What is Lasik?

How the eye is built and why the vision might be disturbed

If you are here, it's most likely because you or a friend or a loved one is thinking about having a lasik treatment and you want to know what exactly Lasik is and how it works. To best understand that, let's first have a look at the way the eye is built up:

The eye and its major parts

First let's look at the entry point of all images that we see, the Cornea:

The cornea is a part of the eye that helps focus light to create an image on the Retina. It works in much the same way that the lens of a camera focuses light to create an image on film. The bending and focusing of light is also known as refraction. Usually the shape of the cornea and the eye are not perfect and the image on the retina is out-of-focus (blurred) or distorted. These imperfections in the focusing power of the eye are called refractive errors.

Properly focused image in a healthy eye

These refractive errors are responsible for disturbed vision:

There are three primary types of Refractive Errors: Myopia, Hyperopia and Astigmatism.

• Persons with Myopia, or nearsightedness, have more difficulty seeing distant objects as clearly as near objects.
• Persons with Hyperopia, or farsightedness, have more difficulty seeing near objects as clearly as distant objects.
• Astigmatism is a distortion of the image on the retina caused by irregularities in the cornea or lens of the eye.

Combinations of myopia and astigmatism or hyperopia and astigmatism are common. Until recently, only glasses or contact lenses could compensate for the eye's imperfections.

For a few years now, not only corrective eye glasses and lenses, but also surgical methods are used to correct bad vision.

Refractive Surgery - Lasik Surgery

These surgical procedures aimed at improving the focusing power of the eye are called Refractive Surgery. In Lasik Surgery, precise and controlled removal of corneal tissue by a special laser reshapes the cornea changing its focusing power. Similar to a wood worker who is shaping a piece of wood with a plane, the lasik laser takes off fine layers of the cornea. The difference is in the precision that is achieved with a lasik laser.

Refractive Surgery - Radial Keratotomy and Photorefractive Keratectomy

Radial Keratotomy or RK and Photorefractive Keratectomy or PRK are other refractive surgeries used to reshape the cornea.

• In Radial Keratotomy, a very sharp knife is used to cut slits in the cornea changing its shape.
• Photorefractive Keratectomy was the first surgical procedure developed to reshape the cornea, by sculpting, using a laser.

Later, Lasik was developed. The same type of laser is used for LASIK and PRK. Often the exact same laser is used for the two types of surgery. The major difference between Photorefractive Keratectomy and Lasik Surgery is the way that the stroma, the middle layer of the cornea, is exposed before it is vaporized with the laser: In Photorefractive Keratectomy, the top layer of the cornea, called the epithelium, is scraped away to expose the stromal layer underneath. In Lasik Surgery, a flap is cut in the stromal layer and the flap is folded back, and then the correction takes place and the flap is placed back over the corrected area.

Refractive Surgery - Thermokeratoplasty and Orthokeratology

Another type of refractive surgery is Thermokeratoplasty in which heat is used to reshape the cornea. The source of the heat can be a laser, but it is a different kind of laser than is used for Lasik and PRK. Other refractive devices include corneal ring segments that are inserted into the stroma and special contact lenses that temporarily reshape the cornea (Orthokeratology).

There is a very good audiovisial presentation about lasik at this site

(This article is based on the information that can be found at the Official Governement Lasik Site).