Editing Cornea (section)

==Clinical significance==
The most common corneal disorders are the following:
* [[Corneal abrasion]] – a medical condition involving the loss of the surface epithelial layer of the eye's cornea as a result of trauma to the surface of the eye.
* [[Corneal dystrophy]] – a condition in which one or more parts of the cornea lose their normal clarity due to a buildup of cloudy material.
* [[Corneal ulcer]] – an inflammatory or infective condition of the cornea involving disruption of its epithelial layer with involvement of the corneal stroma.
* [[Corneal neovascularization]] – excessive ingrowth of blood vessels from the limbal vascular plexus into the cornea, caused by deprivation of oxygen from the air.
* [[Fuchs' dystrophy]] – cloudy morning vision.
* [[Keratitis]] – inflammation of the cornea.
* [[Keratoconus]] – a degenerative disease, the cornea thins and changes shape to be more like a cone.
* Corneal foreign body – a foreign object present in the cornea, one of the most common preventable occupational hazards.<ref>Onkar A. Commentary: Tackling the corneal foreign body. Indian J Ophthalmol 2020;68:57-8.</ref>

===Management===
[[File:Cornea.jpg|thumb|[[Slit lamp]] image of the cornea, iris and lens (showing mild [[cataract]])]]

====Surgical procedures====

Various [[refractive eye surgery]] techniques change the shape of the cornea in order to reduce the need for corrective lenses or otherwise improve the refractive state of the eye. In many of the techniques used today, reshaping of the cornea is performed by photoablation using the [[excimer laser]].

There are also synthetic corneas (keratoprostheses) in development.  Most are merely plastic inserts, but there are also those composed of biocompatible synthetic materials that encourage tissue ingrowth into the synthetic cornea, thereby promoting biointegration. Other methods, such as magnetic deformable membranes<ref>{{cite journal |first1=Steven M. |last1=Jones |first2=Sandra E. |last2=Balderas-Mata |first3=Sylwia M. |last3=Maliszewska |first4=Scot S. |last4=Olivier |first5=John S. |last5=Werner |title=Performance of 97-elements ALPAO membrane magnetic deformable mirror in Adaptive Optics - Optical Coherence Tomography system for ''in vivo'' imaging of human retina |journal=Photonics Letters of Poland |volume=3 |issue=4 |year=2011 |pages=147–9 |url=http://photonics.pl/PLP/index.php/letters/article/view/3-52}}</ref> and optically coherent [[transcranial magnetic stimulation]] of the [[Retina|human retina]]<ref>{{cite book |doi=10.1109/IEMBS.2010.5627660 |pmid=21097016 |chapter=Towards direct head navigation for robot-guided Transcranial Magnetic Stimulation using 3D laserscans: Idea, setup and feasibility |title=2010 Annual International Conference of the IEEE Engineering in Medicine and Biology |volume=2010 |year=2010 |last1=Richter |first1=Lars |last2=Bruder |first2=Ralf |last3=Schlaefer |first3=Alexander |last4=Schweikard |first4=Achim |isbn=978-1-4244-4123-5 |pages=2283–86|s2cid=3092563 }}</ref> are still in very early stages of research.

====Other procedures====
[[Orthokeratology]] is a method using specialized hard or rigid gas-permeable [[contact lens]]es to transiently reshape the cornea in order to improve the refractive state of the eye or reduce the need for eyeglasses and contact lenses.

In 2009, researchers at the University of Pittsburgh Medical center demonstrated that [[stem cell]] collected from human corneas can restore transparency without provoking a rejection response in mice with corneal damage.<ref>{{cite journal |last1=Du |first1=Yiqin |last2=Carlson |first2=Eric C. |last3=Funderburgh |first3=Martha L. |last4=Birk |first4=David E. |last5=Pearlman |first5=Eric |last6=Guo |first6=Naxin |last7=Kao |first7=Winston W.-Y. |last8=Funderburgh |first8=James L. |year=2009 |title=Stem Cell Therapy Restores Transparency to Defective Murine Corneas |journal=Stem Cells |volume=27 |issue=7 |pages=1635–42 |pmid=19544455 |pmc=2877374 |doi=10.1002/stem.91}}
* {{cite news |date=13 April 2009 |title=Stem Cell Therapy Makes Cloudy Corneas Clear, According To Pitt Researchers |work=Medical News Today |url=http://www.medicalnewstoday.com/releases/145528.php}}</ref> For corneal epithelial diseases such as Stevens Johnson Syndrome, persistent corneal ulcer etc., the autologous contralateral (normal) suprabasal limbus derived in vitro expanded corneal limbal stem cells are found to be effective<ref>{{cite journal |doi=10.1089/ten.tea.2008.0041 |title=''Ex Vivo'' Cultivation of Corneal Limbal Epithelial Cells in a Thermoreversible Polymer (Mebiol Gel) and Their Transplantation in Rabbits: An Animal Model |year=2009 |last1=Sitalakshmi |first1=G. |last2=Sudha |first2=B. |last3=Madhavan |first3=H.N. |last4=Vinay |first4=S. |last5=Krishnakumar |first5=S. |last6=Mori |first6=Yuichi |last7=Yoshioka |first7=Hiroshi |last8=Abraham |first8=Samuel |journal=Tissue Engineering Part A |volume=15 |issue=2 |pages=407–15 |pmid=18724830}}</ref>  as amniotic membrane based expansion is controversial.<ref>{{cite journal |doi=10.1001/archopht.124.12.1734 |title=Inherent Risks Associated with Manufacture of Bioengineered Ocular Surface Tissue |year=2006 |last1=Schwab |first1=Ivan R. |journal=Archives of Ophthalmology |volume=124 |issue=12 |pages=1734–40 |pmid=17159033 |last2=Johnson |first2=NT |last3=Harkin |first3=DG|doi-access=free }}</ref> For endothelial diseases, such as bullous keratopathy, cadaver corneal endothelial precursor cells have been proven to be efficient. Recently emerging tissue engineering technologies are expected to be capable of making one cadaver-donor's corneal cells be expanded and be usable in more than one patient's eye.<ref>{{cite journal |pmid=18246029 |year=2008 |last1=Hitani |first1=K |last2=Yokoo |first2=S |last3=Honda |first3=N |last4=Usui |first4=T |last5=Yamagami |first5=S |last6=Amano |first6=S |title=Transplantation of a sheet of human corneal endothelial cell in a rabbit model |volume=14 |pages=1–9 |pmc=2267690 |journal=Molecular Vision}}</ref><ref>{{cite journal |last1=Parikumar |first1=Periyasamy |last2=Haraguchi |first2=Kazutoshi |last3=Ohbayashi |first3=Akira |last4=Senthilkumar |first4=Rajappa |last5=Abraham |first5=Samuel J. K. |year=2014 |title=Successful Transplantation of ''In Vitro'' Expanded Human Cadaver Corneal Endothelial Precursor Cells On to a Cadaver Bovine's Eye Using a Nanocomposite Gel Sheet |journal=Current Eye Research |volume=39 |issue=5 |pages=522–6 |pmid=24144454 |doi=10.3109/02713683.2013.838633|s2cid=23131826 }}</ref>

====Corneal retention and permeability in topical drug delivery to the eye====
The majority of ocular therapeutic agents are administered to the eye via the topical route. Cornea is one of the main barriers for drug diffusion because of its highly impermeable nature. Its continuous irrigation with a tear fluid also results in poor retention of the therapeutic agents on the ocular surface. Poor permeability of the cornea and quick wash out of therapeutic agents from ocular surface result in very low bioavailability of the drugs administered via topical route (typically less than 5%). Poor retention of formulations on ocular surfaces could potentially be improved with the use of mucoadhesive polymers.<ref>{{Cite journal|last=Ludwig|first=Annick|date=2005-11-03|title=The use of mucoadhesive polymers in ocular drug delivery|journal=Advanced Drug Delivery Reviews|series=Mucoadhesive Polymers: Strategies, Achievements and Future Challenges|volume=57|issue=11|pages=1595–1639|doi=10.1016/j.addr.2005.07.005|pmid=16198021|issn=0169-409X}}</ref> Drug permeability through the cornea could be facilitated with addition of penetration enhancers into topical formulations.<ref>{{Cite journal|last1=Khutoryanskiy|first1=Vitaliy V.|last2=Steele|first2=Fraser|last3=Morrison|first3=Peter W. J.|last4=Moiseev|first4=Roman V.|date=July 2019|title=Penetration Enhancers in Ocular Drug Delivery|journal=Pharmaceutics|volume=11|issue=7|pages=321|doi=10.3390/pharmaceutics11070321|pmid=31324063|pmc=6681039|doi-access=free}}</ref>

=== Transplantation ===
{{Main|Corneal transplantation}}
If the corneal stroma develops visually significant opacity, irregularity, or edema, a cornea of a deceased donor can be [[Corneal transplantation|transplanted]]. Because there are no blood vessels in the cornea, there are also few problems with [[Transplant rejection|rejection]] of the new cornea.

When a cornea is needed for transplant, as from an eye bank, the best procedure is to remove the cornea from the eyeball, preventing the cornea from absorbing the aqueous humor.<ref name="ReferenceA" />

There is a global shortage of corneal donations, severely limiting the availability of corneal transplants across most of the world. A 2016 study found that 12.7 million visually impaired people were in need of a corneal transplant, with only 1 cornea available for every 70 needed.<ref name = "Global Survey of Corneal Transplantation and Eye Banking">Gain P, Jullienne R, He Z, et al. Global Survey of Corneal Transplantation and Eye Banking. JAMA Ophthalmol. 2016;134(2):167–173. doi:10.1001/jamaophthalmol.2015.4776</ref> Many countries have years-long waitlists for corneal transplant surgery due to the shortage of donated corneas.<ref>Kramer L. Corneal transplant wait list varies across Canada. CMAJ. 2013;185(11):E511-E512. doi:10.1503/cmaj.109-4517</ref><ref>Hara  H, Cooper  DKC.  Xenotransplantation: the future of corneal transplantation?   Cornea. 2011;30(4):371-378. doi:10.1097/ICO.0b013e3181f237ef</ref> Only a handful of countries consistently have a large enough supply of donated corneas to meet local demand without a waitlist, including the United States, Italy, and Sri Lanka.<ref name = "Global Survey of Corneal Transplantation and Eye Banking"/>