Eye function

Eye function

          The way people can see clearly is caused by the light passing through the cornea and the lens of the eye, and then it is reflected on the retina. If anything blocks the light reflection on the retina, it can lead to an unclear vision, which can be called abnormal eyesight (refractive error).

Abnormal eyesight can be classified as

• Nearsightedness (Myopia): light enters the eyes and focuses in front of the retina, which leads to distant blurry vision.
• Congenital farsightedness (Hyperopia): light enters the eye and focuses beyond the retina, which leads to distant clear vision, but near blurry vision.
• Astigmatism: light enters the eye and focuses different points in each plane, which leads to both far and near blurry vision.
• Elderly presbyopia: lenes of the eyes are stiff with age and the muscles of the eyes used for near vision are fatigue, which leads to near blurry vision.

Vision correction: use a principle of light convergence to focus on the retina.

1. Glasses are the easiest and safest way to correct abnormal vision. However, some people have limitations to use glasses, for example, people with different problems in two eyes, athletes or those who have some occupations that are not suitable for using glasses.

2. Contact lenses, nowadays, are designed to be comfortable to wear. It is clear for vision and good quality, which can be another option for those who do not like to wear glasses. However, using contact lenses requires proper cleaning and takes time to wear, remove, and wash. In addition, some people have problems from using contact lenses such as eye inflammation and corneal infection. In addition, there must be the high cost for lenses and lens cleanser. Therefore, Refractive Surgery may be a better option for you.

3. LASIK light laser: All abnormal eyesight, including nearsightedness, farsightedness, and astigmatism, can be corrected by LASIK, based on a principle that adjusts the curvature of the cornea so that light can hit and focus exactly on the retina. For example, nearsightedness with too convex cornea, it will be flattened. Farsightedness with too flat cornea, it will be risen. Astigmatism with crooked corneas will be adjusted. Presbyopia may not be directly corrected via LASIK, but LASIK can help for near vision better.

Basic Principle of Excimer Laser
Excimer Laser is a UV light (193 nm) with a light source from Argon Fluoride gas. This light is very accurate in the Micron region (See the illustration in Basic LASIK.ppt. It is an image of letters on hair carved by an Excimer Laser.) Excimer Laser has developed from the first models to the current model as follows:

First Generation: Broad Beam Laser is the use of a large beam of light in one time. However, there is a problem with the stability of the energy in the light. If the shot is distorted, it will distort (Decenter) to the entire large area. Therefore, it is developed into the second model.

Second Generation: Slit Scanning Beam Laser, which has a smaller beam size, but it is still not detailed enough, so it has been improved to the next model.

Third Generation: Free Flying Spot Scanning Laser, whose beam size can be reduced to approximately 0.8-2.0 mm. The smaller spot size results in the more homogenous energy control. Moreover, the random shooting can reduce the decentration errors.

Fourth Generation: We are familiar with this model more and more. No one gives an exact definition, but it generally refers to the use of a new technology known as Wavefront System (Customized or Wavefront guided LASIK)

Thank you

Reference: http://www.wavefrontthai.com/