IntraLase, Zeimer and Other Femtosecond Lasers for All-Laser LASIK
In 2001, IntraLase Corp. introduced the first FDA-approved femtosecond laser for laser eye surgery performed in America, marking the beginning of all-laser LASIK in the United States.
In recent years, several other femtosecond lasers have been introduced for eye surgery, giving refractive surgeons alternative lasers for all-laser LASIK and other procedures.
What is a Femtosecond Laser?
A femtosecond laser is a specialized laser used for eye surgery and other medical and technical applications.
The word "femtosecond" refers to the units used to measure the duration of each pulse. One femtosecond is equal to one millionth of one billionth of a second, or one millionth of a nanosecond. (Yes, really.)
How Does a Femtosecond Laser Create a LASIK Flap?
Femtosecond lasers used in all-laser LASIK direct tiny, rapid pulses of infrared light to a precise depth within the cornea. This depth is determined by the surgeon and is entered into the computer that controls the laser.
These high-energy light pulses separate corneal tissue at the molecular level by a process called photodisruption, creating microscopic bubbles of carbon dioxide and water at their point of impact.
The laser moves back and forth across your eye, creating a uniform layer of these bubbles at the junction between what becomes the back surface of the corneal flap and the underlying corneal tissue (called the stromal bed).
The speed with which the femtosecond laser creates a corneal flap depends on the frequency rating of the laser. The frequency of the delivery of the laser pulses is measured in hertz (Hz), which generally define how many times an event occurs per second.
Modern femtosecond lasers for LASIK have repetition rates up to 150 kilohertz (kHz) and higher, meaning they are capable of creating 150,000 laser pulses per second.
Once the flap has been created with the femtosecond laser, the surgeon manually lifts it and folds it back on a small zone of untouched tissue that serves as a hinge for the flap, keeping it attached to the eye. A different laser (called an excimer laser) then is used to reshape the eye.
Early femtosecond lasers had repetition rates of 15 kHz to 30 kHz and required significantly more time to create a flap than a microkeratome, with some lasers requiring 90 seconds or more to finish the procedure. Some of today's modern femtosecond lasers can create a corneal flap in less than 10 seconds.
FDA-Approved Femtosecond Lasers for All-Laser LASIK
The following femtosecond lasers have received FDA approval for use in all-laser LASIK surgery performed in the United States:
AMO's fifth-generation IntraLase femtosecond laser (iFS) gained FDA approval in 2008. This latest iFS laser features a repetition rate of 150 kHz and can create a LASIK flap in less than 10 seconds, according to the company.
The company bundles this latest IntraLase femtosecond laser technology with its Advanced CustomVue excimer laser treatment in an all-laser LASIK procedure they call iLASIK.
Many refractive surgeons continue to use earlier IntraLase lasers that have repetition rates of 30 kHz and 60 kHz. These lasers also create excellent LASIK flaps, but take a bit longer to complete the procedure.
The Femtec femtosecond laser produced by 20/10 Perfect Vision AG (Heidelberg, Germany) received FDA approval in 2004.
A key feature of the Femtec laser is that the applanation cone (the part of the laser housing that touches the eye) is curved to adapt to the natural shape of the cornea. This causes less distortion of the cornea during flap creation and less compression of the eye, so there is less increase of intraocular pressure (IOP) during the procedure, according to the company.
The Femtec laser also has the potential to be used for a new corneal refractive surgery called IntraCor that changes the shape of the cornea from within, without cutting a flap. Though IntraCor is still an investigational procedure, some refractive surgeons feel it may be a viable alternative to LASIK in the future.
Femto LDV - Ziemer
The Femto LDV femtosecond laser (Ziemer Group AG; Port, Switzerland), formerly called the Da Vinci femtosecond laser or Ziemer femtosecond laser, received FDA approval in March 2006. The Femto LDV differs from other femtosecond lasers in that it delivers ultra-short pulses of lower energy, with a very high repetition rate (greater than 1 megahertz).
The Ziemer Femto LDV laser's unique method of overlapping low-energy laser spots makes the corneal flap easier to lift with no manipulation of the cornea, say proponents of the system. The Femto LDV produces no inflammation and does not create an opaque bubble layer (OBL) caused by gases injected into the deep stroma of the cornea during the femtosecond laser treatment — a phenomenon caused by other femtosecond lasers that can lead to flap problems and affect visual outcomes after surgery, according to Ziemer.
The VisuMax femtosecond laser (Carl Zeiss Meditec, Inc.; Dublin, Calif.) received FDA approval in January 2007. Like the Femtec laser, the VisuMax femtosecond laser features a curved applanation cone for less corneal distortion, eye compression and elevation of IOP during the flap creation.
The VisuMax femtosecond laser often is used in combination with Zeiss Meditec's MEL 80 excimer laser for all-laser LASIK.
In addition to creating flaps for LASIK, the VisuMax soon may be used to perform a new all-femtosecond laser refractive procedure called femtosecond lenticular extraction (FLEx). In FLEx, the laser is used to create a small lens-like segment of tissue within the cornea. The tissue segment (or lenticule) is then removed from the cornea, thereby changing the shape of the eye to correct nearsightedness.
A Matter of Surgeon Preference
Clinical studies have shown that all FDA-approved femtosecond lasers are capable of producing excellent corneal flaps in all-laser LASIK, with less risk of certain flap complications associated with mechanical microkeratomes.
The type of femtosecond used by individual refractive surgeons usually is determined by the surgeon's personal preference. Also, some LASIK surgeons offer their patients the choice of either conventional LASIK (with the corneal flap created with a microkeratome) or all-laser LASIK with the flap created with a femtosecond laser for a 100 percent blade-free surgery.
Your refractive surgeon will discuss the type of LASIK procedure he or she recommends for you during your pre-operative consultation. If you prefer all-laser LASIK, be sure to mention this to your surgeon at this visit.
Due to the added expenses associated with a femtosecond laser, all-laser LASIK will increase your LASIK eye surgery cost. Ask your LASIK surgeon for details.
Note: This information is for general education purposes only. It is not to be used as a substitute for medical advice from your eye doctor or refractive surgeon.