FAQs About Contact Lenses

What are "Hard" and "Soft" lenses?
"Hard" lenses were the original contact lenses made several decades ago from a plastic called PMMA. For a long time they were the only kind of lens (if you exclude the glass ones developed during the early part of this century and used as recently as Word War II!) but they are seldom used anymore as they have several drawbacks and have been superseded by "Rigid" (also known as "Gas Permeable") lenses. In fact, when people say hard lenses they are most likely referring to the gas permeable type. Gas permeable lenses are similar to hard lenses in design and appearance, however as the name suggests the material they are made of is permeable to gases (most importantly Oxygen and Carbon Dioxide) whereas PMMA is completely impermeable to gases. "Soft" contact lenses are completely different in that they are slightly larger, flexible and made of materials which soak up water. In fact the uptake of water is what allows soft lenses to transmit Oxygen to the cornea, the plastic itself being impermeable. The water also gives them their flexibility - if you let a soft lens dry out it does become quite brittle.

What are contact lenses?
What are "Hard" and "Soft" lenses?
Why does the cornea need Oxygen?
What are high water content lenses?
Why aren't all soft lenses high water content?
Do gas permeable contact lenses absorb water?
Which lenses are best?
What is astigmatism?
I have astigmatism - can I wear soft lenses?
What is presbyopia?
I have presbyopia - can I wear contact lenses?
What are disposable lenses?
Why are contact lens solutions needed?
Do I need to use protein-removing tablets?
Which solution is best for my lenses?
I've been told not to wear my lenses when in an aeroplane - why?
Can I swim in my contact lenses?
Do I still need spectacles if I wear contact lenses?
What is the difference between tinted and coloured lenses?

See also:
All About Contact Lenses
All About Vision
How to make a complaint