Contact lens

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Lenses contacts , or just contacts , are thin lenses placed directly on the eye's surface. Contact lenses are considered medical devices and may be used for correct vision, or for cosmetic or therapeutic reasons. In 2004, it was estimated that 125 million people worldwide use contact lenses, including 28 to 38 million in the United States. In 2010, the worldwide contact lens market is estimated at $ 6.1 billion, while the US soft lens market is estimated at $ 2.1 billion. Some analysts estimate that the global contact lens market will reach $ 11.7 billion by 2015. In 2010, the average age of contact lens wearers globally was 31 years, and two thirds of users were women.

People choose to wear contact lenses for various reasons. Aesthetics and cosmetics are the main motivating factors for people who want to avoid wearing glasses or changing the appearance of their eyes. Others wear contact lenses for functional or optical reasons. When compared with glasses, contact lenses usually provide better peripheral vision, and do not collect moisture (from rain, snow, condensation etc.) or sweat. This can make them more preferred for sports and other outdoor activities. Contact lens wearers can also wear sunglasses, glasses, or other glasses of their choice without having to match them with prescription lenses or worry about compatibility with eyeglasses. In addition, there are conditions such as keratoconus and aniseikonia which are usually corrected better with contact lenses compared with glasses.

The size of the contact lens market tends to grow due to increased eye-related events such as astigmatism, hyperopia and myopia. Other drivers are population increase, desire to make fashion statement, and technological progress. By the end of 2020, the value of the contact lens market is predicted to reach $ 13.5 billion.

Video Contact lens

Histori

Leonardo da Vinci is often credited with introducing the idea of ​​contact lenses in his eyes, eye codex, Manual D, where he describes a method that directly alters the strength of the cornea by drowning the head in a water bowl or wearing a full glass moisture above the eyes. None of the practical ideas were applicable to da Vinci's time. He does not suggest his idea used to correct the vision, as he is more interested in learning about the mechanisms of accommodation of the eye.

Descartes proposed another idea in 1636 - a glass-filled glass tube in direct contact with the cornea. The protruding ends must be composed of clear glass, formed to correct vision; However, the idea is not practical because it makes flickering impossible.

In 1801, Thomas Young made a pair of basic contact lenses based on the Descartes model. He uses a candle to attach a lens of water to his eyes, which neutralizes his bias strength. He then corrects it with another pair of lenses.

However, like da Vinci's device, Young is not meant to fix refractive errors. Sir John Herschel, in the 1845 edition of the Encyclopedia Metropolitana , proposed two ideas for visual correction: the first "round capsule containing glass of animal jelly" , and "corneal mold " which can be impressed on "a kind of transparent medium". Although Herschel reportedly never tested these ideas, they were later developed by some independent inventors such as the Hungarian Dso with IstvÃÆ'¡n KomÃÆ'¡romy (1929), who perfected the method of making prints from living eyes. This allows the manufacture of lenses that, for the first time, fit the actual shape of the eye.

In 1888, the German eye doctor Adolf Gaston Eugen Fick built and installed his first successful contact lens. While working at ZÃÆ'¼rich, he described the fabrication of afocalal shellfish contacts, located at the edge of less sensitive tissue around the cornea, and experimentally adjusted it; initially on the rabbit, then on himself, and lastly on a small group of volunteers. This lens is made of thick blown glass and 18-21 mm in diameter (0.71-0.83 inches). Fick fills the empty space between the cornea and the glass with the dextrose solution. He published his work, "Contactbrille" , in the journal Archiv fÃÆ'¼r Augenheilkunde in March 1888.

Fick's lens is big and heavy, and can only be worn for a few hours at a time. August MÃÆ'¼ller in Kiel, Germany, corrected its own farsightedness with a glass scleral contact lens more comfortable from its own manufacture in 1888.

Also in 1887, Louis J. Girard discovered a similar form of sclera lens. The opaque glass-scleral lens remained the only form of contact lens until 1930 when Perspex/Plexiglas was developed, allowing plastic scleral lenses to be produced for the first time. In 1936, Optometrist William Feinbloom introduced a plastic lens, making it lighter and more comfortable. These lenses are a combination of glass and plastic. In 1940, the German optometrist, Heinrich WÃÆ'¶hlk, produced a fully plastic lens, based on experiments conducted during the 1930s.

In 1949, the first "cornea" lens was developed. It's much smaller than the original scleral lens, as they just sit on the cornea rather than on all visible eye surfaces, and can be worn up to sixteen hours a day. The polymethyl methacrylate (PMMA) corneal lens became the first contact lens to have mass appeal during the 1960s, as lens design became more sophisticated by improving manufacturing technology.

The early 1950s and 60s corneal lenses were relatively expensive and fragile, resulting in a market development for contact lens insurance. Lens Replacement Insurance, Inc. (now known as RLI Corp) removed its original flagship product in 1994 after contact lenses became more affordable and easier to replace.

One of the major drawbacks of PMMA lenses is that they do not allow oxygen into the conjunctiva and cornea, causing a number of potentially harmful and potentially harmful clinical effects. In the late 1970s and into the 80s and 90s, a variety of oxygen-absorbent but rigid materials were developed to address this problem. Chemist Norman Gaylord plays an important role in the development of this new oxygen-permeable contact lens. Collectively, these polymers are referred to as "rigid gas permeable" or RGP materials or lenses. Although all types of contact lenses above - scleral, PMMA and RGP - can be properly referred to as "stiff" or "hard", the latter term is now used for original PMMA, which is still occasionally installed and used, while "rigid" is a generic term for all kinds of these lenses; so the hard lens (PMMA) is part of a rigid contact lens. Sometimes, the term "gas permeable" is used to describe RGPs, which are somewhat misleading because soft contact lenses can also be on the surface of the gas as it allows oxygen to flow to the ocular surface.

The major breakthroughs in soft lenses were made by Czech chemists Otto Wichterle and Drahoslav LÃÆ'm, who published their work "Hydrophilic Gel for Biological Use" in the journal Nature in 1959. In 1965 , The National Patent Development Corporation (NPDC) purchased the American right to manufacture the lens and subsequently sublicens the rights to Bausch & amp; Lomb, which started producing them in the United States. The work of Czech scientists led to the launch of the first contact lens (hidrogel) contact lens in some countries in 1960 and the first approval of Soflens material by US Food. and Drug Administration (FDA) in 1971. These soft lenses are prescribed more often than rigid, because of direct and much greater comfort (rigid lenses require adaptation period before full comfort, if any, is achieved). The polymer from the resulting soft lens increases over the next 25 years, especially in terms of increased oxygen permeability, by varying the material. In 1972, British optician Rishi Agarwal was the first to suggest disposable soft contact lenses.

In 1998, the first silicone hydrogel contact lenses were released by Ciba Vision in Mexico. These new materials encapsulate the benefits of silicon - which has a very high oxygen permeability - with the comfort and clinical performance of conventional hydrogels that have been used for the previous 30 years. These contact lenses are initially recommended especially for extended users (overnight), although more recently, every day (no night) wearing silicone hydrogels has been launched.

In slightly modified molecules, polar groups are added without altering the silicone hydrogel structure. This is referred to as Tanaka monomer because it was created and patented by Kyoichi Tanaka from Menicon Co. Japan in 1979. Second generation silicon hydrogels, such as galyfilcon A (Acuvue Advance, Vistakon) and senofilcon A (Acuvue Oasys, Vistakon), use Tanaka monomer. Vistakon further enhances Tanaka monomer and adds another molecule, which acts as an internal wetting agent.

Comfilcon A (Biofinity, CooperVision) is the first third-generation polymer. The patent claims that the material uses two different size silicon macromers which, when used in combination, produce very high oxygen permeability (for certain water content). Enfilcon A (Avaira, CooperVision) is another third-generation material that can naturally be moistened; its water content is 46%.

Maps Contact lens

Type

Contact lenses are classified in various ways: with the main function, material, schedule of use (how long the lens can be used), and replacement schedule (how long before the lens should be removed).

Function

Corrective contact lens

Corrective contact lenses are designed to improve vision, most often by correcting bias errors. This is done by focusing the light directly so that it enters the eye with the right force for clear vision.

Spherical contact lenses bend light evenly in all directions (horizontally, vertically, etc.). They are usually used to correct myopia and hypermetropia. Torque contact lenses have a different focusing force horizontally than vertically, and as a result can correct astigmatism. Some round rigid lenses can also correct astigmatism. Since the toric lens must have the right orientation to correct one's astigmatism, it must have additional design characteristics to prevent it from spinning away from ideal alignment. This can be done by weighing the bottom of the lens or by using other physical characteristics to turn the lens back into position. Some torik contact lenses have marks or scratches that may help the ophthalmologist or user in installing the lens. The first disposable torque contact lens was introduced in 2000 by Vistakon.

The correction of presbyopia (the need for different reading recipes from the prescribed prescription for distance) poses additional challenges in the installation of contact lenses. Two main strategies exist: multifocal and monovision lenses.

Multifocal contact lenses (eg bifocals or progressives) can be compared to glasses with bifocal or progressive lenses because they have multiple focal points. Multifocal contact lenses are usually designed for continuous viewing through the lens center, but some designs do combine lens position shifts to see through the reading power (similar to bifocal glasses).

Monovision is the use of single-vision lenses (one focal point per lens) to focus the eyes (usually dominant) for distance vision and the other for close work. The brain then learns to use these settings to see clearly at all distances. A technique called monovision is modified using a multifocal lens and also specializes one eye for distance and the other to close, thus benefiting from both systems. Or, one can only wear reading glasses over their distance contact lenses. Treatment is recommended for people with a history of previous strabismus and those with significant phoriasis, who are at risk for eye disorders under monovision. Studies have shown no adverse effects to promote performance in monovision contact lens wearers.

Another type of vision correction

For those with certain color defects, red X-Chrom contact lenses may be used. Although such lenses do not restore normal color vision, this lens allows some color-blind people to better differentiate colors. Red filtering filtering lenses can also be an option for extreme light sensitivity in some visual deficiencies such as achromatopsia.

ChromaGen contact lenses have been used and are shown to have some night vision limitations despite the reverse producing significant improvements in color vision. Previous research has shown significant improvements in color vision and patient satisfaction.

Then work using ChromaGen lenses with dyslexia in a randomized, double-blind, placebo-controlled trial showed a very significant improvement in the ability to read without a lens. The system has obtained FDA approval for use in the United States.

Enlargement is another area under investigation for future contact lens applications. Embedding telescopic lenses and electronic components suggests that the use of contact lenses in the future can be very diverse. However, there are still obstacles that prevent the transition from this technology, from research and development to practical application and commercial availability.

Cosmetic contact lens

Cosmetic contact lenses are designed to change the appearance of the eyes. This lens can also correct bias errors. Although many brands of contact lenses are slightly colored to make them easier to handle, cosmetic lenses used to change eye color are much more common, accounting for only 3% of matching contact lenses in 2004.

In the United States, the FDA labeled non-corrective cosmetic contact lenses as decorative lens lenses. Like other contact lenses, cosmetic lenses carry the risks of mild to serious complications, including red eye, irritation and infection.

Due to their medical nature, colored contact lenses, similar to the usual ones, are illegal to be purchased in the United States without a valid prescription. Those with perfect vision can buy color contacts for cosmetic reasons, but they still need their eyes to be measured for a "plano" recipe, meaning one with a zero vision correction. This is for safety reasons so that the lens will match the eye without causing irritation or redness.

Some colored contact lenses completely cover the iris, thus dramatically changing the color of the eyes. Other colored contact lenses only color the iris, highlight and beautify the original color. New trends in Japan, South Korea, and China are circular contact lenses, which extend the iris view to the sclera by having a dark area around it. The result is a larger and wider iris appearance, a look that reminds the doll's eyes.

One of the disadvantages of cosmetic lenses is not knowing how they will look before trying physically. This has led to industries where lens retailers are heavily influenced by cutting-edge digital technology, particularly Virtual Dressing Room technology. Virtual Dressing Room technology offers users the option to upload photos so they can try different lenses and feel how they look before they make a purchase. Examples of retailers currently offering this technology are Freshlook Color Studios and Colorful Eyes.

Cosmetic lenses can have more direct medical applications. For example, some contact lenses can restore the look and, to some extent function, of the iris being damaged or lost.

Therapeutic scleral lens

The scleral lens is a large, powerful, oxygenated contact lens that can seep over the sclera and create a tear-filled dome above the cornea. The cause of this unique positioning is usually relevant to a particular patient whose corneas are too sensitive to support the lens directly. Scleral lenses can be used to improve vision and reduce pain and light sensitivity for people suffering from more eye disorders or injuries, such as severe dry eye syndrome (Kerotanconjuctivis sicca), microphthalmia, keratoconus, corneal ecta, Stevens-Johnson syndrome, syndrome SjÃÆ'¶gren, aniridia, neurotropic keratitis (aneasthetic cornea), post-LASIK complications, high-order eye Aberrations, post-transplantation corneal complications and pellucid degeneration. Eye injuries such as surgical complications, distorted corneal implants, and chemical injuries and burns can also be treated with scleral lenses.

Therapeutic soft lenses

Soft lenses are often used in the care and management of non-refractive eye disorders. The contact lens of the bandage protects the injured or sick cornea from constantly rubbing the blinking eyelids allowing it to heal. They are used in the treatment of conditions including bullous keratopathy, dry eyes, corneal abrasion and erosion, keratitis, corneal edema, descemetocele, corneal ecchasia, Mooren ulcers, anterior corneal dystrophy, and neurotrophic keratoconjunctivitis. Contact lenses that deliver the drug to the eye have also been developed.

Materials

Rigid lens

Glass lenses are never comfortable enough to gain widespread popularity. The first lenses to do so are those made of polymethyl methacrylate (PMMA or Perspex/Plexiglas), now commonly referred to as "hard" lenses. Their main disadvantage is that they do not allow oxygen to pass through the cornea, which can lead to a number of poor and often serious clinical events. Beginning in the late 1970s, improved oxygen-permeable rigid materials were developed. Contact lenses made of these materials are called rigid gas permeable lenses or 'RGP'.

The rigid lens can replace the natural form of contact (cornea) with a new refracting surface. This means rigid and round contact lenses can correct astigmatism. Rigid can also be made as front torque, rear-torik, or bitorik. This is different from the spherical contact lens in one or both surfaces of the lens that provides torque correction. Rigidity can also correct corneal irregularities, such as keratoconus. In most cases, patients with keratoconus may see better through the rigid than through the glasses. Rigid is more chemically inert, allowing them to be used in more challenging environments than soft lenses.

Soft lenses

While rigid lenses have been around for about 120 years, soft lenses are a much newer development. The first commercially developed soft contact lenses developed by Dr. Allan Isen, optician from Buffalo, New York who has functioned as a personal optometrist for American President Lyndon B. Johnson.

The main breakthrough in soft contact lenses made by Otto Wichterle led to the launch of the first soft lens (hydrogel) in some countries in the 1960s and the approval of the FDA's "Softens" (polymacon) material in the United States in 1971. Softs are usually comfortable right after insertion, while the rigid requires an adaptation period before some comfort, if any, is reached.

In 1998, silicone hydrogels became available. These materials have a very high oxygen permeability of silicon and the comfort and clinical performance of conventional hydrogels. Because silicon allows more oxygen permeability than water, the silicone hydrogel oxygen permeability is not tied to the water content of the lens. Lenses have now been developed with so much oxygen permeability that they are approved for overnight wear (long wear). Lenses that are approved for everyday wear are also available in silicone hydrogel materials.

The deficiency of silicone hydrogels is that they are slightly more rigid and the surface of the lens can be hydrophobic, making it less "wetted" - the factors that influence the convenience of lens use. New manufacturing techniques and changing multipurpose solutions have minimized this effect. The process of surface modification called the plasma layer changes the hydrophobic properties of the lens surface. Another technique incorporates an internal rewetting agent to create a hydrophilic lens surface. The third process uses longer backbone polymer chains that result in less cross-linking and increased wetting without surface or additive changes.

Hybrid

A small number of hybrid lenses exist. Usually this contact lens consists of a rigid center and a soft "skirt". The same technique is "piggyback" smaller and rigid lenses on the surface of larger and soft lenses. These techniques are often chosen to provide the benefits of vision correction from rigid lenses and soft lens comforts. In 2014, this is a new technology that is only provided by some companies.

Schedule wear

"Everyday clothes" (DW) contact lenses are designed to be worn for a day and released before bed. The "extended wear" contact lens (EW) is designed for continuous overnight usage, usually up to 6 consecutive nights. Newer materials, such as silicone hydrogels, allow longer usage periods of up to 30 consecutive nights; these long-lasting lenses are often referred to as "continuous wear" (CW). EW and CW contact lenses can be worn overnight due to their high oxygen permeability. When awake, the eyes are mostly open, allowing oxygen from the air to dissolve into the tears and pass through the lens to the cornea. Asleep, oxygen is supplied from the blood vessels in the back of the eyelid. A lens blocking the flow of oxygen to the cornea causes corneal hypoxia which can lead to serious complications, such as a corneal ulcer that, if left untreated, can permanently reduce vision. EW and CW contact lenses typically allow 5 to 6 times more oxygen transfer than conventional softs, allowing the cornea to remain healthy, even with closed eyelids.

Wearing lenses designed for everyday nightwear has an increased risk for corneal infection, corneal ulcers and corneal neovascularization - this latter condition, once established, can not be reversed and will ultimately damage visual acuity through diminished corneal transparency. The most common complication of long wear is giant papillary conjunctivitis (GPC), sometimes associated with poorly fitting contact lenses.

Replacement schedule

Contact lenses are often categorized according to their replacement schedule. Disposable lenses (called disposable once a day or day) are discarded after one use. Because they do not have to be resistant to wear and repetitive repeated use, these lenses can be made thinner and lighter, greatly enhancing their comfort. Replaced lenses often collect fewer deposits of allergens and germs, making these lenses better for patients with ocular allergies or for those prone to infection. Disposable lenses are also useful for people who rarely wear contact lenses, or when lens loss may or may not be easily replaced (such as while on vacation). They are also considered useful for children because cleaning or disinfecting is not necessary, leading to increased adherence.

Other disposable contact lenses are designed for replacement every two or four weeks. Quarterly or yearly lenses, which used to be very common, are much less. Rigid gas permeable lenses are very durable and can last for several years without the need for replacement. PMMA hards are very durable and are generally worn for 5 to 10 years, but have some disadvantages.

Lenses with different replacement schedules can be made from the same material. Although the material is the same, the difference in the manufacturing process determines whether the resulting lens will be "daily wear" or recommended for replacement of two or four weeks. However, sometimes manufacturers use lenses that are completely identical and simply pack them with different labels.

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Manufacturing

Typically, soft contact lenses are mass-produced, while stiffness is tailor-made for the exact specifications for each patient.

• Spin-cast lenses - Soft lenses produced by liquid silicone spin in a high-speed rotating mold.
• Diamond play - This type is cut and polished on a CNC lathe. The lens begins as a cylindrical disk stored in the jaws of a lathe equipped with industrial grade diamonds as a cutting tool. The CNC lathe may change at almost 6000 RPM because the cutter removes the desired amount of material from the inside of the lens. The surface of the concave (in) lens is then polished with a fine abrasive paste, oil, and a small polyester cotton ball that is rotated at high speed. To hold the fine lens in an inverted manner, the wax is used as an adhesive. The convex surface of the lens (outer) is cut and polished by the same process. This method can be used to form rigid and soft lenses. In the case of softs, the lenses are cut from a rigid dehydration polymer until water is re-introduced.
• Molded - Molding is used to produce some brands of soft contact lenses. Rotating mold is used and the liquid material is added and shaped by centripetal force. Injection molding and computer control are also used to make the lens almost perfect. The lens is kept moist throughout the printing process and is never dried and rehydrated.

Many companies make contact lenses. In the United States, there are five major manufacturers:

• Valeant Pharmaceuticals: via Bausch & amp; Subsidiary of Lomb.
• Novartis: through a subsidiary of Alcon.
• The Cooper Companies: through its subsidiary CooperVision.
• Johnson & amp; Johnson; makers of Acuvue lenses.
• Custom Contact X-Cel; Westcon lens maker.

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Recipes

Parameters specified in the contact lens prescription may include:

• Material/Brand Name
• The base curve radius (BC, BCR)
• The diameter (D, OAD)
• Dioptimal power
• The thickness of the middle (CT)

Prescriptions for contact lenses and eyeglasses may be similar, but not interchangeable. The prescription of contact lenses is usually limited to various combinations of optometrists, optometrists and optics. An eye exam is needed to determine the eligibility of an individual to wear contact lenses. This usually includes refraction to determine the proper lens strength and the anterior segment health assessment of the eye. Many eye diseases prohibit the use of contact lenses, such as active infection, allergies, and dry eyes. Keratometry is very important in the installation of rigid lenses.

United States

Contact lenses are prescribed by optometrists, optometrists or specialty licensed opticians under the supervision of an ophthalmologist. Contact lenses can usually be ordered in an office that performs eye examinations and installation. The Fairness to Contact Lens Consumers Act gives consumers the right to get a copy of their contact lens prescription, allowing them to fill it in their preferred lens provider.

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Complications

Contact lenses are generally safe for use correctly. Complications of contact lens wear affects approximately 5% of users each year. Factors that cause eye damage vary, and improper use of contact lenses can affect the eyelids, conjunctiva, and most importantly, the entire structure of the cornea. Poor lens treatment can cause infection by various microorganisms including bacteria, fungi, and Acanthamoeba ( Acanthamoeba keratitis).

Many complications arise when contact lenses are worn not as prescribed (inappropriate timetable or lens replacement). Sleeping in lenses that are not designed or approved for long-term use are a common cause of complications. Many people are too long before changing their contacts, wearing lenses designed for 1, 14, or 30 days of use for several months or years. While this saves on the cost of the lens, it risks permanent damage to the eyes and even loss of vision.

One of the main factors that cause complications is that contact lenses are an oxygen barrier. The cornea needs constant supply of oxygen to remain transparent and function properly; usually get oxygen from the surrounding air while awake, and from the blood vessels behind the eyelids during sleep. The most prominent risks associated with chronic low-chronic low oxygen to the cornea include corneal neovascularization, increased epithelial permeability, bacterial adherence, microcysts, corneal edema, endothelial polymegetism, dry eye and increased myopia potential. That is why much research on the latest soft and rigid contact lens materials is centered on increasing the transmission of oxygen through the lens.

Wrong contact lens handling can also cause problems. Corneal abrasion may increase the likelihood of infection. When combined with improper lens cleaning and disinfection, the risk of infection is increasing. Decreased corneal sensitivity after prolonged use of contact lenses may cause the patient to miss some of the earliest symptoms of the complication.

The way contact lenses interact with natural tear film is a key factor in determining lens comfort and visual clarity. People suffering from dry eyes are particularly susceptible to discomfort and short blurred vision episodes. The selection of the right lens can minimize this effect.

Long-term contact lenses (more than five years) can "decrease the entire thickness of the cornea and increase corneal curvature and surface irregularity." Wearing long-term rigid contacts is associated with decreased keratocytes of corneal keratocytes and an increase in the number of Langerhans epithelial cells.

All contact lenses sold in the United States are studied and approved as safe by the FDA when special handling and maintenance procedures, wear schedule, and replacement schedules are followed.

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Usage

Before touching contact lenses or eyes, it is important to wash hands thoroughly with soap and rinse well. Soaps containing moisturizers or allergens should be avoided as they may cause eye irritation. Hand drying using a towel or tissue before handling contact lenses can transfer the fibers (feathers) into the hands and, then, to the lens, causing irritation to the insertion. Towels, unless freshly washed at high temperature washing, are often contaminated with large amounts of bacteria and, thus, should be avoided when handling the lens. Dust, fibers and other impurities can be collected on the outside of contact lenses. Again, hand contact with this material, before holding the contact lens, can transfer it to the lens itself. Rinsing the container under a running water source, before opening it, can help alleviate this problem. Furthermore the lens should be removed from the casing and checked for any defects (eg splits, folds, fibers). A rough or rough appearance onto the lens surface may indicate that large amounts of protein, lipids and debris have formed on it and that additional cleaning is required; this is often accompanied and perceived by a very high irritation in the insertion.

Make sure the soft lens is not put in the exit. The end of the lens that is rotated out has a different appearance, especially when the lens is slightly folded. Inserting the outgoing lenses for a short time (less than a minute) should not cause damage to the eye. Some lens brands have marks (eg numbers) on the rim that make it easy to tell the front of the lens from behind.

Techniques for removing or inserting contact lenses vary depending on whether the lens is soft or rigid. There are many subtle variations for insertion and deletion techniques. Because of differences in anatomy, manual dexterity, and visual limitations, everyone should find the technique that works best for them. In all cases, the insertion and removal of the lens requires some training and exercise on the part of the user.

Insertion

The contact lens is usually inserted into the eye by placing it on the index pad or middle finger with the side concave upwards and then using the finger to place the lens on the eye. Rigid lenses should be placed directly on the cornea. The soft lens can be placed on the sclera (white of the eye) and then slid into place. Another finger of the same hand, or other finger, is used to keep the eyes wide open. Alternatively, the user can close their eyes and then look towards their nose, slide the lens into place above the cornea. Problems may arise if the lens is folded, turns outward, slips off the finger prematurely, or attaches more tightly to the finger than the surface of the eye. A drop of solution can help the lens attach to the eye.

When the first contact lens eyes, it should be comfortable. By ensuring that special attention is paid to the eyelid margins for the presence of inflammation and signs of debris on the lashes, wearing contact lenses should be easy. Short irritation periods may occur, caused by differences in pH and/or salinity between lens and rip solutions. This discomfort fades quickly when the solution disappears and is replaced by natural tears. However, if irritation persists, the cause may be a dirty, damaged, or out-of-the-way lens. Removing and checking for proper damage and orientation, and cleaning back if necessary, should fix the problem. If discomfort persists, the lens should not be worn. In some cases, taking a break from wearing the lens for a day can fix the problem. In case of severe discomfort, or if not completed the next day, the person should be seen as soon as possible by the ophthalmologist to rule out the possibility of serious complications.

Deletion

Unwrapping contact lenses improperly can cause damage to the lens and injury to the eye so that certain precautions must be taken. The rigid contact lens is best removed by pulling tight eyelids and then blinking, where the lens is out. With one finger in the outer corner of the eyelid, or lateral canthus, the person stretches the eyelid toward the ear; The increased tension of the eyelid margin to the edge of the lens allows the flicker to break the capillary action attached to the lens to the eye. The other side is usually cupped under the eyes to catch the lens as it falls out. For soft lenses, which have a stronger adherence to the surface of the eye, this technique is less suitable.

Soft contact lenses can be removed by pinching the edges between the thumb and forefinger. Moving the lens of the cornea first can improve comfort during lifting and reduce the risk of scratching the cornea with fingernails. It is also possible to push or pull a soft lens far enough to the side or base of the eyeball to make it fold and then fall, without pinching and thereby destroying it. If these techniques are used with a rigid lens, it can scratch the cornea.

There are also special small tools for removing the lens. Usually made of flexible plastic, they resemble small tweezers, or plungers that suck into the front of the lens. Usually this tool is only used with a rigid lens. Extreme care should be taken when using mechanical or nail tools to insert or remove contact lenses.

Cares

Care of the lens varies depending on the material schedule and wear and tear. Disposable daily wear is discarded after one use and therefore does not need to be cleaned. Other lenses require regular cleaning and disinfecting to prevent surface coating and infection.

There are many ways to clean and care for contact lenses, commonly called a treatment system or lens solution:

• Multipurpose solution

Versatile solutions are the most common method for rinsing, disinfecting, cleaning and storing soft lenses. In 2002, concerns were raised that the multipurpose solution was ineffective to disinfect Acanthamoeba from the lens. In May 2007, one brand of multipurpose solutions was recalled due to a group of Acanthamoeba infections . Since then, research has shown that multipurpose solutions are not effective against Acanthamoebae . The latest multipurpose solution also contains materials that increase the wet power and comfort of silicone hydrogel lenses.

• The hydrogen peroxide system

Hydrogen peroxide can be used to disinfect contact lenses. Care should be taken not to get hydrogen peroxide in the eye because it is very painful and irritating. With a "two step" product, hydrogen peroxide must be rinsed with saline before the lens may be worn. The "One Step" system allows hydrogen peroxide to react completely, into pure water. So a "one step" hydrogen peroxide system does not require a lens to be rinsed before insertion, provided that the solution has been given enough time to react. Exposure time 2-3 hours to 3% H
₂ O
₂ (non-neutralized solution) enough to kill bacteria, HIV, fungi, and Acanthamoeba . This can be accomplished by using a "two step" product or a "one step" tablet system if the catalytic tablet is not added before 2-3 hours. However, a catalytic "one step" disk system is ineffective against Acanthamoeba .

• Enzymatic cleanser - Used to clean the protein deposit from the lens, usually every week, if daily cleaning is not sufficient. Typically, these cleansers are in tablet form.
• Ultraviolet, vibration, or ultrasonic device - Used to disinfect and clean CL. The lenses are inserted into portable devices (running on batteries and/or plug-ins) for 2 to 6 minutes as long as both microorganisms and protein formation are thoroughly cleaned. These devices are not usually available in optical retailers but are in other stores.
• Salt solution

Sterile saline is used to rinse the lens after it has been cleaned and prepare it for insertion. Salt solution is not disinfected, so it should be used in conjunction with some type of disinfection system. One of the benefits of saline is that it can not cause an allergic response, so it is perfect for individuals with strong sensitive or allergic eyes.

• Daily cleaner

Used to clean the lens every day. A few drops of cleanser are applied to the lens while in the palm of the hand; the lenses are rubbed for about 20 seconds with clean fingertips (depending on the product) on each side. The lens should then be rinsed. This system is usually used to treat rigid lenses.

In addition to cleaning contact lenses, it is advisable to also clean the casing to avoid possible infection. Replacing the casing every month, and storing it in a clean and safe environment is also recommended.

Contact lenses can be mechanically cleaned of the more substantial proteins, lipids and impurities formed by rubbing them between the finger pads and the palm of the hand, using a small amount of cleaning fluid as a lubricant. However, this method does not sterilize the lens and should be performed only before the full sterilization cycle (eg when putting contact lenses at night).

Some products should be used only with certain contact lens types. Water alone will not sterilize the lens, and can cause contamination of the lens that causes irreparable damage to the eyes.

Contact lens solutions often contain preservatives such as benzalkonium chloride and benzyl alcohol. Preservative-free products usually have a shorter shelf life, but are more suitable for individuals with allergies or sensitivity to preservatives. In the past, thiomersal was used as a preservative. In 1989, thiomersal was responsible for about 10% of contact lens problems. As a result, most products no longer contain thiomersal.

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Latest research

The large segment of contact lens research is currently geared towards the care and prevention of conditions resulting from contact lens contamination and colonization by foreign organisms. Doctors tend to agree that the most significant contact lens complication is microbial keratitis and that the most dominant microbial pathogen is Pseudomonas aeruginosa . Other organisms are also a major contributing factor in bacterial keratitis associated with contact lens wear, although the prevalence varies in different locations. These include species of Staphylococcus ( aureus and epidermidis ) and species Streptococcus , among others. Microbial keratitis is a serious focal point of current research because of its potentially damaging effects on the eye, including severe vision loss.

One interesting research topic is how microbes such as Pseudomonas aeruginosa attack the eye and cause infection. Although the pathogenesis of microbial keratitis is not well understood, many different factors have been investigated. One group of investigators showed that corneal hypoxia exacerbates Pseudomonas which binds to the corneal epithelium, microbial internalization, and induced inflammatory responses. One way to reduce hypoxia is by increasing the amount of oxygen that is transmitted to the cornea. Although silicone-hydrogel lenses virtually eliminate hypoxia in patients due to very high oxygen transmissibility rates, they also seem to provide a more efficient platform for bacterial contamination and corneal infiltration than other conventional hydrogel CLs. A recent study showed that Pseudomonas aeruginosa and Staphylococcus epidermis were closely attached to unsanolated hydrocele hydrocele hydrogels compared to conventional hydrogel lenses and Pseudomonas aeruginosa attachment. times stronger than Staphylococcus epidermidis . This may partly explain why Pseudomonas infection is the most dominant. However, other studies conducted with unused and unused silicone and conventional hydrogels show that the CL silicon used is less susceptible to colonization of Staphylococcus epidermidis than conventional hydrogel lenses.

Another important area of ​​contact lens research relates to patient compliance. Compliance is a major issue related to the use of contact lenses because poor patient compliance often results in lens contamination, storage, or both. However, cautious users can extend the use of the lens through proper handling: unfortunately no research is not interested in "compliance" issues or the length of time the user can safely use the lens beyond the stated usage. The introduction of multipurpose solutions and daily disposable lenses has helped alleviate some of the observed problems of inadequate cleansing but new methods of combating microbial contamination are currently being developed. Silver-impregnated lens cases have been developed that help eradicate potentially contaminated microbes that come into contact with the lens case. In addition, a number of antimicrobial agents are being developed that have been embedded into the contact lens itself. Lenses with attached covalent selenium molecules have been shown to reduce bacterial colonization without affecting rabbit cornea and octyl glucoside used as lens surfactants significantly reduces bacterial adhesion. These compounds are very attractive to contact lens manufacturers and optometric prescribes because they do not require patient compliance to effectively reduce the effects of bacterial colonization.

Recent research areas are in the field of bionic lenses. This is a visual display that includes a built-in electrical circuit and a light-emitting diode and can harvest radio waves for their electrical power. Bionic lenses can display information transmitted from mobile devices that address small screen-size issues. This technology involves embedding nano and micro scale electronic devices in the lens. These lenses also need to have a series of microlenses to focus the image so that it looks suspended in front of the wearer's eyes. The lens can also serve as a head-up display for pilots or gamers.

Giving drugs through contact lenses is also a research area. One application is a lens that releases anesthesia to the eye to relieve post-operative pain, especially after a PRK (photorefractive keratectomy) in which the healing process takes several days. One trial showed that silicone contact lenses containing vitamin E gave pain relief drugs up to seven days compared to less than two hours in a regular lens.

Another study on the use of contact lenses is intended to address the problem of macular degeneration (AMD or age-related macular degeneration). An international collaborative researcher is able to develop contact lenses that can divert between enlarged and normal vision. Previously, AMD's solution was to have large glasses or with surgical implants. But the progress of these new contact lenses, made from polymethyl methacrylate, can offer an unobtrusive solution.

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In popular culture

Movies

One of the earliest known films to introduce the use of contact lenses as a make-up artist device to enhance the eyes was by the innovative actor Lon Chaney in the 1926 movie The Road to Mandalay to create the effect of a character who has eyes the blind. Dr Rueben Greenspoon applied it to Orson Welles for the film Citizen Kane in 1940. In the 1950s, contact lenses began to be used in British horror films. Early examples of this are British actor Christopher Lee as Dracula's character in the 1958 dracula horror movie, which helps to emphasize his dreadful black pupils and red-red eyes. Tony Curtis wore it in the 1968 movie The Boston Strangler. The contact lenses were also used to further emphasize the evil outlook of the demonic character in 1968 Rosemary's Baby and 1973's The Exorcist . Custom-made colored contact lenses are now standard makeup for a number of special effects-based films.

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See also

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References

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Further reading

• Efron, Nathan (2002). Contact Lens Practice . Health Sciences Elsevier. ISBNÃ, 0-7506-4690-X.
• Heitz, Robert (2003, 2005, and 2014). "The History of Contact Lenses". In: Julius Hirschberg, History of Ophthalmology , vol. 11/3a, 11/3b, and 11/3c. Ostend, Belgium: Wayenborgh Publishing; Paraguay: Piribebuy. ISBN: 978-90-6299-463-2.

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External links

• Contact lenses and anterior eye journals
• "Glass Disk Under Eyelid Changing Glasses" Monthly Popular Mechanics , July 1930, bottom left pg 31
• Focuses on Contact Lens Security from the Food and Drug Administration

Source of the article : Wikipedia