Continuous-wear contact lenses are usually made from silicone hydrogel, which allows more oxygen through to the eye than conventional soft lens materials.

Oxygen is essential for eye health, while conventional materials are fine for use during the day when the eye is open, they do not let in enough oxygen when the lids are closed overnight, putting eye tissue under stress.

In the 70s and 80s, extended wear lenses were made from materials that were less permeable to oxygen and lead to complications such as irritation and infection. Today's modern lenses are safe and comfortable when wearers follow the care programme of a qualified optician.

As with all lenses, good hygiene is essential for avoiding infection - if you experience any problems, consult your optician urgently.