Historical development of lens
There are two very important factors about this discovery. Improved refraction and improved peripheral visual acuity. The development of contact lenses is an old story, dating back to 1500 – 1508. The first insight into the treatment of optical defects of the cornea with a device is given to the great Italian, Leonardo da Vinci. Master Leonardo filled a bowl with water, then placed a man’s face into it. It is said that for the first time the individual was able to see clearly. Leonardo da Vinci also made a contact lens with a funnel on one side so that water could be poured into it. Of course, this was immediately discarded due to impracticality.
We must remember that early technology did not make it possible to develop and manufacture devices that would fit directly on the eye and produce good vision. That being the case, spectacle lenses were the only devices used to correct vision. Patient’s with regular corneas and normal astigmatism had very good vision. Individuals with corneal astigmatism or diseases and abnormalities of the cornea had minimal visual improvement with glasses. Wearable contact lenses did not begin to evolve until the nineteenth century. In 1801,
Thomas Young described a neutralizing surface for the cornea that was the forerunner of contact lenses. In 1636, after reviewing Leonardo’s work, a French scientist, Renee Descartes, in a special medical treatise, Ways of Perfecting Vision, described a concept of a lens placed directly onto the eye. He developed a tube he could fill with water and place directly against the cornea. This was also impractical and discarded.
Sir John Herschel, the English astronomer and physicist, wrote and circulated an opinion that corneal contact lenses were, in fact, optically feasible. Herschel was also the first to suggest that an actual mould of the cornea might be taken.
In the early 1880’s, glass contact lenses that fit the anterior of the eye, called scleral lenses, were invented by Adolf Fic, Eugene Cult and August Mueller, independently. Dr. Fic was a physician in Zurich, Switzerland, who wrote a treatise entitled A Contact Spectacle, in which he described the first contact lens with a refractive power, to protect the eye and later for visual improvement. This first lens was made by F. A. Mueller in 1887, a manufacturer of artificial eyes. These ideas though, lay dormant for approximately sixty years. His suggestions were theoretically sound but very problematic due to practical applications that were too difficult to overcome. One of the barriers was the need to make a mould of the sensitive corneal tissue. The cornea is totally avascular, with thousands of nerves, making a very sensitive tissue. With the introduction of anesthesia in 1884, contact lens technology advanced because moulding was made possible.
Fic used these lenses quite successfully in treating patients with corneal disease and abnormalities. These abnormalities, such as keratoconus, can cause scarring and a definite obstruction to the refraction of light. Fic’s lenses were quite successful compared to other applications but were still cumbersome and uncomfortable. Fic also recognized a method for correction of different types of irregular astigmatism other than spectacle lenses, which did not adequately correct the refractive power of irregular corneas. This device to neutralize the refractive power of the cornea, consisted of placing a small glass bowl directly on the eye, much like Leonardo had done 300 years prior. Later, Fic prepared a set of trial glass lenses. Fic selected the diagnostic lens that was most suitable for each of his experimental subjects. These original contact lenses were made of very thin glass.
Cult, who was a glass blower from Wiesbaden, Germany, described another method by which keratoconus could be corrected by suppression of the cone and correction of the refraction with glass shells. Over the course of about sixty years, scleral lenses made of glass were the major contact lenses used. Scleral glass lenses were primarily manufactured by Carl Zeiss Company in Jiena, Germany, as early as 1912.
In the 1930’s, the availability of plastics produced lenses that were lightweight and very transparent. They were chemically consistent, stable, unbreakable, scratch resistant and much easier to manufacture. This eventually changed the course of contact lens technology.
In 1937, Theodore Obrig developed manufacturing techniques for making plastic lenses and suggested the use of fluorescein dyes to study the morphology of the lens fit against the patient’s cornea. With the introduction of polymethylmethacrylate (PMMA) a flush fitting scleral lens was made possible. A few Labs still fit and manufacture these types of contact lenses for the treatment of severe keratoconus disease and Stevens-Johnson syndrome.
The therapeutic use of these lenses was developed by Woodly in England in 1954. These lenses also had desirable cosmetic effects. Innovations greatly contributed to the success of contact lenses, for both cosmetic and therapeutic use.
An optician from England, Kevin Touhy, introduced the corneal lens, which covered only the transparent portion of the protective coating of the eye (the cornea) in 1947. The lenses, patented by Touhy in 1948, rested directly against the limbal margin of the cornea. These lenses had diameters of 10.80 to 12.50 mm. They were much more attractive and easier to wear than the glass and plastic scleral lenses that preceded them. Many changes were rapidly introduced to these types of lenses until a product emerged that was safer and could be worn all day, had tremendous optical clarity and was invisible to the human eye. These changes allowed early contact lens patients to address the public with confidence. The new contact lenses could be worn in all kinds of weather and were useful for sporting activities of all kinds. Because the contact lens was large, but smaller than earlier scleral lenses, it was not easily dislodged or lost.
Lens materials and their chemical composition
Contact lenses can be categorized as silicone hydrogel, rigid gas permeable contact lenses and soft conventional hydrogel, According to Contact Lens Spectrum, all contact lenses utilize a polymer backbone. A polymer is a chemical chain formed from linking many smaller molecules.
Silicone hydrogel
Silicone hydrogel contact lenses are also known as breathable contact lenses. These contact lenses can be worn overnight in some cases. Silicone rubber is used as the polymer backbone in silicone hydrogel contact lenses. Other chemicals, such as polydimethylsiloxane, are also added to improve comfort.
Rigid gas permeable
Rigid gas permeable contact lenses are also known as hard contact lenses. Rigid gas permeable contact lenses contain differing amounts of methyl methacrylate, fluorine, silicon and other chemicals to make them comfortable to wear.
Soft conventional hydrogel
Soft conventional hydrogel contact lenses share a common backbone of the polymer polyHEMA. This polymer serves as the base for all soft contact lenses, and different brands are formed by injecting differing amounts of water and other chemicals into the contact lens as it is manufactured.
