PMMA lenses are more likely to scratch the cornea if the lens does not fit properly or if the lens is worn while sleeping. They are also more likely to slide off the cornea and become hidden under the lid. New lens designs have minimized the chance of loosing a contact even during vigorous exercise. Protein build-up results in discomfort, blurring and intolerance to the lenses. You will need special cleaning solutions to dissolve the protein.
Misuse can lead to temporary and even permanent damage to the cornea.
People who wear any type of lens overnight have a greater chance of developing infections of the cornea. These infections are often due to poor cleaning and lens care. Improper overwearing of contact lenses can result in intolerance, leading to the inability to wear contact lenses. Most people who need vision correction can wear contact lenses, but there are some exceptions. Contact lenses must be properly cleaned and disinfected when you remove them to kill germs and prevent infections.