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Refractive Errors

Introduction
Signs and Symptoms
Causes
Complications
Screening and Diagnosis
Treatment
Prevention

Being nearsighted may mean:

• Distant objects appear blurry.
• You need to squint to see clearly.
• You have headaches caused by excessive eyestrain.

Nearsightedness is often first detected during childhood, from early school years through the later teens. A child with nearsightedness may:

• Persistently squint
• Sit very close to the television, movie screen or chalkboard
• Hold books very close while reading
• Seem to be unaware of distant objects

Your eye has two parts that focus images - the cornea, the clear front surface of your eye, and the lens, a clear structure inside your eye that changes shape to help focus objects. In a perfectly shaped eye, each of these focusing elements has a perfectly smooth curvature like the surface of a rubber ball. A cornea and lens with such curvature bend (refract) all incoming light in such a way as to make a sharply focused image at the back of your eye, on the retina.

However, if your cornea or lens isn't evenly and smoothly curved, light rays aren't refracted properly, and you have a refractive error. Nearsightedness is one type of refractive error. Nearsightedness can occur when your cornea is curved too much or when your eye is longer than normal. Instead of being focused precisely on your retina, light is focused in front of your retina, resulting in a blurry appearance for distant objects.

In addition to nearsightedness, other refractive errors include:

• Farsightedness (hyperopia). This occurs when your cornea is curved too little or your eye is shorter from front to back than normal. The effect is the opposite of nearsightedness. Light is focused beyond the back of your eye, making nearby objects blurry. You're able to see faraway objects clearly.
• Astigmatism. This occurs when your cornea is curved more steeply in one direction than in another. Uncorrected astigmatism blurs your vision. Typically, the images you see will be blurred more in one direction than another. For example, horizontal images may be more out of focus than are vertical or diagonal images.

Nearsightedness is diagnosed by a basic eye exam. Three kinds of eye specialists, each with different training and experience, can provide routine eye care:

• Ophthalmologists. An ophthalmologist is an eye specialist with an M.D. (doctor of medicine) degree who provides full eye care, such as performing complete eye evaluations, prescribing corrective lenses, diagnosing and treating common and complex eye disorders, and performing eye surgery when it's necessary.
• Optometrists. An optometrist has an O.D. (doctor of optometry) degree. Optometrists are trained to evaluate vision, prescribe corrective lenses and diagnose common eye disorders. In some states, optometrists are qualified to treat selected eye disorders with drugs. Complicated eye conditions, including those requiring surgery, must be treated by an ophthalmologist.
• Opticians. An optician is an eye specialist who fills prescriptions for eyeglasses - assembling, fitting and selling them. Some states also allow opticians to sell and fit contact lenses.

A complete eye examination involves a series of tests. Your eye doctor may use odd-looking instruments, aim bright lights directly at your eyes and request that you look through an array of lenses. Each test allows your doctor to examine a different aspect of your vision.

According to the American Academy of Ophthalmology, recommendations for regular eye exams include:

Adults

If you don't wear glasses or contacts, have no symptoms of eye trouble and are at a low risk of developing eye disease, it's recommended that you have an eye exam at the following intervals:

• At least once between ages 20 and 39
• Every two to four years between ages 40 and 64
• Every one to two years beginning at age 65

However, if you wear glasses or contacts, have your eyes checked every year. And if you notice any problems with your vision, schedule an appointment with your eye doctor as soon as possible, even if you've recently had an eye exam. Blurred vision, for example, may suggest you need a prescription change.

Children and adolescents

Children need to be screened for eye disease and have their vision tested by a pediatrician, an ophthalmologist or another trained screener at the following ages and intervals:

• Between birth and 3 months
• Between 6 months and 1 year
• Around 3 years
• Around 5 years

Your child or adolescent may need more frequent visits if he or she experiences any problems with vision or has symptoms of eye trouble. In addition, children and adolescents who have a disease that puts their eyes at risk, such as diabetes, may need more frequent eye exams.

Nearsightedness may be associated with several complications, such as:

• Reduced quality of life. Uncorrected nearsightedness can affect your quality of life. You might not be able to perform a task as well as you wish, and your limited vision may detract from your enjoyment of day-to-day activities.
• Eyestrain. Squinting your eyes to see in the distance can cause eyestrain and headaches.
• Impaired safety. For your own safety and that of others, don't drive or operate heavy equipment if you have an uncorrected vision problem.
• Glaucoma. Severe nearsightedness increases your risk of developing glaucoma, a potentially serious eye disease. Nearsighted people have two to three times the risk of developing glaucoma as do people who aren't nearsighted.
• Retinal tear and detachment. If you're significantly nearsighted, it's possible that the retina of your eye is thin. The thinner your retina, the more you're at risk of developing a retinal tear or retinal detachment. If you experience a sudden onset of flashes, floaters or a dark curtain of shadow across part of your eye, seek medical assistance immediately. Retinal detachment is a medical emergency, and time is critical. Unless the detached retina is promptly surgically reattached, this condition can cause permanent loss of vision in the affected eye.

The goal of treating nearsightedness is to help focus light on your retina through the use of corrective lenses or refractive surgery.

Corrective lenses

Wearing corrective lenses treats nearsightedness by counteracting the increased curvature of your cornea or the increased length of your eye. Types of corrective lenses include:

• Contact lenses. A wide variety of contact lenses are available - hard, soft, extended wear, disposable, rigid gas-permeable (RGP) and bifocal. Ask your eye doctor about their pros and cons and what might be best for you.
• Eyeglasses. An alternative to contact lenses is eyeglasses. Like contact lenses, the variety of eyeglasses is wide.

Refractive surgery

This treatment corrects nearsightedness by reshaping the curvature of your cornea. Refractive surgery methods include:

• Laser-assisted in-situ keratomileusis LASIK). LASIK is a procedure in which an ophthalmologist uses an instrument called a keratome to make a thin, circular hinged cut into your cornea. Your eye surgeon then uses an excimer laser to remove layers from the center of your cornea to flatten its domed shape. An excimer laser differs from other lasers in that it doesn't produce heat.
• Laser-assisted subepithelial keratomileusis (LASEK). Instead of creating a flap in the cornea, the surgeon creates a flap only in the cornea's thin protective cover (epithelium). Your surgeon will use an excimer laser to reshape the cornea's outer layers and flatten its curvature and then reposition the epithelial flap. To encourage healing, a bandage contact lens is worn for several days after this procedure.
• Photorefractive keratectomy (PRK). This procedure is similar to LASEK, except the surgeon removes the epithelium. It will grow back naturally, conforming to your cornea's new shape. PRK may cause a little more discomfort than the LASEK procedure. Like LASEK, PRK requires the use of a bandage contact lens following the procedure.