Myopia, Hyperopia, Astigmatism, Presbyopia

In order to decide whether to undergo ASA or LASIK eye surgery, it is helpful to understand how the eye works. The eye is like a camera. The cornea is a clear, dome-shaped window that forms the front wall of the eye. The retina is the light-sensitive tissue in the back of the eye that connects to the brain. The retina acts like the film in a camera. The cornea at the front of the eye acts as a lens that focuses light onto the retina, producing an image on the retina that gets transmitted to the brain and interpreted as vision. The curve of the cornea determines the power of the corneal lens and whether the incoming light rays from distant objects focus directly onto the retina. When light does not focus directly on the retina, the eye is said to have a refractive error. When a refractive error is present, corrective lenses (such as eye glasses or contacts) or refractive surgery (such as laser eye surgery) can be employed so that incoming light rays become focused onto the retina to again produce clear vision.

Myopia or Nearsightedness

In the normal eye, the cornea focuses light rays directly on the retina, resulting in clear vision without eye glasses or contact lenses. In myopia, or nearsightedness, the eye is longer than normal. The light rays come together at a point in front of the retina, and are out of focus. Distant objects are blurred while nearby objects can be clear. Laser eye surgery can correct myopia.

Hyperopia or Farsightedness

In hyperopia, or farsightedness, the eye is shorter than normal. The light rays come together at a point behind the retina, and are therefore out of focus. Nearby objects can appear blurry, while distant objects are clearer. Very farsighted patients will report that even distant objects appear blurry. Laser eye surgery can correct hyperopia.

Astigmatism

In the normal eye, the cornea is curved the same in the horizontal and vertical directions, like a baseball. When the light rays hit the cornea, they focus at a single point. In astigmatism, the curve of the cornea is not the same in the horizontal and vertical directions. The cornea looks like the side a football, with a steeper curve in one axis and a flatter curve in the other. As a result, light rays entering the cornea do not focus at a single point, causing distorted vision. Many people with myopia or hyperopia also have some degree of astigmatism. Laser eye surgery can correct astigmatism.

Presbyopia

As we age, the crystalline lens of the eye may lose its ability to accommodate to nearby objects. This condition, known as presbyopia, usually begins around the age of 40, and can most often be comfortably corrected through the use of eye glasses. Everyone will eventually develop presbyopia and require the use of reading glasses. ASA or LASIK eye surgery will not prevent the development of presbyopia but can compensate for it.

Laser Eye Correction

In all of these conditions, the person needs some type of corrective lens, such as eye glasses or contact lenses to focus the light properly. ASA and LASIK eye surgery can change the shape and curve of the cornea in order to correct or reduce these types of refractive errors. How does laser eye surgery improve myopia, hyperopia, astigmatism and presbyopia? The cool beam of the laser gently reshapes the cornea, making it more like a normal eye. This enables light to focus precisely on the retina making images clearer, thereby improving vision. A “monovision” laser correction can compensate for presbyopia. The dominant eye is reshaped for distance vision. The non-dominant eye is left slightly nearsighted to assist reading. The brain quickly adjusts to the difference and vision seems normal for distance and near.