Spotlight: ON TECHNOLOGY AND TECHNIQUE
Where There's Smoke . . .
Eliminating LASIK laser plume may have a host of beneficial effects -- including improving your outcomes.
By Christopher Kent, Senior Associate Editor

As you may know, the excimer laser was first designed as an industrial laser used to etch computer chips. But the technicians who used the laser for this purpose discovered a problem: The laser didn't etch the chips correctly because the plume of smoke rising from the chip interfered with the laser beam. So, they went to great lengths to design vacuum systems to remove the smoke as rapidly as possible. With the smoke out of the way, they were able to etch the chips exactly as intended.

If you sit next to most patients undergoing LASIK, you can see sparkles in the air above the eye during the ablation. This is caused by the laser beam striking particles in the cloud of laser plume being produced by the ablation. It's the exact same problem encountered at the chip factory -- only in this case, it's someone's vision that's at stake.

Laser profile interference

Laser plume is created when laser energy breaks carbon-nitrogen peptide bonds in cellular protein. This causes the protein to explode, disrupting the cell and releasing debris and complex molecules. Airborne particles form a cloud between the laser and the stromal bed, and this can cause a measurable difference in the resulting ablation. (See illustration,right)

The particles in the laser plume cloud can cause problems in other ways, as well:

• They can interfere with your ability to view the bed during the ablation, decreasing accuracy and increasing stress.
• They can drop back onto the eye and inhibit beam profile, which may be a contributing factor in Sands of the Sahara Syndrome.
• They can attach to the lens of the laser, impairing the laser's performance until the lens is cleaned.

A growing number of doctors have begun addressing this issue by using a vacuum system to evacuate the plume. Most are reporting a noticeable improvement in outcomes.

Comparing outcomes

Currently, only one system specifically designed for laser plume evacuation is available in the marketplace: the Mastel Precision Laser Clean Room System. Most surgeons we spoke to who use the Mastel system bought the device for health reasons -- to prevent staff from inhaling laser smoke -- and then were surprised to discover an improvement in outcomes.

• Impressed by the improvement in outcomes, Stephen S. Dudley, M.D., who practices in Oshkosh, Wisc., conducted a study in his practice. Dr. Dudley used a VISX Star S2 laser to perform LASIK on 42 eyes; 21 using the Mastel system, 21 without. Two weeks after surgery, 100% of the experimental group had UCVA better than 20/40, compared to 95% of the control group; 57% of the experimental group were better than 20/20, compared to only 33% of the control group.
• Robert G. Martin, M.D., of Carolina Eye Associates in Southern Pines, N.C., reports a similar improvement in outcomes. (See chart above.) "I was very surprised to find noticeable improvement in my outcomes. We had quick, dramatic improvement in speed of recovery of good vision, and improvements were still visible at 2 weeks, although the difference at 2 weeks was less dramatic than the difference at 18 hours." Dr. Martin adds: "These days, I'm afraid to not use the Mastel system."
• Richard Foulkes, M.D., who practices in Hinesdale, Ill., hasn't performed a controlled study using the system, so he was hesitant to specify his outcome numbers. However, he's had a similar experience. "Our results at 1 week, for patients with less than 6 diopters of error, are far better than those reported by most surgeons," he says. 
  "Based on my experience, I'd say that using the Clean Room system will improve a surgeon's outcomes by 10 to 15%. Obviously, it does add cost to the procedure, but there's a very real, significant payoff."

Features of the Laser Clean Room System

The Laser Clean Room System first became available 2 years ago. Since then, it's been redesigned several times to improve filtering, simplify use and ensure that it will work with most current lasers and tracking systems. Features include:

• Handpiece. The handpiece is a modified Fine-Thornton ring with a barrel top, which contains vacuum ports -- three close to the eye and one farther away. (The remote port uses a higher vacuum rate than the closer ports.) A console pump connects to the handpiece via two reusable silicone tubes. Vacuum flow rate can be adjusted to compensate for factors such as the amount of smoke being generated, humidity, and how many times the current filter has been used. (The system also includes a footpedal that can be used to turn the vacuum on and off.)
• Filters. The Laser Clean Room System incorporates two filters: an ultralow penetrating 0.1-micron air filter designed to capture airborne particles, and a carbon-activated filter to capture polyaromatic hydrocarbons.
  According to Mastel Precision, Clean Room filters have to be replaced about every 6 to 10 cases.
• Fiberoptic lighting. The system also features a vitrectomy lightpipe applied from the left side of the ablation tube. This allows you to reduce the overhead illumination, providing a clearer view of the ablation and making it easier for the patient to maintain focus on the target.

You apply the Laser Clean Room System after you've created the flap. The modified Fine-Thornton ring has no teeth in the flap area, so the flap remains untouched as the eye is held in place. At the same time, a shelf inside the handpiece covers the hinge and protects the flap from falling debris. (The handpiece is available in two designs, for nasal or superior hinges.)

Other benefits

In addition to removing most of the laser plume, the system has other benefits:

• Fixation. Because the Mastel system handpiece is a modified Fine-Thornton ring, it prevents movement during the ablation. This has obvious benefits in terms of centering, but Dr. Foulkes points out that it also provides control over the z-axis.
  "Some surgeons I've worked with have been unaware that the laser beam is cone-shaped. The farther from the source you are, the smaller an area the energy is concentrated into. This can lead to overcorrection. Likewise, moving closer to the source spreads the energy, resulting in undercorrection. Holding the eye in this manner gives you control over that factor."
• Hydration. Cutting the cornea draws water into the interface, and the cornea absorbs some of it -- not necessarily in an even manner. Because hydration affects the efficiency of ablation, this can result in uneven surfaces, central islands and hot spots.
  Dr. Foulkes says that because the Mastel system moves air across the bed, it dries the tissue a little, minimizing the uneven hydration factor. "After vacuum is initiated, I wait a few seconds for the stromal bed to rise up as it dries. The appearance of the bed changes as some of the moisture evaporates. I've learned from experience when the color of the surface indicates an optimum level of dryness, and that's when I perform the ablation.
  "The dryer bed also makes it much easier to visualize the ablation, which improves accuracy and centration. As a result I've had to shift my nomogram about 10%."
• Patient comfort. Removal of the "burning flesh" odor is not only more pleasant for the patient, but can save you embarrassment. "Ninety-nine out of 100 patients don't smell the plume when I use the Mastel system," says Dr. Dudley. "After telling them this is a 'cold laser,' this saves me from having to explain why a cold laser makes a burning smell." Patients also tend to relax more about possible fixation loss knowing that their eye is being held in place.

In addition to these benefits, by reducing potential health threats the system may reduce the likelihood of litigation by staff or patients, as well as the possibility of OSHA violations.

Changing for the better

All the surgeons we spoke with agreed that changing your nomogram is necessary when using the Mastel Precision system. "Doctors' nomograms are based on confounding issues being present during surgery," says Dr. Foulkes. "Getting rid of these factors and redoing your nomogram is worth the effort. You'll get much more standard results." Dr. Foulkes has offered to share his nomogram (developed for use with the Nidek laser) with any interested surgeons.

For more information about the Mastel Laser Clean Room System, contact Mastel Precision at (800) 657-8057.

None of the surgeons interviewed for this article has a financial interest in the product.