Ординатура / Офтальмология / Английские материалы / Jaypee Gold Standard mini Atlas Series Lasik_Aragawal, Jacob_2009

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Figure 2.8E

Figure 2.8F

Figures 2.8A to F: Zeimer femtosecond laser (Courtesy: Gregg Feinerman). (A) Ziemer femto LDV™ femtosecond laser (Courtesy: Gregg Feinerman); (B) The femto LDV™ handpiece brings the laser optics within two mm of the cornea. This

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significantly increases the numerical aperture. (Courtesy: Gregg Feinerman); (C) Shows the Threshold for disruption scales with pulse intensity many, many photons on the same place, at the same time. Unwanted side effects (bubbles, collateral damage) scales with pulse energy. Photon energy is converted into heat, kinetics, and chemistry; (D) Shows volume of the femtosecond laser spot scales with the numerical aperature NA = wL/f of the focusing lens. The larger the NA, the smaller the focal spot. Two ways to increase the NA are increasing the lens diameter (IntraLase®, etc.) or decreasing the focal length (Femto LDV™);

(E) Shows two different concepts in photodisruption process for higher pulse energy/lower laser frequency lasers the cutting effect is driven predominantly by mechanical forces of the expanding cavitation bubble (Figure D(a)). Conversely, MHz laser frequencies (high frequency) can offer many more pulses that are needed for cutting using lower pulse energies and larger numerical aperture (Figure D (b)). Consequently, the size of the cut is defined solely by the focal spot size, not the expanding bubble; (F) Smooth stromal bed created with Femto LDV™

Ziemer’s Femto LDV™ (Port, Switzerland) is the newest femtosecond laser (Figure 2.8A) for creating the corneal flap and it has several unique features. The Femto LDV™ laser is a compact and mobile femtosecond surgical laser. It provides a powerful and versatile platform for a wide spectrum of applications in corneal surgery. The Femto LDV™ laser incorporates all the developments in femtosecond technology over the past decade. Of

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Short pulse duration, fast repetition rate and more accurately focused power are key attributes that allow Ziemer’s Femto LDV™ to achieve tissue disruption at an energy level in the low nanojoule range, a level far lower than other currently available femtosecond lasers that operate in the microjoule range, such as the IntraLase® FS, Ziess or 20/10 lasers. Lasers such as IntraLase® work by amplifying infrared light to achieve the desired tissue disruption effect. Instead, Ziemer’s Femto LDV™ delivers tightly spaced, smaller spots of shorter duration at a much faster rate. The spots are less than 2 µm; pulse duration is 200-300 femtoseconds; and the repetition rate is faster than 1 megahertz.

Since the laser spots overlap, they result in complete dissection of the stromal bed. The resulting corneal stromal bed is smoother and the flap can be easily lifted with forceps alone.

Ziemer’s Femto LDV™ unique technological characteristics allow surgeons to create large, cleanly dissected, easily lifted flaps with a smooth treatment surface. Additionally, the laser’s small footprint and portability make it space and cost efficient. It is possible for the laser to be placed in a relatively small laser operating room alongside the excimer laser. Thus, patients can have

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Figure 2.9A

Figure 2.9B

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Figure 2.9C

Figure 2.9D

Figures 2.9A to D: SBK (sub-Bowman keratomileusis): Thin flap LASIK (technique and enhancement procedure) (Courtesy: Roberto Pinelli). (A) Thin flap LASIK SBK; (B) Thicker flap; (C) Gebauer SL_PR_03 and (D) Single-use LASIK set

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SBK (Sub-Bowman keratomileusis) is a safe technique to correct all visual defects in patients with pachymetry > 500 microns. It combines the advantages of surface and lamellar procedures, minimal debilitation of corneal biomechanical architecture with the rapid and comfortable visual recovery of lamellar approaches. This technique consists in a natural use of the keratomileusis or LASIK which is spreading even more among the most advance institutes of surgery of vision all over the world.In the past an important problem such as the corneal ectasia was caused especially by the impossibility to catch the flap (which many times was thicker than planned). Today the development of sophisticated microkeratomes and the use of the femtoseconds laser allow the surgeons to establish a specific thickness and uniformity of the cornea.

The SBK (Sub-Bowman keratomileusis) is a technique which is becoming even more popular and consists of the creation of a thin flap (from 80 to 100 microns). The LASIK technique of the last 15 years has been using thicker flaps, up to 160 microns. Recently the sub-Bowman keratomileusis has replaced the LASIK at our institute in all cases. A flap between 80 and 100 microns at least has many advantages.

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difficult than the lifting of a thicker flap. This is the only characteristic a little more complicated and which requires an advanced trial of the surgeon. In fact, the thin flap is more difficult to handle during the lifting phase and whether it is not manipulated in a soft way, it could be the cause of striae. Then, the enhancement techniques that we use at our institute consist of the flap lifting paying the due attention. In those rare cases (2%) of our treatments in which the flap did not lift, as it was integrated with the stroma, an ASA (Advanced Surface Ablation) was performed as post-SBK retreatment. Our instrument for the SBK retreatment is the Pinelli Retreatment Spatula (by Janach, Italy).

Finally, the sub-Bowman keratomileusis is a brilliant innovative technique, that we prefer rather than Epi-LASIK because it allows a fast recovery, no pain and a high level of satisfaction of the patient.

The epithelial ingrowth is a rare event yet possible after the enhancement with SBK. We have the 2% of retreatment cases and it reveals itself between 3 and 6 months after the operation. In this specific case we can lift the flap once again, clean the epithelium very softly with a spatula, replace the flap and, finally, prescribe steroid drops for one week.