5-1. What does the term “laser” mean?

Laser is an acronym for “Light Amplification Stimulated Emission of Radiation.”

5-2. What type of laser is used for laser vision correction?

The excimer laser is used for both LASIK and PRK. “Excimer” is a contraction of the words “excited dimer.” This refers to the two gases, argon and fluorine, which are activated by an electric current to produce a beam of light.

5-3. Are there different types of excimer lasers?

There are two main types: “Broad beam” and “flying spot” lasers. Both types perform well for laser vision correction. Advocates for broad beam lasers cite the uniformity of a large laser beam. The shape of the beam can be changed by rotating different templates in front of the beam. Advocates for flying spot lasers like the flexibility of applying precise treatment patterns to different parts of the cornea. The difference between the two kinds of lasers can be likened to painting with a large paintbrush or a small one. The larger brush may be faster and more efficient. The small one can paint finer detail. There is no clear agreement about which laser is best. Your doctor, most likely, will use the laser he or she considers the best.

5-4. What pattern does the laser use to treat nearsightedness?

The laser treats the center of the nearsighted cornea. If you visualize the cornea as a mountain, the excimer laser “flattens” the top, and makes the cornea more like a plateau than a mountain.

5-5. What pattern does the laser use to treat farsightedness?

The laser treats the periphery of a farsighted cornea. It steepens the cornea by creating a donut-shaped treatment around the periphery of the cornea.

5-6. What is the most popular excimer laser in the United States?

The VISX Corporation, of Santa Clara, California, now part of American Medical Optics, has manufactured about two-thirds of the excimer lasers that are in use throughout the United States. Other popular lasers are made by Alcon, Bausch & Lomb, and Nidek.

5-7. Which laser is the best?

There are several good ones. The best way to choose is to find out which one your surgeon prefers.

5-8. What does a microkeratome do?

A microkeratome cuts a thin, circular flap in the cornea. The typical flap is between 160 and 180 microns in thickness. The flap has a hinge either at the top of the cornea (12 o’clock position), or on the side (3 or 9 o’clock position). When the flap is lifted, the underlying bed is treated with the excimer laser.

5-9. How does the microkeratome work?

Most microkeratomes are automated, that is, cutting is controlled by a motor that moves the blade smoothly through the cornea. Some microkeratomes are controlled manually, but they require a steady hand to guide the cutting instrument evenly through the cornea. The microkeratome makes a horizontal incision through the cornea while the patient is lying down. The incision is in the same direction you would have when slicing a roll to make a sandwich.

5-10. Is the corneal flap removed completely?

No. The microkeratome leaves a 20-degree “hinge,” so the corneal flap remains attached either to the “superior” part of the cornea (12 o’clock position), or to the nasal part of the cornea (3 or 9 o’clock).

5-11. What is the purpose of the “suction ring?”

The suction ring is placed on the surface of the eye, just outside the edges of the cornea. When the suction is turned on, the eye pressure increases, and the eye becomes firm. The microkeratome, which attaches to the suction ring, may be a separate instrument which can be connected to the microkeratome, or it may be part of a one-piece unit. The suction ring accomplishes two things: It holds the eye steady, and it makes the eye firm enough to create a good cut with the microkeratome.

5-12. How accurate is the microkeratome?

Modern day microkeratomes are highly accurate and make extremely precise corneal flaps. Slight variations in the thickness of the flap can occur if the cornea is too steep or too flap. Steep corneas produce slightly thinner flaps and flat corneas produce slightly thicker flaps.

5-13. Which is the best microkeratome?

Same answer. The best way to decide is to find out which one your surgeon thinks will produce the best results in his or her hands.

5-14. Can a laser be used to make a corneal flap?

Yes. A laser, known as a “femtosecond” laser, or IntraLase, can focus inside the cornea and create an excellent LASIK flap.

5-15. What are the advantages of the IntraLase?

One advantage of the IntraLase is that it does not use a sharp cutting blade, so there is less chance of making a poor flap. In addition, the flap diameter and the thickness of the flap can be adjusted to fit the specifications of the surgeon. The IntraLase applies less pressure to the eye than the microkeratome. This can be an advantage in glaucoma, or conditions in which reducing blood flow to the eye could be harmful.

5-16. Are there other possible advantages to the IntraLase?

Some studies show IntraLase LASIK is associated with less astigmatism, fewer higher order aberrations, and more accurate correction of vision.

5-17. Is the IntraLase more accurate that a microkeratome?

The IntraLase is more accurate than the microkeratome, since it can create a LASIK flap with the precise dimensions specified by the surgeon. The microkeratome flap is more variable in its dimensions, since its creation is influenced by anatomical factors of each individual cornea, such as steepness, and thickness.

5-18. What are the disadvantages of the IntraLase?

The IntraLase is an expensive piece of equipment and adds additional cost to the LASIK procedure. It takes slightly longer to make the IntraLase flap, usually about 30 seconds.

5-19. Can the laser track eye movements?

Yes. Most modern excimer lasers have “trackers” which fix on the pupil and keep the laser beam centered on the treatment zone. The technology is similar to aircraft artillery, which “lock” on a target. If the eye movement is extreme, the laser will shut off and treatment will stop. Treatment can be resumed as soon as the eye is back in position.