since then. Balazs developed the procedure of viscosurgery, coined the term, and patented high molecular weight viscoelastic material using purified hyaluronic acid to be used for implantation of IOLs. In 1976 an application for the use of the OVD Healon was made with the FDA, and the next year applications were made for its use in surgery for cataracts, IOL implantation, glaucoma, and corneal transplants. In 1979, 510k permission was granted to market Healon, and FDA approval in January 1983. Since then OVDs have become essential tools in ophthalmic surgery. Polyacrylamide is a synthetic compound that was used for a while but withdrawn from the market in 1991, after its use was found to be associated with elevated intraocular pressure. See also References Further reading </ref>