1. 4 to 12 times the oxygen permeability of older tech lenses (depends
on how old the tech and which current silicone material). The high level
of oxygen reaching the cornea eliminates tissue swelling, engorgement of
the capillaries surrounding the cornea and the potential for
neovascularization (new blood vessels growing where they should not) and
allows for rapid healing of minor cornea surface damage. This in turn
reduces the risk of infection.
2. material does not foster bacteria/virus growth on the surface which
reduces potential for infection.
3. material does not dehydrate on the eye and change fitting
configuration.
4. surface far more resistant to deposits, although some si-hydros will
deposit lipids but generally less so than older tech lenses.
5. material more eye tissue compatible for most people.
6. material does not "soak up" chemical residues from lens care products
or that which is dissolved in tears following exposure to atmospheric
contamination.

In short, silicone hydrogels, IMHO and that of many others, makes all
other soft lens plastics obsolete. Silicone hydrogel lenses mark the
first significant change on soft contact lens chemistry in a decade, and
the previous change was minor in comparison, so perhaps the first real
change in 25 years.

A year ago there was only one lens on the market in the USA. (Not so
elsewhere.) Today, there are four: (in particular order: Acuvue Advance,
Purevision, O2Optix, Focus Night&Day.) There will likely be two more
coming sometime soon.

--LB, O.D.