How does an eye work?

Eyes do not actually see objects -- what they see is the light that objects reflect. When these light rays enter the eye, they are absorbed and converted into electrical signals by retinal nerves. These signals are subsequently sent to the brain where they are interpreted as visual images.

In a normal eye, light rays enter the eye through the "cornea" (window of the eye) and are focused with the help of a "crystalline lens" behind the pupil at a point directly on the retina (the light sensitive nervous tissue at the back of the eyeball). However, only about four in ten people have normal visual acuity. For the rest, clear vision may be achieved by refocusing light rays with the use of corrective lenses.

How does a contact lens work?
Contact lenses are delicately crafted, very thin optical discs generally smaller than a dime, worn directly on the eye. They are comfortably held in place by a natural layer of tears present between the contact lens and the cornea. Contacts eliminate the barriers encountered with spectacles that interfere with the line of sight above, below and to the sides of the eye, offering outstanding peripheral vision. In addition, contacts can reduce or eliminate the image distortion sometimes caused by eyeglasses.

There are several types of contact lenses designed to fit the most common vision conditions. Following are brief descriptions of these conditions:

Myopia
(Nearsightedness)
Myopia is a condition which occurs when the eyeball is too long, or the eye's focusing mechanism is too powerful (cornea and lens), and light rays are focused in front of the retina. People with this condition can see clearly up close but not at a distance. An estimated 30% of Americans are nearsighted to some degree. Lenses to correct this common condition are thinner in the center than on the edges to help redirect light rays to the retina, and are called "minus" or concave lenses.

Hyperopia
(Farsightedness)
Hyperopia occurs when the eyeball is too short from front to back, or the eye's focusing mechanism is too weak, causing light rays to be focused behind, rather than on the retina. People with hyperopia have difficulty seeing objects close up. An estimated 60% of Americans are farsighted to some degree. In order to correct this vision problem, a convex, or "plus" lens is prescribed. This lens is thicker in the center and thinner on the edges.

Astigmatism
Astigmatism is characterized by an irregularly shaped cornea that causes light images to focus on two separate points in the eye, creating a distorted image. Symptoms range from visual discomfort in mild cases, to severe blurring and distortion similar to a reflection in a fun-house mirror. Contact lenses designed to provide astigmatic correction are fitted for each individual. The misshapen cornea is precisely measured and special toric lenses are used to direct light rays to one spot on the retina. There are more than 60 thousand different toric prescriptions available, offering the nearly 71 million Americans affected by astigmatism an alternative to eyeglasses. Rigid Gas Permeable (RGP) lenses, due to their firm design, offer a high degree of corrective ability for this condition and, in many cases, do not require a complicated toric design due to their ability to compensate for the irregularly shaped cornea.

Presbyopia
This is a condition that occurs as the eye’s lens grows older and begins to lose some of the elasticity needed to switch focus between viewing near and far objects. Also known as "aging eye," presbyopia affects most people around the age of forty, even though its onset can occur as early as age ten. As the eye's lens continues to lose its elasticity, the eye takes longer to adjust between objects -- such as the road and the speedometer. Half-glasses or bifocals used to be the only answer for people with presbyopia. Today there are a number of contact lenses that can correct this condition, including multifocal contacts and specialized fitting techniques such as monovision. Click here for more on presbyopia.

CONTACT LENSES: Types & Benefits

CONTACT LENS TYPE BENEFITS
Daily-wear soft lenses
Made of soft, flexible plastics that allow oxygen to pass through to the eyes.
  • very short adaptation period
  • more comfortable and more difficult to dislodge than RGP lenses
  • available in tints and bifocals too
  • great for active lifestyles
  • while careful cleaning is required, lens care maintenance products are unsurpassed in simplicity and efficacy
Daily-wear disposable soft lenses
Single-use, daily wear lens that are designed to be worn for a single day, discarded at night, and replaced with a brand new pair.
  • typically no lens care is required
  • assures fresh and clean lenses when replaced
  • great for active lifestyles
Extended-wear soft lenses
Available for overnight wear. Made of soft, flexible plastics that allow oxygen to pass through to the eyes.
  • can usually be prescribed for up to seven days of wear without removal
Extended-wear disposable soft lenses
Soft lenses worn continuously from one to six nights, and then discarded.
  • require little or no cleaning
  • available in tints and bifocals too
  • spare lenses conveniently on hand
Frequent & planned replacement soft lenses
Soft daily or extended wear lenses that are replaced on a planned schedule, most often every two weeks, monthly or quarterly.
  • assures fresh and clean lenses when replaced
  • available in most prescriptions
  • spare lenses conveniently on hand
Rigid Gas Permeable (RGP)
Made of slightly flexible plastics that allow oxygen to pass through to the eyes
  • vision may be sharper than with soft contact lenses
  • easy to put on and to care for
  • durable with a relatively long life (1-2) years
  • available in tints (for handling purposes) and bifocals
  • daily-wear and extended-wear designs available
  • planned replacement schedule also available

It is important to keep in mind that contact lenses are FDA-regulated medical devices that require regular visits to an eyecare professional.

WHAT HAPPENS DURING AN EYE EXAM?
If you haven't had your eyes examined within the last two years, schedule an appointment now. Routine exams are quick and painless and the only way to ensure good, healthy vision.

Before your exam, your eyecare professional will ask you about:

Next the eyecare professional will check your vision. The vision test will determine if vision problems exist and, if necessary, what prescription to write to properly correct your vision. The test may also include:

WHY ADULTS NEED EYE EXAMS
Good vision is important for everyone. Routine eye exams can uncover conditions such as near-sightedness, far-sightedness, astigmatism and eyestrain early on, allowing for fast treatment of most problems. Eye exams can also provide evidence of other serious, but hidden, medical conditions, including high blood pressure, diabetes, inflammations, infections and the hardening of arteries. Eye ailments have also been linked to learning disabilities that can be treated with vision correction.

NO BETTER TIME THAN NOW!
There is no better time than now to start the habit of regular eye exams for you and your family. If you haven't had an exam within the last two years, schedule one now. During your exam, your eyecare professional will help set a regular schedule for future exams tailored to your personal situation.

WHY CHILDREN NEED EYE EXAMS

One in four children ages 5 to 12 has an undiagnosed vision problem that may affect their educational performance. Unfortunately, children with vision problems often have no way of knowing that what they are seeing is different than what others see. It is up to the adults in their life to help children reach their potential by ensuring that they are free of vision problems.

All children should have their eyes examined at or before their fourth birthday. If there is a family history of misaligned eyes, childhood cataracts or a serious eye disease, children should have their eyes examined before age three. Vision problems often respond to treatment better during the growth and development of a child's visual system, so early detection could be the key to good vision.

Telltale signs that your child could have a vision problem:

  • Squinting, rubbing or blinking eyes a lot
  • Using a finger as a placemark when reading
  • Holding head at an awkward angle when reading
  • Closing or covering one eye to focus
  • Holding reading material close to face
  • Having red or crusty eyes

Eye examinations are quick and painless, but a child who has never had an eye exam may be quite fearful. To set an example, parents can have their own eyes examined first, while the child watches. This allows the child to see what will happen during the exam and ask any questions. You can then sit with them during their exam to calm any remaining fears.

EYECARE PROFESSIONALS

Ophthalmologists (MD) are medical doctors (MD or osteopath) uniquely trained to diagnose and treat all disorders of the eye. An ophthalmologist is trained in all aspects of eyecare - medical, surgical and optical.

Optometrists (OD) are state-licensed healthcare professionals who diagnose and treat vision problems. They prescribe glasses, contact lenses, engage in low vision rehabilitation and vision therapy, can prescribe ophthalmic medications and, in certain states, perform certain surgical procedures. They hold the doctor of optometry (OD) degree.

Opticians are professionals in designing, finishing and dispensing eyeglasses, and cosmetic and therapeutic contact lenses, based on an eye doctor's prescription. Opticians can not actually prescribe contact lenses.

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