keratoconus

Image:Kc simulation.jpg seen by a person with keratoconus.
"... a candle, when looked at, appears like a number of lights, confusedly running into one another" — Nottingham]]

People with early keratoconus often notice a minor blurring or distortion of their vision, as well as an increased sensitivity to light, so they may visit their clinician seeking corrective lenses for reading or driving.{{cite book |vauthors=Feder R, Kshettry P | year = 2005| title = Cornea| chapter = Non-inflammatory Ectactic Disorders, Chapter 78 | editor = Krachmer J | publisher = Mosby | isbn = 978-0-323-02315-3}}{{cite web| author=Epstein A| year=2000| title=Keratoconus and related disorders| work=North Shore Contact Lens| url=http://www.northshorecontactlens.com/KeratoconusText.pdf| access-date=8 September 2007| archive-url=https://web.archive.org/web/20120208101839/http://www.northshorecontactlens.com/KeratoconusText.pdf| archive-date=8 February 2012| url-status=dead}} At early stages, the symptoms of keratoconus may be no different from those of any other refractive defect of the eye. As the disease progresses, vision deteriorates, sometimes rapidly due to irregular astigmatism. Visual acuity becomes impaired at all distances, and night vision is often poor. Some individuals have vision in one eye that is markedly worse than the other eye. The disease is often bilateral though asymmetrical. Some develop photophobia (sensitivity to bright light), eye strain from squinting in order to read, or itching in the eye, but there is normally little or no sensation of pain. It may cause luminous objects to appear as cylindrical pipes with the same intensity at all points.

Image:Kc simulation2.png

The classic symptom of keratoconus is the perception of multiple "ghost" images, known as monocular polyopia. This effect is most clearly seen with a high contrast field, such as a point of light on a dark background. Instead of seeing just one point, a person with keratoconus sees many images of the point, spread out in a chaotic pattern. This pattern does not typically change from day to day, but over time, it often takes on new forms. People also commonly notice streaking and flaring distortion around light sources. Some even notice the images moving relative to one another in time with their heartbeat.

The predominant optical aberration of the eye in keratoconus is coma.{{cite journal |vauthors=Pantanelli S, MacRae S, Jeong TM, Yoon G |title=Characterizing the wave aberration in eyes with keratoconus or penetrating keratoplasty using a high-dynamic range wavefront sensor |journal=Ophthalmology |volume=114 |issue=11 |pages=2013–21 |date=November 2007 |pmid=17553566 |doi=10.1016/j.ophtha.2007.01.008}}{{cite journal |author=Nakagawa T |title=Higher-order aberrations due to the posterior corneal surface in patients with keratoconus |journal=Investigative Ophthalmology & Visual Science |volume=50 |issue=6 |pages=2660–5 |date=June 2009 |pmid=19029032 |doi=10.1167/iovs.08-2754 |author2=Maeda N |author3=Kosaki R |display-authors=3 |last4=Hori |first4=Y. |last5=Inoue |first5=T. |last6=Saika |first6=M. |last7=Mihashi |first7=T. |last8=Fujikado |first8=T. |last9=Tano |first9=Y.|doi-access= }} The visual distortion experienced by the person comes from two sources, one being the irregular deformation of the surface of the cornea, and the other being scarring that occurs on its exposed highpoints. These factors act to form regions on the cornea that map an image to different locations on the retina. The effect can worsen in low light conditions, as the dark-adapted pupil dilates to expose more of the irregular surface of the cornea.

Six genes have been found to be associated with the condition. These genes include BANP-ZNF469, COL4A4, FOXO1, FNDC3B, IMMP2L and RXRA-COL5A1. Others likely also exist.{{cite journal|last1=Rong|first1=SS|last2=Ma|first2=STU|last3=Yu|first3=XT|last4=Ma|first4=L|last5=Chu|first5=WK|last6=Chan|first6=TCY|last7=Wang|first7=YM|last8=Young|first8=AL|last9=Pang|first9=CP|last10=Jhanji|first10=V|last11=Chen|first11=LJ|title=Genetic associations for keratoconus: a systematic review and meta-analysis.|journal=Scientific Reports|date=4 July 2017|volume=7|issue=1|pages=4620|doi=10.1038/s41598-017-04393-2|pmid=28676647|pmc=5496893|bibcode=2017NatSR...7.4620R}}

Patients with a parent, sibling, or child who has keratoconus have 15 to 67 times higher risk in developing corneal ectasia compared to patients with no affected relatives.

File:David G Cogan case 245 keratoconus thin stroma wrinkled endothelium.png

Despite considerable research, the cause of keratoconus remains unclear. Several sources suggest that keratoconus likely arises from a number of different factors: genetic, environmental or cellular, any of which may form the trigger for the onset of the disease.{{cite book | last =Arffa R| year = 1997| title = Grayson's Diseases of the Cornea. Chap. 17 | pages = 452–454| publisher = Mosby | isbn = 978-0-8151-3654-5 }}Brown D. National Keratoconus Foundation: Research Overview. http://www.nkcf.org {{webarchive|url=https://web.archive.org/web/20040322044445/http://nkcf.org/ |date=22 March 2004 }}. Accessed 12 February 2006.Warren, Catherine. What Causes Keratoconus? National Keratoconus Foundation. {{cite web |url=http://www.nkcf.org/what-is-keratoconus/ |title=What is Keratoconus Disease - Bulging Eye Disease Causes, Symptoms | NKCF |access-date=30 March 2015 |url-status=dead |archive-url=https://web.archive.org/web/20131211044918/http://www.nkcf.org/what-is-keratoconus/ |archive-date=11 December 2013}} (14 March 2015) Once initiated, the disease normally develops by progressive dissolution of Bowman's layer, which lies between the corneal epithelium and stroma. As the two come into contact, cellular and structural changes in the cornea adversely affect its integrity and lead to the bulging and scarring characteristic of the disorder. Within any individual keratoconic cornea, regions of degenerative thinning coexisting with regions undergoing wound healing may be found. Scarring appears to be an aspect of the corneal degradation; however, a recent, large, multicenter study suggests abrasion by contact lenses may increase the likelihood of this finding by a factor over two.{{Cite journal |last=Barr JT |last2=Wilson BS |last3=Gordon MO |last4=Rah |first4=Marjorie J |last5=Riley |first5=Colleen |last6=Kollbaum |first6=Pete S |last7=Zadnik |first7=Karla |display-authors=3 |date=January 2006 |title=Estimation of the incidence and factors predictive of corneal scarring in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study |journal=Cornea |volume=25 |issue=1 |pages=16–25 |doi=10.1097/01.ico.0000164831.87593.08 |pmid=16331035 |s2cid=220574540}}{{cite web|title=The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Archive |url=https://vrcc.wustl.edu/clekarchive/ |url-status=dead |archive-url=https://web.archive.org/web/20070630052538/https://vrcc.wustl.edu/clekarchive/ |archive-date=30 June 2007}}

A number of studies have indicated keratoconic corneas show signs of increased activity by proteases, a class of enzymes that break some of the collagen cross-linkages in the stroma, with a simultaneous reduced expression of protease inhibitors.{{cite journal |vauthors=Spoerl E, Wollensak G, Seiler T |title=Increased resistance of crosslinked cornea against enzymatic digestion |journal=Current Eye Research |volume=29 |issue=1 |pages=35–40 |date=July 2004 |pmid=15370365 |doi=10.1080/02713680490513182|s2cid=22361390 }} Other studies have suggested that reduced activity by the enzyme aldehyde dehydrogenase may be responsible for a build-up of free radicals and oxidising species in the cornea.{{cite journal |author=Gondhowiardjo TD |title=Analysis of corneal aldehyde dehydrogenase patterns in pathologic corneas |journal=Cornea |volume=12 |issue=2 |pages=146–54 |date=March 1993 |pmid=8500322 |doi=10.1097/00003226-199303000-00010 |author2=van Haeringen NJ |author3=Völker-Dieben HJ |display-authors=3 |last4=Beekhuis |first4=Houdijn W. |last5=Kok |first5=Jan H.C. |last6=Van Rij |first6=Gabriel |last7=Pels |first7=Liesbeth |last8=Kijlstra |first8=Aize|s2cid=45104769 }} Whatever the pathogenetical process, the damage caused by activity within the cornea likely results in a reduction in its thickness and biomechanical strength. At an ultrastructural level the weakening of the corneal tissue is associated with a disruption of the regular arrangement of the collagen layers and collagen fibril orientation.{{cite journal |vauthors=Daxer A, Fratzl P | year = 1997 | title = Collagen fibril orientation in the human corneal stroma and its implications in keratoconus | journal = Invest Ophthalmol Vis Sci | volume = 38 | issue = 1| pages = 121–129 | pmid = 9008637 }} While keratoconus is considered a noninflammatory disorder, one study shows wearing rigid contact lenses by people leads to overexpression of proinflammatory cytokines, such as IL-6, TNF-alpha, ICAM-1, and VCAM-1 in the tear fluid.{{cite journal |vauthors=Lema I, Durán JA, Ruiz C, Díez-Feijoo E, Acera A, Merayo J |title=Inflammatory response to contact lenses in patients with keratoconus compared with myopic subjects |journal=Cornea |volume=27 |issue=7 |pages=758–63 |date=August 2008 |pmid=18650659 |doi=10.1097/ICO.0b013e31816a3591|s2cid=25238570 |hdl=10651/34844 |hdl-access=free }}

A genetic predisposition to keratoconus has been observed,{{cite journal |vauthors=Edwards M, McGhee CN, Dean S |title=The genetics of keratoconus |journal=Clinical & Experimental Ophthalmology |volume=29 |issue=6 |pages=345–51 |date=December 2001 |pmid=11778802 |doi=10.1046/j.1442-9071.2001.d01-16.x|s2cid=46643398 }} with the disease running in certain families,{{cite journal |author=Zadnik K |title=Baseline findings in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study |journal=Investigative Ophthalmology & Visual Science |volume=39 |issue=13 |pages=2537–46 |date=December 1998 |pmid=9856763 |url=http://iovs.arvojournals.org/article.aspx?articleid=2161642 |author2=Barr JT |author3=Edrington TB |display-authors=3 |last4=Everett |first4=DF |last5=Jameson |first5=M |last6=McMahon |first6=TT |last7=Shin |first7=JA |last8=Sterling |first8=JL |last9=Wagner |first9=H |url-status=dead |archive-url=https://web.archive.org/web/20161003141110/http://iovs.arvojournals.org/article.aspx?articleid=2161642 |archive-date=3 October 2016 |access-date=25 June 2016 }} and incidences reported of concordance in identical twins. The frequency of occurrence in close family members is not clearly defined, though it is known to be considerably higher than that in the general population, and studies have obtained estimates ranging between 6% and 19%.{{cite book | last = Merin S| year = 2005 | title = Inherited Eye Disorders: Diagnosis and Management | publisher = Taylor & Francis | location =Boca Raton | isbn = 978-1-57444-839-9}} Two studies involving isolated, largely homogenetic communities have contrarily mapped putative gene locations to chromosomes 16q and 20q. Most genetic studies agree on an autosomal dominant model of inheritance. A rare, autosomal dominant form of severe keratoconus with anterior polar cataract is caused by a mutation in the seed region of mir-184, a microRNA that is highly expressed in the cornea and anterior lens.{{cite journal | doi = 10.1016/j.ajhg.2011.09.014 | vauthors = Hughes AE, Bradley DT, Campbell M, Lechner J, Dash DP, Simpson DA, Willoughby CE | year = 2011 | title = Mutation Altering the miR-184 Seed Region Causes Familial Keratoconus with Cataract | journal = The American Journal of Human Genetics | volume = 89 | issue = 5 | pages = 628–33 | pmc = 3213395 | pmid = 21996275 | df = dmy-all }} Keratoconus is diagnosed more often in people with Down's syndrome, though the reasons for this link have not yet been determined.{{cite journal |author=Rabinowitz YS |title=Keratoconus |journal=Survey of Ophthalmology |volume=42 |issue=4 |pages=297–319 |year=1998 |pmid=9493273 |doi=10.1016/S0039-6257(97)00119-7}}

Researches also have shed light on the role of hormones in the pathophysiology of keratoconus. Hormones such as androgen, prolactin, estrogen and progesterone have been shown to influence corneal biomechanics and tissue remodeling, potentially affecting the integrity of the cornea in individuals predisposed to keratoconus.{{cite journal |title=Serum androgens and prolactin levels in patients with keratoconus |journal=Clin Exp Optom |date=2023 |doi=10.1080/08164622.2022.2081067 |pmid=35680612 |url=https://pubmed.ncbi.nlm.nih.gov/35680612/ |ref=10.1080/08164622.2022.2081067 |last1=Jamali |first1=Hossein |last2=Heydari |first2=Mojtaba |last3=Masihpour |first3=Nasrin |last4=Khosravi |first4=Amir |last5=Zare |first5=Mousa |last6=Shams |first6=Mesbah |last7=Omrani |first7=Gholamhossein Ranjbar |volume=106 |issue=5 |pages=484–488 |s2cid=249545241 }} Moreover, fluctuations in hormonal levels during puberty and pregnancy have been associated with the onset or exacerbation of keratoconus in some cases.

Keratoconus has been associated with atopic diseases, which include asthma, allergies, and eczema, and it is not uncommon for several or all of these diseases to affect one person. Keratoconus is also associated with Alport syndrome, Down syndrome and Marfan syndrome.{{cite book|last=Kumar|first=Vinay|title=Robbins Basic Pathology|year=2007|publisher=Saunders/Elsevier|location=Philadelphia|isbn=978-1-4160-2973-1|chapter=Eye: Cornea, Degenerations and Dystrophies|edition=8th}} A number of studies suggest vigorous eye rubbing contributes to the progression of keratoconus, and people should be discouraged from the practice.{{cite journal |author=Koenig SB |title=Bilateral recurrent self-induced keratoconus |journal=Eye & Contact Lens |volume=34 |issue=6 |pages=343–4 |date=November 2008 |pmid=18997547 |doi=10.1097/ICL.0b013e31818c25eb}}{{cite journal |vauthors=McMonnies CW, Boneham GC |title=Keratoconus, allergy, itch, eye-rubbing and hand-dominance |journal=Clinical & Experimental Optometry |volume=86 |issue=6 |pages=376–84 |date=November 2003 |pmid=14632614 |doi=10.1111/j.1444-0938.2003.tb03082.x|doi-access=free }}{{cite journal |vauthors=Bawazeer AM, Hodge WG, Lorimer B |title=Atopy and keratoconus: a multivariate analysis |journal=The British Journal of Ophthalmology |volume=84 |issue=8 |pages=834–6 |date=August 2000 |pmid=10906086 |pmc=1723585 |doi=10.1136/bjo.84.8.834}}{{cite journal |vauthors=Jafri B, Lichter H, Stulting RD |title=Asymmetric keratoconus attributed to eye rubbing |journal=Cornea |volume=23 |issue=6 |pages=560–4 |date=August 2004 |pmid=15256993 |doi=10.1097/01.ico.0000121711.58571.8d|s2cid=40534579 }}{{cite journal |vauthors=Ioannidis AS, Speedwell L, Nischal KK |title=Unilateral keratoconus in a child with chronic and persistent eye rubbing |journal=American Journal of Ophthalmology |volume=139 |issue=2 |pages=356–7 |date=February 2005 |pmid=15734005 |doi=10.1016/j.ajo.2004.07.044}}{{cite journal |vauthors=Lindsay RG, Bruce AS, Gutteridge IF |title=Keratoconus associated with continual eye rubbing due to punctal agenesis |journal=Cornea |volume=19 |issue=4 |pages=567–9 |date=July 2000 |pmid=10928781 |doi=10.1097/00003226-200007000-00034|s2cid=8978974 }} Keratoconus differs from ectasia, which is caused by LASIK eye surgery. Post-LASIK Ectasia has been associated with the excessive removal of the eye's stromal bed tissue during surgery.

File:Keratoconus.svg]]

File:Medmont E300 cone.jpg

Prior to any physical examination, the diagnosis of keratoconus frequently begins with an ophthalmologist's or optometrist's assessment of the person's medical history, particularly the chief complaint and other visual symptoms, the presence of any history of ocular disease or injury that might affect vision, and the presence of any family history of ocular disease. An eye chart, such as a standard Snellen chart of progressively smaller letters, is then used to determine the person's visual acuity. The eye examination may proceed to measurement of the localized curvature of the cornea with a manual keratometer,{{cite journal |author=Nordan LT |title=Keratoconus: diagnosis and treatment |journal=International Ophthalmology Clinics |volume=37 |issue=1 |pages=51–63 |year=1997 |pmid=9101345 |doi=10.1097/00004397-199703710-00005|s2cid=38203263 }} with detection of irregular astigmatism suggesting a possibility of keratoconus. Severe cases can exceed the instrument's measuring ability. A further indication can be provided by retinoscopy, in which a light beam is focused on the person's retina and the reflection, or reflex, observed as the examiner tilts the light source back and forth. Keratoconus is amongst the ophthalmic conditions that exhibit a scissor reflex action of two bands moving toward and away from each other like the blades of a pair of scissors.{{cite book | last =Zadnik K | year = 1997| title = The ocular examination : measurements and findings | publisher = W.B. Saunders| location = Philadelphia | isbn = 978-0-7216-5209-2}}

If keratoconus is suspected, the ophthalmologist or optometrist will search for other characteristic findings of the disease by means of slit lamp examination of the cornea.{{cite book | last =Rabonitz Y | year = 2004 | title = The Cornea| chapter = Ectatic Disorders of the Cornea | edition =4th| editor = Foster C| pages = 889–911| publisher = Lippincott Williams & Wilkins| location = Philadelphia| isbn = 978-0-7817-4206-1 |display-editors=etal}} An advanced case is usually readily apparent to the examiner, and can provide for an unambiguous diagnosis prior to more specialized testing. Under close examination, a ring of yellow-brown to olive-green pigmentation known as a Fleischer ring can be observed in around half of keratoconic eyes.{{cite journal |vauthors=Edrington TB, Zadnik K, Barr JT |title=Keratoconus |journal=Optometry Clinics |volume=4 |issue=3 |pages=65–73 |year=1995 |pmid=7767020}} The Fleischer ring, caused by deposition of the iron oxide hemosiderin within the corneal epithelium, is subtle and may not be readily detectable in all cases, but becomes more evident when viewed under a cobalt blue filter. Similarly, around 50% of subjects exhibit Vogt's striae, fine stress lines within the cornea caused by stretching and thinning. The striae temporarily disappear while slight pressure is applied to the eyeball. A highly pronounced cone can create a V-shaped indentation in the lower eyelid when the person's gaze is directed downwards, known as Munson's sign. Other clinical signs of keratoconus will normally have presented themselves long before Munson's sign becomes apparent,{{cite journal |vauthors=Krachmer JH, Feder RS, Belin MW |title=Keratoconus and related noninflammatory corneal thinning disorders |journal=Survey of Ophthalmology |volume=28 |issue=4 |pages=293–322 |year=1984 |pmid=6230745 |doi=10.1016/0039-6257(84)90094-8}} and so this finding, though a classic sign of the disease, tends not to be of primary diagnostic importance.

A handheld keratoscope, sometimes known as "Placido's disk", can provide a simple noninvasive visualization of the surface of the cornea by projecting a series of concentric rings of light onto the cornea. A more definitive diagnosis can be obtained using corneal topography, in which an automated instrument projects the illuminated pattern onto the cornea and determines its topography from analysis of the digital image. The topographical map indicates any distortions or scarring in the cornea, with keratoconus revealed by a characteristic steepening of curvature that is usually below the centerline of the eye. The technique can record a snapshot of the degree and extent of the deformation as a benchmark for assessing its rate of progression. It is of particular value in detecting the disorder in its early stages when other signs have not yet presented.{{cite journal |vauthors=Maguire LJ, Bourne WM |title=Corneal topography of early keratoconus |journal=American Journal of Ophthalmology |volume=108 |issue=2 |pages=107–12 |date=August 1989 |pmid=2757091 |doi=10.1016/0002-9394(89)90001-9}}

File:Corneal topography, stage II keratoconus (Elise A. Slim et al.).svg

Once keratoconus has been diagnosed, its degree may be classified by several metrics:{{cite web | author=Gupta D| title=Keratoconus: A clinical update| url=http://www.optometry.co.uk/files/882ed4bcea848897cbbe928e8bd1b0c3_gupta20050715.pdf | access-date=26 March 2006|archive-url = https://web.archive.org/web/20060515104049/http://www.optometry.co.uk/files/882ed4bcea848897cbbe928e8bd1b0c3_gupta20050715.pdf |archive-date = 15 May 2006|url-status=dead}}

• The steepness of greatest curvature from 'mild' (< 45 D), 'advanced' (up to 52 D) or 'severe' (> 52 D);
• The morphology of the cone: 'nipple' (small: 5 mm and near-central), 'oval' (larger, below-center and often sagging), or 'globus' (more than 75% of cornea affected);
• The corneal thickness from mild (> 506 μm) to advanced (< 446 μm).

Increasing use of corneal topography has led to a decline in use of these terms.

Image:KC-lens.jpg

In early stages of keratoconus, glasses or soft contact lenses can suffice to correct for the mild astigmatism. As the condition progresses, these may no longer provide the person with a satisfactory degree of visual acuity, and most practitioners will move to manage the condition with rigid contact lenses, known as rigid, gas-permeable, (RGP) lenses. RGP lenses provide a good level of visual correction, but do not arrest progression of the condition.{{cite web|url=http://www.rnib.org.uk/eye-health-eye-conditions-z-eye-conditions/corneal-dystrophies|title=Corneal Dystrophies (including Keratoconus)|work=Eye Info|publisher=RNIB|access-date=20 January 2009|url-status=live|archive-url=https://web.archive.org/web/20140424181701/http://www.rnib.org.uk/eye-health-eye-conditions-z-eye-conditions/corneal-dystrophies|archive-date=24 April 2014}}

In people with keratoconus, rigid contact lenses improve vision by means of tear fluid filling the gap between the irregular corneal surface and the smooth regular inner surface of the lens, thereby creating the effect of a smoother cornea. Many specialized types of contact lenses have been developed for keratoconus, and affected people may seek out both doctors specialized in conditions of the cornea, and contact lens fitters who have experience managing people with keratoconus. The irregular cone presents a challenge and the fitter will endeavor to produce a lens with the optimal contact, stability and steepness. Some trial-and-error fitting may prove necessary.

Traditionally, contact lenses for keratoconus have been the 'hard' or RGP variety, although manufacturers have also produced specialized 'soft' or hydrophilic lenses and, most recently, silicone hydrogel lenses. A soft lens has a tendency to conform to the conical shape of the cornea, thus diminishing its effect. To counter this, hybrid lenses have been developed that are hard in the centre and encompassed by a soft skirt. However, soft or earlier generation hybrid lenses did not prove effective for every person.{{cite journal |vauthors=Rubinstein MP, Sud S |title=The use of hybrid lenses in management of the irregular cornea |journal=Contact Lens & Anterior Eye |volume=22 |issue=3 |pages=87–90 |year=1999 |pmid=16303411 |doi=10.1016/S1367-0484(99)80044-7}} Early generation lenses have been discontinued.{{cite web|url = http://www.contactlensheadlines.com/2010/06/softperm-hybrid-contact-lenses-discontinued/|title = SoftPerm Hybrid Contact Lenses Discontinued|url-status = dead|archive-url = https://web.archive.org/web/20101012170024/http://www.contactlensheadlines.com/2010/06/softperm-hybrid-contact-lenses-discontinued/|archive-date = 12 October 2010|df = dmy-all}} The fourth generation of hybrid lens technology has improved, giving more people an option that combines the comfort of a soft lens with the visual acuity of an RGP lens.Davis Robert, Eiden Barry. Hybrid Contact Lens Management. Contact Lens Spectrum: {{cite web |url=http://www.clspectrum.com/article.aspx?article=104099 |title=Contact Lens Spectrum |access-date=12 October 2010 |url-status=dead |archive-url=https://web.archive.org/web/20101223025329/http://www.clspectrum.com/article.aspx?article=104099 |archive-date=23 December 2010 }}.

{{main|Scleral lens}}

File:Scleral lens worn on an eye.jpg

Scleral lenses are sometimes prescribed for cases of advanced or very irregular keratoconus; these lenses cover a greater proportion of the surface of the eye and hence can offer improved stability.{{cite journal |vauthors=Pullum KW, Buckley RJ |title=A study of 530 patients referred for rigid gas permeable scleral contact lens assessment |journal=Cornea |volume=16 |issue=6 |pages=612–22 |date=November 1997 |pmid=9395869 |doi=10.1097/00003226-199711000-00003}} Easier handling can find favor with people with reduced dexterity, such as the elderly.

Some people find good vision correction and comfort with a "piggyback" lens combination, in which RGP lenses are worn over soft lenses, both providing a degree of vision correction.{{cite journal |vauthors=Yeung K, Eghbali F, Weissman BA |title=Clinical experience with piggyback contact lens systems on keratoconic eyes |journal=Journal of the American Optometric Association |volume=66 |issue=9 |pages=539–43 |date=September 1995 |pmid=7490414}} One form of piggyback lens makes use of a soft lens with a countersunk central area to accept the rigid lens. Fitting a piggyback lens combination requires experience on the part of the lens fitter, and tolerance on the part of the person with keratoconus.

{{main|Cornea transplant}}

Image:Cornea transplant.jpg

File:Cornea Transplant.jpg

Between 11% and 27% of cases of keratoconus{{cite journal |vauthors=Schirmbeck T, Paula JS, Martin LF, Crósio Filho H, Romão E |title=[Efficacy and low cost in keratoconus treatment with rigid gas-permeable contact lens] |language=pt |journal=Arquivos Brasileiros de Oftalmologia |volume=68 |issue=2 |pages=219–22 |year=2005 |pmid=15905944|doi=10.1590/S0004-27492005000200012 |doi-access=free }}{{cite journal |author=Javadi MA |title=Outcomes of penetrating keratoplasty in keratoconus |journal=Cornea |volume=24 |issue=8 |pages=941–6 |date=November 2005 |pmid=16227837 |doi=10.1097/01.ico.0000159730.45177.cd |author2=Motlagh BF |author3=Jafarinasab MR |display-authors=3 |last4=Rabbanikhah |first4=Zahra |last5=Anissian |first5=Arash |last6=Souri |first6=Hamid |last7=Yazdani |first7=Shahin|s2cid=45054428 }} will progress to a point where vision correction is no longer possible, thinning of the cornea becomes excessive, or scarring as a result of contact lens wear causes problems of its own, and a corneal transplantation or penetrating keratoplasty becomes required. Keratoconus is the most common grounds for conducting a penetrating keratoplasty, generally accounting for around a quarter of such procedures.{{cite journal |vauthors=Mamalis N, Anderson CW, Kreisler KR, Lundergan MK, Olson RJ |title=Changing trends in the indications for penetrating keratoplasty |journal=Archives of Ophthalmology |volume=110 |issue=10 |pages=1409–11 |date=October 1992 |pmid=1417539 |url=http://archopht.ama-assn.org/cgi/pmidlookup?view=long&pmid=1417539 |doi=10.1001/archopht.1992.01080220071023 |access-date=16 April 2010 |url-access=subscription }}{{dead link|date=June 2022|bot=medic}}{{cbignore|bot=medic}} The corneal transplant surgeon trephines a lenticule of corneal tissue and then grafts the donor cornea to the existing eye tissue, usually using a combination of running and individual sutures. The cornea does not have a direct blood supply, so the donor tissue is not required to be blood type matched. Eye banks check the donor corneas for any disease or cellular irregularities.

The acute recovery period can take four to six weeks, and full postoperative vision stabilization often takes a year or more, but most transplants are very stable in the long term. The National Keratoconus Foundation reports that penetrating keratoplasty has the most successful outcome of all transplant procedures, and when performed for keratoconus in an otherwise healthy eye, its success rate can be 95% or greater. The sutures used usually dissolve over a period of three to five years, but individual sutures can be removed during the healing process if they are causing irritation to the person.

In the US, corneal transplants (also known as corneal grafts) for keratoconus are usually performed under sedation as outpatient surgery. In other countries, such as Australia and the UK, the operation is commonly performed with the person undergoing a general anaesthetic. All cases require a careful follow-up with an eye doctor (ophthalmologist or optometrist) for a number of years. Frequently, vision is greatly improved after the surgery, but even if the actual visual acuity does not improve, because the cornea is a more normal shape after the healing is completed, people can more easily be fitted with corrective lenses. Complications of corneal transplants are mostly related to vascularization of the corneal tissue and rejection of the donor cornea. Vision loss is very rare, though difficult-to-correct vision is possible. When rejection is severe, repeat transplants are often attempted, and are frequently successful.{{cite journal |vauthors=Al-Mezaine H, Wagoner MD |title=Repeat penetrating keratoplasty: indications, graft survival, and visual outcome |journal=The British Journal of Ophthalmology |volume=90 |issue=3 |pages=324–7 |date=March 2006 |pmid=16488955 |pmc=1856933 |doi=10.1136/bjo.2005.079624}} Keratoconus will not normally reoccur in the transplanted cornea; incidences of this have been observed, but are usually attributed to incomplete excision of the original cornea or inadequate screening of the donor tissue.{{cite journal |vauthors=Rubinfeld RS, Traboulsi EI, Arentsen JJ, Eagle RC |title=Keratoconus after penetrating keratoplasty |journal=Ophthalmic Surgery |volume=21 |issue=6 |pages=420–2 |date=June 1990 |pmid=2381677}} The long-term outlook for corneal transplants performed for keratoconus is usually favorable once the initial healing period is completed and a few years have elapsed without problems.

One way of reducing the risk of rejection is to use a technique called deep anterior lamellar keratoplasty (DALK). In a DALK graft, only the outermost epithelium and the main bulk of the cornea, the stroma, are replaced; the person's rearmost endothelium layer and the Descemet's membrane are left, giving some additional structural integrity to the postgraft cornea.{{Cite journal | last = Sugita | first = Juntaru | title = Advances in Corneal Research: Selected Transactions | volume = IV | pages = 163–166 | journal=World Congress on the Cornea| year = 1997}} Furthermore, it is possible to transplant freeze-dried donor tissue. The freeze-drying process ensures this tissue is dead, so there is no chance of rejection. Research from two trials in Iran provide low to moderate evidence that graft rejection is more likely to occur in penetrating keratoplasty than in DALK, though the likelihood for graft failure were similar with both procedures.{{cite journal |vauthors=Keane M, Coster D, Ziaei M, Williams K |title= Deep anterior lamellar keratoplasty versus penetrating keratoplasty for treating keratoconus |journal=Cochrane Database Syst Rev|volume=2014 |issue= 7 |pages= CD009700 |date=2014 |pmid= 25055058 |doi= 10.1002/14651858.CD009700.pub2|pmc= 10714035 |url= https://dspace.flinders.edu.au/xmlui/bitstream/2328/36030/1/Keane_Deep_P2014.pdf |hdl= 2328/36030 |hdl-access= free }}

Rarely, a nonpenetrating keratoplasty known as an epikeratophakia (or epikeratoplasty) may be performed in cases of keratoconus. The corneal epithelium is removed and a lenticule of donor cornea is grafted on top of it. The procedure requires a greater level of skill on the part of the surgeon, and is less frequently performed than a penetrating keratoplasty, as the outcome is generally less favorable. However, it may be seen as an option in a number of cases, particularly for young people.{{cite journal |vauthors=Wagoner MD, Smith SD, Rademaker WJ, Mahmood MA |title=Penetrating keratoplasty vs. epikeratoplasty for the surgical treatment of keratoconus |journal=Journal of Refractive Surgery |volume=17 |issue=2 |pages=138–46 |year=2001 |doi=10.3928/1081-597X-20010301-08 |pmid=11310764}}

{{main|Intrastromal corneal ring segments}}

Image:IntacsAfterInsertion.jpg

A possible surgical alternative to corneal transplant is the insertion of intrastromal corneal ring segments. A small incision is made in the periphery of the cornea and two thin arcs of polymethyl methacrylate are slid between the layers of the stroma on either side of the pupil before the incision is closed by a suture.{{cite book |vauthors=Yanoff M, Duker J | year = 2004 | title = Ophthalmology| edition =2nd | publisher = Mosby | isbn = 978-0-323-01634-6}} The segments push out against the curvature of the cornea, flattening the peak of the cone and returning it to a more natural shape. The procedure offers the benefit of being reversible and even potentially exchangeable as it involves no removal of eye tissue.{{cite journal|last1=Poulsen|first1=DM|last2=Kang|first2=JJ|title=Recent advances in the treatment of corneal ectasia with intrastromal corneal ring segments.|journal=Current Opinion in Ophthalmology|date=July 2015|volume=26|issue=4|pages=273–7|pmid=26058024|doi=10.1097/icu.0000000000000163|s2cid=23437970}}

Corneal intrastromal implantation surgery involving the implantation of a full ring is also available as a treatment option for keratoconus.{{cite web |title=Intracorneal ring: A good alternative to LASIK? |url=https://europe.ophthalmologytimes.com/cataract-refractive-ote/intracorneal-ring-good-alternative-lasik |website=Ophthalmology Times, Europe |access-date=9 May 2020 |language=en |date=1 October 2007 }}{{Dead link|date=May 2023 |bot=InternetArchiveBot |fix-attempted=yes }} Evidence supports that the full-ring implant improves vision outcomes for at least a year.{{cite journal |last1=Janani |first1=Leila |last2=Tanha |first2=Kiarash |last3=Najafi |first3=Fereshteh |last4=Jadidi |first4=Khosrow |last5=Nejat |first5=Farhad |last6=Hashemian |first6=Seyed Javad |last7=Dehghani |first7=Mohsen |last8=Sadeghi |first8=Masoumeh |title=Efficacy of complete rings (MyoRing) in treatment of Keratoconus: a systematic review and meta-analysis |journal=International Ophthalmology |date=1 June 2019 |volume=39 |issue=12 |pages=2929–2946 |doi=10.1007/s10792-019-01121-9|pmid=31154563 |s2cid=172136088 }}

Corneal collagen cross-linking is a developing treatment that aims to strengthen the cornea, however, according to a 2015 Cochrane review, there is insufficient evidence to determine if it is useful in keratoconus.{{cite journal|last1=Sykakis|first1=E|last2=Karim|first2=R|last3=Evans|first3=JR|last4=Bunce|first4=C|last5=Amissah-Arthur|first5=KN|last6=Patwary|first6=S|last7=McDonnell|first7=PJ|last8=Hamada|first8=S|title=Corneal collagen cross-linking for treating keratoconus.|journal=The Cochrane Database of Systematic Reviews|date=24 March 2015|volume=2015|issue=3|pages=CD010621|pmid=25803325|doi=10.1002/14651858.CD010621.pub2|pmc=10645161|url=https://researchonline.lshtm.ac.uk/4086927/1/Corneal%20collagen%20cross-linking_GREEN%20VoR.pdf}} In 2016, however, the FDA approved cross-linking surgery as a treatment for keratoconus and recommended that a registry system should be set-up to evaluate the long-term treatment effect.{{cite web |title=FDA approves first corneal cross-linking system for treatment |url=https://www.aoa.org/news/clinical-eye-care/fda-approves-first-corneal-cross-linking-system-for-treatment |website=www.aoa.org |access-date=21 May 2019 |language=en}}{{cite web |title=203324Orig2s000 |url=https://www.accessdata.fda.gov/drugsatfda_docs/nda/2016/203324Orig2s000SumR.pdf |archive-url=https://web.archive.org/web/20200801015646/https://www.accessdata.fda.gov/drugsatfda_docs/nda/2016/203324Orig2s000SumR.pdf |url-status=dead |archive-date=1 August 2020 |access-date=21 May 2019}} The Save Sight Keratoconus Registry is an international database of keratoconus patients that is tracking outcomes of cross-linking in patients with keratoconus.{{Cite web|title=The Save Sight Keratoconus Registry|url=https://www.keratoconus.org.au/treatments/australian-crosslinking-registry/|access-date=2020-06-09|website=Keratoconus Australia|language=en-AU}}

File:Mini Asymmetric Radial Keratotomy - MARK.jpg

Keratotomies are a group of corneal procedures. Radial keratotomy is a refractive surgery procedure where the surgeon makes a spoke-like pattern of incisions into the cornea to modify its shape. This early surgical option for myopia has been largely superseded by PRK, LASIK and other similar laser procedures. Laser surgery is usually contraindicated in keratoconus and other corneal thinning conditions, as removal of corneal stromal tissue will further damage an already thin and weak cornea.{{cite journal |vauthors=Jabbur NS, Stark WJ, Green WR |title=Corneal ectasia after laser-assisted in situ keratomileusis |journal=Archives of Ophthalmology |volume=119 |issue=11 |pages=1714–6 |date=November 2001 |pmid=11709027 |doi=10.1001/archopht.119.11.1714}} For similar reasons, radial keratotomy has also generally not been used for people with keratoconus.{{cite journal |vauthors=Colin J, Velou S |title=Current surgical options for keratoconus |journal=Journal of Cataract and Refractive Surgery |volume=29 |issue=2 |pages=379–86 |date=February 2003 |pmid=12648653 |doi=10.1016/S0886-3350(02)01968-5}}{{cite journal |vauthors=Bergmanson JP, Farmer EJ |title=A return to primitive practice? Radial keratotomy revisited |journal=Contact Lens & Anterior Eye |volume=22 |issue=1 |pages=2–10 |year=1999 |pmid=16303397 |doi=10.1016/S1367-0484(99)80024-1}}

However, more modern and keratoconus-specific variants, such as Mini asymmetric radial keratotomy (MARK) and Circular keratotomy (CK), have been found to be useful in keratoconus management, particularly when combined with Corneal cross-linking.{{cite journal |vauthors=Abbondanza M, Abbondanza G, De Felice V, Wong, ZSY |title=Long-term Results of Mini Asymmetric Radial Keratotomy and Corneal Cross-linking for the Treatment of Keratoconus |journal=Korean Journal of Ophthalmology |volume=33 |issue=2 |pages=189-195 |date=April 2019 |pmid=30977329 |doi=10.3341/kjo.2018.0028|doi-access=free }}{{cite journal |vauthors=Krumeich JH, Kezirian, GM |title=Circular keratotomy to reduce astigmatism and improve vision in stage I and II keratoconus |journal=Journal of Refractive Surgery |volume=25 |issue=4 |pages=357-365 |date=April 2009 |pmid=19431926 |doi=10.3928/1081597X-20090401-07}}

File:David G Cogan collection Case 244 photo 2 keratoconus Descemet rupture.png (magnified view)]]

Patients with keratoconus typically present initially with mild astigmatism and myopia, commonly at the onset of puberty, and are diagnosed by the late teenage years or early 20s. The disease can, however, present or progress at any age; in rare cases, keratoconus can present in children or not until later adulthood. A diagnosis of the disease at an early age may indicate a greater risk of severity in later life.{{cite journal |doi=10.1016/S0953-4431(96)00201-9 |title=Keratoconus: Current understanding of diagnosis and management |year=1997 |last1=Davis |first1=L |journal=Clinical Eye and Vision Care |volume=9 |pages=13–22}} Patients' vision will seem to fluctuate over a period of months, driving them to change lens prescriptions frequently, but as the condition worsens, contact lenses are required in the majority of cases. The course of the disorder can be quite variable, with some patients remaining stable for years or indefinitely, while others progress rapidly or experience occasional exacerbations over a long and otherwise steady course. Most commonly, keratoconus progresses for a period of 10 to 20 years before the course of the disease generally ceases in the third and fourth decades of life.

{{main|Corneal hydrops}}

Image:Hydrops (descemets membrane rupture) due to keratoconus.jpg

In advanced cases, bulging of the cornea can result in a localized rupture of Descemet's membrane, an inner layer of the cornea. Aqueous humor from the eye's anterior chamber seeps into the cornea before Descemet's membrane reseals. The patient experiences pain and a sudden severe clouding of vision, with the cornea taking on a translucent milky-white appearance known as a corneal hydrops.{{cite journal |vauthors=Grewal S, Laibson PR, Cohen EJ, Rapuano CJ |title=Acute hydrops in the corneal ectasias: associated factors and outcomes |journal=Transactions of the American Ophthalmological Society |volume=97 |pages=187–98; discussion 198–203 |year=1999 |pmid=10703124 |pmc=1298260}}

Although disconcerting to the patient, the effect is normally temporary and after a period of six to eight weeks, the cornea usually returns to its former transparency. The recovery can be aided nonsurgically by bandaging with an osmotic saline solution. Although a hydrops usually causes increased scarring of the cornea, occasionally it will benefit a patient by creating a flatter cone, aiding the fitting of contact lenses. Corneal transplantation is not usually indicated during corneal hydrops.

The National Eye Institute reports keratoconus is the most common corneal dystrophy in the United States, affecting about one in 2,000 Americans,US National Eye Institute, Facts About The Cornea and Corneal Disease [http://www.nei.nih.gov/health/cornealdisease/index.asp#h Keratoconus] {{webarchive |url=https://web.archive.org/web/20051031055107/http://www.nei.nih.gov/health/cornealdisease/index.asp#h |date=31 October 2005 }}. Accessed 12 February 2006.{{cite journal |vauthors=Kennedy RH, Bourne WM, Dyer JA |title=A 48-year clinical and epidemiologic study of keratoconus |journal=American Journal of Ophthalmology |volume=101 |issue=3 |pages=267–73 |date=March 1986 |pmid=3513592 |doi=10.1016/0002-9394(86)90817-2}} but some reports place the figure as high as one in 500.Weissman BA, Yeung KK. Keratoconus. eMedicine: [http://www.emedicine.com/oph/topic104.htm Keratoconus] {{webarchive|url=https://web.archive.org/web/20060112203357/http://www.emedicine.com/OPH/topic104.htm |date=12 January 2006 }}. Accessed 24 December 2011. In the pediatric populations, ages three to 18, the prevalence of keratoconus was found to be as high as one in 334 children.{{Cite journal |last=Harthan |first=Jennifer S. |last2=Gelles |first2=John D. |last3=Block |first3=Sandra S. |last4=Tullo |first4=William |last5=Morgenstern |first5=Andrew S. |last6=Su |first6=Becky |last7=Chung |first7=Daniel |last8=Yu |first8=Austin |last9=Greenstein |first9=Steven A. |last10=Hersh |first10=Peter S. |last11=Eiden |first11=Steven Barry |date=2024-03-01 |title=Prevalence of Keratoconus Based on Scheimpflug Corneal Tomography Metrics in a Pediatric Population From a Chicago-Based School Age Vision Clinic |url=https://pubmed.ncbi.nlm.nih.gov/38345011/ |journal=Eye & Contact Lens |volume=50 |issue=3 |pages=121–125 |doi=10.1097/ICL.0000000000001072 |issn=1542-233X |pmid=38345011}} The inconsistency may be due to variations in diagnostic criteria, with some cases of severe astigmatism interpreted as those of keratoconus, and vice versa. A long-term study found a mean incidence rate of 2.0 new cases per 100,000 population per year. Some studies have suggested a higher prevalence amongst females,{{cite journal |author=Fink BA |title=Differences in keratoconus as a function of gender |journal=American Journal of Ophthalmology |volume=140 |issue=3 |pages=459–68 |date=September 2005 |pmid=16083843 |doi=10.1016/j.ajo.2005.03.078 |author2=Wagner H |author3=Steger-May K |display-authors=3 |last4=Rosenstiel |first4=Carol |last5=Roediger |first5=Teresa |last6=McMahon |first6=Timothy T. |last7=Gordon |first7=Mae O. |last8=Zadnik |first8=Karla}} or that people of South Asian ethnicity are 4.4 times as likely to develop keratoconus as Caucasians, and are also more likely to be affected with the condition earlier.{{cite journal |vauthors=Pearson AR, Soneji B, Sarvananthan N, Sandford-Smith JH |title=Does ethnic origin influence the incidence or severity of keratoconus? |journal=Eye |volume=14 |issue=4 |pages=625–8 |date=August 2000 |pmid=11040911 |doi=10.1038/eye.2000.154|doi-access=free }}

Keratoconus is normally bilateral (affecting both eyes) although the distortion is usually asymmetric and is rarely completely identical in both corneas. Unilateral cases tend to be uncommon, and may in fact be very rare if a very mild condition in the better eye is simply below the limit of clinical detection. It is common for keratoconus to be diagnosed first in one eye and not until later in the other. As the condition then progresses in both eyes, the vision in the earlier-diagnosed eye will often remain poorer than that in its fellow.

Image:Conicalcornea.jpg

The German oculist Burchard Mauchart provided an early description in a 1748 doctoral dissertation of a case of keratoconus,{{cite web|vauthors = Caroline P, Andre M, Kinoshita B, Choo J |title=Etiology, Diagnosis, and Management of Keratoconus: New Thoughts and New Understandings |work=Pacific University College of Optometry |url=http://www.pacificu.edu/optometry/ce/courses/15167/etiologypg1.cfm |access-date=15 December 2008 |url-status=dead |archive-url=https://web.archive.org/web/20090107180802/http://www.pacificu.edu/optometry/ce/courses/15167/etiologypg1.cfm |archive-date=7 January 2009 }} which he called staphyloma diaphanum. However, it was not until 1854 that British physician John Nottingham (1801–1856) clearly described keratoconus and distinguished it from other ectasias of the cornea. Nottingham reported the cases of "conical cornea" that had come to his attention, and described several classic features of the disease, including polyopia, weakness of the cornea, and difficulty matching corrective lenses to the patient's vision.Nottingham J. Practical observations on conical cornea: and on the short sight, and other defects of vision connected with it. London: J. Churchill, 1854. In 1859, British surgeon William Bowman used an ophthalmoscope (recently invented by Hermann von Helmholtz) to diagnose keratoconus, and described how to angle the instrument's mirror so as to best see the conical shape of the cornea.Bowman W, On conical cornea and its treatment by operation. Ophthalmic Hosp Rep and J R Lond Ophthalmic Hosp. 1859;9:157. Bowman also attempted to restore vision by pulling on the iris with a fine hook inserted through the cornea and stretching the pupil into a vertical slit, like that of a cat. He reported that he had had a measure of success with the technique, restoring vision to an 18-year-old woman who had previously been unable to count fingers at a distance of 8 inches (20 cm).

By 1869, when the pioneering Swiss ophthalmologist Johann Horner wrote a thesis entitled On the treatment of keratoconus,Horner JF, Zur Behandlung des Keratoconus. Klinische Monatsblätter für Augenheilkunde. 1869. the disorder had acquired its current name. The treatment at that time, endorsed by the leading German ophthalmologist Albrecht von Graefe, was an attempt to physically reshape the cornea by chemical cauterization with a silver nitrate solution and application of a miosis-causing agent with a pressure dressing. In 1888, the treatment of keratoconus became one of the first practical applications of the then newly invented contact lens, when the French physician Eugène Kalt manufactured a glass scleral shell that improved vision by compressing the cornea into a more regular shape.{{cite journal |author=Pearson RM |title=Kalt, keratoconus, and the contact lens |journal=Optometry and Vision Science |volume=66 |issue=9 |pages=643–6 |date=September 1989 |pmid=2677884 |doi=10.1097/00006324-198909000-00011}} Since the start of the 20th century, research on keratoconus has both improved understanding of the disease and greatly expanded the range of treatment options. The first successful corneal transplantation to treat keratoconus was done in 1936 by Ramón Castroviejo.{{cite journal |author=Castroviejo R |title=Keratoplasty for the Treatment of Keratoconus |journal=Transactions of the American Ophthalmological Society |volume=46 |pages=127–53 |year=1948 |pmid=16693468 |pmc=1312756}}Castroviejo, R.: International Abstract of Surgery, 65:5, December 1937.

According to the findings of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK), people who have keratoconus could be expected to pay more than $25,000 over their lifetime post-diagnosis, with a standard deviation of $19,396.{{cite journal|last1=Rebenitsch|first1=Ronald L.|last2=Kymes|first2=Steven M.|last3=Walline|first3=Jeffrey J.|last4=Gordon|first4=Mae O.|title=The Lifetime Economic Burden of Keratoconus: A Decision Analysis Using a Markov Model|journal=American Journal of Ophthalmology|date=May 2011|volume=151|issue=5|pages=768–773.e2|doi=10.1016/j.ajo.2010.10.034|pmid=21310384|pmc=4714341}} There is limited evidence on the costs of corneal cross-linking,{{cite journal|last1=Godefrooij|first1=Daniel A.|last2=van Geuns|first2=Pepijn|last3=de Wit|first3=G. Ardine|last4=Wisse|first4=Robert P. L.|title=What Are the Costs of Corneal Cross-linking for the Treatment of Progressive Keratoconus?|journal=Journal of Refractive Surgery|date=1 May 2016|volume=32|issue=5|pages=355|doi=10.3928/1081597X-20160318-01|pmid=27163622|hdl=1874/336232|hdl-access=free}} a cost-effectiveness study estimated the costs of the total treatment for one person as £928 ($1,392 U.S.) in the UK National Health Service,{{cite journal|last1=Salmon|first1=H A|last2=Chalk|first2=D|last3=Stein|first3=K|last4=Frost|first4=N A|title=Cost effectiveness of collagen crosslinking for progressive keratoconus in the UK NHS|journal=Eye|date=28 August 2015|volume=29|issue=11|pages=1504–1511|doi=10.1038/eye.2015.151|pmid=26315704|pmc=4645452}} but this may be as high as $6,500 per eye in other countries.{{cite web|last1=Walker|first1=Nicholas|title=Corneal cross-linking patients need Medicare rebate|url=http://www.optometry.org.au/blog-news/2015/1/20/corneal-cross-linking-patients-need-medicare-rebate/|website=Optometry Australia|url-status=dead|archive-url=https://web.archive.org/web/20161112210621/http://www.optometry.org.au/blog-news/2015/1/20/corneal-cross-linking-patients-need-medicare-rebate/|archive-date=12 November 2016|access-date=12 November 2016}} A 2013 cost-benefit analysis by the Lewin Group for Eye Bank Association of America, estimated an average cost of $16,500 for each corneal transplant.{{cite web|title=Cost-Benefit Analysis of Corneal Transplant|url=http://restoresight.org/wp-content/uploads/2014/03/Lewin-Study-Sept-2013.pdf|website=Restoresight.org|url-status=dead|archive-url=https://web.archive.org/web/20170305001930/http://restoresight.org/wp-content/uploads/2014/03/Lewin-Study-Sept-2013.pdf|archive-date=5 March 2017|access-date=12 November 2016}}

The following individuals have publicly stated they have keratoconus:

• Stephen Curry, American basketball player{{cite news |author= |date=5 April 2019 |title=Warriors' Stephen Curry fixed his vision |url=https://abc7news.com/stephen-curry-golden-state-warriors-contacts-shooting-slump/5234666/ |work=ABC7 News|location= |access-date=26 July 2024}}
• Ashton Irwin, Australian musician{{Cite tweet |author-link = Ashton Irwin |user=Ashton5SOS| number=1102950930616672256|title=I have an hereditary eye disease called keratoconus}}
• Mandy Patinkin, American actor{{cite web|last=Moran|first=W. Reed|date=March 6, 2001|title=Mandy Patinkin saves sight with corneal transplants|url=https://usatoday30.usatoday.com/news/health/spotlight/2001-03-06-patinkin-cornea.htm|website=USA Today}}
• Michaela Strachan, British TV presenter{{Cite tweet |author-link = Michaela Strachan |user=michaelastracha | number=1430792835272413184|title=After 15 yrs of wearing hard contact lenses to treat an eye condition called Keratoconus, I’ve now been prescribed soft lenses}}

Several other corneal ectatic disorders also cause thinning of the cornea:

• Keratoglobus is a very rare condition that causes corneal thinning primarily at the margins, resulting in a spherical, slightly enlarged eye. It may be genetically related to keratoconus.
• Pellucid marginal degeneration causes thinning of a narrow (1–2 mm) band of the cornea, usually along the inferior corneal margin. It causes irregular astigmatism that, in the early stages of the disease can be corrected by spectacles. Differential diagnosis may be made by slit-lamp examination.{{cite journal|last=Jinabhai|first=Amit|author2=Radhakrishnan, Hema |author3=O'Donnell, Clare |title=Pellucid corneal marginal degeneration: A review|journal=Contact Lens & Anterior Eye|date=23 December 2010|volume=34|pages=56–63|pmid=21185225|issue=2|doi=10.1016/j.clae.2010.11.007}}
• Posterior keratoconus, a distinct disorder despite its similar name, is a rare abnormality, usually congenital, which causes a nonprogressive thinning of the inner surface of the cornea, while the curvature of the anterior surface remains normal. Usually only a single eye is affected.
• Post-LASIK ectasia is a complication of LASIK eye surgery.

{{Reflist}}

{{commons category|Keratoconus}}

{{Medical resources

| ICD11 = {{ICD11|9A78.50}}

| ICD10 = {{ICD10|H|18|6|h|15}}

| ICD9 = {{ICD9|371.6}}

| DiseasesDB = 7158

| ICDO =

| OMIM = 148300

| MedlinePlus = 001013

| eMedicineSubj = oph

| eMedicineTopic = 104

| MeshID = D007640

| NORD = Keratoconus

| GARDNum = 6824

| GARDName = Keratoconus

| Orphanet = 156071

| Monarch = DOID:10126

}}

{{Eye pathology|globe}}

{{Authority control}}

Category:Disorders of sclera and cornea

Category:Eye diseases

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Category:Wikipedia neurology articles ready to translate