Traditional Soft Contacts

• Because old soft contacts were made from plastic--which blocked oxygen flow to the eye--and water--which quickly dried out--they often gave wearers dry, uncomfortable eyes.
  
  

Gas Permeable Contacts

• Since the 1970s, gas permeable contacts with silicone have been in use, allowing oxygen to pass through the lens.
  
  

Silicone Hydrogel Contacts

• Many soft contacts are now being made with oxygen-permeable silicone. This means they have a lower water content--since water no longer has to be the primary oxygen carrier for the eye--resulting in less dehydration.
  
  

Difference in Oxygen Permeability

• Modern silicone hydrogel contacts are a match for gas permeables when it comes to oxygen flow, because they allow the eye to obtain six to seven times more oxygen than earlier soft contacts.
  
  

The Main Difference

• The key difference between gas permeable and silicone contacts is that silicone soft contacts still use some water to transmit oxygen to the eye--meaning they still dehydrate over time--while gas permeable contacts have no troublesome water content.