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]