LASIK SURGERY

What is LASIK?

LASIK stands for laser in situ keratomileusis, which means using a laser underneath a corneal flap (in situ) to reshape the cornea (keratomileusis). This procedure utilizes a highly specialized laser (excimer laser) designed to treat refractive errors, improve vision, and reduce or eliminate the need for glasses or contact lenses. This laser procedure alters the shape of the cornea, which is the transparent front covering of the eye. Though the excimer laser had been used for many years before, the development of LASIK is generally credited to Ioannis Pallikaris from Greece around 1991.

How does LASIK work?

During the LASIK procedure, a specially trained eye surgeon first creates a precise, thin hinged corneal flap using a microkeratome. The surgeon then pulls back the flap to expose the underlying corneal tissue, and then the excimer laser ablates (reshapes) the cornea in a unique pre-specified pattern for each patient. The flap is then gently repositioned onto the underlying cornea without sutures.

What are the advantages of LASIK surgery?

In summary, despite the risks outlined above, LASIK has been proven to be safe and effective for most people. With careful patient screening and selection, reasonable expectations, and in the care of an experienced surgeon, most patients will be very pleased with their results. These are some of the other advantages of LASIK:

• LASIK is able to accurately correct most levels of myopia (nearsightedness), hyperopia (farsightedness), and astigmatism.
• The procedure is fast, usually lasting only five to 10 minutes, and is generally painless.
• Because the laser is guided by a computer, it is very precise and results are very accurate.
• In most cases, a single treatment will achieve the desired outcome; however, enhancements are possible if needed, even many years after the initial surgery.

What are the disadvantages of LASIK surgery?

• Because each patient will heal slightly differently, results may vary from patient to patient.
• LASIK could make some aspects of your vision worse, including night vision with glare and halos.
• LASIK may make dry-eye symptoms worse in certain individuals.
• In rare circumstances, LASIK can make your vision worse and not correctable with regular glasses or contact lenses.

One of the most common physical ailments that people suffer from is poor vision. The eye is a complicated organ that requires a very exact arrangement of components to function properly. If even one of these components is not precisely the correct shape, then light that falls on the eye will not be focused correctly.

For centuries, people have relied on external lenses to alter the angle of the light entering the eye. Whether in glasses or contact lenses, these appliances have proven invaluable in the correction of poor vision. While external lenses will remain popular for the foreseeable future, advances in technology have made it possible for surgeons to alter the shape of the eye itself.

There are several types of vision correction surgery. One of the most popular is LASIK, which stands for laser-assisted in-situ keratomileusis. In this article, you will find out exactly what happens during a LASIK procedure as you follow this author through his own eye surgery. You will learn what LASIK is, what is involved in the surgery, what equipment is used and how to know if you're a candidate for LASIK. You will also learn what the other forms of eye surgery are and how they differ from each other.

In its simplest sense, your eye is like a camera. Your eye has:

• A variable opening called the pupil
• A lens system, which includes the transparent covering called the corneaand a spherical lens
• A reusable "film" called the retina
• Various sets of muscles(The muscles control the size of the opening, the shape of the lens system and the movements of the eye.)

On the back of your eye is a complex layer of cells known as the retina. The retina reacts to light and conveys that information to the brain. The brain, in turn, translates all that activity into an image. Because the eye is a sphere, the surface of the retina is curved.

In the retina, sensory cells called rods and cones change the photons of light into electrical signals, which are then transmitted to and interpreted by the brain. The ability to focus the light on the retina depends on the shapes of the cornea and the lens, which are controlled by their inherent shapes, their stretchiness or elasticity, the shape of the eyeball and sets of attached muscles. So, when you look at something, muscles attached to the lens must contract and relax to change the shape of the lens system and keep the object focused on the retina, even when your eyes move; this is a complex set of muscle movements that is controlled automatically by your nervous system.

When you look at something, three things must happen:

• The image must be reduced in size to fit onto the retina.
• The scattered light must come together -- that is, it must focus -- at the surface of the retina.
• The image must be curved to match the curve of the retina.

The basis for all laser eye surgery is to reshape the cornea so that it changes the focal point of the eye. Ideally, the focal point is changed so that it focuses perfectly on the retina, just like a normal eye.

As stated in the previous section, myopia (nearsightedness) usually results from the eye being too long. The cornea has a more pronounced curve than a normal eye. Laser eye surgery is great for myopia because it is relatively easy to remove a little of the cornea to flatten out the curve.

Hyperopia (farsightedness) normally means the eye is too short, which means that the cornea needs to curve more to properly focus the light on the retina. Although more intensive than correcting myopia, laser eye surgery can treat hyperopia by reshaping the cornea to make it rounder.

Laser eye surgery works by pulsing a tightly-focused beam of light (laser) onto the surface of the eye. Upon contact with the surface of the cornea, the laser vaporizes a microscopic portion of the cornea (more on this later). By controlling the size, position and number of laser pulses, the surgeon can precisely control how much of the cornea is removed.

LASIK combines the best features of ALK and PRK (see above). Like ALK, LASIK uses a microkeratome to create a "flap" of the outer corneal tissue that can be folded out of the way and then replaced. Once the flap is folded out of the way, LASIK uses the same Excimer laser used in PRK to reshape the underlying corneal tissue. Then the flap is replaced over the reshaped area and conforms to the new shape.

The great thing about the cornea is how quickly it heals. As soon as that flap is replaced, it begins to naturally seal itself to the rest of the cornea. This approach greatly speeds the overall healing process when compared to PRK, which leaves the reshaped area open.

Of course, there are potential problems with LASIK. The three most common problems are:

• Undercorrection - Not enough tissue is removed during the procedure.
• Overcorrection - Too much tissue is removed during the procedure.
• Wrinkling - The corneal flap has a small fold or wrinkle in it when it is replaced, causing a small blurry area in your vision.

Under most circumstances, each of these problems is easily corrected with a second surgical procedure. If the undercorrection or overcorrection is very slight, the surgeon will most likely advise the patient not to attempt to refine his or her vision any further. In fact, many recipients of laser eye surgery never achieve normal vision but are able to reduce their corrective-lens prescription significantly.

In addition to the more common problems listed above, there is a potential for other side effectssuch as blurred vision, halos around lights, increased light sensitivity and even double vision. There is also the chance that damage or scarring can happen to the cornea, resulting in a partial or complete loss of vision.

These other problems occur only rarely when you're dealing with reputable ophthalmologists operating on patients who meet the parameters of an ideal candidate. We'll talk more about what makes an ideal candidate later.

The development of theExcimer laser is the key element that has made laser eye surgery possible. Created by IBM, Excimer lasers (the name is derived from the termsexcited and dimers) use reactive gases, such as chlorine and fluorine, mixed with inert gases such as argon, krypton or xenon. When electrically stimulated, a pseudo molecule (dimer) is produced that, when lased, produces light in the ultraviolet range. 

The Excimer laser is a cool laser, which means that it does not heat up the surrounding air or surfaces. Instead, a very tightly-focused beam of ultraviolet light is emitted. The ultraviolet light is absorbed by the upper layer of the surface that it contacts. The sheer amount of ultraviolet light is too much for most organic materials (such as the cornea of the eye) to absorb, resulting in the breakdown of the molecular bonds of the material.

The ultraviolet beam of light only penetrates a microscopic amount, less than a nanometer (a billionth of a meter), into the surface of the cornea. The heat created from the energy released by the laser is dissipated along with this microscopic layer of the cornea. This process is known asphotoablation.

The Excimer laser is incredibly precise. It has the ability to focus a beam as small as 0.25 microns. Considering that a typical human hair is 50 microns in diameter, that means that the Excimer laser is capable of removing 0.5 percent of a human hair's width at a time!

The operation of the Excimer laser is a complicated and delicate process. In fact, a dedicated technician is used just to set up and operate the machine in conjunction with the ophthalmologist performing the surgery.