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Contact Lenses

Notes

*8/6/2012 
from 4/19/2012

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Notes

4. “A contact lens, or simply contact, is a lens placed on the eye of a human or animal. Contact lenses are considered medical devices and can be worn to correct vision, for cosmetic or therapeutic reasons. In 2004, it was estimated that 125 million people (2%) use contact lenses worldwide, including 28 to 38 million in the United States.  In 2010, worldwide contact lens market was estimated at $6.1 billion, while the U.S. soft lens market is estimated at $2.1 billion.[2] Some have estimated that the global market will reach $11.7 billion by 2015.[2] As of 2010, the average age of contact lens wearers globally was 31 years old and two thirds of wearers were female.

People choose to wear contact lenses for many reasons. Aesthetics and cosmetics are often motivating factors for people who would like to avoid wearing glasses or would like to change the appearance of their eyes.[4] Other people wear contacts for more visual reasons. When compared with spectacles, contact lenses typically provide better peripheral vision, and do not collect moisture such as rain, snow, condensation, or sweat. This makes them ideal for sports and other outdoor activities. Additionally, there are conditions such as keratoconus and aniseikonia that are typically corrected better by contacts than by glasses.”

(Wikipedia, Contact Lenses, 4/19/2012)

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3. “An ophthalmic lens, in particular, a contact lens, must be supplied with oxygen from air, the oxygen being needed for maintaining corneal health condition, and thus, high oxygen permeability is required. In recent years, a contact lens has been developed which uses siloxane monomers as raw materials to improve oxygen permeability.

High hydrophilicity, in addition to oxygen permeability, is required for a contact lens. A contact lens with high hydrophilicity is generally said to provide good wearing feel and to be wearable for an extended period of time with comfort. Hydrophilic monomers are generally used as raw materials in order to improve hydrophilicity of a contact lens.

To produce a contact lens having both high oxygen permeability and high hydrophilicity, both a siloxane monomer and a hydrophilic monomer are required as raw materials; however, since a siloxane monomer has high hydrophobicity in general and thus has poor miscibility with a hydrophilic monomer, a phase separation occurs, thereby making it difficult to produce a transparent contact lens. In order to solve this problem, hydrophilized siloxane monomers have been developed.”

[Ueyama, Ikawa and, US Patent 8,129,442 (3/6/2012)]

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2. “Biomedical devices such as contact lenses are made of various polymeric materials, including rigid gas permeable materials, soft elastomeric materials, and soft hydrogel materials. The majority of contact lenses sold today are made of soft hydrogel materials. Hydrogels are a cross-linked polymeric system that absorb and retain water, typically 10 to 80 percent by weight, and especially 20 to 70 percent water. Hydrogel lenses are commonly prepared by polymerizing a lens-forming monomer mixture including at least one hydrophilic monomer, such as 2-hydroxyethyl methacrylate, N,N-dimethylacrylamide, N-vinyl-2-pyrrolidone, glycerol methacrylate, and methacrylic acid. In the case of silicone hydrogel lenses, a silicone-containing monomer is copolymerized with the hydrophilic monomers. Regardless of their water content, both hydrogel and non-hydrogel siloxy and/or fluorinated contact lenses tend to have relatively hydrophobic, non-wettable surfaces.” [Linhardt, McGee and Nunez, US Patent 8,133,960 (3/13/2012)]

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1. “In recent years, soft silicone hydrogel contact lenses become more and more popular because of their high oxygen permeability and comfort. "Soft" contact lenses can conform closely to the shape of the eye, so oxygen cannot easily circumvent the lens. Soft contact lenses must allow oxygen from the surrounding air (i.e., oxygen) to reach the cornea because the cornea does not receive oxygen from the blood supply like other tissue. If sufficient oxygen does not reach the cornea, corneal swelling occurs. Extended periods of oxygen deprivation cause the undesirable growth of blood vessels in the cornea. By having high oxygen permeability, a silicone hydrogel contact lens allows sufficient oxygen permeate through the lens to the cornea and to have minimal adverse effects on corneal health.” [Chang and Wang, US Patent 8,211,955 (7/3/2012)]

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Copyright 2012 by Roger D. Corneliussen.
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* Date of latest addition; date of first entry is 4/19/2012.