With any type of commodity, there's always the question of how safe it is. It's also true that with every kind of product there will always be risks and side-effects, it's just a thing of knowing how to save yourself and reading the fine print with the instructions. What's a few minutes of reading through the instructions when it's a lifetime of agony that you can avoid?
Contact lenses are one kind of commodity that many people take for granted, even though they probably use them all the time and as regularly as brushing their teeth. Their security basically depends on their handling and care. For example, most contact lenses, with the exception of the daily disposables, all have a tendency to become a breeding ground of infection caused by the accumulated dirt deposits from regular use. The reason why it's imperative to follow the cleansing instructions and be careful with them is that this is the only way to manage the purity of the contact lenses. As much as the cleaning, you also need to use the prescribed solutions for your lenses. Substituting tap water in place of the cleaning solutions will up your danger for infections because tap water by itself also carries its own bacteria. Not only do you need to replace your contact lenses when they're needed but you also have to replace your lens cases at least once every 3 months. Your lenses may be clean but if you don't replace your lens cases then they themselves become a breeding ground for nasty infection.
One other thing that can make your contact lenses dangerous is when you continually use them even though your eyes are experiencing redness, irritation or even dryness. One cause of these symptoms is when you sleep in your contact lenses even though you shouldn't. Granted, there are some contact lens brands that have been classified as safe for wearing even when you sleep but even then you should not misuse them or even wear them on an extended basis.
The bottom line is that the safety of your contact lenses and of your eyes is all within your hand. You just require to practice ultimate attention and precaution when using them.