Contact lenses are fit on the cornea, which is the clear window of the eye.  The cornea is perfectly clear and is living tissue that needs oxygen.  Our body is delivered oxygen by means of blood vessels directly to the tissue, however, the cornea has no blood vessels in it thereby allowing it to be clear.  The cornea gets the majority of its oxygen from the outside air around us.  When a contact lens is on the eye the oxygen getting to the cornea is reduced and this is why it is so important to have contact lenses that let as much oxygen through to the cornea as possible.

Traditional hydrogel lenses are a plastic material that contains water.  The plastic material itself does not allow oxygen through, but rather it is the water in the plastic that moves oxygen to the cornea.  To increase the oxygen getting through you would have to increase the amount of water in the contact lens, however, increasing the amount of water will cause the lens to easily dry out.

Silicon hydrogel lenses on the other hand allow more oxygen to the cornea because the silicon material itself allows oxygen through, in addition to the water in the lens.  These lenses require less water content and as result are less drying and provide better end of day comfort.  It is felt that silicon hydrogel lenses let 3 to 5 times the amount of oxygen to the cornea versus a traditional hydrogel lens.

Silicon hydrogel lenses allow a significant more oxygen through them making them healthier to the eye and reducing risks of infections or ulcers.  In addition they are more comfortable due to the lower water content that decreases the dryness factor of the lens.