What are ‘femtosecond’ eye lasers?

| Feb 09, 2008 | Comments 7

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]

Filed Under: Education • LASIK • Safety • Technology

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About the Author: Mr. Dave Allamby FRCS FRCOphth is a leading London-based laser eye surgeon. You may have seen him on the This Morning TV show with Phillip Schofield and Fern Britton or read one of several articles in the national press, recently for treating Denise Van Outen, rock giant Rick Wakeman and broadcaster Paul Ross. David is Medical Director at Focus Laser Vision, known as a world-leading clinic in the treatment of presbyopia, or age related loss of close vision. Focus Laser Vision is also London's only clinic to offer next-generation Z-LASIK laser eye treatment for short sight, long sight or astigmatism.

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  1. husiin says:
    April 13, 2012 at 11:14 pm

    Hi Dr Allamby,

    I will soon have Z-Lasik operation. Recently I heard about nanosecond lasers produced by Schwind company for flap-creation. Though they are not available in my country, yet. Are they good enough to wait?

    Reply
    • Dave Allamby says:
      April 14, 2012 at 1:16 pm

      Hi Huslin. No need to wait for Schwind’s laser which is still in development. I believe the Ziemer laser used for your Z-LASIK will remain at the front of the pack for quality of flap creation. I recommend to go ahead, if you are happy with the reputation and skill of the surgeon. Regards, Dave

      Reply
  2. Mr Singh says:
    July 8, 2009 at 8:59 pm

    I forgot to ask… how much would the blade-free femtosecond lasik cost for my prescription is: R sph-6.00 cyl-2.25 axis 170.0, L sph-6.00 cyl-2.00. Also I have astigmatism so would it cost extra to fix this or is it within the price?

    Reply
  3. Mr Singh says:
    July 8, 2009 at 8:22 pm

    I am 24 and I want to get laser eye surgery. My prescription is: R sph-6.00 cyl-2.25 axis 170.0, L sph-6.00 cyl-2.00. If I have to do the laser eye surgery again when I am 40-50 yrs old is it better to have the cheaper type of laser surgery done now and then have the most expensive type done later? or is it best to get the most expensive one done first?

    Reply
    • Dave Allamby says:
      July 8, 2009 at 9:28 pm

      Dear Mr Singh
      It’s a large prescription but should be doable, assuming your corneas are too thin. You want the best procedure and results with your lasik operation, so I can only recommend blade free wavefront LASIK. It will be 20-25 years before you need glasses for reading and we cannot know how we will correct presbyopia in 2034! It will certainly be very different from today so no need to think about this in 2009.
      Dave

      Reply
      • Dave Allamby says:
        July 8, 2009 at 9:30 pm

        Mr Singh
        The cost includes correcting your astigmatism, but is higher because of it. The cost would be £1645-£1745 per eye for blade free wavefront LASIK at Focus.
        WIth regards
        Dave

        Reply

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