Refractive Disorders
The majority of people that require glasses for distance vision are candidates for refractive surgery. If you look at your prescription, it is written something like this: OD -8.50 -3.25 x 180 OS -12.25 -0.75 x 175 OD means right eye, and OS means left eye. The first number is the “sphere,” the second number is the “cylinder,” and the third is the “axis.” Generally, if the sphere is negative, then you are myopic, and if the sphere is positive, then you are hyperopic. If there is a cylinder correction, then you have astigmatism. It is very common to have some degree of astigmatism combined with myopia or hyperopia.
Myopia
What is myopia or near-sightedness?
Myopia affects over 60 million Americans and causes blurry distance vision. Since near vision is clearer in this condition, another term for myopia is “near-sightedness”. In myopia, light rays are focused too powerfully within the eye, leading to a blurry image that is in front of the retina. This can occur because the eye is too long or the front surface of the eye, known as the cornea, is too steeply curved. The excimer laser has been used to treat myopia since about 1986.
Hyperopia
What is hyperopia or far-sightedness?
Hyperopia causes blurry vision more at near, but eventually vision becomes blurry at all distances. In this condition, images are focused too weakly within the eye. This can occur when the eye is to short, or when the cornea is not curved enough. The widespread availability of the excimer laser for treatment of hyperopia began in 1998.
Astigmatism
What is astigmatism?
A perfect cornea is spherical in the center. Astigmatism occurs when the central cornea is ovoid. Light is focused differently in one axis from another, causing blurring at all distances. It is very common to have some degree of astigmatism combined with myopia or hyperopia. Most astigmatism can be treated with the excimer laser.
Presbyopia
What is presbyopia?
Presbyopia is often confused with hyperopia. With advancing age, the human eye loses the ability to focus on near objects. Between the ages of about 40 and 50 years, everyone requires a new prescription for reading. This can be achieved by reading glasses, bifocals, or by removing distance eyglasses in certain cases of myopia. Presbyopia cannot be directly treated with the excimer laser, but treatments can be adjusted to decrease dependence on reading glasses. People who only require glasses for reading are usually not good candidates for laser vision correction. Conductive Keratoplasty (CK) is a non-laser procedure approved for the treatment of presbyopia. Laser treatments for presbyopia are under development.