To understand how contacts work, it’s important to understand how we see. Eyesight takes a lot of invisible, behind-the-scenes team work. It starts with collaboration among the cornea, iris, pupil, lens, retina, optic nerve, and brain. Light hits the cornea, which bends it. The light passes into the pupil, with the iris controlling how much light enters. It then hits the lens, which helps focus light on the retina. The ingenious retina then translates light into electrical signals that the optic nerve carries to the brain. It’s an intricate process that occurs in the blink of an eye. Literally nanoseconds.
What causes abnormal vision?
For normal vision, light needs to focus directly on the retina. So abnormal vision occurs when the light misses the retina. According to the National Eye Institute, a misshapen cornea or aging lens prevents light from reaching its target, the retina. The light either over- or under-shoots or bounces around. Common visual disturbances have uncommonly long names. Nearsightedness, farsightedness, astigmatism, and presbyopia. Whatever the name, they have one thing in common. All of them cause blurred or double vision. And the good news? Contact lenses can redirect misdirected light to the retina. With the contact lens in place, we can set our sight on favorite books and films, TV shows, and natural or unnatural wonders.
How do contact lenses redirect the light?You’ve probably heard the word “refraction.” It means bending or redirecting, in this case light. The shape of a contact lens relates to a specific type of vision problem. An eye exam will reveal the problem. Then an eye-care specialist will prescribe lenses tailored for your eyes only. Numbers and pluses or minuses refer to the shape and strength of the lenses. And keep this in sight: It’s critically important that the fit and strength meet your needs. The lenses, or discs, are about 14-15 millimeters, just over half an inch. They float on the tear film layer of the cornea. With the right shape and fit, the contact lenses “bend” light so that it lands on the retinal target. A perfectly aimed ray of light is a virtual bullseye Do some contact lenses work better than others?
The American Optometric Association lists several types of contact lenses: rigid gas permeable (RGP), daily wear soft lenses, and extended-wear soft or RGP lenses. Basically, they are all made of plastic and allow oxygen to get to the eye. Some are rigid and some are soft. Some are meant to be worn only during the day and be removed at bedtime, while others, extended-wear, can remain in the eye for up to seven or even 30 days. Each type has advantages and disadvantages, which are described in What Are My Options for Contact Lenses?