The evolution of contact lenses to correct myopia
Contact lenses have become a staple in correcting refractive errors (myopia, hypermetropia, astigmatism, presbyopia). The evolution of contact lenses over the last 2 centuries has been astounding. From using glass shells, to the soft, hydrogel based contact lenses we know today. But an unfortunate side effect of the drastic advancements in contact lens science, whether that be using safer materials or catering towards comfort, is that there is a trail of myths. Myths such as contact lenses can get stuck behind your eye or concerns that contact lenses are uncomfortable stem from a lack of up-to-date information on modern day contact lenses. Most contact lenses today are made of hydrophilic plastics. This is a special type of water-absorbing plastic that will stay soft and moist, as long as it has water to absorb. This is why it is important to keep your contact lenses wet either in your eye or in their case.
But contact lenses haven’t always been this soft and comfortable.
Where the evolution of contact lenses began
While when the very first contact lenses were produced is often attributed to Leonardo Da Vinci, the idea was actually first put into practice by Thomas Young in 1801 [1]. It wasn’t until 1827 that the idea that man-made lenses built to fit the cornea could be used to improve vision, and was first considered for correcting myopia and astigmatism. John Herschal’s initial idea for such lenses was to use animal jelly which would be held to the shape of the eye with a glass shell! Safe to say that we have come a long way since then.
Throughout the centuries scientists and ophthalmologists have tried numerous designs, formulas, and materials. Some of which have been more successful than others.
In 1888 the German physiologist, Adolf Gaston Eugen Fick produced the first contact lenses that were worn by patients [2]. These were blown-glass shells that rested on the surface of the eye, only lubricated by dextrose solution. Nearly 50 years later polymethylmethacrylate (PMMA – also known as plexiglass) was developed, allowing the shift to softer plastic scleral lenses. Plexiglass is also used in lighthouse light lenses, a liquid filler in cosmetic surgery and to make artificial teeth.
PMMA was a polymer used by Otto Wichterle and Drahoslav Lim in their search for a material that was biocompatible, and therefore does not produce a harmful response when exposed to human tissue, making it safe for medical use [3].
During their search for safe and effective materials, they knew the materials had to fit 3 key criteria; biocompatibility, softness, and absorbent [4].
- Biocompatibility: The materials had to be compatible with human tissue
- Softness: A polymer that could be as close a possible match to the texture of the surface of the eye, while holding its shape
- Absorbent: The compound had to allow metabolites and nutrients through the biomaterial tissue interface – as the cornea relies on these to maintain its structure and visual clarity
Eventually, through a growing interest in the field of polymer development for medical use, the use of hydrogels in contact lenses was introduced [5]. A well-crafted balance of the structural stability of PMMA and the hydrophilic qualities (the tendency to mix with or absorb water) of certain hydrogels allowed for a softer, more comfortable contact lens that could perform similar to that of the natural eye. In 1970, Otto Wichterle settled on poly-hydroxyethyl methacrylate (PHEMA) as their commercialised hydrogel.
A hydrogel is a hydrophilic polymer (a molecule made up of a chain of smaller molecules) that doesn’t dissolve in water. Wichterle decided on PHEMA because of its high water contents, which allows for easier solubility of oxygen and medications.
Improvements to be made
While hydrogel contact lenses were much more effective than the glass-shelled contacts of the 19th Century, there were still problems to address.
A specific area that needed improvement was the permeability of contact lenses. Contact lenses need to be able to allow liquids or gases through their surface (permeable) to give oxygen and medications access to the surface of the eye. The membrane that these polymers form over the cornea must give way to the things that are key to the natural maintenance of the eye: for example, oxygen. Oxygen is key to maintaining the cornea (the clear layer that covers the front of the eye), without enough oxygen, the cornea becomes less transparent, less capable of feeling pain and can develop scarring. Norman Grant Gaylord [6] was a key research scientist behind this effort, and is credited with the development of gas permeable, rigid contact lenses made from siloxane-methacrylate [7].
If you were wearing contact lenses in the 1980s and 1990s, you might remember a contact lens that, while safe, benefitted from the more recent alterations of the 21st century. They were far less comfortable, and ultimately some people were put off.
Are contact lenses safe for use on children?
While most children who need correction for myopia, among other conditions, will be happy with glasses, but for some, soft contact lenses may be considered. When considering soft contact lenses (SCLs), something to note is the strides that have been made to use SCLs to control myopia progression, for example, MiSight [8]. These are disposable daily contact lenses that simultaneously correct existing myopia and control the growth of the eye in a way that reduces the risk of your child’s myopia worsening.
Over the last 30 years, clinical studies focused on the safety of contact lens use in children have tested a variety of different hydrogel polymers [9]. In Mark Bullimore’s compilation and review of these studies, he notes the lack of reports of adverse reactions or incidents. But he also highlights that out of the issues that were reported most related to ill-fitting contact lenses. This is probably because children’s eyes are still growing. So, more flexible hydrogels and frequent fittings are a priority when using contact lenses on children, to prevent incidents of ill-fitting contact lenses.
In 2011 The CLAY Study Group [10] published a study looking into the risk factors of soft contact lenses wear in children and young adults. In their results, they found that the risk peaks in late adolescence and early adulthood, meaning children between 8 and 18 who wore SCLs were less likely to experience risks, or interruptions, than adults.
Overall, contact lenses have come a long way over the last 40 years. Unfortunately, there are still many myths circulating, that bring people to question their safety and comfort. But, in reality, we are at a point where they are, for the most part, trustworthy, comfortable and ultimately the best option for some people, children included.
Do consult an eye health professional on the best options for contact lenses for you or your child’s eye health needs. Regular and timely comprehensive eye checks are also essential for getting updates to your prescription eyeglasses and monitoring your eye health.
References:
[1] The College of Optometrists, Early contact glasses, The College of Optometrists
[2] N Efron, R Pearson. Centenary Celebration of Fick’s Eine Contactbrille, pp. 1370-77, Arch Ophthalmology. 1988.
[3] Paul C. Nicolson, Jurgen Vogt. Soft contact lens polymers: an evolution, pp. 3273-3283, Volume 22 Issue 24. 2001.
[4] Jindrich Kopecek. Hydrogels: From soft contact lenses and implants to self-assembled nanomaterials, Journal of Polymer Science Part A: Polymer Chemistry/ Volume 47, Issue 22, pp. 5929-5946. 2009.
[5] Andrew Gasson, Tim Bowden. The Overseas Contact Lens Pioneers. British Contact Lens Association. 2006
[6] Paul C. Nicolson, Jürgen Vogt. Soft Contact Lens Polymers: An Evolution. Biomaterials, Vol 22, Issue 24, page 3273-3283. 2001.
[7] Jeremy Pearce. Norman Grant Gaylord. The Boston Globe. 2007.
[8] Coopervision, MiSight 1 day contact lenses for children, Coopervision
[9] Mark A. Bullimore. The Safety of Soft Contact Lenses in Children. Optometry and Vision Science Vol 94, No 6. American Academy of Optometry. 2017.
[10] Heidi Wagner et al. Risk Factors for Interruption to Soft Contact Lens Wear in Children and Young Adults, Optometry and Vision Science: August 2011 – Volume 88 – Issue 8 – p 973-980. 2011
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