الفهرس 
PRINCIPLES OF FEMTOSECOND LASEROnly 14 pages are availabe for public view
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Abstract
FS laser technology has been discovered in the late nineties by the famous Nobel prized Egyptian scientist Prof Dr Ahmed Zwail as an advancement from pico and nanosecond lasers.
Modern corneal laser surgery for the correction of optical errors of the eye requires a precise, reliable and reproducible creation of corneal lenticels (flaps).
The FSL technology offers a lot of advancements for corneal and refractive surgeries. With the rapid development of the programs running these machines; modification of old techniques, discovering new approaches and inventing new procedures will be an applicable dream to future ophthalmology surgeons.
The FSL is an infrared laser that gives ultra fast pulses with a spot size of about 1µm, FSL uses a wavelength of 1053 nm that can pass through the outer layers of the cornea with no effect on the tissue until it reaches the pre–programmed target. With the energy and firing pattern controlled by computer, the laser is capable of cutting tissue at various depths and patterns.
The laser essentially vaporizes small volumes of tissue by photodisruption, producing plasma, shock wave, cavitation, and gas bubbles. The laser spots may be fired in a vertical pattern for trephination (side) cuts or in a spiral or raster (zigzag) pattern to achieve lamellar cuts.
FSL applications in corneal and refractive surgeries are increasing day after day, at present, corneal flap creation in LASIK surgery is the most common application. Some studies have shown equivalency between the FSL and the mechanical keratome whereas other studies have reported improved visual results.
Advantages of FSL over mechanical microkeratomes include: reduced incidence of flap complications such as buttonholes, epithelial abrasions, short flaps, and free caps (some complications has never been recorded with FSL),increased precision with more predictable flap thickness, uniform planar flap with more consistent depth throughout (rather than meniscus flap created by MK which is thinner in the center), better choice with wavefront guided treatments, stronger flap adhesion, greater surgeon choice of flap diameter and thickness, side cut angle, hinge position and length, better astigmatic neutrality, faster recovery of corneal sensation, lesser degree of spherical aberration, and some contrast sensitivity value.
There are several commercially available FSL machines; including IntraLase, Visumax, Femto LDV (Davinci) & Femtec.
Side effects and complications unique to FSL include; epithelial gas break through, opaque bubble layer, transient light sensitivity and rainbow glare. Other complications include high incidence of diffuse lamellar keratitis.
Another important application is FS assisted keratoplasty procedures, in Penetrating KP procedures the FS laser is capable of creating straight trephination cuts or complex-pattern trephination cuts for enhanced wound integrity of the graft-host junction as “top-hat”, “mushroom”, zig-zag, and the “Christmas tree” patterns. The choice of shapes and diameters in FSL PK is dependent on individualized clinical requirements. This technique provides a more stable wound with the potential for earlier suture removal resulting in more rapid refractive stability, thereby speeding visual rehabilitation. Also the FSL prepared grafts are more watertight and pressure resistant than those created with a mechanical trephine.
In the Anterior lamellar KP procedures the surgeon can select the diameter and thickness of the tissue to be resected, no sutures are needed for lamellar graft because the FSL enables the transplanted margin between the donor and recipient to fit sufficiently well. Deep anterior lamellar KP can be performed in patients with deep stromal scarring, keratoconus, and ectasia. With this technique, graft edges can be selected as vertical, mushroom, or zigzag shaped. The donor button is sutured over the residual stromal bed, which has a thickness of 70 to 100 μm thus decreasing the risk of endothelial rejection by preserving the host endothelium and avoiding the disadvantages of manual procedures including leaving variable amounts of residual stroma (exaggerating mismatch at the anterior surface of cornea).
FSL is used in correction of post KP high astigmatic errors either by arcuate keratotomy (AK) or by wedge resection. In AK; 70° arc length arcuate incisions are made at the steep corneal meridian reaching 80% depth of corneal thickness, the use of FSL avoids the serious complications of the manual techniques using diamond blade (such as perforation). While in wedge resection; a wedge of corneal tissue is excised from the flatter corneal meridian followed by suturing. Advantages of FSL include avoiding removal of different amount of tissue than intended, or perforation. In addition to simplifying the procedure.
FSL is used in tunnel creation for the insertion of ICRS, laser energy is delivered optically to a precise depth making tunnel resections and entry incisions highly reproducible and safe, minimizing the incidence of serious complications as perforation.
FS lenticular extraction (FLEx) and small-incision FS lenticule extraction (SMILE) to correct myopia are gaining attention. Four subsequent fs incisions are performed: the posterior surface of the refractive lenticule, the lenticule borders, and the anterior surface of the refractive lenticule, the latter which is extended centripetally, then the side cut is either made 270° and a flap is lifted and the lenticule is peeled (FLEx) or the side cut is 2- clock arc only and the lenticule is removed through it (SMILE)
As regards its uses in cataract, FSL is used in laser photolysis for lens rejuvenation, hereby delaying the need for cataract surgery. On the other hand, FSL assisted cataract surgery is gaining popularity where FSL technology can deliver remarkable gains in reproducibility, centration, and safety, delivering the necessary accuracy and precision to improve beyond current clinical outcomes. To date, the systems are engineered to perform four groups of incisions: capsulotomy, lens fragmentation, astigmatic relaxing incisions, and clear corneal incisions (CCIs) including the cataract incision and paracenteses.
Advantages include more control on the size of capsulotomy as well as its centration. FSLs can be used to segment the nucleus, allowing the surgeon to skip the difficult sculpting and chopping steps that most frequently lead to complications. These treatments could reduce the amount of US energy from the phacoemulsification probe, thereby diminishing the risk of capsule complications and corneal endothelial injury. The cataract laser systems can perform limbal relaxing incisions (LRIs) to correct up to 3.5 D of astigmatism, flattening the steepest meridian of the cornea, eliminating a source of refractive error with great precision as regards depth, axis, arc length, and optic zone. Lastly, laser-made corneal wounds may show less features of damage and faster healing, and show water-tightness under physiological IOP levels.
FS intreating presbyopia via AcuFocus Corneal Inlay which depends on the depth of focus in achieving near correction. Also FSL Intra Stromal Correction of Presbyopia (INTRACOR) which is a minimally invasive intrastromal correction for presbyopia via series of femto-disruptive cylindrical rings whose net effect is a central steepening of the anterior corneal surface leading to a multifocal hyperprolate corneal shape, with an ideal pupil-dependent aberration pattern.
On the other hand, FSL can be used in ‘restoring Accomodation’ via fs Lentotomy by which the lens deformation-ability is increased after laser treatment with near-IR ultrashort laser pulses via creating gliding planes inside the lens tissue while leaving the capsule unaffected.
Other application of FSL include fs-assisted diagnostic corneal biopsy (FAB) providing adequate specimen in a rapid way without complication also it can be performed by a novice. CXL in early keratoconus with riboflavin in a FSL created pocket using this rapid novel epithelial-sparing technique the patient is offered a pain-free post operative period and rapid visual rehabilitation. As well as fs-Assisted Anterior Lamellar Corneal Staining–Tattooing (FALT).