There have not been many things designed to be as functional and and convenient as contact lenses, especially for those that need them. Those that use them can attribute to that. However, it definitely seems stunning that mankind has created a device small enough to place ONTO OUR EYE (specifically the cornea) which makes things instantly clear to those who have blurry vision. If we compare the most related such device, namely glasses, we find an alternative which is in turn relatively quite bulky, fragile, and less comfortable. So how is it that we have such an “elegant” solution to what seems to be a rather complex problem. The magic here lies in refraction.

The main goal of the contact lens (or glasses for that matter) is to simply bend light, or refract light, differently that our eye normally does. For someone with good vision, light enters the person’s eye where the lens, which is actually several layers of transparent cells, inside of the eye bend this light so it is well focused for the all-important receptor at the back of the eye, the retina. For people with poor vision, this light is progressively more and more poorly focused as eyesight gets worse and worse. We can liken this to the effect of a magnifying glass. Clearly we can place the magnifying glass at an optimal point between ourselves and the object we want to view, and the object will be magnified and very detailed. A slight disturbance in this distance ratio causes the image to lose focus, or refractive error, essentially allowing you to see what a person with not so perfect vision sees.

Now, let’s say that in our system we move toward magnifying glass a few centimeters. And lets assume that our eye can be considered the “retina,” since we’re working on a large scale here. The goal here is to place another lens in front of the magnifying glass to get that image to be focused again for this new location of the magnifying glass. And that, on a simple level, is the job of our contact lens.

That’s the technical. The practical is shown well in this image:

Where the lines meet is the focal point.

Optimally, we want the light to focus as in the center photo. However, due to different shapes in the eye (this is caused mainly through genetics, NOT sitting with your nose stuck to the TV for a long period of time. The latter has no effect on your vision, contrary to what seems to be popular belief.) the retina is not where the lens’ focal point is. It is as if in our system described above we moved toward or away from the “magnifying glass”, which in this case is the lens inside of our eye. To fix this, we place a contact lens on our cornea, or wear glasses in order to pass light through the eyes inner lens in a way such that the focal point will be on the retina of the eye.

That’s all there really is to it. For those still interested, The following links are rather interesting:

http://www.enotes.com/how-products-encyclopedia/contact-lens

- This link has a particularly interesting history section. Contacts have been around for about a hundred years, though back then, they were made with actual glass and supposedly, “To fit these early lenses, an impression had to be made of the patient’s eyeball”. Ouch.

http://www.youtube.com/watch?v=62tha1Kxa2c

- This link is a video that explains how contact lenses are made. Really thorough, and supposedly the actual process to make a contact lens takes only 15 minutes. Pretty short considering its a pretty complicated process, and everything needs to be perfectly done.

Image from : Vision Associates

Categories: Science
Tags: Contact Lenses, Optics
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