Farsightedness

(Hyperopia, Presbyopia)

In this condition factsheet:

• The Facts
• Causes
• Symptoms and Complications
• Making the Diagnosis
• Treatment and Prevention

The Facts

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

Causes

The cornea is the clear front 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 by the age of 6. As people get older, their eye muscles become less able to change the lens shape in order to see close things clearly.

Around the age of 40, some people start to have some difficulty seeing close-up details clearly. This is called presbyopia. As you continue to age it becomes increasingly common. 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 symptoms of hyperopia may be headaches and frequently rubbing the eyes, not blurring.

In some children, research has linked farsightedness 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 chart, to look for nearsightedness (myopia), but it can't always 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 options: glasses, contact lenses, and laser surgery. Intraocular surgery (e.g., artificial lens insertion) may also be considered, although it carries a unique set of potential complications.

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. 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 contact 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 nearsightedness (myopia), can now also treat farsightedness. Canadians can now choose between different types of laser eye surgery to correct their vision:

• Photo-refractive keratectomy (PRK) involves removal of  the outer layer of the cornea then using a laser to burn away small amounts of tissue under the surface of the cornea in order to change the shape of the cornea (the front surface of the eye). This change in shape helps you to see better.
• Laser assisted in situ keratomileusis (LASIK) involves making a small incision (cut) through the surface of the cornea creating a "flap" so that the surgeons can reach tissues below it. Small amounts of tissue are removed using a laser to burn away the tissue. The flap is placed back over the cornea, and the cornea heals readily afterwards. A new advancement involves the use of a computer-generated detailed map of your eye to help the surgeon make a more precise correction.
• Laser epithelial keratomileusis (LASEK) is a variation of PRK and LASIK that involves making cuts to the outer layer of the cornea and using an alcohol solution to help lift off a single layer so that a laser can burn away small amounts of tissue under the surface of the cornea. The layer is then placed back onto the eye.
• Epi-LASIK is modified version of LASEK that uses a mechanical device to remove the outer layer of the cornea.

Newer refinements of these procedures are constantly under development.

These techniques are about equally effective in improving sight. Infection of the area that was operated on may occur a day or two after the operation, but antibiotic eye drops are usually given to prevent infection.

The operations themselves are quick (a few 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 and any other potential complications thoroughly with your eye doctor before opting for laser surgery.

All material copyright MediResource Inc. 1996 – 2024. Terms and conditions of use. The contents herein are for informational purposes only. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Source: www.medbroadcast.com/condition/getcondition/Farsightedness