea, leaving the eye without contact lens or eyeglasses correction during the day. Orthokeratology ( Ortho-K, also known as "dream lens" and "dream vision" is the use of rigid gas-permeable Contact lenses normally worn only at Myopia (from Greek: μυωπία myopia "near-sightedness" also called near- or short-sightedness, is a refractive defect
For those with certain color deficiencies, a red-tinted "X-Chrom" contact lens may be used. Color blindness, a Color vision deficiency is the inability to perceive differences between some of the Colors that others can distinguish Although the lens does not restore normal color vision, it allows some colorblind individuals to distinguish colors better. Color vision is the capacity of an organism or machine to distinguish objects based on the Wavelengths (or frequencies) of the Light they reflect or emit 
ChromaGen lenses have been used and these have been shown to have some limitations with vision at night although otherwise producing significant improvements in colour vision.  An earlier study showed very significant improvements in colour vision and patient satisfaction
Later work that used these ChromaGen lenses with dyslexics in a randomised, double-blind, placebo controlled trial showed highly significant improvements in reading ability over reading without the lenses This system has been granted FDA approval in the United States, which is reassuring to patients.
A cosmetic contact lens is designed to change the appearance of the eye. These lenses may also correct the vision, but some blurring or obstruction of vision may occur as a result of the color or design. In the United States, the FDA frequently calls non-corrective cosmetic contact lenses decorative contact lenses. 
Theatrical contact lenses are a type of cosmetic contact lens that are used primarily in the entertainment industry to make the eye appear pleasing, unusual or unnatural in appearance, most often in horror and zombie movies, where lenses can make one's eyes appear demonic, cloudy and lifeless, or even to make the pupils of the wearer appear dilated to simulate the natural appearance of the pupils under the influence of various illicit drugs. The entertainment industry (much of which is informally known as show business or show biz) consists of a large number of sub-industries devoted to Entertainment Horror films are Movies that strive to elicit Fear, Horror and terror responses from viewers zombie is a reanimated human corpse Stories of zombies originated in the Afro-Caribbean spiritual belief system of Vodou, which told of the people being controlled
Scleral lenses cover the white part of the eye (i. A scleral lens is a large type of Contact lens that rests on the Sclera and creates a tear -filled vault over the Cornea. e. sclera) and are used in many theatrical lenses. The sclera, called the white or white of the eye, is the opaque (usually white though certain animals such as horses and lizards can have black sclera fibrous  Due to their size, these lenses are difficult to insert and do not move very well within the eye. They may also hamper the vision as the lens has a small area for the user to see through. As a result they generally cannot be worn for more than 3 hours as they can cause temporary vision disturbances. 
Similar lenses have more direct medical applications. For example, some lenses can give the iris an enlarged appearance, or mask defects such as absence (aniridia) or damage (dyscoria) to the iris. The iris consists of Pigmented Fibrovascular tissue known as a stroma. Aniridia is a rare Congenital condition characterized by the underdevelopment of the Eye 's iris.
Although many brands of contact lenses are lightly tinted to make them easier to handle, cosmetic lenses worn to change the color of the eye are far less common, accounting for only 3% of contact lens fits in 2004. 
Soft lenses are often used in the treatment and management of non-refractive disorders of the eye. A bandage contact lens protects an injured or diseased cornea from the constant rubbing of blinking eyelids thereby allowing it to heal.  They are used in the treatment of conditions including bullous keratopathy, dry eyes, corneal ulcers and erosion, keratitis, corneal edema, descemetocele, corneal ectasis, Mooren's ulcer, anterior corneal dystrophy, and neurotrophic keratoconjunctivitis. Keratoconjunctivitis sicca (KCS, also called Keratitis sicca, sicca syndrome, For corneal abrasions in dogs and cats see Corneal ulcer. Corneal abrasion is a medical condition involving the loss of the surface Epithelial Recurrent corneal erosion is a disorder of the Eyes characterized by the failure of the Cornea 's outermost layer of Epithelial cells to attach to the underlying Keratitis is a condition in which the Eye 's Cornea, the front part of the eye becomes inflamed Oedema (or Edema in American English formerly known as dropsy or hydropsy, is the increase of Interstitial fluid in any organ &mdash swelling A corneal ulcer, or ulcerative keratitis, is an inflammatory condition of the Cornea involving loss of its outer layer  Contact lenses that deliver drugs to the eye have also been developed. 
The first contact lenses were made of glass, which caused eye irritation, and were not wearable for extended periods of time. Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many But when William Feinbloom introduced lenses made from polymethyl methacrylate (PMMA or Perspex/Plexiglas), contacts became much more convenient. William Feinbloom ( Brooklyn 1904-1985 was an American Optometrist considered to be a pioneer in the field of low vision Visual rehabilitation, and the Poly(methyl methacrylate ( PMMA) or poly(methyl 2-methylpropenoate is a Thermoplastic and transparent Plastic. Poly(methyl methacrylate ( PMMA) or poly(methyl 2-methylpropenoate is a Thermoplastic and transparent Plastic. These PMMA lenses are commonly referred to as "hard" lenses (this term is not used for other types of contacts).
However, PMMA lenses have their own side effects: no oxygen is transmitted through the lens to the cornea, which can cause a number of adverse clinical events. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. In the late 1970s, and through the 1980s and 1990s, improved rigid materials—which were also oxygen-permeable—were developed. Oxygen permeability (abbreviated Dk) is a parameter of a Contact lens. Collectively, these polymers are referred to as rigid gas permeable or 'RGP' materials or lenses. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds One advantage of hard lenses is that, due to their non-porous nature, they do not absorb chemicals or fumes. The absorption of such compounds by other types of contacts can be a problem for those who are routinely exposed to painting or other chemical processes.
Rigid lenses offer a number of unique properties. In effect, the lens is able to replace the natural shape of the cornea with a new refracting surface. The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. This means that a regular (spherical) rigid contact lens can provide good level of vision in people who have astigmatism or distorted corneal shapes as with keratoconus. Keratoconus (from Greek: kerato- horn cornea and konos cone is a degenerative disorder of the
While rigid lenses have been around for about 120 years, soft lenses are a much more recent development. The principal breakthrough in soft lenses made by Otto Wichterle led to the launch of the first soft (hydrogel) lenses in some countries in the 1960s and the approval of the 'Soflens' material (polymacon) by the United States FDA in 1971. Otto Wichterle ( 27 October, 1913 in Prostějov in Austria-Hungary, now in the Czech Republic &ndash 18 August, 1998 A gel (from the lat gelu &mdashfreezing cold ice or gelatus &mdashfrozen immobile is an apparently solid jelly-like material formed from a The United States of America —commonly referred to as the Soft lenses are immediately comfortable, while 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. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds Oxygen permeability (abbreviated Dk) is a parameter of a Contact lens.
A small number of hybrid rigid/soft lenses exist. An alternative technique is piggybacking of contact lenses, a smaller, rigid lens being mounted atop a larger, soft lens. This is done for a variety of clinical situations where a single lens will not provide the optical power, fitting characteristics, or comfort required. Optical power ( dioptric power or refractive power) is the degree to which a lens or Mirror converges or diverges light
In 1999, 'silicone hydrogels' became available. Silicones are largely inert compounds with a wide variety of forms and uses Silicone hydrogels have both the extremely high oxygen permeability of silicone and the comfort and clinical performance of the conventional hydrogels. Oxygen permeability (abbreviated Dk) is a parameter of a Contact lens. Silicones are largely inert compounds with a wide variety of forms and uses These lenses were initially advocated primarily for extended (overnight) wear, although more recently daily (no overnight) wear silicone hydrogels have been launched.
While it provides the oxygen permeability, the silicone also makes the lens surface highly hydrophobic and less "wettable. Oxygen permeability (abbreviated Dk) is a parameter of a Contact lens. " This frequently results in discomfort and dryness during lens wear. In order to compensate for the hydrophobicity, hydrogels are added (hence the name "silicone hydrogels") to make the lenses more hydrophilic. However the lens surface may still remain hydrophobic. Hence some of the lenses undergo surface modification processes which cover the hydrophobic sites of silicone. Some other lens types incorporate internal rewetting agents to make the lens surface hydrophilic.
A daily wear contact lens is designed to be removed prior to sleeping. An extended wear (EW) contact lens is designed for continuous overnight wear, typically for 6 or more consecutive nights. Newer materials, such as silicone hydrogels, allow for even longer wear periods of up to 30 consecutive nights; these longer-wear lenses are often referred to as continuous wear (CW). Generally, extended wear lenses are discarded after the specified length of time. These are increasing in popularity, due to their obvious convenience. Extended- and continuous-wear contact lenses can be worn for such long periods of time because of their high oxygen permeability (typically 5-6 times greater than conventional soft lenses), which allows the eye to remain healthy. Oxygen permeability (abbreviated Dk) is a parameter of a Contact lens.
Extended lens wearers may have an increased risk for corneal infections and corneal ulcers, primarily due to poor care and cleaning of the lenses, tear film instability, and bacterial stagnation. See Corneal ulcers in animals for information about the condition in animals Corneal neovascularization has historically also been a common complication of extended lens wear, though this does not appear to be a problem with silicone hydrogel extended wear. Corneal neovascularization is the excessive ingrowth of Blood vessels from the Limbal vascular plexus into the Cornea, caused by a low reception of The most common complication of extended lens use is conjunctivitis, usually allergic or giant papillary conjunctivitis (GPC), sometimes associated with a poorly fitting contact lens. Allergy is a disorder of the Immune system often also referred to as Atopy. Conjunctivitis (commonly called " Pink Eye " or " Red Eye " in North America and " Madras eye " in India) is an inflammation
The various soft contact lenses available are often categorized by their replacement schedule. The shortest replacement schedule is single use (daily disposable) lenses, which are disposed of each night. These may be best for patients with ocular allergies or other conditions, because it limits deposits of antigens and protein. Allergy is a disorder of the Immune system often also referred to as Atopy. An antigen (from antibody-generating) or immunogen is a substance that prompts the generation of Antibodies and can cause an immune response Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Single use lenses are also useful for people who use contacts infrequently, or for purposes (e. g. swimming or other sporting activities) where losing a lens is likely. More commonly, contact lenses are prescribed to be disposed of on a two-week or monthly basis. Quarterly or annual lenses, which used to be very common, have lost favor because a more frequent disposal schedule allows for thinner lenses and limits deposits. Rigid gas permeable lenses are very durable and may last for several years without the need for replacement. PMMA hard lenses were very durable, and were commonly worn for 5 to 10 years.
A spherical contact lens is one in which both the inner and outer optical surfaces are portions of a sphere. A toric lens is one in which either or both of the optical surfaces have the effect of a cylindrical lens, usually in combination with the effect of a spherical lens. In Optics, a toric lens is a type of lens whose surface is a combination of a Sphere and a cylinder. Myopic (nearsighted) and hypermetropic (farsighted) people who also have astigmatism and who have been told they are not suitable for regular contact lenses may be able to use toric lenses. Myopia (from Greek: μυωπία myopia "near-sightedness" also called near- or short-sightedness, is a refractive defect Hyperopia, also known as farsightedness or longsightedness, is a Defect of vision caused by an imperfection in the Eye (often when If one eye has astigmatism and the other does not, the patient may be told to use a spherical lens in one eye and a toric lens in the other. Astigmatism is an optical defect whereby vision is blurred due to the inability of the optics of the eye to focus a point object into a sharp focused image on the retina Toric lenses are made from the same materials as regular contact lenses but have a few extra characteristics:
Like eyeglasses, contact lenses can have one (single vision) or more (multifocal) focal points. In Geometrical optics, a focus, also called an image point, is the point where Light rays originating from a point on the object converge.
For correction of presbyopia or accommodative insufficiency multifocal contact lenses are almost always used; however, single vision lenses may also be used in a process known as monovision: single vision lenses are used to correct one eye's far vision and the other eye's near vision. Presbyopia (Greek word "presbys" (πρέσβυς meaning "old person" describes the condition where the Eye exhibits a progressively diminished ability Accommodative insufficiency (AI involves the inability of the eye to focus properly on an object Alternatively, a person may wear single vision contact lenses to improve distance vision and reading glasses to improve near vision.
Rigid gas permeable bifocal contact lenses most commonly have a small lens on the bottom for the near correction, when the eyes are lowered to read, this lens comes into the optical path. RGPs must translate (move vertically) to work properly, and thus the gaze of the eye can change from the near to the distant sections, much like bifocal eyeglasses.
Multifocal soft contact lenses are more complex to manufacture and require more skill to fit. All soft bifocal contact lenses are considered "simultaneous vision" because both far and near vision corrections are presented simultaneously to the retina, regardless of the position of the eye. Of course, only one correction is correct, the incorrect correction causes blur. Commonly these are designed with distance correction in the center of the lens and near correction in the periphery, or vice versa.
Intraocular lenses, also known as an implantable contact lenses, are special small corrective lenses surgically implanted in the eye's posterior chamber behind the iris and in front of the lens to correct higher degrees of myopia and hyperopia. An intraocular lens (IOL is an implanted lens in the Eye, usually replacing the existing crystalline lens because it has been clouded over by a Cataract The posterior chamber is a narrow chink behind the peripheral part of the iris of the human eye and in front of the Suspensory ligament of the lens and the Ciliary The iris consists of Pigmented Fibrovascular tissue known as a stroma. The lens is a transparent biconvex structure in the Eye that along with the Cornea, helps to Refract Light to be focused
Most contact lenses are mass produced.
Although many companies make contact lenses, there are four major manufacturers: Vistakon/Johnson & Johnson, CIBA Vision, Bausch & Lomb, and CooperVision. ACUVUE was the first-ever brand of disposable Contact lenses They are made by VISTAKON a subsidiary of Johnson & Johnson. Johnson & Johnson ( is a global American Pharmaceutical, Medical devices and consumer packaged goods Manufacturer founded in 1886 CIBA VISION, a Novartis company is a company that researches develops and manufactures contact lenses and lens care products Bausch & Lomb is an American company based in Rochester New York, is one of the world's leading suppliers of Eye health products such as Contact CooperVision was founded in 1979 and is the 4th largest Contact lens maker in the world and the number one manufacturer of toric lenses 
The prescribing of contact lenses is usually restricted to appropriately qualified eye care practitioners. An eye care professional is an individual who provides a service related to the Eyes or vision. In countries such as the United States (where all contact lenses are deemed to be medical devices by the Food and Drug Administration), the United Kingdom and Australia, optometrists are usually responsible. A medical device is an object which is useful for diagnostic or therapeutic purposes Optometry is a health care profession concerned with Eyes and related structures as well as vision, Visual systems and vision information In France and eastern European countries, ophthalmologists play the major role. Ophthalmology is the branch of Medicine which deals with the diseases and surgery of the visual pathways including the Eye, Brain In other parts of the world, opticians usually prescribe contact lenses. Scientific Equipment OpticianAn optician is an Eye care professional who provides corrective lenses based on a prescription for the correction of a Refractive Prescriptions for contact lenses and glasses may be similar, but are not interchangeable. Glasses, also called eyeglasses or spectacles, are frames bearing lenses worn in front of the Eyes normally for vision correction,
The practitioner or contact lens fitter typically determines an individual's suitability for contact lenses during an eye examination. An eye examination is a battery of tests performed by an Optometrist or Ophthalmologist assessing vision and ability to focus on and discern Corneal health is verified; ocular allergies or dry eyes may affect a person's ability to successfully wear contact lenses. Keratoconjunctivitis sicca (KCS, also called Keratitis sicca, sicca syndrome, Especially above the age of 35 years dry eyes often makes wearing contact lenses too risky, especially soft lenses. Keratoconjunctivitis sicca (KCS, also called Keratitis sicca, sicca syndrome,
The parameters specified in a contact lenses prescription may include:
Many people already wearing contact lenses order contact lenses over the internet at their own risk. Oxygen permeability (abbreviated Dk) is a parameter of a Contact lens. Base curve radius, abbreviated BCR or BC, is a parameter of a Contact lens. Geometry, a diameter of a Circle is any straight Line segment that passes through the center of the circle and whose Endpoints are on the Optical power ( dioptric power or refractive power) is the degree to which a lens or Mirror converges or diverges light A dioptre, or diopter, is a Unit of measurement of the Optical power of a lens or curved Mirror, which is equal to the reciprocal In the US, The Fairness to Contact Lens Consumers Act, which became law in February, 2004, was intended to ensure the availability of contact lens prescriptions to patients.  Under the law consumers have a right to obtain a copy of their contact lens prescription, allowing them to fill that prescription at the business of their choice.
Complications due to contact lens wear affect roughly 4% of contact lens wearers each year. Complication, in Medicine, is an unfavorable evolution of a Disease, a Health condition or a medical treatment  Excessive wear of contact lenses, particularly overnight wear, is associated with most of the safety concerns.  Problems associated with contact lens wear may affect the eyelid, the conjunctiva, the various layers of the cornea, and even the tear film that covers the outer surface of the eye. An eyelid is a thin fold of skin that covers and protects an Eye. The conjunctiva is a clear membrane that covers the Sclera (white part of the Eye) and lines the inside of the Eyelids It is made of lymphoid tissue The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. Tears are the liquid product of a process of lacrimation to clean and lubricate the Eyes The word lacrimation may also be used in a medical or literary sense 
Studies conducted on side effects from long term wearing of contact lens, ie, over 5 years, such as by: Zuguo Liu PhD, MD and Stephen C. Pflugfelder MD "The effects of long-term contact lens wear on corneal thickness, curvature, and surface regularity" Ophthalmology , Volume 107 , Issue 1 , Pages 105 - 111 concludes that: Long-term contact lens wear appears to decrease the entire corneal thickness and increase the corneal curvature and surface irregularity.
It has also suggested elsewhere that the thinning of the cornea results in patients unable to have catracts operations later on in life if required because off their reduced corneal thickness.
Before touching the contact lens or one's eyes, it is important to thoroughly wash & rinse hands with a soap that does not contain moisturizers or allergens such as fragrances. Ptosis is an abnormally low position (drooping of the upper Eyelid. Contact dermatitis is a term for a Skin reaction resulting from exposure to Allergens (allergic contact dermatitis or irritants (irritant contact dermatitis Conjunctivitis (commonly called " Pink Eye " or " Red Eye " in North America and " Madras eye " in India) is an inflammation Superior limbic keratoconjunctivitis is an ocular surface disease characterized by episodes of recurrent inflammation of the superior Cornea and Limbus, as well In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body For corneal abrasions in dogs and cats see Corneal ulcer. Corneal abrasion is a medical condition involving the loss of the surface Epithelial Recurrent corneal erosion is a disorder of the Eyes characterized by the failure of the Cornea 's outermost layer of Epithelial cells to attach to the underlying See Corneal ulcers in animals for information about the condition in animals Chronic Hypoxia is a pathological condition in which the body as a whole ( generalized hypoxia) or region of the body ( tissue hypoxia) is deprived of adequate An infection is the detrimental Colonization of a host Organism by a foreign Species. Keratitis is a condition in which the Eye 's Cornea, the front part of the eye becomes inflamed The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular Acanthamoeba is a genus of Amoebae one of the most common Protozoa in soil and also frequently found in Fresh water and other habitats Fusarium is a large genus of filamentous Fungi widely distributed in soil and in association with plants Keratitis is a condition in which the Eye 's Cornea, the front part of the eye becomes inflamed Keratoconus (from Greek: kerato- horn cornea and konos cone is a degenerative disorder of the The corneal endothelium is a monolayer of specialized flattened mitochondria-rich cells that lines the posterior surface of the Cornea and faces the Anterior Hand washing is the act of cleansing the Hands with Water or another Liquid, with or without the use of Soap or other Detergents SOAP (see below for name and origins is a protocol for exchanging XML -based messages over Computer networks normally using Moisturisers or moisturizers (see spelling differences) are complex mixtures of chemical agents specially designed to make the external layers of the Skin An allergen is a nonparasitic Antigen capable of stimulating a Type-I hypersensitivity reaction in atopic individuals Perfume is a mixture of fragrant Essential oils and Aroma compounds Fixatives and Solvents used to give the human body animals objects and living The soap should not be antibacterial due to risk of improper hand washing and the possibility of destroying the natural bacteria found on the eye. Antiseptics (from Greek αντί - anti, '"against" + σηπτικός - septikos, "putrefactive" are antimicrobial These bacteria keep pathogenic bacteria from colonizing the cornea. The technique for removing or inserting a contact lens varies slightly depending upon whether the lens is soft or rigid.
Contact lenses are typically inserted into the eye by placing them on the index finger with the concave side upward and raising them to touch the cornea. The other hand may be employed to keep the eye open. Problems may arise particularly with disposable soft lenses; if the surface tension between the lens and the finger is too great the lens may turn itself inside out; alternatively it may fold itself in half. For the work of fiction see Surface Tension (short story. Surface tension is a property of the surface of a Liquid that causes it to When the lens first contacts the eye, a brief period of irritation may ensue as the eye acclimatises to the lens and also (if a multi-use lens is not correctly cleansed) as dirt on the lens irritates the eye. Irrigation may help during this period, which generally should not exceed one minute.
A soft lens may be removed by holding the eyelids open and grasping the lens with opposing digits. This method can cause irritation, could risk damage to the eye and may in many cases be difficult, in part due to the blink reflex. The corneal reflex, also known as the blink reflex, is an involuntary Blinking of the Eyelids elicited by stimulation (such as touching or a foreign body If the lens is pushed off the cornea it will buckle up (due to the difference in curvature), making it easier to grasp.
Rigid contact lenses may be removed by pulling with one finger on the outer or lateral canthus, then blinking to cause the lens to lose adhesion. Canthus (pl canthi, palpebral commissures) is either corner of the Eye where the upper and lower Eyelids meet Adhesion is the tendency of certain dissimilar molecules to cling together due to Attractive forces. The other hand is typically cupped underneath the eye to catch the lens. There also exist small tools specifically for removing lenses, which resemble small plungers made of flexible plastic; the concave end is raised to the eye and touched to the lens, forming a seal stronger than that of the lens with the cornea and allowing the lens to be removed from the eye. A plunger is a common device used to release stoppages in Plumbing.
While daily disposable lenses require no cleaning, other types require regular cleaning and disinfecting in order to retain clear vision and prevent discomfort and infections by various microorganisms including bacteria, fungi, and Acanthamoeba, that form a biofilm on the lens surface. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Acanthamoeba is a genus of Amoebae one of the most common Protozoa in soil and also frequently found in Fresh water and other habitats A biofilm is a structured community of Microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface There are a number of products that can be used to perform these tasks:
Some products must only be used with certain types of contact lenses: it is important to check the product label to make sure that it can be used for a given type of lens. It is also important to follow the product's directions carefully to reduce risk of eye infection or eye irritation. In addition, one should remember to wash the contact cases or lens covers thoroughly with water and multipurpose solution or hydrogen peroxide to avoid formation of biofilms on its surfaces.
It is important to ensure that the product does not become contaminated with microorganisms: the tips of the containers for these solutions should never touch any surface, and the container should be kept closed when not in use. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually To counteract minor contamination of the product and kill microorganisms on the contact lens, some products may contain preservatives such as thiomersal, benzalkonium chloride, benzyl alcohol, and other compounds. A preservative is a natural or synthetic chemical that is added to products such as foods pharmaceuticals paints biological samples wood etc Thiomersal ( INN) (C9H9HgNaO2S commonly known in the United States as thimerosal, is an Organomercury compound (approximately Benzalkonium chloride, also known as alkyldimethylbenzylammonium chloride and ADBAC, is a mixture of alkylbenzyldimethylammonium chlorides of various even-numbered Benzyl alcohol is an Organic compound with the formula C6H5CH2OH In 1989, thiomersal was responsible for about 10% of problems related to contact lenses: because of this, many products no longer contain thimerosal. Preservative-free products usually have shorter shelf life. Shelf life is that length of time that Food, drink Medicine and other perishable items are given before they are considered unsuitable for sale or For example, non-aerosol preservative-free saline solutions can typically be used for only two weeks once opened. The introduction of silicone-hydrogel soft contact lens materials in 1999 made selection of the proper disinfecting solution more important. One study has noted several incompatibilities between these new lens materials and some solutions resulting in corneal staining. 
A large segment of current contact lens research is directed towards the treatment and prevention of conditions resulting from contact lens contamination and colonization by foreign organisms. It is generally accepted by clinicians that the most significant complication of contact lens wear is microbial keratitis and that the most predominant microbial pathogen is Pseudomonas aeruginosa. Keratitis is a condition in which the Eye 's Cornea, the front part of the eye becomes inflamed Pseudomonas aeruginosa is a Gram-negative, aerobic, rod-shaped Bacterium with unipolar motility.  Other organisms are also major causative factors in bacterial keratitis associated with contact lens wear, although their prevalence varies across different locations. These include both the Staphylococcus species (aureus and epidermidis) and the Streptococcus species, among others. Staphylococcus (in Greek σταφυλη staphyle means bunch of grapes and κοκκος coccos means granule is a genus of Gram-positive Streptococcus is a Genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the  Microbial keratitis is a serious focal point of current research due to its potentially devastating effect on the eye, including severe vision loss. 
One specific research topic of interest is how microbes such as Pseudomonas aeruginosa invade the eye and cause infection. Pseudomonas aeruginosa is a Gram-negative, aerobic, rod-shaped Bacterium with unipolar motility. Although the pathogenesis of microbial keratitis is not well understood, many different factors have been investigated. One group of researchers showed that corneal hypoxia exacerbated Pseudomonas binding to the corneal epithelium, internalization of the microbes, and induction of the inflammatory response.  One way to alleviate hypoxia is to increase the amount of oxygen transmitted to the cornea. Although silicone-hydrogel lenses almost eliminate hypoxia in patients due to their very high levels of oxygen transmissibility, they also seem to provide a more efficient platform for bacterial contamination and corneal infiltration than other conventional hydrogel soft contact lenses. A recent study showed that Pseudomonas aeruginosa and Staphylococcus epidermis adhere much more strongly to silicone hydrogel contact lenses than conventional hydrogel contact lenses and that adhesion of Pseudomonas aeruginosa was 20 times stronger than adhesion of Staphylococcus epidermidis. Pseudomonas aeruginosa is a Gram-negative, aerobic, rod-shaped Bacterium with unipolar motility. Staphylococcus epidermidis is a member of the bacterial genus Staphylococcus, consisting of Gram-positive cocci arranged in clusters  This might help to explain one reason why Pseudomonas infections are the most predominant.
Another important area of contact lens research deals with patient compliance. Compliance is a major issue surrounding the use of contact lenses because patient noncompliance often leads to contamination of the lens, storage case, or both.  The introduction of multipurpose solutions and daily disposable lenses have helped to alleviate some of the problems observed from inadequate cleaning but new methods of combating microbial contamination are currently being developed. A silver-impregnated lens case has been developed which helps to eradicate any potentially contaminating microbes that come in contact with the lens case. Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen  Additionally, a number of antimicrobial agents are being developed that have been embedded into contact lenses themselves. An antimicrobial is a substance that kills or inhibits the growth of Microbes such as Bacteria, Fungi, or Viruses. Contact lenses with covalently attached Selenium molecules have been shown to reduce bacterial colonization without adversely affecting the cornea of a rabbit eye and octylglucoside used as a contact lens surfactant significantly decreases bacterial adhesion. Selenium (səˈliniəm is a Chemical element with the Atomic number 34 represented by the chemical symbol Se, an atomic mass of 78  These compounds are of particular interest to contact lens manufacturers and prescribing optometrists because they do not require any patient compliance to effectively attenuate the effects of bacterial colonization.