You know the feeling, you're at home at the end of a long day and inevitably you get that 'tired' sensation come over you. Know the one? It seems to happen every day at about the same time. Then you spend the next few hours puddling around, instead of going to bed like you know you should. In earnest, you vow to yourself to make tomorrow night an early night - but of course that never happens... Sleep. It's something we know we need a lot of but hardly ever seem to get. When you finally make your way to your bedroom, your mind is filled with all the activities from the past day. You flop onto the bed and pass out for several hours. When that alarm goes off on your phone, you know it. It's brutally obvious. You left your contacts in last night! You're eyes feel terrible. They're dry and red and all you want to do is prise that horrible lens out of your eye, but should you?

The Effects

It doesn't affect everyone the same, but sleeping with contacts is not a good practice for anybody - yes, and that means you too! So what's the reasoning behind this? Without getting too technical, I'll try explain this as best I can. The front part of the eye is called the cornea. it's made up of transparent 'tissue'. This tissue is made up of many many 'cells'. The cells need oxygen to perform their little tasks. Usually cells get their oxygen from blood vessels, however there are no blood vessels in your cornea because it is transparent. How does the cornea get oxygen then? From your tears and from the air. When you're awake this works well, you blink a lot to get the tear-fluid flushing over your eye, and the modern breathable contacts you wear allow enough air to pass through and come in contact with the eye. When you're asleep however, you're not blinking and neither are your eyelids open, so the amount of oxygen getting to your eye is majorly reduced. Add a contact lens in there and this creates yet another barrier for the oxygen to get through. Now (and hopefully you're still following along ok), if the brain knows that the cornea is not getting enough oxygen, an alarm goes off and this triggers small blood vessels to start growing into the cornea to give it some oxygen. This is known in the medical world as Corneal Neovascularisation or CNV (we're not expecting you to remember that!). In a very extreme case, CNV can threaten your eyesight! I know - scary huh? The good news is, leaving your contacts in for one night isn't likely to cause CNV so you're pretty safe on that front. The fact is, that if you repeat this night after night after night, you are putting yourself at risk.

More Effects

Without oxygen, another effect this has on the cornea is that it starts to swell up. This swelling is fairly minute, but what it does is creates cracks in the between the surface cells where bacteria can lodge itself. This is less than ideal as the bacteria could cause infection or inflammation. This process happens a lot quicker than CNV, as the cornea doesn't have a good immune system to deal with the foreign items. This might be stating the obvious, but when the eye gets inflamed, this causes the redness you may experience in your eye. It can also strain the eye and cause it to be painful. The longer you sleep for, the longer the swelling will be active for and as time goes by, the exposure puts you at greater risk of the bacteria growing.

Extended Wear Contact Lenses

Now for the better news: In recent years, contact lenses have been developed extensively and the manufacturers have developed lenses that are approved to be worn for up to 30 days and nights continuously! As you probably guessed, the technology in these lenses has been developed to let as much oxygen in as possible, however any lens will block some level of oxygen. It is still recommended that even if you get these contact lenses, leave them out at least one night per week to give your eyes a break. Even though extended wear lenses are 'approved' they don't eliminate the risk of getting infection or long-term CNV.

What to do if you accidentally (or out of necessity) sleep with your contacts in

So, you've read of the harm that sleeping in contacts can cause, but what about those occasions where you forget to take solution with you on an overnight stay, or when you are on a long-haul flight? Good question. At times, leaving your contacts in overnight may be the only option you have. In this case, if you can, sleep for short stints at a time and wake up every so often to put drops in your eye. If you do sleep for the whole night be sure to give your eyes plenty of drops in the morning in the effort to restore the moisture and oxygen levels. Immediately taking a dry contact lens out first thing in the morning, could damage your cornea so be sure to add plenty of drops in beforehand.

In summary

Wearing contact lenses while sleeping is a no-no, the risks just simply aren't worth it. If you've got extended wear contact lenses, then sleeping is ok, but remember to leave the lenses out at least once per week to give your eyes a break. If you simply forget, it's not the end of the world, just make sure you put plenty of drops in in the morning. Don't let this become a habit!