HISTORY Leonardo da vinci is frequently credited with introducing the general principle of contact lenses in his 1508 Codex of the eye, Manual D, where he described a method of directly altering corneal power by submerging the eye in a bowl of water. Leonardo, however, did not suggest his idea be used for correcting vision—he was more interested in learning about the mechanisms of accommodation of the eye .In 1801, while conducting experiments concerning the mechanisms of accommodation, scientist Thomas Young constructed a liquid-filled "eyecup" which could be considered a predecessor to the contact lens. On theeyecup base, Young fitted a microscope eyepiece. However, like Leonardo's, Young's device was not intended to correct refraction errors.In 1999, an important development was the launch of the first silicone hydrogels onto the market. These new materials encapsulated the benefits of silicone—which has extremely high oxygen permeobility—with the comfort and clinical performance of the conventional hydrogels which had been used for the previous 30 years. These lenses were initially advocated primarily for extended (overnight) wear although more recently, daily (no overnight) wear silicone hydrogels have been launched.
A contact lens (also known simply as a contact) is a corrective,cosmetic, or therapeutic lens usually placed on the cornea of the eye. Modern soft contact lenses were invented by the Czech chemists otto wichterle andDrahoslav lim, who also invented the first gel used for their production.
Corrective 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. wearers must usually take their contact lenses 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 color deficiencies, a red-tinted "X-Chrom"contact lens may be used. Although the lens does not restore normal color vision, it allows some colorblind individuals to distinguish colors better.A cosmetic contact lens is designed to change the appearance of the eye. These lenses may also correct the vision, but some blurring or obstruction of vision may occur as a result of the color or design. In the United States, the FDA frequently calls non-corrective cosmetic contact lenses decorativ.
By wear time
A daily wear contact lens is designed to be removed prior to sleeping. An extended wear (EW) contact lens is designed for continuous overnight wear, typically for 6 or more consecutive nights. Newer materials, such as silicone hydrogels, allow for even longer wear periods of up to 30 consecutive nights; these longer-wear lenses are often referred to as continuous wear (CW). Generally, extended wear lenses are discarded after the specified length of time. These are increasing in popularity, due to their obvious convenience. Extended- and continuous-wear contactlenses can be worn for such long periods of time because of their high oxygen permeability (typically 5-6 times greater than conventional soft lenses), which allows the eye to remain healthy.
Extended lens wearers may have an increased risk for corneal infections and corneal ulcers, primarily due to poor care and cleaning of the lenses, tear film instability, and bacterial stagnation. corneal neovascularization has historically also been a common complication of extended lens wear, though this does not appear to be a problem with silicone hydrogel extended wear. The most common complication of extended lens use is conjunctivitis, usually allergic orgiant papillary conjunetiv.
Complications
complications due to contact lenswear affect roughly 4% of contact lens wearers each year.[40] Excessive wear of contact lenses, particularly overnight wear, is associated with most of the safety concerns.[2] Problems associated with contact lens wear may affect the eyelid, the conjunctive, the various layers of the cornea, and even the tear film that covers the outer surface of the eye.
Studies conducted on side effects from long-term wearing of contact lenses, i.e. over 5 years, such as by Zuguo Liu PhD, MD and Stephen C. Pflugfelder MD: "The effects of long-term contact lens wear on corneal thickness, curvature, and surface regularity", Ophthalmology , Volume 107 , Issue 1 , Pages 105 - 111, concludes that: Long-term contact lens wear appears to decrease the entire corneal thickness and increase the corneal curvature and surface irregularity.
Usage
Before touching the contact lens or one's eyes, it is important to thoroughly wash and rins hand with a soap that does not contain moisturzers or allergens such as fragrances. The soap should not beantibacterial 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.
Studies conducted on side effects from long-term wearing of contact lenses, i.e. over 5 years, such as by Zuguo Liu PhD, MD and Stephen C. Pflugfelder MD: "The effects of long-term contact lens wear on corneal thickness, curvature, and surface regularity", Ophthalmology , Volume 107 , Issue 1 , Pages 105 - 111, concludes that: Long-term contact lens wear appears to decrease the entire corneal thickness and increase the corneal curvature and surface irregularity.
Care
While daily disposable lenses require no cleaning, other types require regular cleaning and disinfecting in order to retain clear vision and prevent discomfort and infections by various microorganisms including bacteria, fungi, and Acomthamoeba, that form abiofilm on the lens surface. There are a number of products that can be used to perform these tasks:
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