**8.2 Keratoplasty (penetrating, femtosecond laser-assisted, anterior and posterior lamellar keratoplasty)**

Penetrating keratoplasty (PKP) has evolved substantially over the years, and various alternative surgical procedures have been introduced to improve patients' outcomes. The introduction of FS laser into PKP (full-thickness keratoplasty) has improved postoperative outcomes in different keratoplasty procedures, owing to the reduced misalignment, higher precision, and wound stability. Tension-free incisions and waterproof-adapting incision margins can be achieved with the use of a perfect trephination device [17]. Trephination systems include hand-held, motorized, excimer-laser, and fs-laser. Graft alignment is better with motortrephine and excimer-based trephination [18]. Treatment of the eye that receives trephination frequently lacks appropriate centering. Another challenge with trephination is how the recipient eye and donor button are fixed and stabilized; any mechanical stress on the tissue produces compression and distortion, reducing recipient and donor fit. Vacuum and applanation are common fixing methods (vacuum suction with applanation). fs- and excimer-assisted trephination demonstrated superior alignment in all sutures-out keratoplasty patients in the excimer group. Patterned trephination increases the strength and structural integrity of the graft-host junction and reduces the number of requisite sutures, which results in reduced astigmatism, and possibly the time of visual recovery. FS laser has also improved the shaped corneal cuts with various patterns and angles of incisions, as well as different wound configurations, such as "top-hat", "mushroom", "zigzag" and "Christmas tree", which improve wound healing and result in improved best spectacle-corrected visual acuity.

When only specific layers of the five corneal layers (such as anterior or posterior layers of the cornea), lamellar keratoplasty is performed, which has several modifications [19]. In deep anterior lamellar keratoplasty (DALK), the use of FS allows for precise trephination cuts for separation of corneal layers with desired depths, diameters, centration, shape, and size [20], which facilitates big bubble formation, which has several advantages over manual technique in terms of accelerated wound healing/stability (owing to the different side-cut profiles), precise sutureless cuts of both donor and recipient cornea (increased alignment), and preservation of healthy recipient corneal endothelium [21]. Also, conversion into full-thickness keratoplasty is feasible with FS-assisted lamellar keratoplasty. New big bubble formation approaches, such as the IntraBubble technique, creates a channel in the posterior stromal for the introduction of air injection, which results in cleavage of the corneal tissue. FSL has also been introduced into endothelial lamellar keratoplasty techniques such as deep lamellar endothelial keratoplasty (DLEK) and Descemet's stripping automated endothelial keratoplasty (DSAEK). Posterior trephination cut prevents the intrastromal cavitation bubbles in the lamellar interface with a shorter applanation lens assembly used to create LASIK flaps. However, the effectiveness of FSL in DSAEK requires further studies on the eye banks, as scanning electron microscopic studies have shown occasional mild stucco-like texture of the lamellar surface caused by laser scatter and attenuation in deep stroma. Additionally, poorer visual outcomes are anticipated during the laser procedure, owing to the increased roughness at the deep intrastromal dissection surface and irregularities of the endothelial surface [4, 5, 14, 15].

*Fundamentals of Femtosecond Laser and Its Application in Ophthalmology DOI: http://dx.doi.org/10.5772/intechopen.106701*

### **8.3 Cataract surgery**

In cataract surgery, the current FS systems allow imaging and measurement of the anterior segment of the eye, cutting the tissue at the desired location depth, pattern, and size, full-thickness corneal incisions for the introduction of instruments to the eye, partial thickness corneal incisions for treatment of corneal astigmatism, circular incision to the anterior lens capsule (capsulotomy), and fragmentation of the cataractous lens nucleus (**Figure 11**). Advantages of FSL-assisted cataract surgery include precision and repeatability of incisions, lower ultrasound energy used for lens nucleus emulsification/liquefication), perfect sizing, and predictability of corneal incisions and capsulotomy (**Figure 12**). Despite the numerous studies suggesting the superiority of different FSLs used for cataract surgery (**Table 1**) over the conventional phacoemulsification manual operation and emphasis of review studies on the advantages of FSL method, meta-analysis studies failed to prove its superiority considering the overall outcome of patients. The introduction of low-energy lasers may have improved outcomes compared with first-generation FSL [5, 14].

Despite the above-mentioned clear benefits and multiple studies indicating superiority of femto laser cataract surgery in completing the single surgical stages [22, 23]. Review papers stress fs-assisted cataract surgery in specific patient groups, i.e., those with low corneal endothelial cell numbers, but a clear advantage of the fs approach over manual phacoemulsification is not found in normal cases [24, 25]. Primary posterior capsulotomy assisted by fs laser, as well lens capsule labeling, altering the power of the intraocular lens (IOL) postoperatively using more mobile, and adaptable fs-laser systems will make the future of femtosecond laser brighter (**Figure 13**) [26].

### **Figure 11.**

*History and Evolution of Femtosecond Laser Assisted Cataract Surgery (FLACS.*

### *Terahertz, Ultrafast Lasers and Their Medical and Industrial Applications*

### **Figure 12.**

*Femtosecond Laser Assisted Cataract Surgery (FLACS) vs. Micro Incision Cataract Surgery (MICS); Effects of Learning Curve.*


*Fundamentals of Femtosecond Laser and Its Application in Ophthalmology DOI: http://dx.doi.org/10.5772/intechopen.106701*


### **Table 1.**

*The commercial machines for FLACS.*

**Figure 13.** *Femtosecond Laser-Assisted Cataract Surgery (FLACS).*
