according to the internal or external diameter of the cartridge and the injection technique used.

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

For the wound-assisted technique of injection, we use the value of the internal diameter. Therefore, the internal diameter of the cartridge should be less than 1.4 mm to attain the objective of an incision size of less than 2 mm.

8.2.4.4 The Plunger Tips (or plunger)

The plunger tips are very specific and determine the mechanical efficiency of the injector and ensure the preservation of the cartridge and the implant during insertion in the tunnel by their adaptability to the form of implant in the cartridge. The injectors meant for microincision inject only the monobloc implants and not the 3-piece implants that are not appropriate for this incision size. These tips are meant to obtain maximum efficiency while pushing the implant, preserving the haptics and the optic regardless of their form and material. Their form has been designed to avoid the tip getting stuck in the folded implant during insertion, a risk which could affect the efficiency of insertion and increase the possibility of lesion of the implant and the cartridge. These plunger tips can be rigid or soft. Generally, soft plunger tips are made of silicone. The purpose of these soft tips is to limit traumas by their flexibility and to reduce the diameter of the injection tunnel mainly for highly fragile implants. In practice, deformable plunger tips are most commonly used. They allow using a Visco-injection that makes the injection easier and more secure. The principle of “Visco-injection” or “hydraulic injection” using a soft plunger tip usually made of silicone and a viscoelastic substance (VES) is followed by most of the companies claiming an incision of less than 2 mm. In practice, it is of great relevance. In fact, this instrument allows maintaining the VES and the IOL in front of the plunger tip.

This serves two purposes: protecting the haptics during injection (they cannot get stuck by the tip) and easing the pressure on the plunger while inserting through smaller diameters. Thus, the injections become easier and more secure. Moreover, the deformability of this plunger tip avoids bursting of tunnel or bevel caused by the required size of a rigid tip.

8.2.4.5 Pushing Systems

The plunger tips can usually be operated by a screw or a piston.

The systems using a screw have the advantage of being more precise and easy to control as they require less force, help making a soft release of the implant and facilitate rotation operations if required. However, they require bimanual usage.

Generally a syringe-type plunger is used for injection through microincision, which allows an injection on planes by simple, mono manual pressure, useful especially if a counter pressure using a second instrument is required. This plunger has a return spring which increases the precision and facilitates its return at the end of injection. The regularity of pressure and control on the implant release can sometimes be tricky during the first injection.

8.2.4.6 Injector Bodies

Injector bodies can be resterilized or be of single-use type.

The resterilizable injectors are the oldest injectors, but as single-use instruments are now the global trend, these injectors are commonly used in injections through microincision. They are mainly meant for monobloc implants.

Currently, preloaded injectors for incision sizes of less than 2 mm do not exist. Their conception proves to be very difficult. In the case of hydrophobic materials, the difficulty in folding a less deformable material creates a problem. In the case of hydrophilic materials, the conservation of lubrication capacity in humid environments becomes problematic.

The ergonomic design of the injector bodies, mostly for single-use, allows an optimal prehension that increases the efficiency and security during the injection procedure.

8.2.4.7 Principal Sub-2 Injectors

• Viscoject (Medicel) (Fig. 8.19)

The Viscoject injector is manufactured by Médicel (Switzerland) who supplies a large number of laboratories around the world. Through the laboratories that use this injector, Medicel has popularized the use of the Visco-injection. Their Viscoglide 1.8 cartridge makes incision size of 1.8 mm feasible. It injects, among others, the MI 60, Bausch & Lomb and microSlim, Physiol IOLs.

• Thinroller (Thinoptx) (Fig. 8.20)

Fig. 8.20 ThinRoller injector meant for the Ultrachoice 1.0 (ThinOptx) IOL

This historical sub-2 injector is meant for the Ultra choice 1.0, ThinOptx confocal hydrophilic acrylic monobloc implant. Its main characteristic, other than the incision size between 1.5 and 2 mm, is that the IOL is rolled in the injector unlike in most of the cases where it is folded in a U-shape. It has a rigid plunger tip, which is not common in sub-2 injectors.

• Acrishooter (Zeiss) (Fig. 8.21)

Meant for Acri.Smart 36 A, Acri.Confort 646 TLC bitorique and Acri.LISA 366 D bifocale difractive IOLs, the Acrishooter is a resterilizable injector having a Laser 2 cartridge (same as for INJ 01) that allows a sub-2 injection.

• INJ 01 (Adriamed) (Fig. 8.22)

Meant for Acri.Smart 36 A, Acri.Confort 646 TLC bitorique and Acri.LISA 366 D bifocale difractive IOLs and having the same Laser 2 cartridge as in Acrishooter, it has a single-usage design made of polycarbonate. The plunger tip is deformable and separated, and a stop collar secures the insertion and prevents excessive pressure on the plunger.