of injection via an incision of less than 2mm. Moreover, the integrity of the implant and the intraocular structures should be maintained during the injection.

A new technical approach is necessary as the woundassisted technique, which does not require introducing the cartridge bevel in the anterior chamber, is currently the only technique of injection that allows making the smallest possible incision. However, for it to be reliable and reproducible the technique should be understood and followed rigorously.

While the sub-2 mm incision, which is the new standard in cataract surgery, is difficult to attain, a sub-1 mm incision goal seems all the more difficult.

This race to achieve the smallest incision size shall continue, since it proves to be beneficial to the patient.

8.2.1 Definition

If we talk specifically about microincisions, the definition of microincisions keeps changing according to the changes in technology, which, as we know, are rapid.

In 1985, Sharing suggested separating ultrasound and irrigation, a little before Agarwal described the Biaxial Phaconit technique using an incision size of less than 1.5 mm.

Jorge Alio [1] suggested the term Micro Incision Cataract Surgery (MICS) for incisions smaller than 2 mm.

Currently, the phacoemulsification by biaxial microincision (Bi-MICS) is used for 1.5 mm to less than 1 mm incisions.

On the other hand, the coaxial microincision (Co-MICS), which is similar to the usual technique, is used for incisions of 1.8 mm and soon, less.

However, because of the constraints of injection (implants, cartridges, injectors), the surgeons supporting the Bi-MICS technique are forced to increase their incision sizes to between 1.5 and 2mm before implanting.

For this chapter on implantation techniques through microincision, we shall consider an incision size less than 2 mm.

8.2.2 Prerequisites to a Sub-2 Injection

It is necessary to follow certain rules in order to insert an intraocular lens (IOL) through an incision of less

than 2.0 mm. There are four prerequisites:

1.The implant material should not be damaged and should be able to bear the high stress of injection. Currently, all the products used for microincision are made of acrylic hydrophilic material. This hydrophilia is one of the factors that help its flexibility.

2.The diameter of the optical zone should be about 6.00 mm at + 20 dpt. Reducing the size of the optical zone excessively has the risk of optical aberrations that could create problems for the patient even in case of a slight decentration.

3.The implant haptics should support 1–2.00 mm compression in the capsular sac without causing optical decentration. The use of large ansae, multiple to divide the efforts or even angular ones to increase the pressure on the posterior capsule and strengthen the effect of the 360° barrier, is recommended. The anterior and the posterior capsule should be able to adhere to each other immediately.

4.The cartridge determines the incision size after injection, mainly the internal diameter of its tip in case of an injection using the wound-assisted technique (without inserting the bevel in the anterior chamber). An empirical rule that allows deciding the post implantation incision measurement according to the internal or external diameter of the cartridge and the injection technique used is as follows:

5.Incision size in mm = [(cartridge diameter at the tip in mm × π)/2] × 0.9.

6.The value of the internal diameter is used for the injections in the wound-assisted technique, whereas the value of the external diameter is used when the bevel is inserted in the anterior chamber. In our experience, this empirical rule correlated very well with our clinical observations.

8.2.3IOLs Used for Injection Through Microincision

The design of intraocular lenses (IOLs) used in incisions close to 2.2 mm is similar or identical to that usually used in standard incisions of about 3 mm, whereas the IOLs used in microincisions of less than 2 mm require an original and specific design.

In fact, these implants should be resistant enough in order to inject them through the incisions of 1.5–2mm

and they should also have a postoperative intra-saccular behavior comparable with the existing reliable implants.

Only a few materials and designs used today can claim to attain this objective.

The flexibility of the material as well as the design and the volume of the IOL are the characteristics that define the mechanical aptitude of the lens to be injected through a microincision.

8.2.3.1 Material

It is very important to note that the IOLs made of hydrophobic acrylic material whose optical quality and postoperative behavior is well known and proven cannot yet compete with those made of hydrophilic acrylic material, which are more deformable in terms of incision size.

Therefore, two parallel developments could be considered.

Those who support the performance of hydrophobic acrylic material defend the technologies, techniques and IOLs using 2.2 mm incisions [2]. They prefer the known intraocular behavior and the long follow-up of these IOLs.

Whereas those supporting the use of hydrophilic acrylic material are confident about the deformability of this material and the new IOLs having competitive optical capacities, and prefer an incision size of 1.5– 1.8 mm [1, 3].

In the case of hydrophilic material, resistance to mechanical stress is a preliminary condition for design-

ing an IOL meant for microincision. In fact, it should allow the insertion of the implant through the injection tunnel of a cartridge with an internal diameter of less than 1.40 mm for incisions less than 2 mm, and 1.10 mm for incisions less than 1.50 mm.

However, this material should not get damaged while trying to conform to the main constraints of microinjection. Properties like deformability and resistance to tear prove to be more important than the refraction index that allows reducing the thickness of optics.

The first hydrophilic acrylic IOLs were poly-HEMA lenses (38% water content) which were found to be extremely deformable in the recovery period. Many companies then decided to work on more rigid hydrophilic material by copolymerizing HEMA with PMMA, and a good result was obtained with a water content rate of approximately 26% (Fig. 8.16), which is now the base of most of the acrylic hydrophilic materials used worldwide.

Currently, the products meant for microincision are made of acrylic hydrophilic material [4] for which the clinical follow-up is more than 10 years.

In future, some new materials will probably allow reducing the incision size further and improve the optical quality and behavior of IOLs.

8.2.3.2Design

For the first implants meant for microincision, more importance was given to the incision size and the ease of injection than to the postoperative behavior. They were

Methyl MethAcrylate: MMA

Both radical (A) and (R) are a methyl group

C C

HC O O

CH3 (methyl group)

Hydroxy Ethyl MethAcrylate: HEMA

Radical (A) is a methyl group

(R) is a ethyl group with a hydroxy group

C C

HC O

O

C2H4 (ethyl group)

OH (hydroxy group : water transmitter)