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Farsightedness

The Facts

Farsightedness, known medically as hyperopia, refers to being able to see fairly well at a distance but not close up.

Hyperopia affects about 25% of the population.

Causes

The cornea is a special layer on the surface of the eye that does most of the work of bending light as it enters the eye. Light must be bent properly so that it creates a sharp image. When parallel light rays pass through the cornea, they should be bent just enough to meet and focus on the retina (the light-sensitive membrane that lines the back of the eye). The lens is responsible for fine adjustments of focus.

In farsightedness, the light rays meet at a point behind the retina. This causes nearby objects to be blurred. It could be said that the eye is too short back to front, or alternatively that the cornea is too flat.

Farsightedness is at least partly genetic. Many children are born with a degree of farsightedness, but some are able to counteract it with strong eye muscles. These muscles squeeze and stretch the lens just behind the cornea, which fine tunes the focus after the cornea does most of the work of bending light. In some children, the close vision becomes naturally sharper as they reach adulthood.

As people get older, their eye muscles become less able to compensate for hyperopia. After age 60, most people have some difficulty seeing close-up details clearly. This is called presbyopia. It becomes increasingly common in the years after age 50. The lens becomes thicker and more rigid, and the range of distances at which you can focus (called accommodation) narrows.

Symptoms and Complications

The main symptoms of farsightedness are difficulty seeing near objects clearly, headaches, and eyestrain.

You might think that farsightedness would be obvious to an adult. If your morning newspaper is getting increasingly blurred, you're likely to notice. In reality, the process is sometimes just too slow for the brain to detect. Farsightedness in children also often goes unnoticed. Some children born with farsightedness have never seen close objects clearly and may not be aware that it's possible to see them better. Also, hyperopic children can sometimes see close objects clearly by unconsciously straining their eyes. In such children, the main symptom of hyperopia may be headaches, not blurring.

Current research is investigating a possible link between farsightedness in children and poor reading and school performance. Children who may appear to lack an interest in reading quite often turn out to be slightly farsighted.

Many older people with farsightedness have a great deal of difficulty reading. Fortunately, farsightedness doesn't usually interfere with your ability to drive a car.

Making the Diagnosis

Eye doctors use the well-known poster with rows of smaller and smaller letters, called the Snellen sight card, to look for nearsightedness (myopia), but it can't detect farsightedness. This is why it's often missed in school eye tests.

A proper eye test in an optometrist or ophthalmologist's office involves sitting in a chair with a device called a phoropter or refractor attached at eye level. You look through the device at a wall poster and the eye doctor slips various lenses in and out of your field of view. This test can detect both farsightedness and nearsightedness.

Treatment and Prevention

You can't prevent farsightedness, but you certainly can treat it. There are three options: glasses, contact lenses, and laser surgery.

Glasses can correct almost any type of vision problem. They're particularly useful for people with poor vision at both long range and very close range, because they can use "bifocal" lenses. Looking through the upper lens gives you long-range vision, while looking through the lower one gives you close-range vision.

Contact lenses can also correct these problems. Lenses with high correction factors (i.e., those made to correct very poor vision) are likely to be thicker and heavier than lenses that correct less severe cases of hyperopia, and some people find them uncomfortable. This is particularly true of lenses that correct for astigmatism. There are also bifocal contact lenses, but some people find them difficult to use. Soft lenses have generally taken the place of hard and gas-permeable versions, as they're more comfortable and easier to adjust to, though they may be harder to clean. Wearing lenses makes you somewhat more prone to eye infection - this risk can be minimized by cleaning them according to instructions, throwing away disposables on time, and never sleeping with the lenses in.

Laser surgery, originally developed for myopia, can now also treat hyperopia. The most common techniques are called holmium laser thermokeratoplasty (LTK), photorefractive keratectomy (PRK), and laser-assisted in situ keratomileusis (LASIK).

In LTK, a laser removes the epithelium (the very top protective layer over the cornea in the front of the eye), then ablates (destroys) a measured layer of the cornea, following preset instructions from a computer.
In PRK, a computer-controlled laser removes the epithelium and reshapes the cornea by ablating tissue in the periphery or outer part.
LASIK is much the same, except that a flap is cut in the epithelium with a diamond blade, then the laser removes tissue from inner layer of the cornea, and the flap is put back in place, where it sticks without glue or stitches.

Newer refinements of these procedures are constantly under development. One example is "wavefront" or "custom" LASIK, in which a computer maps the visual problems needing correction, increasing the accuracy of the result.

These techniques are about equally effective in improving sight. Infection of the area that was operated on may occur day or two after the operation, but antibiotics are usually given to prevent infection. Otherwise, if infection does occur, it's usually easily treated with antibiotics. The operations themselves are quick (less than several minutes per eye) and painless, though the eye will sting for a few days afterwards.

Laser surgery can only be performed on uninfected healthy eyes. These surgeries are not suitable for children and teenagers because their vision is still changing.

Eye operations don't always produce the desired results. Study results vary, but the majority of farsighted people who have laser surgery for hyperopia end up with improved vision. It is important to be aware, however, some people do not notice any improvement in their vision and a few end up with poorer vision.

Laser surgery can reduce the quality of your best-corrected vision (the absolute best you could see with the right lenses). It can also reduce night vision. In addition, having the operation doesn't mean the eye is permanently "fixed" - it can change again. Sometimes, it heals from surgery into much the same shape it had before, producing only temporary improvement. Because eye doctors like to err on the side of caution, they may "undercorrect" vision, and you may need follow-up procedures. You should discuss these potential complications thoroughly with your eye doctor before opting for laser surgery.

Finally, although laser surgery has been around for over 15 years, we still don't know the long-term consequences. Most people are still seeing well 10 years after surgery, but we don't know how they'll be seeing 30 years from now. While there's no reason to believe they'll have problems, we can't be absolutely sure. It is important to thoroughly discuss potential complications with an eye doctor before opting for laser surgery.

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