Don't Overlooked Vision Problems

by Food and Drug Administration (FDA)

Eye problems, in general, tend to get overlooked in a crowd of broader health issues such as heart disease and cancer. For this reason, the vision health care community has been working hard in recent years to emphasize the importance of proper eye care.

The focus, primarily, has been on increasing the number of people who receive regular vision checks, and addressing diseases, injuries and, according to the National Eye Institute (NEI), the most frequent eye problems in the United States - defects or refractive errors - most often responsible for impairing vision. As a result, vision goals have been added recently to a set of national health objectives, called Healthy People 2010, which are aimed at preventing disease and promoting health.

"These objectives are important because they give vision a prominent place on the public health agenda," says Rosemary Janiszewski, the Healthy People 2010 coordinator for the NEI. "It is an acknowledgment from our country's leading health officials that vision plays a significant role in the nation's overall health."

How We See

The "Snellen Eye Chart," a series of letters arranged in lines, is the standard for measuring how well each eye sees. People view the chart at a distance of 20 feet. One eye is covered while the other is tested.

Having 20/20 vision means seeing at 20 feet what a person with normal vision sees at 20 feet. Someone able to read additional lines smaller than the line representing normal vision has 20/15, or even 20/10, vision. A person who has worse-than-normal vision and can only read letters larger than the 20/20 line has 20/40 vision, or higher. As a result, a person who has 20/40 vision can see at 20 feet what the person with normal vision sees at 40 feet. And so on.

The eye does not actually "see" objects. Instead, it sees the light that objects reflect. To see clearly, light striking the eye must be bent or "refracted" through the cornea - the clear window at the front of the eye that provides most of the focusing power. Light travels through the lens, where it is fine-tuned to focus properly on the nerve layer that lines the back of the eye, the retina, and is then sent to the brain through the optic nerve. The retina acts like the film in a camera, and clear vision is achieved only if light from an object is precisely focused on it. If not, the image you see is blurred. This problem is called a refractive error.

Refractive Errors

Refractive errors usually occur in otherwise healthy eyes, and are caused mostly by an imperfectly shaped eyeball, cornea, or lens, according to the NEI. Nearsightedness (myopia) and farsightedness (hyperopia) are the most common refractive errors. People with myopia see near objects clearly, while distant ones are blurred. People with hyperopia experience just the opposite - they see distant objects clearly, while near ones are blurred. Uneven focus or distorted vision (astigmatism) and aging eye that can't focus close up (presbyopia) are other common refractive errors.

The magnitude of refractive error is measured in units called diopters. Each diopter of refractive error affects a person's ability to read smaller lines of an eye chart.

Why refractive errors develop is not known. The NEI says that most infants have some degree of hyperopia, but that vision becomes more normal with age, usually leveling off by age 6. However, some children remain farsighted, or become so later in life. While some children may be nearsighted early in life, most myopia occurs later during adolescence. Refractive error can continue to change over a person's lifetime. According to the NEI, 60 percent of Americans have refractive errors that need correcting for sharper vision.

Glasses, contact lenses, and various eye surgeries and procedures are aimed at reducing refractive errors by focusing light rays properly on the retina. The past 20 years have seen many innovations in vision correction methods, including implantable intraocular lenses and different types of lasers used to reshape parts of the eye, which are regulated as medical devices by the Food and Drug Administration.

The FDA says that it's important to learn as much as possible about the differences between the available corrective lenses, new and older surgeries, and any other vision correction procedures. It's also important to know what factors make some a good candidate for certain procedures but a poor candidate for others.

Malvina B. Eydelman, M.D., director of the FDA's Division of Ophthalmic and Ear, Nose and Throat Devices, adds that it's important to weigh the benefits and risks of each vision correction option, and to have realistic expectations.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.