Contact Lenses: How do They Work?

Over half of the population of the world has some problems with their eyesight, most of them being myopia or hyperopia. These people are given prescriptions for a form of corrective devices such as glasses or contact lenses by oculists. However, most of the time, especially in rainy weather and now with surgical masks on our face, glasses are not so convenient to use. Therefore, many people, who have an eye structure suitable for putting contact lenses on, use contacts to fix their vision during the day. So, basically, contact lenses are widely used around the world, but how many people using these know about the science behind their mechanism?

Contact lenses are made of polymer plastic which is perfect for eye structure as discovered by professors at the Institute of Chemical Technology in Prague. These contact lenses are produced in either two ways: lathe cutting or injection molding. Lathe cutting involves placing soft contact lens disks on a spinning shaft that rotates 6000 times a minute while some computerized cutting tools shape the lenses [2]. On the other hand, injection molding involves heating the contact lens material until it’s a liquid and injecting it into pressurized molds. 

Contact lenses refract and focus light to correct refractive errors, maintain ocular health and make objects clear for the patient. By changing the direction of light coming into the eyes, lenses allow the light to focus on the retina only on a single focal point (one specific spot). In this mechanism, the outer curve of the lenses plays an important role since it is the outer surface that focuses the incoming light onto a focal point. This is their main working principle. However, for different vision problems, these lenses are designed for specific refraction angles. For example, in myopia, the patient sees distant objects blurry because the light falls in front of the eyes’ retina. For the correction of this disease, contacts divert the light to a focal point directly on the retina. In these cases, you will see an “+” sign on your contact lens prescription which is in correlation with the outer shape of the contacts. On the other hand, for hyperopia, the patient sees close up objects blurry because the eye cannot focus the light onto a single point but instead radiate the light rays around the retina. For the correction of this disease, contacts converge the light rays into a single beam of light [2]. In these cases, you will see an “-” sign on your contact lens prescription which is in correlation with the outer shape of the contacts.

Contact lenses float on the tear film layer on the surface of the cornea and by sticking, they act in accordance with your eye movements. This is possible by the sticky nature of the inside curvature of the contact lenses. With the help of the natural moisture of the eyes, lenses can stay in place for so long. What is more convenient is that every shape and curve is precisely determined to suit the shape of a person’s eyes. The oculists run some tests and measurements to create the perfect lenses for one’s eyes. This sticky nature of lenses that move with the eyes allows for excellent peripheral vision and creates a realistic view for the patients. 

Since 1991, the number of people who use contact lenses has increased by 4% per year because when used correctly, contact lenses are a perfectly safe alternative to traditional eyeglasses. However, you must be really careful while using your lenses, especially with your hygiene. Your hands must always be clean and dry before handling your contact lenses. You must remove and clean your contact lenses with the storage solution each evening before going to bed. It is also important to replace your lenses when instructed, whether it’s a daily, weekly, or monthly schedule.

Citation

[1] “How Contact Lenses Work.” CooperVision, https://coopervision.com/about-contacts/how-contact-lenses-work. 

[2] Perfectlens.ca. “Uncover the Mystery: How Do Contacts Work?” Perfectlens.ca, 12 June 2018, https://www.perfectlens.ca/articles/how-do-contacts-work. 

[3] Lenspure.com. “How Do Contact Lenses WORK? The Science behind Them.” Lenspure.com, 12 June 2018, https://www.lenspure.com/articles/how-do-contact-lenses-work. 

[4] image only https://fecarlington.com/differentiating-nearsightedness-farsightedness/

[5] image only https://www.aao.org/eye-health/glasses-contacts/contact-lens-102

[6] image only https://www.wired.com/story/mojo-vision-smart-contact-lens/

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