Course:HIST104/ContactLens
Acuvue Oasys Silicone Hydrogel Contact Lens
THE SILICONE HYDROGELS
Silicone Hydrogel lens is an invention that combines modern technology and materials
with the concept of refractive correction
originally described by Leonardo da Vinci.
The silicone provides remarkable oxygen permeability, while the hydrogel component
allows for the transport of water and ions across the lens.
Several decades of work on combining the two types of material,
while maintaining the desired optical characteristics, led to the invention
of the first successful silicone hydrogels in 1998.
Today, there are seven silicone hydrogel materials, each with a unique composition.
Acuvue Oasys contact lens is made of the polymer called senofilcon A.
In contrast to the original silicone hydrogels
that had a hydrophilic material applied to the surface,
senofilcon A lenses have the wetting agent incorporated within their structure,
which allows them to remain hydrated during the entire day.
FORCES THAT SHAPED HISTORY
The History of contact lenses spans over several centuries. Though the principles of corneal neutralization were described by Leonardo as early as in 1508, it was not until late 19th century that the written descriptions were put into practice, and the first prototypes of the modern contact lenses were created.
Since the invention of the first glass contact lenses in the 1880s, a number of forces combined to shape the transformation of the heavy, impermeable to oxygen lenses that covered much of the eye, into the contact lenses that millions of people are using today. The main factors that directed the “evolution” of contact lenses were the availability of polymers with the desired properties, search for design that would make wearing contact lenses comfortable and safe, and also their commercial success.
DEVELOPMENT OF MATERIALS
The first big advancement in the history of contact lenses was made by William Feinbloom (1904-1985) with his introduction of plastic to the contact lens in 1936. The addition of plastic to the lens was a huge step towards developing the contact lenses people commonly use today. Feinbloom initially used an opaque resin plastic, which wasn’t suitable for the corneal portion of the lens (glass was still used there), but after the PMMA (Poly methyl 2-methylpropenoate) was introduced in the U.S. that same year, he patented the new contact lens, entirely made of PMMA. This new lens quickly became widely used.
The next breakthrough on the way to developing materials used in the modern contact lens occurred in 1954,when Otto Wichterle (1913-1998), a Czech polymer chemist, invented the first hydrogel material, hydroxyethyl methacrylate, or HEMA. Although HEMA was not initially intended for the use in contact lenses, Wichterle's conversation with an ophthalmologist, who he accidentally met on a train, led to this remarkable idea. HEMA’s permeability to oxygen and water-soluble nutrients was the main feature which made it suitable for the construction of lenses. In 1962 and also in 1965, he patented the soft HEMA lens, an item which millions of people still use.
Although the soft hydrogel lens was an incredible improvement over the rigid PMMA, the problem of corneal hypoxia was not fully solved, and so the eye's requirements for oxygen became the main subject of study. From 1974 to 1998, the improved comfort was achieved mainly by manipulations of already discovered substances. The problem of dehydration and poor oxygen permeability of existing materials were still restricting the continuous wear to one day. Up until the silicone hydrogels were introduced in 1998.
Contact Lens Materials on YouTube
WORKING ON THE DESIGN
The first rudimentary glass contact lenses were invented independently by Adolph Eugen Fick, a Swiss ophthalmologist, Eugene Kalt, a French ophthalmologist, and August Müller, a German medical student in the 1880s. Crafted out of either blown glass bubbles or ground and polished glass, they were covering the entire sclera, better known as the white part of the eye, and thus they were very large. Due to their size, weight, the discomfort that they created by being impermeable to oxygen and water, patients in need of refractive correction could only wear these lenses for short periods of time, creating the demand for advancements to be made.
The next stage in the evolution of the contact lens design began in 1948, when the optician Kevin M. Tuohy (1921-1968) patented the first corneal contact lens, made entirely of PMMA. Tuohy’s invention of the corneal lens caused the sales of contact lenses to skyrocket from 50,000 in 1946 to 200,000 in 1949. The smaller corneal lens didn’t trap tears in eye as the larger scleral lens did, which helped to slow the development of corneal hypoxia, allowing the user to comfortably wear the lens much longer than they would with the original scleral lens of the same material.
Just a year later, in 1950, George Buttefield introduced the modern technique of adding peripheral curves to the posterior surface of the new lens, to match the shape of the eye's cornea more closely for a better fit. As new technologies an materials became available, thanks to the work and collaboration of experienced scientists and clinicians, the modern lenses feel natural and are very comfortable to wear. It almost feels like the lens is not there.
COMMERCIAL SUCCESS
From the time they were invented to the present, a number of different methods were used to produce contact lenses. The first glass contact lenses performed poorly, but they were also very expensive and difficult to produce. Originally, the lenses were made by blowing glass bubbles, grinding them, and polishing the glass. When glass was replaced by PMMA, the contact lenses were mainly produced by injection molding, and polished manually by a technician. The breakthrough in technology of producing contact lenses was made by Otto Wichterle. Not only did he develop the first hydrogel material (HEMA), but he also suggested a new revolutionary way of producing contact lenses using a spin casting device, which he patented in 1961. His idea was later purchased from him by Bausch and Lomb, and the invented device was automated. Thanks to the development of high reproducibility methods of production, contact lenses became affordable to more people, and today a pair of disposable contact lenses costs about the same as a can of Coke. In addition to making the lens affordable, the effort was made to promote the contact lens in public, and to educate people about the benefits. Over the past hundred year, many practices specializing in contact lenses were established, and clinical studies were conducted to raise the confidence of public and practitioners in the safety of contact lenses. As the demand for contact lenses grew, more companies entered the market, and more funding became available for research to drive further improvement.
A PRODUCT OF INTERACTION
The history of contact lenses traces the process of interaction and collaboration between individuals, groups, and entire cultures. Like Newton Wesley, who developed the first commercially successful contact lens based on Tuohy’s corneal design and Butterfield’s improvements to the shape, many, if not all, scientists and practitioners built on achievements and foundations established by pioneers in the field. In addition to that, the improvements made to the original contact lens would have been impossible without coordination between practitioners and research groups and competition between companies that financed the development in contact lens industry to increase their sales. Practitioners became members of societies, like the American Society of Contact Lens Specialists, and had regular meetings to share the news. Among the most successful researchers are the American Berkley Group, which studied the eye’s requirements for oxygen, and Australian CCLRU (Cornea and Contact Lens Research Unit), which conducted studies on extended wear lenses and is now a leading research centre in modern optometry. Though success of the companies leading the industry (Bausch and Lomb, CIBA Vision and Vistakon) is rooted in the discoveries of pioneers, today these companies are the ones who are driving the innovation.
There has also been cultural interaction in shaping the history of contact lens, an interaction that started long before the era of globalization began. Otto Wichterle’s discoveries of HEMA, a material that revolutionized the whole industry, and also the new method of production “might have died behind the iron curtain were it not for the persistence of Robert Morrison”, says Joe Shovlin, a clinical editor for
Review of Cornea and Contact Lenses
. During the Nazis and later Soviet invasion of Czechoslovakia, Wichterle’s research was interrupted for political reasons, and it was not until after the revolution in 1989 that his contributions were recognized. While Wichterle was struggling against the regime, his discoveries were used in the U.S. and promoted by Morrison, who had purchased Wichterle’s HEMA patents. The technology was later acquired by a large corporation, and millions of people today continue to benefit from Wichterle’s discovery.
THE REFERENCES
http://cms.revoptom.com/contactlens/pdf/clp_full.pdf
http://www.acuvue.ca/
http://www.optometric.com/article.aspx?article=101727
http://www.clspectrum.com/article.aspx?article=101744
http://en.wikipedia.org/wiki/Contact_lens