Excessive usage of contact lenses would be harmful to your eyes indeed. What is cornea? It is a membrane covering the surface of eyeballs. It is transparent and thin, full of nerve ends, yet no vessels. Wearing contact lenses is to put the lenses on the surface of eyeball, which means contacts directly lay over cornea. No matter how thin and soft your contact lenses are, they are still not one part of our eyes. Maybe you couldn't notice them, but they are foreign objects in eyes which might abrade eyes, especially the cornea because they are directly in touch with cornea. Technology for contact lenses develops very well and mature, yet we still have to note some points when we wear contact lenses. It is better not to wear them for over 10hours, which might make your eyes strain, dry, and easier to get scratched. Sanity is very important. Wash your hands with neutral liquid soap completely whenever you need to touch the lenses. Care solution is a must for storing and washing the contacts. Contact lenses are really magic and convenient. I love wearing them, at the same time I also obey the rules above. We need to be careful with everything about eyes. Hope you could enjoy wearing contact lenses too, with health.