molding process and is never dried and rehydrated. many companies make contact lenses. in the united states, there are five major manufacturers: johnson & johnson; maker of acuvue lenses the cooper companies: through its coopervision alcon bausch health: through its bausch & lomb subsidiary x-cel specialty contacts; maker of westcon lenses. prescriptions diameter and base curve radius the parameters specified in a contact lens prescription may include: material / brand name base curve radius (bc, bcr) diameter (d, oad) power in diopters center thickness (ct) prescriptions for contact lenses and glasses may be similar, but are not interchangeable. prescribing of contact lenses is usually restricted to various combinations of ophthalmologists, optometrists and opticians. an eye examination is needed to determine an individual's suitability for contact lens wear. this typically includes a refraction to determine the proper power of the lens and an assessment of the health of the eye's anterior segment. many eye diseases prohibits contact lens wear, such as active infections, allergies, and dry eye. keratometry is especially important in the fitting of rigid lenses. united states contact lenses are prescribed by ophthalmologists, optometrists, or specially licensed opticians under the supervision of an eye doctor. they are typically ordered at the same office that conducts the eye exam and fitting. but the fairness to contact lens consumers act guarantees consumers a copy of their contact lens prescription, allowing them to obtain lenses at the provider of their choice. usage before touching the contact lens or the eye, it is important to wash hands thoroughly with soap and rinse well. soaps containing moisturizers or allergens should be avoided as these can cause eye irritation. drying of hands using towels or tissues before handling contact lenses can transfer lint (fluff) to the hands and, subsequently, to the lenses, causing irritation upon insertion. towels, unless freshly laundered on high temperature wash, are frequently contaminated with large quantities of bacteria and, as such, should be avoided when handling lenses. dust, lint and other debris may collect on the outside of contact lenses. again, hand contact with this material, before handling contact lenses, may transfer it to the lenses themselves. rinsing the case under a source of clean running water, before opening it, can help alleviate this problem. next the lens should be removed from its case and inspected for defects (e.g. splits, folds, lint). a 'gritty' or rough appearance to the lens surface may indicate that a considerable quantity of proteins, lipids and debris has built up on it and that additional cleaning is required; this is often accompanied and felt by unusually high irritation upon insertion. care should be taken to ensure the soft lens is not inserted inside-out. the edge of a lens turned inside out has a different appearance, especially when the lens is slightly folded. insertion of an inside-out lens for a brief time (less than one minute) should not cause any damage to the eye. some brands of lenses have markings on the rim that make it easier to tell the front of the lens apart from the back. insertion inserting a contact lens contact lenses are typically inserted into the eye by placing them on the pad of the index or middle finger with the concave side upward and then using that finger to place the lens on the eye. rigid lenses should be placed directly on the cornea. soft lenses may be placed on the sclera (white of the eye) and then slid into place. another finger of the same hand, or a finger of the other hand, is used to keep the eye wide open. alternatively, the user may close their eyes and then look towards their nose, sliding the lens into place over the cornea. problems may arise if the lens folds, turns inside-out, slides off the finger prematurely, or adheres more tightly to the finger than the eye surface. a drop of solution may help the lens adhere to the eye. when the lens first contacts the eye, it should be comfortable. a brief period of irritation may occur, caused by a difference in ph and/or salinity between that of the lens solution and the tear. this discomfort fades quickly as the solution drains away and is replaced by the natural tears. however, if irritation persists, the cause could be a dirty, damaged, or inside-out lens. removing and inspecting it for damage and proper orientation, and re-cleaning if necessary, should correct the problem. if discomfort continues, the lens should not be worn. in some cases, taking a break from lens wear for a day may correct the problem. in case of severe discomfort, or if it does not resolve by the next day, the person should be seen as soon as possible by an eye doctor to rule out potentially serious complications. removal young woman removing contact lenses from her eyes in front of a mirror removing contact lenses incorrectly can result in damage to the lens and injury to the eye, so certain precautions must be taken. rigid contact lenses can best be removed by pulling the eyelid tight and then blinking, whereupon the lens drops out. with one finger on the outer corner of the eyelids, or lateral canthus, the person stretches the eyelids towards the ear; the increased tension of the eyelid margins against the edge of lens allows the blink to break the capillary action that adheres the lens to the eye. the other hand is typically cupped underneath the eye to catch the lens as it drops out. for soft lenses, which have a stronger adherence to the eye surface, this technique is less suitable. a soft contact lens may be removed by pinching the edge between the thumb and index finger. moving the lens off the cornea first can improve comfort during removal and reduce risk of scratching the cornea with a fingernail. it is also possible to push or pull a soft lens far enough to the side or bottom of the eyeball to get it to fold then fall out, without pinching and thereby damaging it. if these techniques are used with a rigid lens, it may scratch the cornea. there are also small tools specifically for removing lenses. usually made of flexible plastic, they resemble small tweezers, or plungers that suction onto the front of the lens. typically, these tools are used only with rigid lenses. extreme care must be exercised when using mechanical tools or fingernails to insert or remove contact lenses. care lens case to store contacts contact lenses soaking in a hydrogen peroxide-based solution. the case is part of a "one-step" system and includes a catalytic disc at the base to neutralise the peroxide over time. lens care varies depending on material and wear schedule. daily disposables are discarded after a single use and thus require no cleaning. other lenses need regular cleaning and disinfecting to prevent surface coating and infections. there are many ways to clean and care for contact lenses, typically called care systems or lens solutions: multipurpose solutions the main attraction of multipurpose solutions is that the same solution can clean, rinse, disinfect and store lenses. some multipurpose solutions also contain ingredients that improve the surface wettability and comfort of silicone hydrogel lenses. studies showed that multipurpose solutions are ineffective against acanthamoebae. there is preliminary research on creating a new multipurpose solution that kills amoeba. hydrogen peroxide contact solutions 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 "two-step" products, the hydrogen peroxide must be rinsed away with saline before the lenses may be worn. "one-step" systems allow the hydrogen peroxide to react completely, becoming pure water. thus "one-step" hydrogen peroxide systems do not require the lenses to be rinsed before insertion, provided the solution has been given enough time to react. an exposure time of 2-3 hours to 3% h2o2 (non neutralized solution) is sufficient to kill bacteria, hiv, fungi, and acanthamoeba. this can be achieved by using a "two-step" product or a "one-step" tablet system if the catalytic tablet isn't added before 2-3 hours. however, the "one-step" catalytic disk systems are not effective against acanthamoeba due to insufficient exposure time. enzymatic cleaner used for cleaning protein deposits off lenses, usually weekly, if the daily cleaner is not sufficient. typically, this cleaner is in tablet form. ultraviolet, vibration, or ultrasonic devices these devices intend to disinfect and clean contact lenses. the lenses are inserted inside the portable device (running on batteries and/or plug-in) for 2 to 6 minutes during which both the microorganisms and protein build-up are supposed to be cleaned. however these devices can not be used to replace the manual rub and rinse method because vibration and ultrasound can not create relative motion between contact lens and solution, which is required for proper cleaning of the lens. these devices are not usually available in optic retailers but are in other stores. rub and rinse method contact lenses can be mechanically cleaned of more substantial protein, lipid and debris build up by rubbing them between the clean pad of a finger and the palm of a hand, using a small amount of cleaning fluid as a lubricant; and by rinsing thereafter. this "rub and rinse" method is thought to be the most effective method for multipurpose solutions, and is the method indicated by the american academy of ophthalmology regardless of cleaning solution used. in 2010, the fda recommended that manufacturers removed the "no rub" from product labeling, "because 'rub-and-rinse' regimens help prevent microbial adhesion to the contact lens, help prevent formation of biofilms, and generally reduce the microbial load on the lens and the lens case." physical rubbing devices this type of devices mimic digital rubbing. the lenses are sandwiched by silicone parts inside the portable device. the device applies a gentle yet high speed rubbing action on the lens surface and remove debris. saline solution sterile saline is used for rinsing the lens after cleaning and preparing it for insertion. saline solutions do not disinfect, so it must be used in conjunction with some type of disinfection system. one advantage to saline is that it cannot cause an allergic response, so it is well suited for individuals with sensitive eyes or strong allergies. daily cleaner used to clean lenses on a daily basis. a few drops of cleaner are applied to the lens while it rests in the palm of the hand; the lens is rubbed for about 20 seconds with a clean fingertip (depending on the product) on each side. lens must then be rinsed. this system is commonly used to care for rigid lenses. water is not recommended for cleaning contact lenses. insufficiently chlorinated tap water can lead to lens contamination, particularly by acanthamoeba. on the other hand, sterile water will not kill any contaminant that get in from the environment. some products must be used only with certain types of contact lenses. aside from cleaning the contact lenses, contact lens case should also be kept clean and be replaced at minimum every 3 months. contact lens solutions often contain preservatives such as benzalkonium chloride and benzyl alcohol. preservative-free products usually have shorter shelf lives, but are better suited for individuals with an allergy or sensitivity to a preservative. in the past, thiomersal was used as a preservative. in 1989, thiomersal was responsible for about 10% of problems related to contact lenses. as a result, most products no longer contain thiomersal. complications further information: effects of long-term contact lens wear on the cornea clare (contact lens associated red eye) is a group of inflammatory complications from lens wear contact lenses are generally safe as long as they are used correctly. complications from contact lens wear affect roughly 5% of wearers yearly. factors leading to eye damage varies, and improper use of a contact lens may affect the eyelid, the conjunctiva, and, most of all, the whole structure of the cornea. poor lens care can lead to infections by various microorganisms including bacteria, fungi, and acanthamoeba (acanthamoeba keratitis). many complications arise when contact lenses are worn not as prescribed (improper wear schedule or lens replacement). sleeping in lenses not designed or approved for extended wear is a common cause of complications. many