If you’re a contact lens wearer, you’re in good company–over 24 million people wear contacts in the United States alone. But have you ever wondered how those little circles of plastic actually improve your vision? Read on to take a closer look at contact lenses:
How The Eye Works
To understand how contact lenses work, it’s important to know a little about how the eye works. When light reflects off an object, it passes through the cornea (the transparent covering of the eye) and the pupil (the black part of the eye), and then the light passes through the lens, which focuses the rays on the retina at the back of the eye. The retina is full of rods and cones that convert the light into electrical impulses that are sent to the brain. Blurred vision occurs because of “refractive errors.” In other words, the shape of the eye prevents the light from hitting the retina directly, thereby causing distortion.
How Contacts Fix Refractive Errors
Contact lenses are miniature prescription lenses that float in “contact” with the tear film of the eye. Like eyeglasses, the contact lens refracts and focuses the light on the retina. There are different types of contacts for different types of refractive errors:
Myopia (nearsightedness) is a condition in which far objects appear blurry and close objects are seen clearly. This occurs when light enters the eye without being correctly focused which is directly caused by the shape of one’s eye. Standard contacts such as Coopervision’s Avaira lenses can correct this very common condition.
Hyperopia (farsightedness) is the opposite of myopia in which near objects appear blurry due to light focusing past the retina. This condition also uses standard contact lenses available in all modalities.
Presbyopia is an age-related condition that resembles hyperopia in that it causes near objects to be blurry. Presbyopia, however, stems from a different cause. While hyperopia is caused by the eye being misshapen, presbyopia is caused by the hardening of the lens in the eye which ultimately happens to everyone as they get older. Many with this condition require multifocal contact lenses, such as Proclear Multifocals, which can correct for both near and far distance prescriptions.
Astigmatism is a condition that occurs when the eye does not focus light evenly onto the retina due to an irregularly shaped cornea or lens. In order to correct for this, a special type of lens called a toric contact lens is needed. To compare the difference between a lens that corrects for astigmatism and one that does not, imagine the cross section of two types of balls. A sphere lens, a lens that does not correct for astigmatism, can be imagined as a simple cross section of a beach ball, whereas a toric lens, a lens that corrects for astigmatism, is like a cross section of a football. Because toric lenses need to be oriented in a specific way, they need to be carefully designed to be stable and accurate. A good example of this type of lens is the Biofinity Toric.
Contact lenses have come a long way since the first contact lens was worn in 1801 by scientist Thomas Young who used wax to secure a lens in his eye. Advanced research and technology have significantly improved contact lens design and the lens material which have helped increase the number of patients seeing clearly again without the hassle of eyeglasses. If you would like to learn more about how contacts work, click here.