Laser Eye Center of Hawaii - About Refractive Disorders

About Refractive Disorders

Measurement of Refractive Disorders

Vision Correction Choices

Refractive visual disorders affect the way light is focused by the eye. The factors that influence how an eye focuses light are the curvature of the cornea, the power of the lens and the length of the eye.

MYOPIA (Nearsightedness) Myopia occurs when the eye is too long in relation to the curvature of the cornea. Images fall in front of the retina or too far forward and vision at a distance appears blurred. Patients with myopia are able to see objects near to them.

ASTIGMATISM Many people have some degree of astigmatism. This means that the eye is slightly oval and the cornea is shaped like a football rather than a sphere. Those with astigmatism may experience distortion or tilting of images due to unequal bending of the rays of light entering the eye. High degrees of astigmatism will cause blurred vision for near and distant objects.

HYPEROPIA (Farsightedness) Hyperopia occurs when the eye is functionally too short. The rays of light are focused behind the retina, producing a blurred image. Those who are farsighted may be able to use their focusing muscle and bring the image forward, allowing them to see clearly. This focusing ability becomes difficult with age, and reading glasses or bifocals may be needed. Farsighted individuals see distant objects more clearly than objects near to them.

PRESBYOPIA Presbyopia is a condition of the normal aging process where the lens of the eye loses its ability to flex and focus at near objects. The onset of presbyopia typically occurs between 40 and 50 years of age. When this occurs, people who wear glasses may require special reading glasses. One advantage of mild myopia is the ability to remove your glasses after presbyopia “sets in” and still have the ability to read. Presbyopia is an important concept to understand. The excimer laser has no effect on your focusing muscles and therefore cannot treat presbyopia. After having laser vision correction, you will typically become “normal sighted” (ability to see clearly in the distance), and you may require reading glasses for small print-reading up close.

Refractive disorders are measured in units called diopters. Diopters represent the power of corrective lenses needed to normalize vision. The more nearsighted or farsighted you are, the higher your prescription is in diopters. When your refractive disorder is corrected, your prescription is used to determine treatment.

Your prescription for glasses may be comprised of three numbers. Let’s take the prescription:

-4.00 –1.50 x 90

The 1st number (-4.00) identifies the amount of nearsightedness or farsightedness. The sign is an indication of whether you are nearsighted (represented by a “-“ sign) or farsighted (represented by a “+” sign).
The 2nd number (-1.50) represents the level of astigmatism. This can be written as either + or -.
The 3rd number (90) represents where the astigmatism “lies.” In this person the astigmatism is at 90 degrees, or vertical.

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Refractive disorders may be corrected in a variety of different ways. All methods have benefits and drawbacks.

GLASSES Glasses have been proven over time with its existence for a thousand years. They are affordable, easy to maintain, and versatile. Glasses may, however, restrict peripheral vision, be difficult to wear in certain weather conditions and have a limited life span. They may interfere with certain recreational activities and many people dislike the cosmetic impact that glasses have on their appearance.

CONTACT LENSES Contact lenses are another common solution. Advantages include no change in cosmetic appearance, more freedom in recreational activities, and better peripheral vision. They may require high maintenance, get lost easily, be less comfortable for patients with dry eyes, and always carry a risk of infection.

ORTHOKERATOLOGY This is a technique that uses a series of rigid contact lenses to flatten the cornea to treat myopia. The effects are not permanent and may require continued dependence on a part-time retainer lens, involve high maintenance, and require continuous follow-up visits to an eye care professional.

RADIAL KERATOTOMY (RK) RK is also a treatment for myopia. Flattening the cornea is accomplished by placing deep incisions in the cornea in a radial fashion using a hand held diamond blade. A variation of RK, called Astigmatic Keratotomy or AK, is used to correct astigmatism. During the past twenty years, more than a million people worldwide have reduced their dependence on glasses or contact lenses by having their myopia treated with RK. However, laser vision correction has largely replaced this technique.


	About Refractive Disorders Refractive visual disorders affect the way light is focused by the eye. The factors that influence how an eye focuses light are the curvature of the cornea, the power of the lens and the length of the eye. MYOPIA (Nearsightedness) Myopia occurs when the eye is too long in relation to the curvature of the cornea. Images fall in front of the retina or too far forward and vision at a distance appears blurred. Patients with myopia are able to see objects near to them. ASTIGMATISM Many people have some degree of astigmatism. This means that the eye is slightly oval and the cornea is shaped like a football rather than a sphere. Those with astigmatism may experience distortion or tilting of images due to unequal bending of the rays of light entering the eye. High degrees of astigmatism will cause blurred vision for near and distant objects. HYPEROPIA (Farsightedness) Hyperopia occurs when the eye is functionally too short. The rays of light are focused behind the retina, producing a blurred image. Those who are farsighted may be able to use their focusing muscle and bring the image forward, allowing them to see clearly. This focusing ability becomes difficult with age, and reading glasses or bifocals may be needed. Farsighted individuals see distant objects more clearly than objects near to them. PRESBYOPIA Presbyopia is a condition of the normal aging process where the lens of the eye loses its ability to flex and focus at near objects. The onset of presbyopia typically occurs between 40 and 50 years of age. When this occurs, people who wear glasses may require special reading glasses. One advantage of mild myopia is the ability to remove your glasses after presbyopia “sets in” and still have the ability to read. Presbyopia is an important concept to understand. The excimer laser has no effect on your focusing muscles and therefore cannot treat presbyopia. After having laser vision correction, you will typically become “normal sighted” (ability to see clearly in the distance), and you may require reading glasses for small print-reading up close. Measurement of Refractive Disorders Refractive disorders are measured in units called diopters. Diopters represent the power of corrective lenses needed to normalize vision. The more nearsighted or farsighted you are, the higher your prescription is in diopters. When your refractive disorder is corrected, your prescription is used to determine treatment. Your prescription for glasses may be comprised of three numbers. Let’s take the prescription: -4.00 –1.50 x 90 The 1st number (-4.00) identifies the amount of nearsightedness or farsightedness. The sign is an indication of whether you are nearsighted (represented by a “-“ sign) or farsighted (represented by a “+” sign). The 2nd number (-1.50) represents the level of astigmatism. This can be written as either + or -. The 3rd number (90) represents where the astigmatism “lies.” In this person the astigmatism is at 90 degrees, or vertical. Vision Correction Choices Refractive disorders may be corrected in a variety of different ways. All methods have benefits and drawbacks. GLASSES Glasses have been proven over time with its existence for a thousand years. They are affordable, easy to maintain, and versatile. Glasses may, however, restrict peripheral vision, be difficult to wear in certain weather conditions and have a limited life span. They may interfere with certain recreational activities and many people dislike the cosmetic impact that glasses have on their appearance. CONTACT LENSES Contact lenses are another common solution. Advantages include no change in cosmetic appearance, more freedom in recreational activities, and better peripheral vision. They may require high maintenance, get lost easily, be less comfortable for patients with dry eyes, and always carry a risk of infection. ORTHOKERATOLOGY This is a technique that uses a series of rigid contact lenses to flatten the cornea to treat myopia. The effects are not permanent and may require continued dependence on a part-time retainer lens, involve high maintenance, and require continuous follow-up visits to an eye care professional. RADIAL KERATOTOMY (RK) RK is also a treatment for myopia. Flattening the cornea is accomplished by placing deep incisions in the cornea in a radial fashion using a hand held diamond blade. A variation of RK, called Astigmatic Keratotomy or AK, is used to correct astigmatism. During the past twenty years, more than a million people worldwide have reduced their dependence on glasses or contact lenses by having their myopia treated with RK. However, laser vision correction has largely replaced this technique.