Complications of hard and soft contact lenses.

The number of contact lenses worn has increased steadily in the last decades. The number and types of complications have increased in approximately the same degree. New, hitherto unknown, complications are continually described. The complications are classified according to the factors which cause them: complications of mechanical origin; complications due to metabolic disorders; allergic reactions; exogenous infections; disorders of tear production. The lesions found in the cornea and the conjunctiva are described. The complications caused by hard lenses are usually noticed earlier by the patient than those due to soft lenses, because the lesions caused by hard lenses are usually painful, whereas those due to soft lenses are not.