Viscoelastics have two distinct features: they can coat and maintain space. As an additional feature, they are also excellent in stopping a hemor-rhage18:
• Coating. This attribute is utilized when the endothelium must be protected during manipulations of the lens or condensation of fluid on the IOL's or capsule's surface must be fought in an air-filled eye. In general,
17 The air bubble's presence is especially short-term if it was introduced during general anesthesia using nitrogen-dioxide.
18 Working as a tamponading agent.
viscoelastics of low viscosity (e.g., Viscoati®) are used for this purpose (dispersive viscoelastic).
• Space tactics. Viscoelastic materials are incompressible and hard to dislodge. If they are placed underneath a corneal wound, for instance, they tend to stay there and prevent the iris from adhering to the wound; they are also able to counter silicone oil prolapse into the AC irrespective of whether the eye is aphakic, pseudophakic, or phakic.2° These cohesive or viscous viscoelastics (e.g., Healon2i) have a much wider use in ocular traumatology, including pre- and even subretinal applications (see Chap. 2.9).
• When a cohesive viscoelastic is injected, it is especially crucial to use a low force22 to avoid increased resistance ("backfiring") by the material.
• Before injection, a plan must be designed to make viscoelastic use efficient.
• Viscoelastics are not intended to push tissue back into the eye. The material is to be used after the prolapsed tissue has been repositioned (see Chap. 2.4). The viscoelastic should be injected through a paracentesis, not through the original wound.
• When a space is to be created/filled, injection should be started at the most distal point and advanced backwards (i.e., as the surgeon is slowly withdrawing the cannula).
• If the viscoelastic is used for breaking a synechia, it must be kept in mind that the material works indiscriminately: where the tissue breaks is not necessarily where the surgeon wanted it to break.
As mentioned above, viscoelastics are occasionally left in the AC to prevent silicone oil prolapse or synechia formation. The risk of IOP elevation is higher with less viscous materials, and they are also more difficult to re
19 Alcon, Fort Worth, Texas.
20 Prophylactic filling of the AC with a cohesive viscoelastic should be considered in every eye undergoing silicone oil implantation.
21 Advanced Medical Optics, Santa Ana, Calif.
move during surgery. Just as when injecting the viscoelastic, the key during viscoelastic removal is to start distally and limit the force with which the BSS is applied.
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