How do you take out night contact lenses?

What are the potential long term effects of over-wearing contact lenses - specifically vis oxygen exposure to the eye?

• I wear contact lenses - specifically acuvue oasys - and generally misuse them by wearing them day and night for sometimes months at a time. I regularly 1-2 times annually attend my optician for an eye check and prescription update to allow them the opportunity to spot any damage. So far so good I'm told I have healthy eyes! On asking my Optician today what the risks were she mentioned that it basically increased the probability risk of infections - perhaps relating it to the lack of oxygen contact with the surface of the eye. What references are there for potential harm (papers or reputable sources please - or qualified opinion (I've seen many amateur anecdotes around!) is there to suggest what potential damage I am opening myself to. I am at the moment fairly confident in my choice and take precaution against the first signs of eye infection (I've never had one so far!), but am always open to behavior change on the grounds of good evidence. Thank you for your time!

• Answer:

  I have a good friend that is an optometrist. Here's how he explained it to me... Your cornea is naturally gas permeable. Think of a screen, like on a screen door. Throughout the day, there's all sorts of microscopic debris that sticks to the "screen". Tears wash away or dissolve much of the debris, and it gets washed into your tear ducts (like gutters). The debris that can't be removed by tears is dealt with by small blood vessels just under the surface of the cornea. Modern contact lenses are also gas permeable, so when they're clean, no worries. When you leave them in two things happen. First, they get clogged with not just debris in the air - proteins in tears also stick to them. Second, the dirtier they get, the more your body starts to see them as a foreign body. This causes the blood vessels under the cornea to start growing up through the cornea in preparation to attempt to absorb the contact lenses into the body and then have the internal immune system deal with them. This process generally takes a long time because the irritation isn't severe (unless you get a bad eye infection - that'll speed up the process). By the way, once those blood vessels grow through the cornea, they don't grow back. And once they get thick enough, it starts to effect the quality of your vision. My optometrist always checks carefully under my upper eyelids to see how much blood vessel growth is going on. This area will show the worst of what's going on because it's the part of the eye that receives the least oxygen due to being covered by the eyelids most of the time. So take your lenses out at night and keep them clean. Even if they're extended wear. It's worth the trouble.