The only issue is that these silicone is hydrophobic (water-repelling). As such, it’s prone to problems such as sticking to the eyes if used on its own. To solve this problem, the first generation of silicone hydrogel lenses used surface treatments in order to make them hydrophilic. The second generation switched to the use of wetting agents such as polyvinylpyrrolidone (PVP), and more recently the third generation simply contained a modified polymer which was itself designed to be hydrophillic.