Fig. 6.71 Set up CoMics vs.

BiMics

6.9.2 Historical Background

Biaxial and coaxial microincision cataract surgeries are complementary and, as Olson [16] says, are likely to dominate lens surgical techniques in the very near future.

6.9.3BiMICS. BiManual MicroIncision Cataract Surgery

6.9.3.1 Introduction

BiMICS (Fig. 6.72) is a surgical technique performed through two microincisions, one for irrigation and the other for aspiration, of reduced sizes, usually under 1 mm [1, 2, 6, 13.

6.9.3.2 Instrumentation

The instruments for BiMICS (Fig. 6.73) present only slight changes from conventional phaco instruments. However, particular attention will have to be given to

Fig. 6.72 BiMics technique

microphacodynamics, as well as to the incisions made, which have to be chosen and tested meticulously.

6.9.3.3 Microphacodynamics [3, 5, 8]

The incoming flow should be superior to the outgoing flow. Using the Poiseuille’s law (Fig. 6.74), it is

Fig. 6.76 Capsulorhexis forceps

6.9.3.5 Phacotips

The phacotips are usually equipped with an external diameter of 21 G (0.9 mm). It is important to control the internal diameter of these tips also in order to avoid surge. The tip is straight with a 30° bevel.

6.9.3.6 Capsulorhexis

The needle is the simplest way to create a capsulorhexis through a microincision (Fig. 6.76). It can be easily performed with a viscoelastic gel such as methylcellulose. The microinstrument for capsulorhexis is a bit more complex. Furthermore, using vitrectomy forceps is also not a simple task.

The capsulorhexis forceps should have a smaller diameter than the incision, with a distal opening mechanism that can be maneuvered without creating much movement of the body of the instrument. It should also be curved on both sides in order to permit grasping the edges of the rhexis with ease, especially near the area of the corneal incision.

6.9.3.7 Phaco Knives

The straight blades allow a smoother incision than the triangular blades. There are numerous trapezoidal blades of different sizes which would allow the surgeon to perform the desired incision. However, it is essential to note that variation in incision sizes is much more sensitive to fluid dynamics when using BiMICS. The slightest change in incision size makes a big difference in microphacodynamics. If the incision is too large, fluid loss is excessive, the anterior chamber becomes unstable and there is a prolapse of the iris. If the incision is too small, corneal burns and Descemet folds may occur.

6.9.3.8 The Phaco Machines

The newest generation phaco machines considerably simplify the transition to microincision cataract surgery. Recent phaco machines allow sufficient aspiration flow rate, in spite of its smaller diameter tips. Conventional phacodynamics dictates that in order to obtain an adequate suction, greater aspiration flow rate should be applied. This is not the case with these new phaco machines. Another advantage of the latest generation phaco machines is that it regulates heat emitted by the phaco tip at the incision site.

6.9.3.9 Phaco Pumps

The newer phaco pumps combine the benefits of both the peristalic and venturi systems. They allow for more flexibility and are more effective in the presence of hard nuclei. They are also equipped with systems, which enable a considerably better stabilization of the anterior chamber.

6.9.3.10 Ultrasound Power Delivery

The most recent machines have notably reduced thermal energy due to power modulation that includes pulses and bursts with microsecond duration. However, even with the old phaco machines, it is possible to reduce the thermal energy using the foot pedal during the short interval, reducing the phaco power time.

6.9.3.11 IOL Implantation (Fig. 6.77)

Rather than enlarging one of the microincisions, which can induce Seidel’s positive incisions, a third incision can be made in between the first two, to implant the IOL.

6.9.3.12 Astigmatism (Fig. 6.78)

This technique allows total neutralization of induced astigmatism, wherein the microincisions leave the original astigmatism unchanged, if not eliminated (Table 6.5).

•1 Paracentesis for irrigation,

•1 Paracentesis for Phacoemulsification

•1 Incision to Injecte the lens

Fig. 6.78 BiMics incision

6.9.4CoMICS: Coaxial MicroIncision Cataract Surgery [12, 15, 18]

(Figs. 6.79 and 6.80)

CoMICS surgical technique was developed after BiMICS surgical technique, to lessen the learning curve and the difficulties encountered with the BiMICS technique. CoMICS was the perfect choice for the implantation of a lens at 2.2mm incision width without changing much of the conventional phacoemulsification technique. At that size, there is no risk of inducing anterior chamber instability, as well as producing corneal burns. Likewise, there is no need to change all the instruments, thus making this technique more cost-effective than BiMICS.

Fig. 6.79 CoMics technique

6.9.4.1 Capsulorhexis

Most of the fine capsulorhexis forceps can be used through a 2.2 mm incision. It becomes necessary to use a capsulorhexis forceps that has a distal opening mechanism for incisions smaller than this size.

6.9.4.2 Phacotips

Two sizes of phacotips with external diameter sizes of 0.9–1.1 mm are used. Both have an angle of 30 or 45°.