Refractive Errors What are refractive errors? In order for our eyes to be able to see, light rays must be bent or refracted by the cornea and the lens so they can focus on the retina, the nerve layer that lines the back of the eye.
The retina receives the picture formed by these light rays and sends the image to the brain through the optic nerve.
A refractive error means that the shape of your eye doesn't refract the light properly, so that the image you see is blurred. Although refractive errors are called eye disorders, they are not diseases.
In a normal eye, the cornea and lens focus light rays on the retina. What are the different types of refractive errors?
Myopia (nearsightedness) A myopic eye is longer than normal or has a cornea that is too steep, so that the light rays focus in front of the retina. Close objects look clear, but distant objects appear blurred.
In myopia, distant objects appear blurry because the eye is too long, and images focus in front of the retina instead of on it. Myopia is inherited and is often discovered in children whey they are between 8 and 12 years old. During the teenage years, when the body grows rapidly, myopia may become worse. Between the ages of 20 and 40, there is usually little change.
If the myopia is mild, it is called low myopia. Severe myopia is known as high myopia. If you have high myopia, you have a higher risk of detached retina. Your ophthalmologist (Eye M.D.) should discuss the warning signs of retinal detachment with you if you are in this risk category. If the retina does detach, a surgical procedure is the only way to repair it. It is important to have regular eye examinations by an ophthalmologist to watch for changes in the retina.
Hyperopia (farsightedness) A hyperopic eye is shorter than normal. Light from close objects, such as the page of a book, cannot focus clearly on the retina.
Like nearsightedness, farsightedness is usually inherited. Babies and young children tend to be slightly hyperopic. As the eye grows and becomes longer, hyperopia lessens.
In hyperopia, close objects appear blurry because the eye is too short, and images are not in focus when they reach the retina. Astigmatism (distorted vision) The cornea is the clear front window of the eye. A normal cornea is round and smooth, like a basketball. When you have astigmatism, the cornea curves more in one direction than in the other, like a football.
Astigmatism distorts or blurs vision for both near and far objects. It's almost like looking into a fun house mirror in which you appear too tall, too wide or too thin. It is possible to have astigmatism in combination with myopia or hyperopia.
Presbyopia (aging eyes) When you are young, the lens in your eye is soft and flexible. The lens of the eye changes its shape easily, allowing you to focus on objects both close and far away.
After the age of 40, the lens becomes more rigid. Because the lens can't change shape as easily as it once did, it is more difficult to read at close range. This normal condition is called presbyopia.
You also can have presbyopia in combination with myopia, hyperopia or astigmatism.
How are refractive errors corrected?
Eyeglasses or contact lenses are the most common methods of correcting refractive errors. They work by refocusing light rays on the retina, compensating for the shape of your eye. Refractive surgery is also an option to correct or improve your vision. These surgical procedures are used to adjust your eye's focusing ability by reshaping the cornea, or front surface of your eye.
There is not adequate scientific evidence to suggest that eye exercises, vitamins or pills can prevent or cure refractive errors.
Refractive exam Eyeglasses Glasses are an easy method to correct refractive errors. They also can help protect your eyes from harmful light rays, such as ultraviolet (UV) light rays. A special coating that screens out UV light is available when you order your glasses.
Bifocals are glasses used to correct presbyopia. They have a correction for reading on the bottom half of the lens and another for seeing at a distance on the top. Trifocals are lenses with three different lens corrections in one set of eyeglasses.
If you don't need correction for seeing at a distance, you can receive a prescription for reading glasses or buy them over the counter to correct presbyopia.
No exercise or medication can reverse presbyopia. You will probably need to change your prescription from time to time between the ages of 40 and 60, because your lens will continue to lose flexibility.
Contact Lenses There are now a wide variety of contact lenses available. The type that is best for you depends on your refractive error and your lifestyle. If you want to wear contact lenses, discuss the various options with your ophthalmologist.
You may have heard of a process called orthokeratology to treat myopia. It uses a series of hard contact lenses to gradually flatten the cornea and reduce the refractive error.
Improvement of sight from orthokeratology is temporary. After use of the lenses is discontinued, the cornea returns to its original shape and myopia returns.
Astigmatic Keratotomy (AK) Astigmatic keratotomy is a microsurgical procedure. The surgeon makes deep incisions in the cornea (usually one or two) in a curvilinear pattern. The incisions flatten the areas of the cornea that are too steeply curved.
Photorefractive Keratectomy (PRK) The excimer laser is used to reduce myopia and astigmatism in a procedure called photorefractive keratectomy (PRK). Using an invisible, high-energy light, the laser sculpts the cornea. No surgical blades are used in PRK.
Laser In Situ Keratomileusis (LASIK) LASIK is a combined microsurgical and excimer laser procedure to correct myopia, hyperopia and astigmatism. In LASIK, a highly specialized instrument (microkeratome) is used to cut a thin flap in the cornea. This flap is folded back, and the excimer laser sculpts the exposed corneal tissue to reshape it. The flap is then replaced and allowed to heal back into position. Stitches are not used in this procedure.
Complications and Side Effects Because AK, PRK and LASIK are surgical procedures, it is very important to make an informed decision when deciding whether refractive surgery is for you. Complications and side effects from these procedures may include:
Temporary discomfort Blurry and fluctuating vision Glare and haloes Under- or over-correction Poor night vision Irregular astigmatism Corneal scarring Permanent vision loss Intrastromal Corneal Rings Intrastromal corneal rings, sometimes called intracorneal rings, are crescent-shaped plastic segments surgically implanted in the eye to flatten the cornea. They are used to correct mild nearsightedness. Intrastromal corneal rings can be removed, but because surgery is involved, there are risks. In some cases, side effects may be permanent. Side effects include glare, haloes and problems with night vision. Surgical complications can lead to induced astigmatism, glare and haloes. Rare complications include infection, vision loss and penetration of the eye.
What is the best method of correcting refractive errors?
There is no best method for correcting refractive errors. The most appropriate correction for you depends on your eyes and your lifestyle. You should discuss your refractive errors and your lifestyle with your ophthalmologist to decide which correction will be most effective for you.