Editing Contact lens (section)

==Complications==
{{Main|List of contact lens complications}}
{{Further|Effects of long-term contact lens wear on the cornea}}

[[File:Clare-314.jpg|thumb|alt=Closeup of an eye infection after wearing contact lenses|[[Contact lens acute red eye]] (CLARE) is a group of inflammatory complications from lens wear]]

Contact lenses are generally safe as long as they are used correctly. [[Complication (medicine)|Complications]] from contact lens wear affect roughly 5% of wearers yearly.<ref name="Stamler">{{Cite journal |last=Stamler |first=John F. |date=August 1998 |title=The complications of contact lens wear |journal=Current Opinion in Ophthalmology |volume=9 |issue=4 |pages=66–71 |doi=10.1097/00055735-199808000-00012 |pmid=10387472}}</ref> Factors leading to eye damage varies,<ref name="Factors Leading to Eye Damage Caused by Contact Lenses">{{Cite web |title=Do Contact Lenses Damage The Eye? |url=https://www.lensite.co.uk/Lens-Wearing-Guide/Contact-Lenses-Facts |url-status=dead |archive-url=https://web.archive.org/web/20181002020453/https://www.lensite.co.uk/Lens-Wearing-Guide/Contact-Lenses-Facts |archive-date=2 October 2018 |access-date=30 March 2018 |publisher=Lensite}}</ref> and improper use of a contact lens may affect the [[eyelid]], the [[conjunctiva]], and, most of all, the whole structure of the [[cornea]].<ref name="Stamler" /> Poor lens care may lead to infections by various [[microorganism]]s including [[bacteria]], [[fungi]], and the amoeba ''[[Acanthamoeba]]'' ([[Acanthamoeba keratitis|''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 potential increase in myopia.<ref name="What's the Best Prescription for Healthy Contact Lens Wear?">{{Cite web |title=What's the Best Prescription for Healthy Contact Lens Wear? |url=http://www.clspectrum.com/article.aspx?article=12590 |publisher=Contact Lens Spectrum}}</ref> Much of the research into soft and rigid contact lens materials has centered on improving oxygen transmission through the lens.

Silicone-hydrogel lenses available today have effectively eliminated hypoxia for most patients.<ref name="Sweeney2013">{{Cite journal |last=Sweeney |first=Deborah F. |year=2013 |title=Have Silicone Hydrogel Lenses Eliminated Hypoxia? |journal=Eye & Contact Lens: Science & Clinical Practice |volume=39 |issue=1 |pages=53–60 |doi=10.1097/ICL.0b013e31827c7899 |pmid=23271474 |s2cid=205659587}}</ref>

Mishandling of contact lenses can also cause problems. [[Corneal abrasion]]s can increase the chances of infection.<ref name="Corneal Abrasion in Emergency Medicine">{{Cite journal |last=Khan |first=Feras H |date=2023-04-13 |title=Emergency Care of Corneal Abrasion: Overview, Clinical Evaluation, ED Treatment Considerations |url=https://emedicine.medscape.com/article/799316-overview |access-date=2024-08-25 |website=Medscape Reference}}</ref> When combined with improper cleaning and disinfection of the lens, a risk of infection further increases. Decreased corneal sensitivity after extended contact lens wear may cause a patient to miss some of the earliest symptoms of such complications.<ref name="The effects of long-term contact lens wear on corneal thickness, curvature, and surface regularity">{{Cite journal |last=Liu |first=Z. |last2=Pflugfelder, S. |date=January 2000 |title=The effects of long-term contact lens wear on corneal thickness, curvature, and surface regularity |journal=Ophthalmology |volume=107 |issue=1 |pages=105–111 |doi=10.1016/S0161-6420(99)00027-5 |pmid=10647727}}</ref>

The way contact lenses interact with the natural tear layer is a major factor in determining lens comfort and visual clarity. People with [[Keratoconjunctivitis sicca|dry eyes]] are particularly vulnerable to discomfort and episodes of brief blurry vision. Proper lens selection can minimize these effects.

[[Effects of long-term contact lens wear on the cornea|Long-term wear]] (over five years) of contact lenses may "decrease the entire corneal thickness and increase the corneal curvature and surface irregularity."<ref name="pmid10647727">{{Cite journal |vauthors=Liu Z, Pflugfelder SC |date=January 2000 |title=The effects of long-term contact lens wear on corneal thickness, curvature, and surface regularity |journal=[[Ophthalmology (journal)|Ophthalmology]] |volume=107 |issue=1 |pages=105–11 |doi=10.1016/S0161-6420(99)00027-5 |pmid=10647727}}</ref> Long-term wear of rigid contacts is associated with decreased [[corneal keratocyte]] density<ref name="pmid16303530">{{Cite journal |vauthors=Hollingsworth JG, Efron N |date=June 2004 |title=Confocal microscopy of the corneas of long-term rigid contact lens wearers |journal=[[Cont Lens Anterior Eye]] |volume=27 |issue=2 |pages=57–64 |doi=10.1016/j.clae.2004.02.002 |pmid=16303530 |doi-access=free}}</ref> and increased number of [[corneal epithelium|epithelial]] [[Langerhans cells]].<ref name="pmid17198013">{{Cite journal |vauthors=Zhivov A, Stave J, Vollmar B, Guthoff R |date=January 2007 |title=''In vivo'' confocal microscopic evaluation of langerhans cell density and distribution in the corneal epithelium of healthy volunteers and contact lens wearers |journal=[[Cornea]] |volume=26 |issue=1 |pages=47–54 |doi=10.1097/ICO.0b013e31802e3b55 |pmid=17198013 |s2cid=22951471}}</ref>

All contact lenses 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.