Spotlight ON TECHNOLOGY & TECHNIQUE

The Femto LDV: A Low-Energy Laser Delivery System

By Leslie Goldberg, Associate Editor

Refractive surgeons have been looking for alternatives to using a blade to create the flap as the initial step in LASIK. The wish to offer patients an "all-laser LASIK" option has stimulated demand for femtosecond lasers, as they offer the potential of cutting corneal tissue with extremely short laser pulses minimizing the production of heat.

While surgeons have reported favorably on the quality of outcomes and patient satisfaction with these lasers, the sheer bulk and inflexibility of available femto lasers, coupled with their complex operation and maintenance, have been obstacles to their wider acceptance.

Ziemer's Leonardo DiVinci Femtosecond Laser (Port, Switzerland), a compact, mobile femtosecond surgical laser, provides a versatile, powerful platform for a wide spectrum of applications in corneal surgery.

"The LDV laser incorporates all the developments in femtosecond technology over the past decade," says Richard Foulkes, M.D., principal of the Future Laser Vision Center in Hinsdale, Ill. "The physics of this system are fundamentally different from other femto second lasers being produced."

The Ziemer LDV Design

"This laser works without amplification of the cavity energy, which means that the energy per pulse is in the nano joule region," says Dr. Foulkes. "This low amount of energy will not create an ablating effect, so the idea is to overlap the spots. This is accomplished by extremely fast repetition where the oscillator is approaching the speed of sound (a technical limit)."

The pulse rate is in the megahertz range. The pulses are moved back and forth across the eye in narrow overlapping swaths. To get the most effect from each pulse, the final optic is placed very close to the focal plane at about 2 mm, explains Dr. Foulkes.

"The ergometric head that can treat under most lasers was not what drove this design," says Dr. Foulkes. "It was the physics. The tight focal length results in a round plasma that fully ablates without cavitation bubbles as a mechanism for dissection."

The result is that an opaque bubble layer (OBL) does not form. "OBL can be thought of as inflation of the stroma, and aside from blocking the tracker, the primary problem with OBL is difficult lift. Tissue bridges are larger and inflation of the stromas need to be treated, which slows the excimer, undercorrecting in the area. With the LDV laser, the bed is glassy smooth as there are essentially no tissue bridges," says Dr. Foulkes.

Translation speed is one of the variables that can be used to fine-tune the ablation, as well as to overlap areas and fast and slow scan zones. "These are fully programmable to the surgeon via a touch screen interface," say Dr. Foulkes. In addition, a true remote evaluation and adjustment of the laser can be done via the Internet.

Lifting of the Flap

"The lift of the flap is done with forceps, and, for the microkeratome surgeon, this procedure will seem very familiar," says Dr. Foulkes. "Additionally, the LDV is hearty and can be moved if needed without affecting its efficacy."

The laser leaves the eye at the natural curve to the edge of the microprocessor-controlled vacuum ring or about 30°. "There is no gap," says Dr. Foulkes, "as the spot size is round and 0.2 μm in size and the edge is invisible the next day.

"The smooth lift without the forceful maneuvers required at times with IntraLase leads to no epithelial disruption around or on top of the flap," says Dr. Foulkes. "We have seen no epithelium ingrowth to date. We see no inflammation in the corneal stroma or transient light sensitivity with the LDV, either.

"Because the laser does not use cavitation bubbles, you can cut several times through the cornea on top of the last treatment and create precision smooth surfaces as deep as 430 μm," says Dr. Foulkes. "In addition, unlike the long-focal distance lasers, the ability to work near the endothelium seems to be safe."

Currently, depth in the LDV is created using spacer plates. However, the focal distance can be easily manipulated within the head and this feature will be available in the near future.

"The ablation surface is the key to any flap," says Dr. Foulkes. "The major advantage to femtosecond lasers, and the Femto LDV in particular, is the glassy smooth surface and the fact that water has not gotten up to the treatment surface. The ablation surface that is the best in terms of laser uptake is Bowman's and this surface looks and behaves like Bowman's. The avoidance of OBL and ease of lift without manipulation issues like water on the treatment bed seems to be the reason.

"The Femto LDV is the best combination available of the microkeratome and the femtosecond laser. It's mobile and stable and works by physics that are completely different from any available system This low energy, fast repetition rate, tightly focused method is clearly the future of lamellar dissection with clean smooth cuts, no inflammation and less concern for damage to the inner eye from the longer energy fields. I think, along with better imaging tools and lamellar dissecting tools like LDV, that our work in the cornea is poised to make giant leaps forward," concludes Dr. Foulkes. OM