In traditional LASIK, a mechanical handheld microkeratome moves over the corneal surface to create a LASIK flap. Many complications from LASIK are related to the unpredictable performance of this device as the flap is created.1 Intraoperative risks include corneal flap size (eg, free cap, small cap, large cap, incomplete cap); corneal flap depth (eg, buttonhole, epithelial tear, thin flap, full-thickness anterior chamber penetration); corneal flap form (eg, wrinkled, oedematous, irregular, shrunken); flap location (eg, flap displacement); or corneal hinge (eg, short, large, absent, burns).2
A buttonhole or irregular flap may occur if the keratectomy was performed without adequate suction, with a defective blade, or in the case of very steep corneas with K-readings greater than 50.00 D.3 Moreover, the edge and average thickness of the flap are variable and often irregular, because each microkeratome performs differently.4,5 Tham and Maloney6 found an overall rate of microkeratome complications of 0.68% (1 in 150). In a surgeon's first 1,000 eyes, the microkeratome complication rate was 1.3% (1 in 77), decreasing to 0.4% (1 in 250) in the latest 1,000 eyes. These results are surely related to a significant learning curve with the microkeratome.
It is probable that the choice of microkeratome affects the percentage of risks and intraoperative complications, as each microkeratome creates unique morphologic features when corneal tissue is excised. Such features include instrument design, mechanics of tissue excision and blade oscillation, and instrument traverse combined with surgical skill influence the configuration of lamellar keratotomy.7 The quality of the cutting edge may be influenced by the relationship between the speed of the pass and the rate of blade oscillation/rotation. Therefore, it seems that a lower feed during oscillation/rotation results in a smoother pattern of the cutting edge.8
CAUSES OF IATROGENIC KERATECTASIA
There is also an increasing percentage of progressive corneal ectasia after LASIK, a particularly insidious postoperative complication5 occurring a few to several months after surgery.7 The etiology of iatrogenic keratectasia is still unknown, but it hypothetically is related to residual corneal bed thickness. Other causes include (1) error in measuring the overall corneal thickness by means of pachymetry, (2) underestimation of excimer laser ablation depth, or (3) underestimation of flap thickness.9 According to the literature, the greatest care must be taken with flap measurements (ie, thickness, diameter, hinge length) and surgical planning to reduce risks and complications.4
The technology of the femtosecond laser brings a new level of safety and guarantee of better results to refractive surgery. It provides an all-laser approach for optimal precision. A computer-assisted laser creates a corneal LASIK flap with a preset diameter and a precise thickness.10 Intra-LASIK take about 30 seconds per eye to perform a corneal flap; in approximately 10 minutes, the entire procedure is completed. To perform the LASIK flap, the femtosecond laser is focused into a little spot that passes harmlessly through the superficial layers. It focalizes at a precise deepness into the corneal stroma, and a microplasma is then created, forming water and gas bubbles to expand the corneal lamellae. When the gas bubbles are absorbed, a cleavage plane with tiny stromal bridges remains in the corneal stroma. These bridges are excised with a blunt spatula, and the flap is lifted to perform the stromal ablation with the excimer laser.
The femtosecond laser-assisted computerized procedure ensures that all of the spots are focalized at the same definite deepness, resulting in a precise thickness on the overall surface of the flap. Talamo et al11 found that mean achieved flap thickness was more reproducible with the IntraLase laser, reducing the comparative risk of overly thick flaps.
DEFINITIVE SOLUTION
If flap-related problems are the weak point of LASIK, then the femtosecond laser may represent the definitive solution! We will be able to take full advantage of the technique; IntraLase (IntraLase Corp., Irvine, California) (Figure 1) is the most sophisticated and advanced technology for flap creation available today.
While traditional microkeratomes create meniscus-shaped flaps (ie, thicker in the periphery and thinner in the center), the consistent thickness on the overall extension of femtosecond laser flaps does not require corneal curvature or pachymetry. No buttonholes or free caps have been reported.12 Moreover, the versatility of femtosecond systems allow the surgeon to precisely plan the hinge position, flap diameter, thickness, and centering over the cornea. It permits different flap thicknesses—thinner than mechanical ones (ie, from 90 µm to 120 µm)—saving more tissue for the ablation. Therefore, higher refractive errors may be treated, even in thinner corneas. Femtosecond technology allows the surgeon to tailor the corneal flap for each individual eye.10 The resultant flap comes out as planned, with little deviation from the target.
PERSONAL EXPERIENCE
We performed a study to evaluate the accuracy and predictability of corneal flap thickness with a femtosecond laser. Thirty-five eyes (23 patients; mean age, 38.2 ±2.6 years) with a refractive error in spherical equivalent ranging from 3.50 D to -8.25 D underwent LASIK. We used the IntraLase femtosecond laser to perform a 120-mm thick and 9-mm wide corneal flap. For each eye, an intraoperative differential pachymetry measurement with contact ultrasound pachymetry (Pachmate; DGH Technology, Inc., Exton, Pennsylvania) was performed before and after flap lift. Optical pachymetry measurements with Confoscan 4 (Nidek Inc., Gamagori, Japan) were taken 30 days postoperatively.
We compared data from ultrasound and optical pachymetry readings. The difference between the attempted and the real pachymetric values of the flap performed with the IntraLase femtosecond laser were irrelevant. No significant variability between the intraoperative ultrasound pachymetry values and the postoperative optical values was found (117.51 ± 5.76 SD vs 118.25 ±8.9 SD) (Figure 2). No significant differences related to refractive defect were found.
Because intraoperative and follow-up measurements were comparable, the safety and predictability of IntraLase for LASIK corneal flaps was proved.
There are many reasons to chose a femtosecond laser when conducting LASIK procedures. Below is a list of our top reasons:
• Intra-LASIK provides patients with an extra margin of safety, eliminating the potential risks associated with mechanical microkeratomes.
• Intra-LASIK allows the surgeon to perform more refractive procedures, even in thin corneas that require more precise and shallow flaps, permitting the correction of higher refractive errors.
• Intra-LASIK provides more reassurance for both patient and surgeon, because there is less danger of microkeratome-related complications.
• Intra-LASIK is an all-laser procedure, significantly adding to its precision and predictability.
• Intra-LASIK creates the best-fitting flap. Once back in place, the flap forms a tight seal, making flap dislocation difficult.
• The Intra-LASIK procedure is painless and more comfortable; less pressure is placed on the eye with the femtosecond laser compared with the microkeratome.
LIMITATIONS
The femtosecond laser also has limitations. There is a longer surgical time, but this is a small price to pay for the safety and predictability offered by the laser device. The higher costs of all-laser procedures should be taken into consideration as well. Lastly, transient light sensitivity syndrome is seen in some patients between 3 weeks and 6 weeks after surgery.10
In conclusion, the femtosecond laser ensures safety, precision, and good visual results during LASIK. This technology is definitely contributing to a new standard of care in refractive surgery, and it is increasing the number of LASIK candidates in future years who could not undergo the standard mechanical procedure.
Emilio Balestrazzi, MD, is Professor of Ophthalmology, Head of Eye Clinic, at the A. Gemelli Polyclinic, Eye Clinic, Catholic University of Sacro Cuore of Rome. Dr. Balestrazzi states that he has no financial interest in the products or companies mentioned. He may be reached at +39 0630156008; emilio.balestrazzi@rm.unicatt.it.
Romina Fasciani, MD, is a postdoctoral fellow at the A. Gemelli Polyclinic, Eye Clinic, Catholic University of Sacro Cuore of Rome. Dr. Fasciani states that she has no financial interest in the products or companies mentioned. She may be reached at +39 0630156008; romina.fasciani@tiscali.it.
Luca Mosca, MD, is an observer at the A. Gemelli Polyclinic, Eye Clinic, Catholic University of Sacro Cuore of Rome. Dr. Mosca states that he has no financial interest in the products or companies mentioned. He may be reached at +39 0630156008; lucazanzis@yahoo.it.
Luigi Mosca, MD, is Chief of Cornea and Refractive Surgery Service, at the A. Gemelli Polyclinic, Eye Clinic, Catholic University of Sacro Cuore of Rome. Dr. Mosca states that he has no financial interest in the products or companies mentioned. He may be reached at +39 0630156008; l.mosca@tin.it.
Up Front | Apr 2007
Is the Femtosecond Laser the Key to LASIK?s Future?
Safety and precision of the femtosecond laser contribute to a new standard of care in refractive surgery.
Emilio Balestrazzi, MD; Luigi Mosca, MD; Romina Fasciani, MD; and Luca Mosca, MD
