fingertip (depending on the product) on each side. Lens must then be rinsed. This system is commonly used to care for rigid lenses. Water is not recommended for cleaning contact lenses. Insufficiently chlorinated tap water can lead to lens contamination, particularly by Acanthamoeba. On the other hand, sterile water will not kill any contaminant that get in from the environment. Some products must be used only with certain types of contact lenses. Aside from cleaning the contact lenses, contact lens case should also be kept clean and be replaced at minimum every 3 months. Contact lens solutions often contain preservatives such as benzalkonium chloride and benzyl alcohol. Preservative-free products usually have shorter shelf lives, but are better suited for individuals with an allergy or sensitivity to a preservative. In the past, thiomersal was used as a preservative. In 1989, thiomersal was responsible for about 10% of problems related to contact lenses. As a result, most products no longer contain thiomersal. Complications Contact lenses are generally safe as long as they are used correctly. Complications from contact lens wear affect roughly 5% of wearers yearly. Factors leading to eye damage varies, and improper use of a contact lens may affect the eyelid, the conjunctiva, and, most of all, the whole structure of the cornea. Poor lens care can lead to infections by various microorganisms including bacteria, fungi, and Acanthamoeba (Acanthamoeba keratitis). Many complications arise when contact lenses are worn not as prescribed (improper wear schedule or lens replacement). Sleeping in lenses not designed or approved for extended wear is a common cause of complications. Many people go too long before replacing their contacts, wearing lenses designed for 1, 14, or 30 days of wear for multiple months or years. While this does save on the cost of lenses, it risks permanent damage to the eye and even loss of sight. For non Silicone-Hydrogel lenses, one of the major factors that causes complications is that the contact lens is an oxygen barrier. The cornea needs a constant supply of oxygen to remain completely transparent and function as it should; it normally gets that oxygen from the surrounding air while awake, and from the blood vessels in the back of the eyelid while asleep. The most prominent risks associated with long-term, chronic low oxygen to the cornea include corneal neovascularization, increased epithelial permeability, bacterial adherence, microcysts, corneal edema, endothelial polymegethism, dry eye and