Laser keratome may create better and safer flaps

By Cheryl Guttman

La Jolla, CA - Early clinical results with the 105 nm femtosecond laser (Pulsion FS, Intralase) suggest that the new technology offers LASIK surgeons safety, precision and versatility in flap creation, says specialist Lee T Nordan MD.

Using this device, surgeons have the flexibility to vary a number of flap parameters, including its dimensions, edge bevel, and hinge location, simply by programming their choices into the computer. Flap geometry and diameter can be any thickness and may be selected in the range of 160 to 200 microns.
Nordan reports that the outcome of every procedure is a truly plano, accurately sized flap overlying an exquisitely pristine stromal bed with the new laser keratome.

"Flap-related problems are the leading cause of complications post-LASIK, and so obtaining a quality flap is still the single most important step in achieving a favorable visual outcome.

When using a mechanical bladed microkeratome, obtaining a good flap remains a highly surgeon-dependent variable relating to the judgment and experience of the operator.
The femtosecond laser minimises that human factor and has safety as its single biggest advantage," said Dr Nordan, Director of the Nordan Laser Eye Medical Group.
The Intralase Pulsion has now been used to treat more than 1,000 patients in clinical trials in the US. Dr Nordan reported that he has not encountered any significant complications using the femtosecond laser for flap creation during almost two years of experience.

Within this large series, there has not been a single button-hole or any eyes with perforations, epithelial defects, decentred flaps, diffuse lamellar keratitis or irregular astigmatism. Moreover, the flaps are cut reproducibly to the selected dimensions.
"The accuracy and predictability of flap thickness has become a big issue in discussions about use of different microkeratomes because there are safety issues relating to both flaps that are too thin and too thick and so leave less residual cornea than expected.

"Studies evaluating the accuracy of the femtosecond laser show that the surgeon can be confident that the flap produced measures within 10 microns of the desired thickness," said Dr Nordan who is also an Assistant Clinical Professor of Ophthalmology, Jules Stein Eye Institute, University of California at Los Angeles
To create the LASIK flap using the femtosecond laser, the eye is united to the laser using a suction ring that is applied to the limbus and features a disposable glass applanation lens.

The suction ring is connected directly to the laser via a cone, and it is used with minimum vacuum, causing IOP to increase no higher than 40 mm Hg.
"There are several nice features about the suction ring. First, <it is not necessary for the surgeon to achieve precise centration on the cornea>," Dr Nordan observed.

The laser emits very small (3 to 4 microns) spots of light in rapid sequence (up to 5,000 pulses/second), first focusing them precisely at a specified stromal depth, where they are placed closely together in a spiral, expanding pattern to produce a lamellar dissection of the desired diameter. Then the cut is brought to the surface around the border of the resection, leaving an uncut section at the desired location to serve as the hinge.

If a problem is encountered during femtosecond laser flap creation, the procedure can be interrupted and reinitiated 30 minutes later, rather than requiring that the patient return after an interval of several months once the cornea is allowed to heal.

Dr Nordan noted that visual outcomes in eyes undergoing 'IntraLASIK' with flap creation using the femtosecond laser also speak to the quality of the flap produced with this technology.

At the one day postoperative visit, eyes have routinely achieved UCVA in the 20/25 to 20/30 range and at one week, the outcomes are at least as good as those achieved in procedures performed with mechanical microkeratomes.

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