Soft contact lens Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic ...

es are one of several types of contact lenses for corrective vision eyewear as prescribed by

optometrists Optometry is a specialized health care profession that involves examining the eyes and related structures for defects or abnormalities. Optometrists are health care professionals who typically provide comprehensive primary eye care. In the Un ...

and

ophthalmologist Ophthalmology ( ) is a surgery, surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Followin ...

Background

In the US market, soft contact lenses are approved by the US

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...

. The

American Optometric Association The American Optometric Association (AOA), founded in 1898, represents approximately 37,000 doctors of optometry, optometry students and para-optometric assistants and technicians in the United States. Overview The AOA states that: The American O ...

published a contact lens comparison chart called ''Advantages and Disadvantages of Various Types of Contact Lenses'' on the differences between them. These include: * soft contact lenses * rigid gas-permeable (RGP) * daily wear * extended wear * disposable * planned replacement contact lenses. The US Food and Drug Administration (FDA) defines soft contact lenses as:

History

The first contact lenses were made of glass, in 1888. Initially the glass was blown but soon lenses were made by being ground to shape. For the first fifty years, glass was the only material used. The lenses were thin, yet reports of injury were rare. In 1938 perspex (

polymethylmethacrylate Poly(methyl methacrylate) (PMMA) belongs to a group of materials called engineering plastics. It is a transparent thermoplastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and brands Crylux, Plexiglas, Acrylit ...

, or PMMA) began to replace glass in contact lens manufacture. PMMA lenses were easier to produce so the production of glass lenses soon ended. Lenses made of PMMA are called hard lenses. Soft contact lenses were first produced in 1961 by Czech chemical engineer

Otto Wichterle Otto Wichterle (; 27 October 1913 – 18 August 1998) was a Czech chemist, best known for his invention of modern soft contact lenses. Wichterle is the author or co-author of approximately 180 patents and over 200 publications. The studie ...

using polyhydroxyethylmethacrylate (pHEMA), a material that achieved long-term commercial application. Lenses made of

polyacrylamide Polyacrylamide (abbreviated as PAM) is a polymer with the formula (-CH2CHCONH2-). It has a linear-chain structure. PAM is highly water-absorbent, forming a soft gel when hydrated. In 2008, an estimated 750,000,000 kg were produced, mainly f ...

were introduced in 1971.

Types

The FDA classifies soft contact lenses into four groups for the US market. They are also subcategorized into 1st generation, 2nd generation, and 3rd generation lens materials. These 'water-loving' soft contact lens materials are categorized as "Conventional Hydrophilic Material Groups ("-filcon"): Note: Being ionic in pH = 6.0 - 8.0". The FDA has been considering updating soft contact lens group types and related guidance literature.

Contact lens polymers

The materials that are classified in the 5 FDA groups include the ones listed in the next 5 sections:

Hydrogel groups

Below is a list of most contact lens materials on the market, their water percentage, their oxygen permeability rating, and manufacturer brands. Note that the higher the oxygen transmissibility rating, the more oxygen gets to the eye.

Low water nonionic

High water nonionic

Low Water ionic

High Water ionic

Silicone hydrogel polymers

Production generations

There are three generations of silicone

hydrogel A hydrogel is a crosslinked hydrophilic polymer that does not dissolve in water. They are highly absorbent yet maintain well defined structures. These properties underpin several applications, especially in the biomedical area. Many hydrogels ar ...

contact lens materials:

References

{{Reflist Contact lenses Eye care in the United States Medical equipment Medical technology Medical devices Czech inventions