We noticed you’re blocking ads

Thanks for visiting CRSTG | Europe Edition. Our advertisers are important supporters of this site, and content cannot be accessed if ad-blocking software is activated.

In order to avoid adverse performance issues with this site, please white list https://crstodayeurope.com in your ad blocker then refresh this page.

Need help? Click here for instructions.

Refractive Surgery | Jul 2012

The Next Generation of LASIK Flaps

Several studies over recent years have confirmed what the experiences of many refractive surgeons have suggested: that femtosecond lasers have become valuable flap-creation tools in LASIK.1 Flaps made with a femtosecond laser are more precise, more regular, and thinner, and complications related to the cut are less common compared with flaps made with a microkeratome.2

Today, femtosecond lasers are multipurpose surgical devices, used not only for LASIK flap creation but also for creating intrastromal corneal tunnels or pockets and corneal relaxing incisions; for different types of keratoplasty; and for intrastromal presbyopia-correction approaches. In the recent past, they have been applied to the correction of refractive errors using intrastromal lamellar cuts without application of the excimer laser and even in cataract surgery, for performing capsulotomy, lens fragmentation, and corneal incisions.

Problems with femtosecond lasers, such as increased risk of damaging the optic nerve due to increased duration of suction and applanation of the cornea, have been reported.3 However, the extent of such problems differs from device to device, and their clinical relevance has not yet been shown. More practical problems include the price, size, and mobility of the systems. Femtosecond lasers also require specific environmental conditions and cooling systems. Compared with mechanical microkeratomes, femtosecond laser devices are expensive and large, and most of them are not mobile. Additionally, it is said that cuts with femtosecond lasers are not as smooth as those of microkeratomes;4 however, it is unclear why less smooth lamellar cuts would be a problem. At any rate, the differences between modern femtosecond lasers and mechanical microkeratomes appear to be decreasing.

NANOSECOND LASER TECHNOLOGY

The SmartTech Laser (Schwind eye-tech-solutions; Figure 1) could further change the way laser flaps are created. Like a femtosecond laser, the SmartTech Laser applies laser-induced low-density plasma to achieve separation of corneal tissue (Figure 2). However, instead of using complex femtosecond laser technology, it uses an innovative microchip laser. Short wavelengths in the ultraviolet range (355 nm) and an aberration-free optical system ensure the precision of the SmartTech laser. Its focal spot size is one-third that of standard femtosecond lasers.

The low-density plasma combined with the short wavelength ensures significantly finer structures (Figure 3), leading to more precise cuts, smoother cut surfaces and increased safety in LASIK flap creation. The SmartTech’s microchip laser is more compact, durable, and robust than femtosecond laser platforms under usual operating conditions. It requires a normal power supply and works without elaborate cooling systems. The laser also has a pupil recognition technology that positions the flap on the planned ablation center, enhancing the reliability of treatment results. To ensure the proper fixation of the eye under the laser, an integrated interface suction system is used to applanate the cornea.

Flap creation takes approximately 15 seconds, including formation of the stromal bed and sidecuts. By means of an optimized docking process, suction time is minimal, starting after the cornea is correctly positioned. The suction is automatically released immediately after the flap is created.

The flap cut can be performed with variability of position, diameter, hinge position, thickness, and sidecut angles. In the future, the SmartTech laser will also offer therapeutic treatment modes for lamellar keratoplasty, intrastromal corneal ring segments, corneal inlays, and astigmatic keratotomy.

EARLY RESULTS

In yet-unpublished preliminary animal models, treatment of rabbit eyes has shown promising results.5 Neither histologic pathologies nor terminal dUTP nick end labeling-positive cells were found in the corneas of treated rabbits. Also, no significant inflammatory factors in the aqueous humor were observed. The predictability of the flap thickness was about ±6 μm, and the achieved flap thickness was slightly thinner than the intended flap thickness, showing high correlation for various flap thicknesses. Linearity of planned versus achieved flap thickness was shown within 80 to 450 μm.

The SmartTech laser system will be evaluated soon in human clinical trials.

CONCLUSION

The SmartTech nanosecond laser with 150-kHz pulse frequency is a promising approach to further increasing LASIK flap precision without interfering with surgeons' LASIK workflow with the femtosecond laser. Results of cuts in animal corneas are promising, and the first clinical studies in human patients will be performed soon. The results of these studies will demonstrate the feasibility of nanosecond laser technology for LASIK flap creation.

Oliver K. Klaproth, Dipl Ing(FH), is the Trial Centre Manager at the Department of Ophthalmology, GoetheUniversity Frankfurt, Germany. Mr. Klaproth states that he has received travel reimbursement from Schwind eye-techsolutions. He may be reached at e-mail: o.klaproth@med. uni-frankfurt.de.

Thomas Kohnen, MD, PhD, FEBO, is Professor and Chairman of the Department of Ophthalmology at Goethe-University, Frankfurt, Germany. Professor Kohnen is a member of the CRST Europe Editorial Board. He states that he is a consultant to Schwind eye-techsolutions and he has received research grants, lecture honoraria, and travel reimbursement from the company. He may be reached at tel: +49 69 6301 3945; e-mail: kohnen@em.uni-frankfurt.de

  1. Salomao MQ ,Wilson SE. Femtosecond laser in laser in situ keratomileusis. J Cataract Refract Surg. 2010;36(6):1024-1032.
  2. Kohnen T, Klaproth OK, Derhartunian V, Kook D. Results of 308 consecutive femtosecond laser cuts for LASIK [in German]. Ophthalmologe. 2010;107(5):439-445.
  3. Chen S, Feng Y, Stojanovic A, Jankov MR 2nd ,Wang Q. IntraLase femtosecond laser vs mechanical microkeratomes in LASIK for myopia: a systematic review and meta-analysis. J Refract Surg. 2012;28(1):15-24.
  4. Heichel J, Hammer T, Sietmann R, Duncker GI ,Wilhelm F. Scanning electron microscopic characteristics of lamellar keratotomies using the Femtec femtosecond laser and the Zyoptix XP microkeratome. A comparison of quality [in German]. Ophthalmologe. 2009;107(4):333-340.
  5. Reitsamer H. Effect of corneal surgery with a novel nanosecond laser on various ocular tissues in rabbits. Paper presented at: the European Society of Cataract and Refractive Surgeons; September 18, 2011; Vienna.

NEXT IN THIS ISSUE