The excimer laser produces a high-energy, cool ultraviolet light beam in pulses and delivers the pulses to a surface of the eye’s cornea. These pulses break the bond between molecules and tissue cells so that a controlled amount of tissue can literally be vaporized away to reshape the cornea — one microscopic layer at a time.

With some lasers, e.g. the WaveLight system from Germany, it only takes 5-10 seconds to complete the entire laser process to correct most levels of glasses or contact lens prescription.

You can see above and below to the right just how precise and gentle the excimer laser can be. Above a human hair has been etched into precise grooves. Below even words have been carved into the hair!

The excimer laser is computer controlled and programmed to custom treat each individual eye with a high degree of precision. For most cases, the thickness of the layer removed by the laser is less than the thickness of a human hair. The laser only needs to remove 13 thousandths of a millimeter to correct one unit of glasses strength (dioptre)!

Update from the ASCRS in Chicago. LASIK for long sight was shown safe, effective and predictable through 5 years of follow-up.

During the American Society of Cataract and Refractive Surgery (ASCRS) meeting, Dr. Stephan Kaminski, MD, presented data on 29 eyes of 17 patients followed through 5 years after undergoing LASIK with the Allegretto WaveLight laser, which we also use here at FOCUS Laser Vision.

Hyperopic LASIK for “up to +6 D appears to be safe and effective and is predictable, but we do need longer term follow-up to determine regression of treatment effect,” according to Dr. Kaminski.

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I get asked about the so-called ‘femtosecond‘ lasers now being used in LASIK laser eye surgery, and what these devices do. OK, here are the answers.

First of all, LASIK eye surgery is a laser procedure with two parts. First we have to make a thin flap from the top part of the cornea, basically a thin hinged layer we can temporarily fold to the side (painlessly!).

Next we use an ‘excimer‘ laser to reshape the exposed cornea to correct the vision focusing problem. The laser will polish away certain areas, depending on your prescription, to bring back clear vision.

The flap is put back in place and heals over very quickly. The eye feels gritty or scratchy for about 3-4 hours only. OK, so far so good.

For the first stage, making a flap, we have used a mechanical device called a keratome (or microkeratome). Keratomes have been around for 50 years and use a blade to make a controlled cut. This stage is where significant complications can occur, so we have been looking for a way to make this corneal flap but without the need for a blade.

Along come femtosecond lasers.

The eye lasers use ultra-short infra-red low energy pulses to create microscopic bubbles at a precise depth below the surface of the cornea. If you do this millions of times, you can create a super precise separation as a sheet, and hence a near-perfect corneal flap, which you can now fold to the side ready for vision correction with a second laser.

The femtosecond laser means we no longer run risks from using a blade to cut a flap. This means safer LASIK eye surgery.

You can watch a video of femtosecond laser eye surgery here.

More on femtosecond lasers coming soon.

Definition for femtosecond:

(This definition follows U.S. usage in which a billion is a thousand million and a trillion is a 1 followed by 12 zeros.)

A femtosecond is one millionth of a nanosecond or 10^-15 of a second and is a measurement sometimes used in laser technology. So that’s one billionth of a millionth of a second! As a comparison, one femtosecond to a second is like one second to 32 million years.

For comparison, a millisecond (ms or msec) is one thousandth of a second and is commonly used in measuring the time to read to or write from a CD-ROM player.

A microsecond (µs) is one millionth (10^-6) of a second.

A nanosecond (ns or nsec) is one billionth (10^-9) of a second and is a common measurement of read or write access time to random access memory. A picosecond is one trillionth (10^-12) of a second, or one millionth of a microsecond. An attosecond is one quintillionth (10^-18) of a second and is a term used in photon research.

[tags] LASIK, femtosecond, laser eye surgery, safety, risks, compications [/tags]

Video showing a very brief overview of the LASIK procedure, as well as covering short sight, long sight and astigmatism. Simple and to the point.