Contact lens

Contact lenses are small visual devices made with curved pieces of plastic shaped in a way to conform directly to the wearers eye. They provide an artificial refracting surface to the human eye and are used to correct vision problems like myopia and hypermetropia. Contact lenses aid in eye focusing in the same manner as spectacles do. A contact lens (also known simply as a contact) is corrective, cosmetic, or therapeutic lens usually placed on the cornea of the eye. Modern soft contact lenses were invented by the Czech chemist Otto Wichterle and his assistant Drahoslav Lm, who also invented the first gel used for their production. 1

Contact lenses usually serve the same corrective purpose as glasses, but are lightweight and virtually invisiblemany commercial lenses are tinted a faint blue to make them more visible when immersed in cleaning and storage solutions. Some cosmetic lenses are deliberately colored to alter the appearance of the eye. Some lenses now have a thin surface treatment which is a UV coating; this helps to reduce UV damage to the eye's natural lens. People choose to wear contact lenses for their appearance and practicality. When compared with spectacles, 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. The lenses are made from different types of materials soft and rigid and come in a variety of designs and colors. These include disposable, colored, astigmatic, aphakic, presbyopic and keratoconic lenses. The initial fitting and follow up care are important parts of contact lens usage to give maximum benefits of vision, appearance, and comfort and tissue integrity.

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Chapter: 1a) History b) Concept & theory c) application

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HISTORYMany people believe that the contact lens is a modern invention, but that's actually not the case. In fact, the origins of the contact lens extend as far back as the early sixteenth century. Even the modern form of contact lenses first emerged several decades ago. Since the very first conception of the principle behind contact lenses, these optical devices have undergone many different changes at the hands of several different inventors and eye care professionals. In fact, contacts have gone from cumbersome and uncomfortable devices made of glass to today's plastic lenses which offer a high level of comfort while providing sharp, clear vision for those with a wide variety of vision problems. A Brief History of Contact Lens Materials Rigid Beginnings The first glass lenses were scleral devices that Muller made in 1887 as a protective shell and Fick made in 1888 for refractive correction. Feinbloom made the first hybrid lens in 1936 by creating a scleral lens with a PMMA hepatic and a central glass zone covering the cornea. Around 1940, the first solid PMMA lenses appeared and remained the primary materials until the late 1970s. Soft Lens Innovations Almost 60 years ago, Professor Otto Wichterle began developing the first hydrogel contact lens in Prague. He first synthesized HEMA and glycol diester in 1954. Their first material, the poly-hydroxyethylmethacrylate gel (poly-HEMA-gel), contained about 40 percent water.

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Dr. Wichterle initially tried to produce these lenses by using closed polystyrene molds and polymerizing an aqueous monomer solution. This process resulted in irregular lens edges, so in 1961 he began to cast lenses in open, rotating forms. Using glass molds, a mechano set and a generator from his son's bike, he constructed a casting device on Christmas Eve 1961. Within a week he was producing usable lenses and needed a stronger generator, so he switched to using his gramophone's motor. To maximize the equilibrium content of water in a swollen gel, Dr. Wichterle produced the first several hundred lenses from a mixture consisting of 80 percent hydroxyethyl-methacrylate (HEMA) and 20 percent diethylenglycol-methacrylate (DEGMA). However, he later began using pure HEMA. In 1963, Dr. Wichterle met George Nissel, the most famous producer of hard lenses and lathing instruments of the time. Nissel gave him the idea of producing the poly-HEMA without solvent, turning it on a lathe and later swelling it with water while it maintained its optics. Wichterle quickly patented this material and technique and called it "xerogel." The Emergence of GP Materials In 1978, the FDA approved the first rigid gas permeable lens in the United States in cellulose acetate butyrate (CAB). Syntex introduced its Polycon lens, a silicone-acrylate material, in 1979 in a much thinner design than the first CAB lenses because of the material's improved stability. We continue to see hybrid lenses, which now feature a GP core and a hydrophilic skirt. The SoftPerm Lens (CIBA Vision) and the SynergEyes lens series introduced in 2005 are examples of these material marriages. Developing Silicone Hydrogel Silicone elastomer lenses appeared in 1981 when the FDA approved the Silsoft lens (Bausch & Lomb), owned by Dow Corning at the time. However, development of the silicone elastomer lens dates back to 1956 with Becker, a Pittsburgh optician. In 1998, B&L introduced the first silicone hydrogel lens followed by CIBA in 2001.

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Concept & theory Lenses made with surfaces of small radii have the shorter focal lengths. A lens with two convex surfaces will always refract rays parallel to the optic axis so that they converge to a focus on the side of the lens opposite to the object. A concave lens surface will deviate incident rays parallel to the axis away from the axis, so that even if the second surface of the lens is convex, the rays diverge and only appear to come to a focus on the same side of the lens as the object. Concave lenses form only virtual, erect, and diminished images. If the object distance is greater than the focal length, a converging lens forms a real and inverted image. If the object is sufficiently far away, the image is smaller than the object. If the object distance is smaller than the focal length of this lens, the image is virtual, erect, and larger than the object. The observer is then using the lens as a magnifier or simple microscope. The angle subtended at the eye by this virtual enlarged image is greater than would be the angle subtended by the object if it were at the normal viewing distance. The ratio of these two angles is the magnifying power of the lens. A lens with a shorter focal length would cause the angle subtended by the virtual image to increase and thus cause the magnifying power to increase. The magnifying power of an instrument is a measure of its ability to bring the object apparently closer to the eye. This is distinct from the lateral magnification of a camera or telescope.

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The cornea makes up about two-thirds of the eye's total power to focus the light precisely on the retina (receiving screen) which is located in the back of the eye. By slight modifications in the shape of the cornea, clear functional vision may be restored for a period of time.

Optical defects and normal eye vision:

Normal Vision

Myopic Vision

Hypermetropic Vision

Astigmatic Vision 7

PrincipleA contact lens works on the principle which is the same as of a lens used in the spectacles, i.e. Concave and Convex lens.

Convex Lens A convex lens curves outward; it has a thick center and thinner edges. Light passing through a convex lens is bent inward, or made to converge. This causes an image of the object to form on a screen on the opposite side of the lens. The image is in focus if the screen is placed at a particular distance from the lens that depends upon the distance of the object and the focal point of the lens. The lens in the human eye is convex, but unlike a glass lens, it is elastic so that it can change shape to focus on objects at varying distances. The lens becomes short and fat when viewing close objects and elongated and thin when viewing distant objects. Sometimes eye muscles are unable to focus light on the retina, the screen at the back of the eyeball. If the image forms behind the retina for nearby objects, a condition called farsightedness (hypermetropia) results. Convex lenses are prescribed for hypermetropics to assist the eye in making light converge on the retina for nearby objects.

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Concave Lens A concave lens is curved inward; it is shaped like two dishes placed back-to-back. Light passing through a concave lens bends outward, or diverges. Unlike convex lenses, which produce real images, concave lenses produce only virtual images. A virtual image is one perceived by the visual portion of the brain and appears as a smaller image just in front of the actual object (in this case a shamrock). Concave lenses are generally prescribed for myopic, or near-sighted, people. Concave lenses help the eyes to produce a focused image on the retina instead of in front of it.

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Chapter: 2a) Physical and chemical properties of materials used in manufacturing of contact lenses b) Manufacturing processes

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Construction materialsSR. NO. 1. 2 MATERIAL WATER CONTEN T (%) 55 PHYSICAL AND CHEMICAL PROPERTIES Ultra high molecular weight copolymer of 2-Hydroxyethyl methacrylic and methacrylic acid, ionic polymer Hydrophilic polymer of 2-hydroxyethyl methacrylate Hydrophilic copolymer of 2hydroxyethyl methacrylate and Nvinyl pyrrolidone CHARACTERISTICS THAT JUSTIFY ITS SELECTION Polymerization process ensures a material that results in a lens with good dimensional stability

Methafilcon A

2. 3 3. 4

Polymacon Hilafilcon A

38.6 70

Makes the lens less likely to dry and curl away from the eye between blinks, so it's more comfortable, particularly towards the end of the day

4. 5 5. 6

Hilafilcon B Balafilcon A

59 36 A silicone hydrogel material Provides a high level of oxygen to your eyes and has been surface treated to wet with your tears Light blue tint on the lens and increases the visibility of the lens when not worn on the eye

6. 7

Tetrafilcon A

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Hydrophilic random terpolymer of 2hydroxyethyl methacrylate, Nvinyl-2-pyrrolidone and methylmethacrylate joined in a 3-D network of terpolymer chains by divinylbenzene cross-links, handling tint-Reactive

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7. 8

Galyfilcon A

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Blue163 dye Hydrophilic lens material

8. 9

Senofilcon

9. 1 1 0. 1

Lotrafilcon B Omafilcon A

33 59

1 1. 1 1 2. 1

Phemfilcon A

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Silicon hydrogel, 110 Dk, base curve of 8.6 mm Polymer of 2hydroxyethylmethacrylate and 2methacryloyloxyeth yl phosphorylcholine cross linked with ethyleneglycol dimeth-acrylate, Hydrophilic, Permanently fixed tint using color additive Reactive Blue 4, soft material Opaque prosthetic soft contact lens, effective and safe prosthetic SCL

De-centres and moves less. It is a remarkable moisture rich element that lies throughout the interior and exterior of the contact lens creating a unique soft silky feel. Minimizes dryness symptoms associated with exposure to adverse environmental conditions. Light blue coloured handling tint For daily wear for the correction of visual acuity in not aphakic persons with nondiseased eyes that are myopic or hyperopic and exhibit astigmatism of 2.00D or less that does not interfere with visual acuity

For correction of visual acuity or cosmetic improvement Less susceptible to fungal attack, used for therapeutic purposes for epithelial healing

Vifilcon A

55

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The Dk (oxygen permeability) of hydrogel contact lenses is a function of the water content, i.e., lower water content materials have lower Dk values and higher water content lenses have higher Dk values. Dk values are theoretically an absolute for any given material, but practically the values found by different researchers vary somewhat. Each generic material below is accompanied by a representative Dk number. It is also important to remember that Dk/L (central transmissibility) and Dk/L (average overall transmissibility) are dependent upon lens thickness configuration and are more important than Dk.Group1 Low Water (50% H20) Nonionic Polymers

Group3

Low Water (50% H20) Ionic Polymers

Group4

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MANUFACTURING. Most contact lenses are mass produced. Spin-cast lenses - A spin cast lens is a soft contact lens manufactured by whirling liquid silicone in a revolving mold at high speed. Lathe turned - A lathe turned contact lens is cut and polished on a CNC lathe. The lens starts out as a cylindrical disk held in the jaws of the lathe. The lathe is equipped with an industrial grade diamond as the cutting tool. The CNC Lathe turns at nearly 6000 RPM (revolutions per minute) as the cutter remove the desired amount of material from the inside of the lens. The concave (inner) surface of the lens is then polished with some fine abrasive paste, oil, and a small polyester cotton ball turned at high speeds. In order to hold the delicate lens in reverse manner, wax is used as an adhesive. The convex (outer) surface of the lens is thus cut and polished by the same process. Molding - Molding is used to manufacture some brands of soft contact lenses. Rotating moulds are used and the molten material is added and shaped by centrifugal forces. Injection moulding and computer control are also used to create nearly perfect lenses. Hybrids- hybrid contact lens is the one which incorporates a gas permeable lens with a soft lens skirt.

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Although many companies make contact lenses, there are a few major manufacturers:

Acuvue/Vistakon (Johnson & Johnson) Ciba Vision (Novartis) Bausch & Lomb Cooper Vision Wesley Jessen Ocular Sciences Boston Smaller manufacturers include:

Bescon Conptica Conta Optic Daysoft Marietta Vision Menicon SafiLens UltraVision Whlk/Zeiss ContactlinsenEXAMPLE OF A LENS PARAMETER AVAILABLE IN THE MARKETMaterial Water content Centre thickness O2 permeability (Dk) O2 transmissibility (Dk/t) Contact angle Spectral and luminous transmittance Refractive index Handling tint Base curve Power range* Modality Asmofilcon A (non-ionic) FDA group 1 ISO 18369-1 40% 0.08mm 129x10-11 161x10-9 centre -3.00D 27 (captive bubble method) 98% 1.423 Light blue 8.30mm, 8.60mm +6.00D to -6.50D in 0.25D steps -6.50D to -13.00D in 0.50D steps Daily wear: fortnightly replacement Extended wear: weekly replacement

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Chapter: 3a) Uses b) Applications c) Types

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usesCORRECTIVE CONTACT LENSES

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 contact lens neutralizes this mismatch and allows for correct focusing of light onto the retina. Conditions correctable with contact lenses include near (or short) sightedness (myopia), far (or long) sightedness (hypermetropia), astigmatism and presbyopia. 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. For those with certain colour deficiencies, a red-tinted "X-Chrom" contact lens may be used. Although the lens does not restore normal colour vision, it allows some colorblind individuals to distinguish colors better. 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.

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COSMETIC (COLORED) CONTACT LENSES 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 colour or design. Colored contact lenses come in three kinds: visibility tints, enhancement tints and opaque color tints. A visibility tint is usually a light blue or green tint added to a lens, just to help you see it better during insertion and removal, or if you drop it. Since it's a very light tint, it does not affect your eye color. An enhancement tint is a solid but translucent (see-through) tint that is a little darker than a visibility tint. An enhancement tint does change your eye color. As the name implies, it's meant to enhance the existing color of your eyes. These types of tints are usually best for people who have light colored eyes and want to make their eye color more intense Opaque Color tints are deeper, opaque tints that can change your eye color completely. Usually they are made of patterns of solid colors. If you have dark eyes, you'll need this type of color contact lens to change your eye color. Color contacts come in a wide variety of colors, including hazel, green, blue, brown-black, violet, amethyst and gray.

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Costume or theatrical contact lenses also fall into the category of opaque color tints. Long used in the movies (examples are The Man Who Fell to Earth and Twilight), these special-effect contact lenses are now widely available for novelty use and can temporarily transform the wearer into an alien or jaguar, among others. Theatrical contact lenses 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. Scleral lenses cover the white part of the eye (i.e. sclera) and are used in many theatrical lenses.. 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. 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.

1. Icefire, 2. Wildfire, 3. Zooming, 4. Jaguar, 5. Zebra, 6. Cat Eye, 7. Knockout, 8. Black-out, 9. Red Hot, 10. White-out, and 11. Hypnotica.

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THERAPEUTIC CONTACT LENSES Soft lenses are often used in the treatment and management of nonrefractive 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. Contact lenses that deliver drugs to the eye have also been developed.

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APPLICATIONS1. The primary use of contact lenses is to correct myopia (short sightedness). They can also be used to rectify hyperopia, astigmatism, presbyopia and aphakia. 2. Rigid lenses are used to correct irregular corneal trauma. Soft lenses are used as bandages for conditions like bullous keratopathy, recurring corneal erosion as well as to increase comfort, vision and postoperative wound healing. 3. Contact lenses are capable of correcting most of the problems that spectacles can as well as some additional ones that glasses cannot. People not satisfied with their appearance using glasses can opt to use contact lenses for improved appearance. 4. Contact lenses are not in the danger of slipping off, getting wet, or fogging up, which can easily happen with spectacles. 5. Extremely hypermetropiac people or those who have had cataracts removed, feel better wearing contact lenses as compared to spectacles, which in these cases produce uneven vision. Moreover, contact lenses give improved vision for people with damaged corneas due to disease or injury. 6. Also for sportsmen, wearing contact lenses prove to be more practical as in the case of those where wearing spectacles pose a problem in their jobs. In addition to all these, contact lenses provide better side vision compared to glasses.

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TYPESContact lenses, when categorized on the basis of the material used ,are of two types: SOFT CONTACT LENS RIGID CONTACT LENS

Soft contact lenses are those that are made of hydrophilic plastics and absorb liquid and must be kept moist for softness and easier moulding to the corneal surface. They are extremely comfortable and are used by majority of contact lens users. 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. Rigid contact lenses or gas permeable (RPG) which are composed of durable and flexible plastics, which permit oxygen to pass through to the cornea and are easier to maintain. The original hard lenses, or PMMAs (polymethyl methacrylate), used earlier did not allow oxygen to pass to the eye and have been replaced by the RPGs. 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. 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.

HYDROPHOBIC, HYDROPHYLIC, PMMA

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Chapter: 4Design and geometrical features

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DESIGN and geometrical featuresLens Design: Lenses are rotationally symmetric, geometrically symmetric or asymmetric front and back surfaces with atoric spherical effect optics Single Vision Lens Design: Single vision designs are the foundation for all of our designs. First and foremost to success for any of our designs is proper fit. All designs begin with our Multiple Aspheric(atoric) Design concept; lenses are made very thin to make a flatter base curve. Each lens design consists of multiple curves as small as All design controls are available with single vision design except the multifocal controls. Once you do enter additive power, the lens does become multifocal. Likewise, if you enter astigmatism, the resultant power is spherical equivalent and the design remains 'spherical'. But as soon as you enter an astigmatic over refraction the design becomes a front surface toric, i.e. the lens surface becomes cylindrical. But keeping in mind the thinner people usually avoid choosing toric lens designs.

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Multifocal Design: In multifocal designs attention is given to the lens periphery for precise centration. Next the proper tear film thickness is optimized across the lens until the designer is satisfied.

Toric Design Conventionally made toric designs typically cut a lens so that the cylinder is the same power across the entire axis. 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

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Corneal Molding (Ortho K) Design: Corneal Molding (Ortho K) Design is a more comfortable fit with better centration. The corneal periphery is duplicated into the periphery of the lens to further enhance centration. The designer has the option of four peripheral lens design combinations: spherical/spherical, toric/spherical, toric/toric, free form (asymmetric)/spherical. To avoid any problems, the proximity of the molding transition zone to the pupil diameter is defined, which is an important indicator of potential flare or glare.

Long-term contact lens wear appears to decrease the entire corneal thickness and increase the corneal curvature and surface irregularity. Long-term wear of rigid contact lens is associated with decreased corneal keratocyte density and increased number of epithelial Langerhans cells.

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Keratoconus Design The specific keratoconus fits a keratoconic eye. Each lens is designed to fit the cone. For example take the cone below (right). The resultant lens design (left) shown on the left shows the back surface of the lens. Notice how the geometry is off center to accommodate the position of the nipple cone.

Freeform Design Free Form design is unlike any other. Simply put, free form designs are asymmetric. The designer may make adjustments with an effect over 90, 180 or 360 degrees of the lens. These contact lenses have a specific 'top' and 'bottom', as they are not symmetrical around their centre and must not be rotated. Lenses must be designed to maintain their orientation regardless of eye movement. Often lenses are thicker at the bottom and this thicker zone is pushed down by the upper eyelid during blinking to allow the lens to rotate into the correct position (with this thicker zone at the 6 o'clock position on the eye).

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GEOMETRIC FEATURES:

Rigid contact lenses Diameter: lies between 8.5 -15mm Center thickness: lies between 0.12-1.0mm Edge thickness: lies between 0.10 - 0.30mm

Soft contact lenses Diameter: lies between 13 - 15mm Center thickness: lies between 0.08 -1.0mm Edge thickness: lies between 0.10 - 0.30mm

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Chapter: 5Mechanism and functioning

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USAGE- INSERTION AND REMOVALBefore 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. 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. 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. INSERTION 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. When the lens first contacts the eye, a brief period of irritation may ensue as the eye acclimatizes 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. It may be noted that although it is easy to tell if you have inserted the lens backwards (as it is usually painful and vision is impaired) you are able to determine the lens's correct position before hand by holding the lens on the tip of your finger and squeezing the bottom of it with two fingers from your other hand, you will know you have it the correct way if the edges of the lens curve inward like a taco. If they curve out you need to flip the lens rigid.

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REMOVAL A soft lens may be removed by holding the eyelids open and grasping the lens with opposing digits. This method may cause irritation, could risk damage to the eye and may in many cases be difficult, in part due to the blink reflex. If the lens is pushed off the cornea (by touching the lens with your forefinger and looking towards your nose, moving the lens) 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. 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. CARE 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. 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. Lenses should not be kept in dry air, they should be immersed in the liquid solution.

DRIED OUT SOFT LENS

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Chapter: 6Environmental issues and compliance parameters

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Environmental impactEnvironmental impact is calculated by sorting the packaging used in the supply of contact lens systems into their constituent materials (liquid, plastic, paper, metal and glass), determining their mass, calculating the annual consumption by a typical contact lens wearer, and factoring the data against published indices of the environmental impact of the constituent materials. Conventional lens wear has the highest impact and planned replacement lens wear (monthly disposable) has the lowest impact. The overall environmental impact of waste generated through the use of contact lens products by the end consumer is insignificant (0.5%) compared with the amount of waste generated in our everyday life.

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Summary of compliance of daily wear and extended wear respondents

Behaviour of daily wear group

High level of compliance

Using the correct solution Lenses stored in a lens case Lenses covered with solution during disinfecting Case lid closed tightly Bottle cap closed tightly Case not shared Too many days of wear Overnight wear with lenses prescribed for daily wear only Correct hand-washing Replacement of all solution each day (ie no topping up)

Moderate level of compliance

Low level of compliance

Napping with lenses Monthly replacement of lens case Always cleaning lens case Regular checking of expiry dates

Behaviour of extended wear group Using the correct solution Lenses stored in a lens case Lenses covered with solution during disinfecting Case lid closed tightly Bottle cap closed tightly Case not shared Too many days of wear Too many nights sleeping in lenses Correct hand-washing Replacement of all solution each time (ie no topping up) Regular checking of expiry dates Monthly replacement of lens case Always cleaning lens case

The areas where improved compliance should lead to reduced risks for significant and serious keratitis are: Correct adherence to lens wearing schedules (not sleeping in lenses prescribed for daily wear and discarding lenses at the correct interval) Rub-cleaning and rinsing lenses to clean the lens surfaces and as an aid to disinfection Cleaning the lens case after each use and allowing it to air-dry Good handwashing before lens handling.

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Chapter: 7Technological advancement and future scope

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wave contact lens systemWave contact lenses are made using the Wave Contact Lens Software. The idea is simple. Creation of a lens that nearly mirrors the cornea for the most precise and comfortable fit available. The efficient process begins with thousand of data points from the topographer. With the data, the Wave software recommends the starting custom design. Single vision, front surface multifocal, toric or bi-toric lens or reverse geometry (with or without toric periphery) are all available. Lens designs have multiple aspheric curves as small as 10 microns wide and are rotationally symmetric, geometrically symmetric or asymmetric depending upon the shape of the cornea. One can make as many design changes as you wish with an easy drag-and-drop approach to adjust any single meridian or combination of meridians, seeing the results in the simulated fluorescent map. After the finishing of designing the patient's one-of-a-kind contact lenses onscreen, the Wave software delivers the precise design.

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THE WAVE SCREEN: Wave's design screen show a complete overview offers a complete overview of the design parameters. With virtually unlimited control of the design, almost any design is possible.

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Ortho-kOrtho-K is a non-surgical process which reshapes (flattens by compression) the cornea of the eye using contact lenses to reduce refractive errors (nearsightedness and astigmatism). Accelerated Ortho-K uses reverse geometry contact lenses, i.e. lens designs have a flat central base curve. Flattening the cornea reduces the focusing power of the eye. Since the amount of corneal flattening can be accurately controlled, it is possible to bring the eye into correct focus and compensate for the refractive error. After the contact lens is removed, the cornea retains its flattened shape for part or all of the remainder of the day. A retainer lens must be used each day to maintain the corneal flattening, or the myopia will revert to the pretreatment level. Ortho-K is also successful for some degrees of farsightedness by steepening the central cornea. Now, with the advent of space-age polymers, computer-assisted lathes, and technological advancement in the procedure, it is possible to achieve reduction of myopia in a matter of days. This high tech version of Ortho-K goes by many names. Among them are: AOK - Accelerated Orthokeratology CRT - Corneal Refractive Therapy (TM) CCC - Corneal Corrective Contacts EZM - Eccentricity Zero Molding (TM) GVSS - Gentle Vision Shaping System VST -- Vision Shaping Treatment(TM)

(TM)

Ortho-K is not only an excellent alternative to the wearing of spectacles, but it also frees the individual from the distractions caused by perspiration, dust, wind weather and temperature. There are no more blind spots caused by frame or lens edges.

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It is great to wear "regular" fashion sunglasses, to get up at night or in the morning and see, to go swimming and skiing, to drive in a convertible with the top down, to work in the dust, grass or in the garden, and to be able to see in cases of emergencies. Ortho-K might open new horizons to you. People in occupations that are hindered by the use of glasses or contacts may be good candidates for Ortho-K pilots, policemen, firemen, etc. PROCESS: The central portion of the contact lens fits closer to the eye than a standard contact lens, exerting a gentle pressure. It does not touch the cornea because there is a tear layer protecting the eye. As the central cornea is flattened, the mid periphery is steepened, creating a red ring. This is due to the cells from the central portion moving towards the periphery The flattening or re-shaping improves the vision.

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LASIKRecently, several surgical procedures have been developed to attempt to accomplish changing the curvature of the cornea. Since the cornea is soft, it can continue to change shape as time goes by. The individual prescription may continue to vary leading to increased dependence upon eyewear within years to just a few months after the surgical procedure. Some surgical procedures produce scars causing surface irregularities on the cornea, resulting in permanent blurring that even glasses or contacts cannot eliminate. LASIK is less likely to produce scarring of the cornea and has become a hot topic in eye care. Surgery is not an option for children or those whose vision is changing. It does not stop the progression of myopia in children or adults.

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future scope: bionic contact lensesThe bionic contact lens is being developed to provide a virtual display that could have a variety of uses from assisting the visually impaired to the video game industry. The device will have the form of a conventional contact lens with added bionics technology. The lens will eventually have functional electronic circuits and infrared lights to create a virtual display. The lenses require organic materials that are biologically safe and also use inorganic material for the electronic circuits. The electronic circuits are built from a layer of metal a few nanometers thick. The lightemitting diodes are one third of a millimeter across. A grey powder is sprinkled onto the lens. Then a technique called micro fabrication or 'self-assembly' is used to shape each tiny component. Capillary forces pull the pieces into their final position. The prototype does not light up or display information. It is a proof that it is possible to create a biologically safe electronic lens that does not obstruct a persons view. Engineers have tested the finished lenses on rabbits for up to 20 minutes and the animals showed no problems.

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Advanced edge technologyThrough its new state-of-the-art manufacturing facility based in Hampshire, Sauflon is using the latest automated nano-precision equipment and advanced robotics to produce millions of new aspheric daily disposable contact lenses to exacting standards. It is a UK based company. By using a high degree of automation, Sauflon is able to produce extremely high quality, reproducible lenses are competitive prices. Extreme comfort does not have to cost more now. Sauflons high quality aspheric contact lenses are generated using a patented manufacturing process Advanced Edge Technology (AET). This process applies design and production parameters to the nanometer level of four decimal places. The result is a lens edge that is so thin and accurate it assures extreme comfort with every lens

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