Over 36 million people wear them, but how do they work?

Kendra's picture

My mother could not believe my decision, she thought I was crazy. But I was going to be a junior in high school and I thought this decision would make my life so much easier. So, at the dismay of my mother, I went to the vision center closest to my home, sat in front of my optometrist and said to him “I want contact lenses”. It took me about a week of putting the lenses in and taking them out for me to be completely comfortable with placing my finger near my eyeball, a practice that my mother found repulsive. I’m not judging her opinion, as an avid eyeglass wearer since the fifth grade; I too thought the use of contact lenses was revolting. I used to observe one of my friends in middle school, whose older brother was an optometrist, put in different color contacts daily. Besides not seeing the point of them, I thought the whole process was scary. That was until I started to realize the various reasons why the use of contacts trumped that of glasses, one the biggest being that during cold winter days, my glasses tended to fog whenever I went from the outside in. So, on the eve of my junior year I decided enough was enough. I’ve been wearing contacts for about four years now and it was only recently that I pondered to myself how contacts were developed and ultimately, how did they work? The question clearly had not crossed my mind. To me, my contacts were just magical little pieces of plastic that aided my nearsightedness and honestly, I was happy enough with the idea of not having to wear glasses during the day.

Corrective lenses, or contact lenses, are simply defined as “small, thin, transparent discs, designed to sit on your cornea and correct your vision” [5]. But contact lenses were not always seen as such, in fact, they have come a long way from the first pair designed in 1888 by the German physiologist, Adolf Eugen Fick [6]. Fick fabricated his design of contact lenses from afocal scleral contact shells- which rested on a less sensitive part of the cornea- and tested his design on rabbits and a small group of volunteers, which included him [6]. In Fick’s published work, Contactbrille (1888), he describes his contacts as being made out of heavy brown glass and being 18-21mm in diameter. These lenses were much larger than modern contacts and could only be worn for a few hours at a time. Fick’s design- glass blown scleral lens- was very popular up until the 1930’s when polymethyl methacrylate (PMMA) was developed [6]. PMMA allowed the development of plastic scleral lenses in 1936 by optometrist William Feinbloom [6]. One of the main problems with contacts developed through the use of PMMA is that the contacts didn’t receive oxygen transmitted through the lens to the cornea, so as a result, throughout the 1980’s and 1990’s, a range of “oxygen permeable but rigid materials were developed to overcome this problem”[6]. Although Feinbloom’s design was lighter and more convenient, the first corneal contact was designed in 1949 and was smaller because they only sat on the cornea rather than across the visible ocular surface and could be worn much longer- up to sixteen hours per day [6]. These previous designs of contacts gave rise to the most important breakthrough in contact lens design made by the Czech chemist Otto Wichterle whose 1959 published work “ Hydrophilic gels for biological use” in Nature provided the foundation needed for the first approval of the ‘Soflens’ material by the US FDA in 1971 [6]. Because of Wichterle’s work, the ingredients that made up the polymers of the Soflens improved over the next 25 years such as to provide increasing oxygen permeability [6]. The aim of each of these scientists was to create a device that could be used to perfect a person’s vision, but what is perfect vision?

Perfect vision in a human being happens when “light rays enter the cornea in the front of the eye and are focused into a single point on the retina in the back of the eye. Once it hits the retina the light is converted into signals, which go to the brain to be processed into images” [1] and is generally known as 20/20 vision. Some people are more genetically prone to not have perfect vision while some people, by the over usage of technology, such as the television or computer, or reading without sufficient light can taint their perfect vision. In my case, because I tended to read without sufficient lighting as a child, I developed nearsightedness. Myopia, or nearsightedness, occurs when “the eyeball is too long or the cornea is too steep, so images are focused in the vitreous inside the eye rather than on the retina at the back of the eye” [2]. Basically, those who are nearsighted see nearby objects clearly but distant objects are blurred. Another form of refractive defect of the eye is hyperopia, or farsightedness and this defect has the opposite effect than that of nearsightedness, where the eyeball is too short “ causing inability to focus in near objects and in extreme cases causing a sufferer to be unable to focus on objects at any distance” [3]. Astigmatism is a less common refractive defect where “vision is blurred by an irregularly shaped cornea …instead of being shaped like a sphere, it is ellipsoidal (like an egg)” [4]. All three of these refractive defects are diagnosed by their severity and in most cases can be helped by corrective efforts, like glasses or removable contacts.

Today, there are two different types of removable contacts, corrective and cosmetic lenses. Many contact lenses wearers, including myself, choose to wear corrective lenses, which are ultimately designed to improve ones vision. A mismatch between the refractive power of the eye and the length of the eye leads to a “refraction error” and a corrective lens is used to “neutralize this mismatch and allow correct focusing of light into the retina” [6]. Wearers of corrective lenses usually take the lenses out every night or every few days, depending on the make of the contact lens. Another way in which contact lenses are used is cosmetically. A cosmetic contact lens is “designed to change the appearance of the eye” [6] and although these contacts can also be worn to correct vision, some obstruction of vision can occur because of the color or the overall design of the lens. Cosmetic lenses can have natural effects ones eyes, like changing them from dark brown to blue, or can have unnatural affects that are mostly used in theater productions and movies, an example being a completely white eyeball.

Although corrective and cosmetic lenses are used, in most cases, for different purposes, the eye does most of the work in keeping the actual contact in place. Contact lenses, whether corrective or cosmetic, rest on your cornea atop a constant supply of tears [7]. As it turns out, blinking is very important in maintaining ones contact lens, for with each blink comes a slight movement of the contact lens that allows the tears to gently wash away any of the debris that can collect in ones eye [5]. In the cases of both corrective and cosmetic lenses, an optometrist makes sure that the lens fit perfectly with their patient’s eyeball, by measuring the cornea, so the lens is able to “direct light rays to one place on the cornea, which in turn corrects your vision”[7].

Knowing how corrective lenses work makes one see them in a different light. It is fascinating to make the realization that such small, plastic entities help so much in correcting ones vision. It is true that the soft, plastic contacts I put in my eyes every morning have come a long way from its first design when they were made out of glass for the idea of putting glass into my eye is unimaginable! Though eyeglasses still serve as improvement for many people’s vision, the corrective contact lens acts more internally as a clear, second layer for the cornea which in turn, allows for clear vision. For the past four years, I never had a second thought as to how corrective lens work and thus realized that it is important to know how the small things in life work, so as to not overlook them and take advantage. Knowing how a corrective lens works with the eye to improve ones vision makes one fully appreciate the eye as an important organ of the human body.

 

References

[1] http://health.howstuffworks.com/contact-lens2.htm

[2] http://en.wikipedia.org/wiki/Myopia

[3] http://en.wikipedia.org/wiki/Hyperopia

[4] http://en.wikipedia.org/wiki/Astigmatism_%28eye%29

[5] ] http://www.howitworks.net/how-contact-lenses-work.html

[6] http://en.wikipedia/org/wiki/contact_lenses

[7] http://ezinearticles.com/?How-Do-Contact-Lenses-Work?&id=22463

Comments

C. Sanders's picture

Contact Lenses

I totally understand the "revolting" feeling you described. It took me a long time to get used to wearing lenses.

Serendip Visitor's picture

Nowadays

"Over 36 million people wear them, but how do they work?"

According to Wikipedia the number is nowadays about 125 million.

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