<unk> ARE<unk>  associated red eye) is a group of inflammatory complications from lens wear<unk> es are generally safe as long as they are used correctly. Complications from<unk>  wear affect roughly 5% of wearers yearly. Factors leading to eye damage varies, and improper use of a<unk>  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<unk> es 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<unk> s, 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<unk>  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 potential increase in myopia. Much of the research into soft and rigid<unk>  materials has centered on improving oxygen transmission through the lens. Silicone-Hydrogel lenses available today have effectively eliminated hypoxia for most patients. Mishandling of<unk> es can also cause problems. Corneal abrasions can increase the chances of infection. When combined with improper<unk> eaning and disinfection of the lens, a risk of infection further increases. Decreased corneal sensitivity after extended<unk>  wear may cause a patient to miss some of the earliest symptoms of such complications. The way<unk> es interact with the natural tear layer is a major factor in determining lens comfort and visual<unk> arity. People suffering from dry eyes are particularly vulnerable to discomfort and episodes of brief blurry vision. Proper lens selection can minimize these effects. Long-term wear (over five years) of<unk> es may "decrease the entire corneal thickness and increase the corneal curvature and surface irregularity." Long-term wear of rigid<unk> s is associated with decreased corneal keratocyte density and increased number of epithelial Langerhans cells. All<unk> es sold in the United States are studied and approved as safe by the FDA when specific handling and care procedures, wear schedules, and replacement schedules are followed.
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