Hi
I think Zana's figure of 1,5 days equivalent for a night's sleeping in
contact lens originates from the way the cornea derives it's oxygen.
In daytime, eye open, oxygen flows to the cornea (which has no capillary blood supply normally) via the tear film and the air around the lens. The contact lens is a physical barrier and will reduce this oxygen flow, but the newer silicone gel lenses have much higher oxygen permeability and are better for the eye's oxygen supply.
At night when the eyes are closed, the oxygen supply to the cornea is via the capillaries in the eye lid, but the oxygen supply is less that would occur in daylight when the eyes are open. This causes the eyes to swell by around 4%, (but some lower figures around 2.5% are also being quoted).
If you wear
contact lenses (which are for day time use only) at night, the oxygen supply to the eye will be further critically restricted - hence the equivalent of 1.5 days for one night's sleep with contact lenses.
As has been posted here already, the newer silicone hydrogel lenses are claimed to be able to exceed the eye's oxygen requirements, even wearing the lenses 24/7 for a month.
My previous optician always recommended that when I awoke in the morning, I should try and wait 45 mins before I put my (yearly soft) lenses in - this was in order that my corneas could obtain as much oxygen after sleeping, before I restricted the oxygen flow by wearing contact lenses.
I discussed the capillary problem earlier here:
Post #30
http://www.lens101.com/general-eye-health/21755-if-you-dont-stop-youll-go-blind.html
knotlob