Editing Intraocular lens (section)

==Medical uses==
Intraocular lenses have been used since 1999 for correcting larger errors in [[myopic|near-sighted]], [[farsightedness|far-sighted]], and [[astigmatism|astigmatic]] eyes. This type of IOL is also called [[phakic intraocular lens]] (PIOL), as it is implanted without removing the patient's natural crystalline lens.<ref name="Kohnen et al 2010">{{Cite journal |last1=Kohnen |first1=Thomas |last2=Kook |first2=Daniel |last3=Morral |first3=Merce |last4=Güell |first4=Jose Luis |date=2010-12-01 |title=Phakic intraocular lenses: Part 2: Results and complications |url=https://www.sciencedirect.com/science/article/pii/S0886335010014240 |journal=Journal of Cataract & Refractive Surgery |language=en |volume=36 |issue=12 |pages=2174 |doi=10.1016/j.jcrs.2010.10.007 |pmid=21111322 |s2cid=44683984 |issn=0886-3350|url-access=subscription }}</ref>

Phakic IOL appear to be lower risk than [[LASIK|excimer laser surgery]] (LASIK) in those with significant near-sightedness.<ref name=Barsam2014>{{cite journal |vauthors=Barsam A, Allan BD |title=Excimer laser refractive surgery versus phakic intraocular lenses for the correction of moderate to high myopia |journal=The Cochrane Database of Systematic Reviews |volume=2014 |issue=6 |pages=CD007679 |date=June 2014 |pmid=24937100 |doi=10.1002/14651858.CD007679.pub4 |pmc=10726981 }}</ref>

More commonly, IOLs are implanted via ''Clear Lens Extraction And Replacement'' (CLEAR) surgery, also known as refractive lens exchange (RLE)<ref name="Poothullil and Azar 2007" /> or [[clear lens extraction]] (CLE). During CLEAR, the crystalline lens is extracted and an IOL replaces it in a process that is very similar to cataract surgery: both involve lens replacement, local anesthesia, last approximately 30 minutes, and require making a small incision in the eye for lens insertion. People recover from CLEAR surgery 1–7 days after the operation. During this time, they should avoid strenuous exercise or anything else that significantly raises blood pressure. They should visit their ophthalmologists regularly for several weeks to monitor the IOL implants.{{cn|date=February 2023}}

CLEAR has a 90% success rate (risks include wound leakage, infection, inflammation, and astigmatism). CLEAR can be performed only on patients ages 40 and older. This is to ensure that eye growth, which disrupts IOL lenses, will not occur post-surgery.{{dubious|date=December 2023}}{{cn|date=February 2023}}

Once implanted, IOLs have three major benefits. First, they are an alternative to the [[LASIK|excimer laser]] procedure (LASIK), a form of eye surgery that does not work for people with serious vision problems. Effective IOL implants also eliminate the need for glasses or contact lenses post-surgery for most patients.<ref name="Zamora" /> Cataracts will not appear or return, as the lens has been removed. The disadvantage is that the eye's ability to change focus (accommodate) has generally been reduced or eliminated, depending on the kind of lens implanted.{{cn|date=February 2023}}

Some of the risks that were found in the early 2000s during a three-year study of the Artisan lenses were:{{cn|date=February 2023}}
* a yearly loss of 1.8% of the [[Corneal endothelium|endothelial cells]],
* 0.6% risk of [[retinal detachment]],
* 0.6% risk of [[cataract]] (other studies have shown a risk of 0.5–1.0%), and
* 0.4% risk of corneal swelling.

Other risks include:{{cn|date=February 2023}}
* 0.03–0.05% eye infection risk, which in worst case can lead to blindness. (This risk exists in all eye surgery procedures and is not unique to IOLs.)
* [[glaucoma]],
* [[Astigmatism|astigmatism]],
* remaining near- or far-sightedness,
* rotation of the lens inside the eye one or two days after surgery.

Toric IOLs must be of the correct power and aligned inside the eye on a meridian that counteracts the preexisting astigmatism. One of the causes of unsatisfactory refractory correction is that the lens may be incorrectly placed by the surgeon, or rotate inside the eye if is too short, which may occur if the eye was incorrectly measured, or because the [[Ciliary sulcus|sulcus]] has a slightly oval shape. If misaligned, preexisting astigmatism may not be corrected completely or may even increase.{{cn|date=February 2023}}

When standard IOLs are implanted with a CLEAR procedure, in substitution of the patient's crystalline, astigmatism is typically not corrected, as astigmatism is mainly attributable to a deformation of the [[cornea]]. [[#Toric|Toric IOLs]] may be used during the CLEAR procedure to correct astigmatism.{{cn|date=February 2023}}

The surgeon can ascertain the astigmatic, or steepest, meridian in a number of ways, including manifest refraction or [[corneal topography]]. Manifest refraction is the familiar test where the eye doctor rotates lenses in front of the eye, asking the patient, "Which is better (or clearer), this one or this one?" Corneal topography is considered a more quantitative test, and for purposes of aligning a toric IOL, most surgeons use a measurement called simulated keratometry (SimK), which is calculated by the internal programming of the corneal topography machine, to determine the astigmatic meridian on the surface of the cornea. The astigmatic meridian can also be identified using corneal wavefront technology or paraxial curvature matching.{{cn|date=February 2023}}

===Indications for refractive lens exchange===
{{Main|Clear lens extraction}}
Severe [[myopia]] or [[hyperopia]] with coexisting [[presbyopia]] are the primary indicators for refractive lens exchange (RLE), as RLE leads to complete loss of accommodation. Underlying regular astigmatism can also be managed by RLE, even beyond the scope of corneal incisional techniques, by toric lens implants. Marginal indications for RLE are presbyopia without ametropia, using a multifocal lens implant, presbyopia with underlying astigmatism, and prepresbyopoa hyperopia of from +5 to +10 D not amenable to keratorefractive surgery or phakic IOL due to a shallow anterior chamber.<ref name="Kook and Kohnen 2012" />

====Complications====
Complications of RLE are similar to those after cataract surgery, but with the difference that RLE is often used in very short or very long eyes and patients’ ages tend to be significantly lower, so consideration must be given to longer-term effects.<ref name="Kook and Kohnen 2012" />