If you wear lenses, or even if you don’t, chances are you have asked yourself, “how do contact lenses work?” After all, it’s just a little piece of plastic. It’s amazing that without them, your vision can seem awful. And with a little thin lens, everything is clear. So let’s take a closer look; how do contact lenses work?
In their simplest form, contact lenses are nothing more than an optical lens; similar to that in a pair of eyeglasses, only much smaller and of a different material.
For the nearsighted eye, the lens is a minus power. On eyeglasses, this makes for a thin center and thick edge. The same goes for contact lenses, a very thin center and a thicker edge. The variation of the thin to thick makes up the power of the lens. For example, a -14.00 lens has thicker edges than a -2.00.
The inside curve of the lens, also called the base curve, is designed for optimum fitting on the cornea. Base curves are measured in mm of radius. For example, a base curve of 8.6 means that the lens has the same inside curves of a circle with a radius of 8.6mm.
Another major factor in answering how do contact lenses work?, the diameter. Diameter is measured edge to edge, also in millimeters. The diameter is altered for physical fit and comfort. Any time the diameter is changed, the base curve needs to be revised. For example, a lens with a base curve of 8.6 and a diameter of 13.8 will be overall flatter than a lens with a base curve of 8.6 and a diameter of 15.0.
To picture this in your mind, picture a circle and imagine the top quarter of the circle is a lens. Now imagine the top half of a similar circle is a lens. Can you begin to see how different those two lenses would be?
Contact lenses only work properly when they have the proper prescription and they are fit correctly. A contact lens that is too steep will not only be uncomfortable, it will also create a blurry image because of the distance between the front of your cornea and the back of the lens. A lens that is too flat will not center properly and the edges will buckle or lift off the white of the eye.
Once properly fit, the lens must stay hydrated in order to work properly. On soft contact lenses, this is accomplished simply by blinking. Think of your lids as windshield washers that constantly clean the lens. If you wear lenses, you may notice that they blur a little after long term computer use. This is directly related to the fact that a persons blink rate slows when focusing on anything up close, i.e. the computer screen.
As you can see the optical qualities, proper fitting, and constant blinking are the main factors when figuring how contact lenses work.
Steve Cogger is a contact lens specialist from New York City and a fellow of the Contact Lens Society of America. In order to provide a resource for all lens wearers, he is also the webmaster of the site