Overnight wear with silicone hydrogel contact lenses

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Definitions

The definition of extended wear (EW) is widely accepted to be six nights followed by a night of no lens wear.

Continuous wear (CW) is widely accepted to be up to 30 nights followed by a night of no lens wear.

History of overnight wear

The overnight wear of soft contact lenses was spearheaded in the UK in the early 1970s by John de Carle, who first published his experiences with Permalens.1 Similar positive experiences and publications in the US led to the Food and Drug Administration approving the use of cosmetic soft contact lenses for continuous wear in 1981. In the following years much was learned about the physiological requirements of the cornea, including the hypoxic stress that the cornea undergoes beneath a contact lens and the relationship this stress has with infection risk. Indeed, by 1989 this association was so closely proven2,3 that the FDA changed their approval for cosmetic overnight lens wear from 30 consecutive nights of wear to just six.