First, the development of contact lenses is a history full of attempts and failures, but also full of challenges and continuous progress. The advancement of science and technology is the driving force behind the development of modern contact lenses. People have been looking for the ideal contact lens, i.e., a contact lens that meets the following conditions.
Clarity: good imaging quality, providing excellent corrective vision;
Comfortable: the wearer does not feel a significant foreign body sensation;
Long lasting: able to be worn for long periods of time;
Safety: no eye irritation and toxicity; Ningbo Sixth Hospital Ophthalmology Wang Yuwen
Oxygen permeability: it can ensure the oxygen supply needed by the eyes while wearing;
Stable: does not react easily with the biological tissues and tear components of the eye;
Durable: long service life;
Good wettability: maintain good wettability of the surface to improve wearing comfort;
Anti-precipitation: the surface does not easily form precipitates, which prolongs the life of the lens;
Convenience: easy care and maintenance;
Easy to fit: easy fitting process, easy to promote.
To achieve such goals, contact lenses have undergone tremendous and profound developments in concept, materials and design, fitting and replacement methods, from the inspiration of talented scientists to the continuous practice of countless distinguished individuals in the fields of medicine, material chemistry, optics, etc. Although contact lenses are still not perfect, they have never been more successful and have a larger number of wearers than ever before. In developed countries, contact lens wear accounts for 5%-15% of refractive error correction.
Second, a brief history of the development of contact lenses
1, “contact lens” conceiver
Many documents between the 16th and 19th centuries record the prototype of the contact lens concept. Da Vinci of the Renaissance was the first to describe the “contact lens” concept. The first person to describe “contact” lenses was Leonardo da Vinci, who in 1508 described in a diagram the mechanism by which the refractive power of the cornea could be neutralized when the eye was immersed in a container of water. Although he was trying to understand the regulation mechanism of the eye, he inadvertently expressed the basic principle of contact lenses.
In 1637, Rene Descartes introduced a water-filled glass tube device to achieve an increase in axial length and increase the retinal image, which could lead to better vision. If a lens is used instead of glass, the same magnification of the image is achieved.
The physicist Thomas Young, who studied accommodation in 1801, used a 25 mm long tube in contact with the eye, filled with water and closed at one end with a biconvex mirror.
Sir John Herschel was an English astronomer who, in 1845, based on the ideas of Thomas Young and George Airy and others, speculated on the use of an apparatus in contact with the eye to correct corneal astigmatism, envisioning a spherical glass or a gel-like substance covering the surface of the cornea to make a mold. “the father of contact lenses.”
In the late 19th century, cataract surgery was performed by surgeons who did not use sutures, and the rate of corneal infection was high. in 1886 Xavier Galezowski covered the corneal incision with a 0.25 to 0.50 mm thick gel soaked in medicinal water, which significantly reduced postoperative infection. He was the first person to apply a therapeutic contact appliance.
2. Who was the inventor of the contact lens
In the years after 1886, a great deal of contact lens research was carried out, but who was the real inventor of the world’s first contact lens to be worn in the human eye?
In 1888, Adolf Fick, a German ophthalmologist working in Zurich at the time, tried to develop corrective lenses in contact with the eye, first trying them on rabbit eyes and then on his own eyes and on the eyes of patients with irregular scarred corneas, avoiding the removal of the eye. However, the lenses he designed were difficult to make and wear in and caused more pronounced mechanical irritation.
Also in 1888, Eugene Kalt, a Frenchman, applied a glass shell instead of a compression dressing in the treatment of patients with conical corneas, which had the same curvature as the cornea and could significantly improve the patient’s vision.
According to a 1910 textbook, August Mller, a German, had announced that in 1887 they put a partially transparent glass protective shell cover on patients. Unlike the first two, Mller was the first physician to develop a refractive correction effect. Being himself highly myopic, he made the posterior surface of the lens similar to the anterior surface of the cornea, which was in contact with the eye and could correct his myopia of up to 14D. He believes that the siphoning action of the tear film allows the lens to attach to the cornea and improves tear circulation by improving the curvature of the edge of the lens. The honor of fitting patients with contact lenses with refractive power must undoubtedly go to him. He described his invention in his inaugural lecture at Kiel University and called it the “contact lens”.
In the decades that followed, interest in contact lenses began to wane and little progress was made in the field.
3.Miles of contact lens development
In chronological order, the main landmark events in the development of contact lenses are as follows.
Table 1 I 1 Contact lens development mileage
Era Epithet Event Significance
1508 Leonardo da Vinci In his work Codex of the Eye, Leonardo da Vinci expressed a principle similar to that of the contact lens and is considered the first recorded description of a “contact” lens
1845 John Herschel
Explained the principles of contact lenses in a paper considered the “father of contact lenses”
1888 Adolf Fick, August Mller and others pioneered the development of scleral lenses, experimenting with them in animals and human eyes From concept to reality, entering the era of glass scleral lenses
1930s PMMA is introduced and used to make contact lenses, entering the era of plastic scleral lenses
1946 Kvein Tuohy
Unintentional production of corneal contact lenses, entering the era of corneal contact lenses
1950s Otto Wiehterle developed HEMA material and entered the era of soft lenses
1960’s to 1970’s Dr. Lund and other American companies
Purchased patents for soft lens rotational molding technology and began mass production The soft lens era was in full swing
1960s Silicone materials are introduced, but no significant progress is made due to surface wettability issues
1970s John de Carle
Long-wearing lens concept, but no significant progress due to material and design constraints
1970s – RGP material emerges, PMMA lenses fade into obscurity RGP era begins
1980s – Johnson & Johnson introduced the concept of disposable lenses, bringing about a change in the way they were worn
1990s PTC Corporation, Minicon Corporation, and others improved RGP materials and design, resulting in a dramatic increase in oxygen permeability RGP lenses became increasingly popular in developed countries
Late 1990s to early 2000s New generation of silicone hydrogel material developed New high oxygen permeability soft lens material; can be used for continuous wear
The following is a review of the history of contact lenses and an outlook on the future with regard to the development of contact lens materials, designs, wearing styles and replacement cycles.
Development of contact lens materials
1. PMMA
The first contact lenses were made of glass, and in the 1930s, polymethyl methacrylate (PMMA) was introduced in the United States, which was more suitable as a contact lens material than glass.
At that time, the form of lenses made from PMMA material was scleral lenses, and later Tuohy designed and patented PMMA corneal contact lenses in 1946. Since then, the design of lenses has gradually progressed from single-arc corneal contact lenses to multi-arc corneal contact lenses.
PMMA is clear and less dense than glass, allowing it to be designed and processed into thinner contact lenses, so PMMA quickly became the popular contact lens worldwide.
PMMA lenses have many advantages, including easy manufacturing, durability, changeable parameters, good optical properties, good surface wetting, stable parameters, and the ability to correct corneal astigmatism. It can be said that PMMA is almost the perfect contact lens material, but it has one fatal weakness – impermeability, which leads to many clinical complications caused by hypoxia, such as neovascularization, endothelial polymorphism, etc. Although efforts were made to try to remedy this defect by improving the design and wearing style, the non-breathable nature of PMMA eventually ended its fate. Nowadays, clinical fitting with PMMA lenses is only attempted in very few cases in the world.
People began to believe that the most ideal contact lens material was all the advantages of PMMA plus oxygen permeability, and this was the driving force behind the search and development of contact lens materials thereafter.
2. Hydrogel soft lenses
Soft lenses occupy more than 80% of the current global contact lens market. The earliest soft lens material is HEMA, a hydrophilic (38.6% water content) polymer developed by Czechoslovakian scientist Professor Otto Wichterle in 1954, which has a certain permeability to nutrients and metabolites. Professor Wichterle also invented an automated production line for rotational molding of contact lenses, and the rotational molding production technology, lens materials and design developed by Professor Wichterle attracted the interest of the American industry, which purchased the patents and began large-scale commercialization by the American company PhD. and entered the market in 1972.
With the quest for continuous contact lens wear, attempts were made to increase oxygen permeability by increasing the water content of the lenses, and by achieving this goal, other different types of soft lens materials were developed, including materials with water content up to 71%, which are collectively referred to as non-HEMA materials because they differ in molecular structure from HEMA materials.
The advent of soft lenses has led to a new era of rapid development in the popularity of contact lenses and a rapid increase in the number of wearers. However, the ensuing misunderstandings about lens wear and improper use have led to the emergence of clinical complications, prompting more improvements in the development of new materials, wearing methods, and replacement cycles to achieve safe and healthy wear.
3.Silicone soft lenses
Silicone is a unique class of contact lens material that belongs to the soft lens category based on its physical properties, but unlike ordinary hydrogel soft lenses, silicone elastomer does not contain water, so in some ways it is somewhat similar to hard lens materials.
The silicone material is highly permeable to oxygen and carbon dioxide, so there is little interference with corneal respiration. However, the hydrophobic nature of the silicone material makes it more difficult to manufacture and must be treated to be comfortable to wear. Because it is quite difficult to improve surface wettability, few major advances occurred after its introduction in the late 1950s. Until the development of new technology in the 1990s, silicon and hydrogel materials to obtain a stable combination, the formation of silicon hydrogel (silicon hydrogel) material, this material not only maintains the characteristics of silicon high oxygen permeability, but also hydrogel material hydrophilic advantages, significantly improving the wettability of the material, in the United States and other countries to obtain permission to wear for 30 days.
4.RGP lens
RGP (rigid gas permeable abbreviation) material, is a class of both hard and oxygen permeable contact lens material general term. The ideal contact lens material, approximately equivalent to PMMA plus higher oxygen permeability. The first attempts were therefore made to incorporate highly oxygen-permeable silicone materials into the PMMA structure, and these materials were called silicone acrylates. The later emergence of fluorosilicone acrylates improved the disadvantages of silicone acrylate surfaces due to poor wettability and easy formation of protein deposits caused by the high silicone content.
In terms of its health for the cornea, rigid gas permeable contact lenses (RGP) are currently the best lenses and have good optical properties to correct astigmatism. However, RGP fitting requires more clinical fitting knowledge and skills on the part of the fitter, a certain level of quality and understanding on the part of the wearer to successfully adapt to these lenses, and a more personalized design and lens production laboratory to provide well-made lenses. For all these reasons, RGP fitting is still in its infancy in China, but with a bright future.
Development of contact lens design
The earliest form of contact lens design was the scleral contact lens. The first corneal contact lens in history can be traced back to a thoughtless mistake: In 1946 when Kevin Tuohy made a mistake in making PMMA contact lenses, he separated the scleral part from the corneal part when turning the lenses. On a whim, he polished the corneal part and put the lens in his own eyes and found that the lens was resistant to it. Further experiments were then conducted to develop an early rigid corneal contact lens.
Tuohy designed the lens with a single-arc spherical design, which had two drawbacks: excessive pressure of the lens on the central zone of the cornea, excessive warping of the edges, leading to central corneal wear and edema, and the tendency for the lens to fall out of the eye. This problem was later properly solved by changing the peripheral curvature of the rear surface of the lens, resulting in the multi-arc design.
Later designers continued to be inspired by the aspheric shape of the corneal surface and designed the posterior surface of the contact lens to be aspheric as well, in order to obtain an even better fit. The multifocal design of contact lenses brought a new way of correction for presbyopes. The reverse geometric design of contact lenses developed for postoperative cornea and keratoplasty has a flat center and steep periphery.
V. Development of contact lens fitting methods and replacement cycles
An important criterion for the ideal contact lens is a convenient wearing style for the wearer, which is polarized in the development of contact lens wearing style and replacement cycle: either wear longer and longer – long wearing or continuous wearing; or wear shorter and shorter – discard or even One day abandonment.
1.The development of wearing style
Early soft lenses emerged in the 1970s as low water content hydrogel soft lenses, and contact lenses were regulated as medical devices by the Food and Drug Administration (FDA) in the U.S. The FDA regulated them as daily wear lenses at that time.
By the late 1970s, consumers expected to wear lenses overnight. Optometrists at the time believed that this could be achieved by increasing the water content of the soft lens material. However, the concept of long wear was severely challenged by a series of reports of clinical problems such as corneal hypoxia and lens contamination due to long wear.
Through continuous research, the basic requirements for corneal oxygen supply under contact lens conditions were gradually understood and, based on these findings, more proactive improvements in lens design and materials were made to achieve safe and even desirable long wear. The emergence of RGP materials with high oxygen permeability and new silicone hydrogel materials has made long wear or continuous wear possible.
2. Development of the replacement cycle
Prior to the mid-1980s, it was believed that lenses could continue to be used as long as they were relatively clean, unbroken, and continued to effectively correct the wearer’s refractive error. Even if the lens was cracked or had varying degrees of deposit deposits on its surface, the lens should still be used for as long as possible. Contact lenses with this type of replacement are called conventional contact lenses. Depending on the type of lens, the general contact lens life according to the traditional type of wear, that is, the replacement cycle is 3 to 5 years for PMMA hard lenses, 1 to 2 years for RGP lenses, and about 1 year for traditional type of soft lenses.
The first disposable lenses appeared in Denmark in 1985. The following year, Johnson & Johnson acquired the technology for mass production and sales. Disposable lenses are made of the same materials as conventional soft lenses and have a similar design, but are characterized as single-use medical devices, meaning that they are worn only once, either daily for one day or continuously for one week or 30 days, and then discarded.
The advantages of disposable lenses are: significant reduction of sedimentation and surface damage associated with conventional lenses; and greater convenience without or with simplified lens care. One of the keys to the popularization of disposable lenses, which have become common in some developed countries such as the United States and Japan, is the good repeatability, the manufacturing process suitable for mass production and the resulting reasonable and low cost.
VI. History of contact lens development in China
Contact lenses are also called contact lenses in Chinese. Shanghai Wu Liangcai Optical Shop was the first to introduce contact lenses produced abroad in China in 1946, but it was not until 1962 that Shanghai Medical College and Shanghai Optical No. 2 Factory jointly developed and produced the earliest corneal contact lenses in China, when the material was PMMA. by the 1970s, they again jointly developed the first pair of soft corneal contact lenses in China.