The modern contact lens is designed to be more comfortable and wearable than ever, but that doesn't mean you should disregard the instructions of the manufacturer and your optometrist. There are several 'bad habits' that contact lenses wearers can fall into, and sleeping with your contact lenses in is just one of them. Even if it might seem like too much effort to remove your lenses properly, you should always clean and store them back in their case before falling asleep.

This is because the tissues of your eyes need oxygen in order to function properly. When you're awake, your open eye gets oxygen from your tears and the air. However, when you are sleeping your eyelids are shut and there is less oxygen being transmitted to your cornea from the surrounding air.If you have left your contact lenses in, this prevents even more oxygen from getting to your eye because the plastic acts as a physical barrier to the process. When the eye doesn't get enough oxygen, a condition called corneal neovascularisation can occur where small blood vessels grow in the cornea in order to provide an oxygen supply to the area.

Aside from this condition, leaving your contact lenses in overnight can also lead to redness in the eyes, eye strain or pain and increased sensitivity to light. The lens itself may tighten while on the eye, which can result in tiny rips or tears on your cornea (the front surface of your eye).This may increase the risk of an eye infection, inflammation or abrasions. For these reasons, it's important to never sleep with your contact lenses whether they're hard or soft.There are some types of lenses that have been specifically designed for overnight or extended wear, but you will need to see your optometrist first to get more information about these types of products.