Fig. 7.71 Avoid the subcapsular fibrosis making the rhexis more peripheral

use a MicroUtrata tip (MicroSurgical Technology – MST) to create a central tear (Fig. 7.70b) and start the rhexis in slow manner avoiding any zonular tension.

If there is some fibrosis underneath the anterior capsule, it is recommended to go more peripheral to this fibrosis and avoid passing through it (Fig. 7.71).

If it is impossible to avoid it, care must be taken to avoid force that can direct the tear towards the periphery. In some cases, the fibrosis covers almost the whole anterior capsule preventing a normal rhexis with the Microutrata. For this purpose, Microscissors (MicroSurgical Technology – MST) can be used to cut the fibrosis and continue the rhexis. However, there are some cataracts with severe fibrosis and the whole rhexis needs to be performed with microscissors (MicroSurgical Technology – MST) using both incisions (main and sideport) to achieve a complete continuous Capsulorhexis (Fig. 7.72a, b).

When the surgeon starts the capsulorrhexis, he should always lift it up and fold it over to have control of the tear. Grasp the flap as many times as needed. The size of the rhexis is very important in these cases. Even if it is recommended to create a 5.5–6.0 mm capsulorrhexis to avoid posterior capsule opacification in order to prevent the contact of both the capsules with the anterior capsule over the optic zone of the IOL, a larger rhexis is needed. This facilitates the removal of the pieces of the nucleus that are very large, rigid and adherent to the bag. It also prevents any zonular traction, tension and forces against the zonular fibers, thereby avoiding zonular dialysis.

b

Fig. 7.72 (a) Rhexis with Microscissors because the severe fibrosis of the anterior capsule, using the main incision. (b) Rhexis with Microscissors because they severe fibrosis of the anterior capsule, using the side port incision

7.3.6Hydrodissection

This is another surgical step that is very important, especially in these kinds of cataracts. One has to be certain that the nucleus is free from adherences to the bag, mainly from the equator and also from the posterior capsule plaque.

Unlike the coaxial Phaco, in biaxial phaco, the incision is very small and tight. To prevent any sudden rise of the IOP that can cause backward distension of the zonula, before injecting BSS into the bag, some of the Viscoelastic must be extracted from the anterior chamber. Always use a blunt cannula. Begin with an anhydric dissection, which means that the anterior capsule in its edge is lifted, separating the anterior surface of the nucleus from the posterior surface of the anterior

capsule. In hard cataracts with reabsorbed cortex, where the space between the two is very tight, this technique helps to create some space that allows the surgeon to introduce the cannula and the fluid. In intumescent cataracts, the surgeon aspirates the cortex, most of the time, the nucleus is already loose and it is not necessary to perform hydrodissection.

A stream of BSS is injected in a controlled and continuous fashion. Since it is impossible to see the wave underneath the nucleus, the surgeon needs to be aware of the time when the nucleus moves up and forward against the edges of the rhexis, and at that precise moment stop injecting BSS. The nucleus is pushed away 180° from the injection site to avoid bag distension that can cause rupture of the posterior capsule and nucleus drop by blocking the egress of BSS (capsular block syndrome). The nucleus is also pushed back to allow the fluid, retained underneath the hard cataract, to escape thereby releasing the nucleus from its adherences, to the equator and facilitating its rotation.

The surgeon has to be sure that the nucleus is free of all its attachments to the capsule by rotating it carefully bimanually with two hooks (Sinskey, Lester or Kuglen) with viscoelastic or with a curved blunt cannula, irrigating continuously to avoid zonular stress, because in most of the cases of hard cataracts, its zonules are weak.

7.3.7 Phacoemulsification

When performing Biaxial or MicroBiaxial microincision Phacoemulsification surgery, knowledge and management of fluidics are crucial [1, 2, 6, 7]. The issue of an unstable anterior chamber during the procedure, mentioned by several authors [8, 9], like Tsuneoka et al. [10], is basically due to the fact that more fluid is going out of the eye than the amount that is entering into the anterior chamber in a given moment. Although smaller-incision surgery provides a more tightly closed and stable anterior chamber, the equilibrium between inflow and outflow is still critical. This has been one of the biggest problems for surgeons learning Biaxial or MicroBiaxial Phaco, since the rate of irrigation in this technique is usually less than in standard Coaxial Phacoemulsification (Table 7.2).

The factors that influence the fluid balance in Biaxial or MicroBiaxial microincision Phacoemulsification are the following:

Table 7.2 Comparative Inflow between coaxial and most of the irrigating choppers in the Market

Table 7.3 Relative flow depends on the phaco needle diameter

based on Poiseuille’s law (courtesy Uday Devgan, M.D.)

Relative Flow vs. Phaco Needle Diameter

•The infusion rate of the irrigating instruments: This is determined by the fluidic resistance of the irrigat-

ing line and the instruments (determined by the inner diameter of tubing and instruments – chopper

– and the irrigating port size) and the pressure of the fluid (bottle height or amount of positive pressure applied to the bottle by any active system).

The flow of the fluid may be calculated using the Poiseuille’s equation (Table 7.3):

F = DP . pr4 / 8hL,

where F: flow; DP: pressure gradient; p: 3.1416; r4: radius of the tube at fourth power; h: viscosity of fluid; L: length of the tube. So inflow is directly proportional to the radius of the tube or instrument’s hollow shaft and the pressure gradient of the fluid (determined by gravity according to bottle height, or the amount of positive pressure applied to the bottle by any active

system), and inversely proportional to the length of the tube and the viscosity of the fluid. In clinical settings, usually the first two factors may be modified easily. The last two usually, are rather constant.

•The amount of leakage through the incisions: This is determined by the relation between the outer diameter of the instruments (Phaco needle and irrigating chopper) and the incisions’ architecture (shape, size and presence of an inner valve).

•The amount of fluid aspirated through the phaco needle: This is determined by the resistance of the aspirating line (the inner diameter of tubing, needle and tubing compliance) and the level of the vacuum in venturi pumps and the level of the flow and the vacuum in peristaltic pumps.

This may be calculated again using the Poiseuille’s equation (Table 7.3), which states that the amount of fluid aspirated through the phaco needle is directly related with the inner diameter of the tubing and the needle (which determines the resistance) and the pressure gradient inside the tubing (determined by the level of vacuum in venturi pumps and the level of flow and vacuum in peristaltic pumps).

It is necessary to maintain the equilibrium between those factors in order to achieve a stable anterior chamber, without jeopardizing the intraocular tissues (iris, endothelium, posterior capsule).

To reach this objective, the surgeon must take into account several issues, namely, infusion rate of the irrigating instruments, amount of leakage through the incisions, and amount of fluid aspirated through the phaco needle.

In Biaxial or MicroBiaxial phaco, it is not possible to have the same high vacuum levels that the surgeon was used to, because the inflow that he got through an irrigating chopper would never be like the one that could be obtained through coaxial irrigation in standard phacoemulsification (Table 7.2). It is, however, very similar with the new Microcoaxial Phacoemulsification with the Ultrasleeve. The Inflow in Biaxial with the Vejarano’s Irrigating chopper 20 guage (AC7340, Accutome, Malvern) (Fig. 7.73) is 49% of the Coaxial and 84% of the Microcoaxial. The Inflow in MicroBiaxial with the Vejarano’s Irrigating Chopper 22 guage (MicroSurgical Technology – MST) (Fig. 7.74) is 41% of the Coaxial and 70% of the Microcoaxial, and the Microcoaxial is 58% of the standard Coaxial Phaco (Table 7.4). It is recommended that the surgeon

Fig. 7.73 Vejarano’s irrigating chopper 22 guage. with rectangular lateral holes

change and adapt the parameters depending on the irrigating chopper that he is going to use. For example, if the irrigation is located in front, he has to reduce the parameters to 65%, if it has inferior irrigation, to 58%, and if the irrigation is at the lateral side to 50% (based on the data of the Table 7.2 comparing with a Coaxial Inflow).

Also the aspiration flow has to be adjusted in order to avoid surpassing levels above 25–30 mL/min, using the fluidic control software of the phaco machine with bimodal or linear aspiration. This reduces the rise time and makes the events inside the anterior chamber more controllable [11–13].

Since the goal of the surgery is not solely to maintain the anterior chamber depth, but also to permit the emulsification of the nucleus, it is necessary to use levels of vacuum which would allow the surgeon to achieve a good hold of the nucleus and its fragments, and likewise, perform an effective chopping procedure. In peristaltic machines, it is necessary to use standard flow levels between 25 and 30 mL/min and vacuum levels of 250–300 mmHg. In venturi machines, a vacuum level of 120–160 mmHg would suffice.

Table 7.4 Comparative Inflow depending on the phaco tip, sleeve and incision size in coaxial and microcoaxial phacoemulsification (courtesy Armando Crema, M.D.)

Fig. 7.74 Impaling the nucleus with the phaco tip bevel down, before the chopping maneuver

Poiseuille’s equation states that with a smaller diameter of the needle, the flow will be less (Table 7.3). This means that the vacuum needs to be increased to be comparable with the holding power of needles with larger diameters.

In Biaxial phacoemulsification, although any technique can be used to emulsify the nucleus such as divide and conquer, nucleus disassembly or nucleus fracture, these are not recommended in hypermature cataracts due to its bare tip, less maneuverability and tight incisions which makes it more difficult for these maneuvers.

For this reason, in these hypermature cataracts, it is better to use chopping techniques that the surgeon is familiar with. However, the authors recommend the Vejarano’s safe chop [14–24].

Briefly described, the phaco tip, with its bevel down after aspirating the anterior cortex and epinucleus, is placed in the proximal portion of the nucleus, and pulsed or preferably applied with burst ultrasound energy, so that it penetrates deep into the nuclear core (Fig. 7.74).

When the tip is impaled into the nucleus, the foot pedal is switched to position two. At this moment, the irrigating chopper is lightly rotated horizontally, tilted, so that the longest length of the tip is against the space between the CCC edge and the lens material (space that, in brunescent and very hard cataracts is very small, or even absent). The tilted chopper is slid beneath the anterior capsule, 180° from the side port incision (Fig. 7.75). This maneuver is much easier to perform,

Fig. 7.75 Irrigating chopper tilted, sliding underneath anterior capsule avoiding its damage, going to equator capsular bag previous to its rotation; (a) 3D animation, (b) surgeon view, (c) Miyake view

than trying to slide it under the anterior capsule, just in front of the phaco tip. Afterwards, when reaching the equator of the nucleus, the chopper is rotated vertically

and moved inside the bag, to the position in front of the phaco tip (Fig. 7.76). The chopping maneuver takes place. In hard cataracts the nucleus is held between the two instruments for a moment, and a small amount of additional pulsed ultrasound energy is applied, so that the tip penetrates deeper in the nuclear material improving the holding power (Fig. 7.77). This allows to gain improved control of the whole nucleus during the chopping process, since it doesn’t become easily dislodged, as long as the high vacuum and the deep position of the tip maintain a tight occlusion seal around the tip. One very important advantage of this technique is that with this very good purchase of the nucleus, especially in hard cataracts, the chopping process is more effective, and helps us to separate the leather-like very hard posterior layers of those cataracts, that often present a challenge to the surgeon.

After dividing the nucleus into halves, it is rotated 45° to try to get the first piece of the heminucleus. The technique to avoid damaging the CCC while chopping the nuclear fragments, is to insert the irrigation chopper vertically and along the fracture lines of the nucleus (Fig. 7.78), where there is more room for the chopper. It is moved to reach its chopping position again only

when it is already at the lens’ equator, inside the capsular bag, thereby, making this step completely SAFE (thus the name of the technique). It is repeated as many times as necessary to remove the first piece (Fig. 7.79).

The features of the fluidics and the design of the Vejarano’s irrigating chopper (AC7340, Accutome, Malvern – MicroSurgical Technology – MST), with lateral oval irrigating ports and olive-tip at its end makes it easier to slide the chopper’s tip inside the bag, since it inflates the bag (Fig. 7.76a), and also protects the posterior capsule from accidental puncture.

The subsequent fragments are managed in the same way. When several nuclear fragments have been emulsified, the amount of remaining nuclear material is less and there is more room in the center, so that it is not usually necessary to go beneath the anterior CCC in order to chop them.

The epinucleus, if present, is aspirated using a flip technique. The posterior capsule is protected with the irrigation chopper that is used like a barrier, to avoid damaging the tissues. Bimanual Irrigation/Aspiration of cortical remnants using bimanual handpieces and, if necessary, posterior capsule polishing are done.