Article Date: 6/1/2002

IntraLASIK
All-Laser IntraLASIK
Marketing hype or a new generation in refractive surgery?

BY LOUIS J. CATANIA, O.D., F.A.A.O., Atlantic Beach, Fla.

 

This photo demonstrates the cleavage plain that the Femtosecond laser creates.

The list of technological advances in refractive care grows longer every year (see Table 1). Marketing hype surrounding these introductions can be significant, so the challenge for us is to evaluate the effectiveness of each technology. Here, I'll address keratectomy and a development in refractive technology, the femtosecond infrared laser.

Prominent authorities, including Vance Thompson, M.D., say that a weakness in refractive surgery lies in cutting the corneal flap (keratectomy) during laser- assisted in situ keratomileusis (LASIK) with a mechanical microkeratome. Table 2 lists some of the concerns about this procedure.

How it works

The IntraLase FS femtosecond infrared laser, manufactured by IntraLase, addresses keratectomy. The scientific basis of femtosecond infrared photodisruption rests on these two principles:

1 It's best to use a laser beam that will only be absorbed at the site of the energy focus (the microplasma)

2 The beam should apply that energy at a speed that will break carbon bonds, vaporizing tissue at the focal site without causing collateral damage to surrounding cells.

The computer-controlled application of an infrared laser at femtosecond delivery speeds achieves these goals.

Infrared laser light passes through corneal tissue without being absorbed; thus, the ophthalmologist can focus its microplasma at a given depth without affecting the tissue above, below or lateral to it. Delivering the energy at femtosecond speed produces a discrete gas and water cavitation bubble that expands to about 2 µm, separating the corneal lamellae before being reabsorbed by the endothelial pump.

By computer programming the adjacent application of the expanding (connected) cavitation bubbles in a circular or linear pattern, on a horizontal and/or vertical plane, ophthalmologists can create the cleavage (dissection) of corneal tissue with ±5-µm accuracy. This precision dramatically improves the ±60-µm accuracy of a typical microkeratome blade.

TABLE 1: Refractive Technological Developments in the Past 2 Years

  • LASIK epithelial keratomileusis (LASEK)
  • Wavefront aberrometry (companies include Alcon, VISX and Bausch & Lomb)
  • Eye trackers (laser manufacturers such as Alcon and VISX)
  • Phakic intraocular lenses (IOLs) [companies such as Allergan and Staar Surgical]
  • Corneal photocoagulation (laser thermal keratoplasty by Sunrise, conductive keratoplasty by Refractec)
  • Femtosecond infrared lasers (IntraLase FS by IntraLase)
  • Presbyopic reduction procedures (companies and procedures include anterior ciliary sclerotomy, Presby Corp.)

 

The technology

The IntraLase FS uses a specially designed applanation ring and cone that momentarily raise the intraocular pressure to only 35 mm Hg to stabilize ocular movement during delivery of the laser to the corneal stroma.

The computer is programmed to focus the laser's microplasma to a specific depth and to apply the pattern, direction, hinge position and number of femtosecond pulses to create a flap with a precise diameter, consistent thickness and perfect edge.

After the ophthalmologist creates the flap, he rotates the patient (remaining in the inclined position) to the excimer laser (whichever model he uses) for photoablation.

The IntraLase FS Laser replaces the mechanical microkeratome in LASIK, thus providing an "all-laser" procedure called IntraLASIK.

While the market hype has been minimal since its FDA clearance in December 1999, the IntraLase FS has been accepted as a new generation in safety and efficacy by authorities in the field, including Stephen Slade, M.D., Lee Nordan, M.D., and Jonathan Christenbury, M.D.

The only measurable, clinical complication reported with IntraLASIK is slight accumulation of stromal edema after creation of the flap. This tends to be greater than the edema that mechanical microkeratomes create, and can produce a slower visual recovery (by one or two Snellen lines) during the first week or two postoperatively. However, this effect is short lived, as the edema regresses rapidly.

IntraLase introduced the IntraLase FS laser in October 2000 and released it on a limited basis in 2001. The company plans for regional release of the Intralase FS as its infrastructure and manufacturing capacity increase.

 

Here you see the docking ring with the applanation lens securely positioned on the eye. Notice the perfectly round treatment pattern with well-defined flap edges and hinges.

What are the benefits?

With femtosecond infrared laser technology, you're referring patients for safe, precise LASIK. In almost 4,000 surgeries performed to date with IntraLASIK, no adverse events (as defined by the FDA) have been reported.

Flaps are consistent and virtually free of the risks associated with mechanical microkeratomes. Postoperative care for femtosecond infrared laser technology is less worrisome and time consuming for both you and your patients.

An indirect but potentially long-term benefit is also associated with this new-generation technology: The ability to offer your patients a new, safer, more accurate technological advancement will raise you higher in your patient's estimation.

No hype

Now's the time to learn about femtosecond infrared laser technology. It's not just hype -- it's the technology of the future, here today. I'm convinced that by educating yourself, your patients and your refractive surgeon about the values and benefits of all-laser IntraLasik, you'll produce rewards for all concerned.

Dr. Catania is an internationally acclaimed clinical educator, author and recognized expert in anterior segment care, refractive surgery and new eyecare technologies.

 

TABLE 2: Weaknesses Associated with Mechanical Microkeratome Use

  • Flap too thin
  • Flap too thick
  • Non-planar (uneven) cuts
  • Buttonhole flaps
  • Incomplete flaps
  • Flap slippage
  • Flap dislocation
  • Risk of perforation
  • Striae
  • Folds
  • Difficulty obtaining suction
  • Difficulty maintaining suction
  • Loss of suction
  • Effects of suction ring
  • IOP increase to > 65 mm Hg
  • "Blind" procedure: surgeon can't see what he's cutting
  • diffuse lamellar keratitis (DLK)
  • Epithelial injury
  • Disturbing anterior basement membrane disorders (ABMDs)
  • Epithelial ingrowth
  • Corneal infection
  • Neurotropic effects
  • Biomechanical effects
  • Assembly risks
  • Blade quality risks
  • Sterilization risks
  • Toxins from "mechanisms"
  • Intraoperative bleeding.
 

 


Optometric Management, Issue: June 2002