Folding intraocular lenses: materials and methods

The change in cataract surgery technique to ever smaller incisions requires the use of folding intraocular lenses (IOLs). Leaming1 in his annual survey of practice styles of members of the American Society of Cataract and Refractive Surgeons reports that in 1995 38% of respondents were using a 3 mm incision, with 14% using silicone and 9% acrylic IOLs, a considerable change from 1994. Polymethylmethacrylate (PMMA) remains the gold standard IOL material since first implanted by Ridley2 in 1949 with a track record of close to 50 years, and it still is the preferred material of US surgeons in 1995.1

Which materials are in use in folding IOLs in 1997 and what methods of implantation are available? Silicone has been in use as an IOL material since the early 1980s with Food and Drugs Administration (FDA) approval obtained in 1990 for a three piece silicone lens. Silicone in IOLs is a biologically inert polymer, polydimethylsiloxane (PDMS), which cannot leach out—unlike silicone in breast implants. The earlier lenses had a refractive index of 1.41 making folding of three piece lenses over 22 D difficult. The refractive index of most three piece silicone IOLs is now 1.47 reducing optical thickness and facilitating folding. Plate haptic silicone lenses have a refractive index of 1.41 making a thicker lens which, the manufacturers suggest, fills the capsular bag reducing the incidence of posterior capsular opacification. Silicone folds easily but springs open unless delivery is controlled. It is difficult to handle when wet as it becomes slippery. Silicone IOLs should not be used in the presence of silicone oil in the vitreous cavity, or if silicone oil may be required in the future, as condensations will occur on the lens, in particular in the presence of a posterior capsulotomy.3 Silicone lenses are currently the …