*3.10.1. Descemet's stripping endothelial keratoplasty (DSEK)*

DSEK has been the preferred approach for treating corneal endothelial diseases, such as bullous keratopathy, Fuchs dystrophy, congenital hereditary endothelial dystrophy, and endothelium failure in previous penetrating keratoplasty. It removes the diseased endotheli‐ um and leaves the posterior cornea intact. However, technical challenges always afflict corneal surgeons. The application of the femtosecond laser alleviates certain difficulties. Significant advantages over manual dissection are that the femtosecond laser allows for increased automation and standardization in donor tissue preparation. In addition, lamellar interface preparation can be performed up to 3 weeks before the surgery, making it feasible for conversion to PKP owing to complications during preparation of the donor disk. It also creates a smoother donor-recipient interface to minimize induced refractive astigmatism. However, whether the femtosecond laser has an effect on endothelial cell loss and visual acuity after donor tissue preparation has yet to be determined [18, 30].

#### *3.10.2. Descemet's membrane endothelial keratoplasty (DMEK)*

Descemet's membrane endothelial keratoplasty (DMEK) has been proven to result in faster visual recovery, fewer higher order aberrations, and lower rejection rates by abundant evidence. The crucial technique is selective endothelial transplantation. The femtosecond laser offers a precise and predictable means to create the uniform thickness of the posterior stromal rim and control big bubble expansion that cannot be achieved by manual operation. The femtosecond laser not only avoids energy-associated damage but also results in smooth stromal interface by closer spots, line separations, and a low energy level. Thus, the femtosec‐ ond laser can be a novel approach for the donor grafts preparation of DMEK, which may reduce intraoperative graft manipulation and postoperative detachments [29, 31].

#### **3.11. Cataract surgery**

incisions within the graft button present precise geometry and reliable depth of incision. Specific complications associated with femtosecond laser-assisted AK such as self-healing micro-corneal perforations and low-grade inflammation at the incision site appeared [18, 29].

Intracorneal ring segments were small and curved when first proposed in 1978. Clear ring segments made of polymethylmethacrylate are implanted in the deep corneal stroma with the aim of generating modifications of corneal curvature and refractive changes. Peripheral intracorneal implantation has been permitted to correct low to moderate astigmatism and myopia and keratoconus by Food and Drug Administration (FDA). Complications such as incomplete tunnel formation, corneal perforation, endothelial perforation, corneal melting, and uneven implant placement may occur with the traditional technique. The femtosecond laser can be programmed to create corneal channels at a specific depth and orientation with high predictability and precision to allow safer insertion of Intacs segments. In patients with keratoconus, the femtosecond laser can be programmed to cut tunnels for the implantation of intracorneal ring segments, and it results in better safety owing to greater consistency of depth

Penetrating keratoplasty (PKP) developed rapidly after first being introduced in the early 1900s. The surgical outcomes rely on a centered and perpendicular cut of cornea, a wellmatched donor button, and a recipient bed [18]. Manual PKP requires a long learning curve and a lengthy procedure time, which can be optimize using the femtosecond laser. The femtosecond laser can also achieve a higher precision in surgical steps, such as the donor cornea cutting. Moreover, the choice of shapes and diameters in femtosecond laser-assisted PKP is dependent on individualized clinical requirement. It enables advanced shaped corneal cuts creation, eliminates manual dissection, thus minimizing misalignments, and increases the stability of the wound. Some pattern of incisions that are not compassable with conventional technique can be achieved by femtosecond laser. However, postoperative regular and irregular

Anterior lamellar keratoplasty (ALK) is a partial thickness corneal transplantation indicated for management of anterior corneal dystrophies degenerations, ulcers, and scars. The advantages of ALK over PKP include being less invasive and having a decreased rate of rejection. Femtosecond laser-assisted suture less anterior lamellar keratoplasty (FALK), first described in 2008, has been reported to be safe, effective, and stable. The femtosecond laser has reduced irregular astigmatism and accelerated visual recovery by its precision of pre‐ programmed corneal dissections at a variety of depths and orientations. As the corneal incision is well shaped, it can be converted to full-thickness keratoplasty in case of Descemet mem‐ brane perforation. The donor and recipient tissue are better positioned because of highly precise cuts assisted by the femtosecond laser, and thus sutures are typically removed earlier.

astigmatism remain a major challenge in full-thickness keratoplasty.

**3.7. Intracorneal ring segments**

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and uniformity [29, 30].

**3.8. Penetrating keratoplasty (PKP)**

**3.9. Anterior lamellar keratoplasty (ALK)**

At 2008, the femtosecond laser was first performed in Europe in cataract surgery and was approved by the FDA in 2010. It was applied in the steps of corneal incision, arcuate corneal incisions, capsulorhexis, lens fragmentation, and liquefaction. The short pulses duration (10−15 s) make it a promising tool in cataract surgery [32].

#### *3.11.1. Corneal incisions*

Clear self-sealing corneal incision is of most importance in cataract surgery. In terms of length and tunnel structure, manual incision is difficult to control. In addition, bacteria have a chance to enter at low intraocular pressure because of the instability of manual incision and thus lead to endophthalmitis. Compared with manual incisions, corneal incisions made using the

femtosecond laser are more precise in width, depth, and length. More consistency in the architecture is also achieved, which leads to better incision sealing without stromal hydra‐ tion at the end of the surgery. The stability of the wound makes it more resistant to deforma‐ tion and leakage. The femtosecond laser is used to create a clear corneal incision according to pre-programming, which requires a large amount of patient data to confirm, and definitive results. In cases of corneal astigmatism, an arcuate or a relaxing incision can be created, which has been reported to provide more stable and accurate long-term outcomes compared with toric intraocular lenses (IOLs). The femtosecond laser shows less damage by virtue of its construction and reduced mechanical stress during surgery, which may decrease corneal swelling after surgery.

#### *3.11.2. Capsulotomy*

A precise size and centration capsulorhexis are essential to optimize the IOL position. The IOL's longitudinal displacement per millimeter will lead to approximately 1.25-D refractive change, inducing myopia for an anterior shift and hyperopia for a posterior displacement. Capsulorhexis size is correlated with effective lens position. An insufficient overlap of the IOL, results in decentration, oblique astigmatism, and increased higher order aberration. A small capsulorhexis has been associated with anterior capsule fibrosis. Manual continuous curvi‐ linear capsulorhexis (CCC) relies on the technique and proficiency of the surgeon. The femtosecond laser can be used to create a more precise, better-sized, and centered opening of the anterior capsule compared with the conventional CCC by dissecting it with a spiral laser pattern. Compared with the manual CCC group, the laser CCC group showed more accura‐ cy and stability in anteroposterior and central IOL positioning. It is also more predictable in the refractive outcome, which is more important to patients with high expectation [33, 34].

#### *3.11.3. Lens fragmentation and liquefaction*

The increased energy for lens fragmentation and liquefaction delivered from the phacoemul‐ sification probe to the eye can result in energy-associated capsule complications and corneal endothelial cell injury in manual phacoemulsification. The reduction in ultrasound energy can decrease the risk of such complications. It is reported that the femtosecond laser reduced the ultrasonic energy delivered during phacoemulsification significantly. However, its effect on endothelial damage is still unknown.

#### *3.11.4. Limitation and complications*

Although the femtosecond laser showed excellent advantages over manual operation in cataract surgery, there are still some inevitable limitations and complications.

**1.** Additional operating room shifting time

Patients need to be shifted under the operating microscope after application of laser treatment. This logistical issue results in increased time spent with each patient, which could lead to overall delay.

### **2.** Applicability

femtosecond laser are more precise in width, depth, and length. More consistency in the architecture is also achieved, which leads to better incision sealing without stromal hydra‐ tion at the end of the surgery. The stability of the wound makes it more resistant to deforma‐ tion and leakage. The femtosecond laser is used to create a clear corneal incision according to pre-programming, which requires a large amount of patient data to confirm, and definitive results. In cases of corneal astigmatism, an arcuate or a relaxing incision can be created, which has been reported to provide more stable and accurate long-term outcomes compared with toric intraocular lenses (IOLs). The femtosecond laser shows less damage by virtue of its construction and reduced mechanical stress during surgery, which may decrease corneal

A precise size and centration capsulorhexis are essential to optimize the IOL position. The IOL's longitudinal displacement per millimeter will lead to approximately 1.25-D refractive change, inducing myopia for an anterior shift and hyperopia for a posterior displacement. Capsulorhexis size is correlated with effective lens position. An insufficient overlap of the IOL, results in decentration, oblique astigmatism, and increased higher order aberration. A small capsulorhexis has been associated with anterior capsule fibrosis. Manual continuous curvi‐ linear capsulorhexis (CCC) relies on the technique and proficiency of the surgeon. The femtosecond laser can be used to create a more precise, better-sized, and centered opening of the anterior capsule compared with the conventional CCC by dissecting it with a spiral laser pattern. Compared with the manual CCC group, the laser CCC group showed more accura‐ cy and stability in anteroposterior and central IOL positioning. It is also more predictable in the refractive outcome, which is more important to patients with high expectation [33, 34].

The increased energy for lens fragmentation and liquefaction delivered from the phacoemul‐ sification probe to the eye can result in energy-associated capsule complications and corneal endothelial cell injury in manual phacoemulsification. The reduction in ultrasound energy can decrease the risk of such complications. It is reported that the femtosecond laser reduced the ultrasonic energy delivered during phacoemulsification significantly. However, its effect on

Although the femtosecond laser showed excellent advantages over manual operation in

Patients need to be shifted under the operating microscope after application of laser treatment. This logistical issue results in increased time spent with each patient, which

cataract surgery, there are still some inevitable limitations and complications.

swelling after surgery.

386 388High Energy and Short Pulse Lasers

*3.11.3. Lens fragmentation and liquefaction*

endothelial damage is still unknown.

**1.** Additional operating room shifting time

*3.11.4. Limitation and complications*

could lead to overall delay.

*3.11.2. Capsulotomy*

The femtosecond laser relies on good anterior chamber imaging. Patients with poor eyelid opening, nystagmus, poor pupillary dilatation, corneal opacities, and ocular surface disease are poor candidates. It is also not suitable for patients with tremors or dementia in the initial docking system. The femtosecond laser is not available for grade 4 cataract according to the Lens Opacities Classification System III (LOCS III).

**3.** Complications

Capsular blockage syndrome: Large diameter hydrodissection cannula with high-speed fluid may inhibit a gas bubble that is formed from leaving the nucleus. Pressure eleva‐ tion between the capsule leads to the rupture of the posterior capsule, and the lens may drop into the vitreous cavity. This is a learning curve-related complication, which can be avoided by a more cautious and skilled surgeon

Pupillary constriction: Bubble formation and suction force can trigger pupillary constric‐ tion by releasing small amounts of free radicals. In addition, a delay between femtolaser pretreatment and cataract surgery may result in pupil diameter changes (5–10 min is recommended).

Corneal incision sizing and positioning the initial docking of the laser ring is crucial to the accuracy of the intended femtolaser-created incision. Imperfect interface positioning causes inaccuracy of corneal incision sizing and positioning, which results in surgically induced astigmatism and complication in the manual final procedure [18, 35].
