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Future Applications for Femtosecond Lasers

European Ophthalmic Review, 2007:51-3 DOI:
Received: January 24, 2011 Accepted: January 24, 2011

Femtosecond lasers (fs-lasers) have developed rapidly, and several approved laser systems are on the market. The spectrum of applications has also expanded considerably. In corneal surgery, the precise intrastromal use of the fs-laser has opened numerous new applications and led to totally new surgical standards. The fs-laser is an infrared laser that functions with much less heat stress than other laser systems. Its use enables surgeons to separate corneal tissue precisely without a scalpel. The tissue should be largely transparent so that the laser can make precise incisions at any site on the cornea. At the clinic for refractive and ophthalmic surgery in Duisburg, Germany, we use a modern 40khz version of the Femtec fs-Laser (20/10 Perfect Vision, Heidelberg, Germany). When using the fs-lasers now available on the market, the cornea is subjected to applanation, leading to vision blackouts during treatment. The Femtec fs-laser has a patented, curved patient interface. Thanks to the curvature, only moderate suction is needed to couple the eye to the laser. The treatment itself is performed with minimal applanation and therefore without vision blackouts during the surgeries. The procedures performed are endothelium-sparing. In our opinion, there are two approaches to future applications of fs-lasers. One is to survey the present practical applications closely and further improve and develop existing surgical techniques. We will start with this approach and illustrate it with case studies. The second approach entails examining current research for which concrete scientific publications are available. However, it must be questioned to what extent the, admittedly very attractive, approaches can be applied in practice and when – if ever – this will be the case. This preview will conclude our overview.

Flap Preparation
Laser-assisted in situ keratomileusis (LASIK) flap preparation in refractive corneal surgery was the first application in which we used the fs-
laser.1 Compared with mechanical microkeratomes, using the fs-laser resulted in greater precision at the intended flap depth with considerably less standard deviation.2,3 Another advantage is the possibility of fitting the flap individually to the corresponding LASIK, i.e. the hinge position, flap diameter and thickness can be selected as required. Use of the fs-laser is especially advantageous in thin corneas. We can also make safer laser cuts in cases of greater astigmatisms since the cornea is flattened to about 35 diopter (D). The laser cut is made under complete visual control and can be terminated if necessary. The following case illustrates our procedure.After cararact surgery, the 68-year-old patient had refraction of +1.0–4.0/35º=0.63. Pachymetry measured 569μm at the thinnest place. We selected a diameter of 8.5mm with superior hinge position, a flap thickness of 140μm and an angle of 90º as parameters for flap preparation. The procedure took only 45 seconds.

The precise angle in particular facilitated repositioning the flap. One day post-operatively, vision was identical to the pre-operative value, with an astigmatism reduction to 3.5D. Four weeks post-operatively, the astigmatism was 3.25D. We observed that less tissue had to be removed in patients with greater astigmatism in a double surgery, since tension can be reduced in the cornea only by the flap preparation. As soon as the value was stable, we performed the LASIK in a second session. After LASIK, the patient had refraction of -0.25=0.80 immediately post-operatively. This value remained stable four months post-operatively. We now perform Femto- LASIK routinely in Duisburg. We consider the greater precision in flap preparation and the possibility of individualised procedures to be clear advantages. We will see further development of this application in using oval flap forms in astigmatisms in the future. In addition, as in lamellar keratoplasties (KPL), an intrastromal pouch can be created in which the intracorneal inlays can be reversibly implanted.

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