**5. Clear Corneal Incisions (CCls)**

Sutureless clear corneal incisions are the most common incisions for cataract surgery with phacoemulsification, replacing scleral tunnel and limbal incisions. There are several reasons for the popularity of clear corneal approach based on different advantages compared to scleral tunnel incisions. Some of them include reduced procedure time, lower induced astigmatism, faster visual recovery and less complications.

The aim of cataract surgery today is rapid visual rehabilitation, the best possible uncorrected visual acuity, and minimal postoperative astigmatism. The phacoemulsification procedure results in less surgically induced astigmatism than extracapsular cataract extraction, in which the incision is much larger. Clear corneal incision is the most used type of incision in phacoe‐ mulsification surgery, because it is less time-consuming and does not require cauterization or wound suturing. The location of the CCI affects the degree of postoperative astigmatism. One of the possible complications of cataract surgery is surgically induced astigmatism (SIA), which is a major cause of functional disturbance and insufficient uncorrected visual acuity. CCI is made deliberately in the steepest meridian if astigmatism is addressed. It can be made at superior, oblique or temporal locations.Temporal CCI induces regular astigmatism 90 degrees away from the incision (with-the-rule astigmatism) thus minimizing the postoperative astigmatism [13-15]. It is known to induce the least postoperative astigmatism. Also, the smaller the CCI, the lesser the induced astigmatism. Oblique scleral tunnel incision predictably reduces astigmatism by simultaneously producing corneal flattening and steepening [16].

Some studies have shown that a small superior CCI induces greater postoperative astigmatism than a small supero-oblique CCI, and a small supero-oblique CCI induces higher postoperative astigmatism than a small temporal CCI [17-19]. Some authors reported that, although temporal CCI is reported to result in the least induced astigmatism, locating the incision superotem‐ porally or superonasally may ease surgical manipulations during the phacoemulsification cataract surgery for a right-handed surgeon who works from the 12 o'clock position relative to the patient [20]. Performing the procedure from the patient's temporal side may not be possible with the most operating tables, and locating the CCI temporally in the left eye may be difficult for a right-handed surgeon who sits at the 12 o'clock position.

Several groups of authors analyzed refractive astigmatism in patients who have had phacoe‐ mulsification cataract surgery performed by the oblique clear corneal incision. They provided evidence that the supero-oblique clear corneal incision does not induce the clinically significant amount of oblique astigmatism [21-23]. Also, evidence is provided that the superotemporal or superonasal CCI has minimal effect on corneal astigmatism [23]. Many studies investigated the influence of different factors, such as the type of a surgery, length of incision and its type (curved, straight, frown), location and width of incision (central vs. peripheral-limbal or scleral), presence or absence of a suture and the suturing method, on postoperative astigma‐ tism [16, 19, 24, 25]. Any incisions that are made in the cornea have the potential to change the curvature and therefore the dioptric power of the cornea in that meridian. The location as well as the width of the incision affects the degree of postoperative astigmatism.Surgically induced astigmatism is positively correlated with incision size (larger incisions generating more astigmatism) and location (scleral or limbal incision inducing less astigmatism than clear corneal), though for small incisions the effect of location appears less critical [26, 27]. Wound construction also appears to have an effect, with square incisions reported to affect astigmatism the least [28]. Despite all the advantages of clear corneal incisions, they are not without problems. Reported disadvantages include poor wound healing [29], induction of irregular astigmatism [29], the risk of wound dehiscence following trivial trauma [30], and increased loss of endothelial cells [31].

#### **5.1. Overview of the technique**

Phacoemulsification in most cases begins with a 2.2 to 3.0 mm tunnel in the peripheral corneal to enter to the anterior chamber. Reduced incision size to 2.2 mm and smaller led to several innovations in instrumentation, phacoemulsification technology, and intraocu‐ lar lens (IOL) design. Each step taken in reducing the incision size comes with mixed success but has led ultimately to measurable improvements in outcomes [32]. During intraocular surgery, the anterior chamber is stabilized with an ophthalmic viscoelastic device (OVD).Continuous curvilinear capsulorhexis is made at the anterior surface of the lens capsule, followed by hydrodissection that separates the capsule and cortex and hydrodelineation that separates the nucleus from epinucleus and cortex (in cases of medium or medium-hard nucleus). Phacoemulsification begins when the tip of a handpiece connect‐ ed to the phaco machine is placed within the anterior chamber to fracture the lens into the small pieces and to aspirate the remaining small particles. Aspiration uses pumping to remove liquid and debris generated during the surgery. Pumping creates a partial vacuum and the negative pressure forces liquid out. To maintain the anterior chamber volume, irrigation of the saline-like solution is performed at the same time. After fragmentation and aspiration, insertion of the artificial intraocular foldable lens via injector follows. Continu‐ ous longitudinal ultrasound (US) has an inherent repulsive characteristic that can induce turbulence, cause chatter, and create substantial heat along the shaft of the phaco needle. Larger bore needles allow greater fluid flow allowing better cooling and transfer of larger fragments of nuclear material. Fortunately, none of the current generation phaco units rely solely on continuous longitudinal power [32]. Micropulse phacoemulsification is a result of advancements in phacoemulsification modalities that include less power use and shorter procedure times. The operating temperature of the needle in the incision is decreased [33, 34]. The next progression provided torsional phacoemulsification (Ozil, Alcon Laborato‐ ries, Inc.) with needle temperature also reduced [35]. Transversal phacoemulsification (Ellips, Abbott Medical Optics, Inc.), the next nonlongitudinal movement, has a similar effect. Each of these power modulations has resulted in improved ultrasonic efficiency and can use smaller gauge needles to effectively emulsify nuclear material [32].
