The use of viscoelastics transformed cataract surgery decades ago. We use the viscoelastic to protect delicate tissues like the corneal endothelium and also to maintain space such as when performing a capsulorhexis or inserting the IOL. There is a wide spectrum of viscoelastics though we tend to divide them into two general categories: dispersive and cohesive.
In order to classify viscoelastics as devices instead of drugs, the name OVD (ophthalmic visco-surgical device) was introduced about a decade ago. There are important techniques that you must learn with OVDs such as the viscoelastic wave, the soft-shell technique, and even the angle sweep to avoid retained material.