**6. Phacodynamics**

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

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

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

be difficult for a right-handed surgeon who sits at the 12 o'clock position.

loss of endothelial cells [31].

188 Advances in Eye Surgery

**5.1. Overview of the technique**

Modern phacoemulsification machines generate the required vacuum and aspiration based on one of three pumping systems:


In this type of pump, the fluid is displaced through flexible tubing using a series of rollers on a rotating wheel. As the wheel rotates, the rollers move the fluid trapped between them, which result in more fluid being drawn into the tubing in the direction of rotation (Figure 1). The flow rate is directly proportional to the speed of the rotary mechanism. At low speeds of rotation a vacuum is not produced unless the tip is occluded. As the speed of rotation is increased, a vacuum is produced in the aspiration line without occlusion. A desired flow rate and vacuum is determined by the surgeon.

**2.** Venturi pump

There is no moving part in this pump. This type of pump works on Bernoulli's principle. When the speed of flow of a fluid is increased in one part, the pressure in that part is decreased. Compressed gas, such as air or nitrogen, flowing through a pipe (Figure 2) reduces the pressure in the next region and creates a partial vacuum within the rigid drainage cassette.

**3.** Diaphragm pump

In this type of pump, a flexible metal or rubber diaphragm moves up and down. This move‐ ment, along with the vertical motion of two valves, maintains the vacuum (Figure 3). Clinically, this type of pump is similar to the Venturi pump.

**Figure 1.** Peristaltic pump

**Figure 2.** Venturi pump

**Figure 3.** Diaphragm pump

The peristaltic pump has a slower rise time unlike the Venturi and diaphragm pumps that have rapid flow rates and rise times. Rise time measures how rapidly a vacuum builds up once occlusion has occured at the aspiration tip. Flow rate measures the amount of fluid passing through the tubing (cc/min) and indicates how quickly events will progress once the aspiration tip is either suddenly occluded or suddenly cleared. Venturi and diaphragm pumps have higher flow rates and therefore they build up vacuums in the aspirate line without occlusion of the aspiration tip. Once the tip is occluded, a vacuum builds up rapidly [2, 36-38].


**Table 1.** Differences between pumps, as reported by Devgan [38].
