Editing Keratoconus (section)

== Diagnosis ==
[[File:Keratoconus.svg|thumb|right|A schematic diagram showing change in [[cornea]]]]
[[File:Computerised Corneal Topography.jpg|thumb|Corneal topographer, used for mapping the surface curvature of the cornea]]
Prior to any [[physical examination]], the [[medical diagnosis|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 [[optotype|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]],<ref>{{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 }}</ref> with detection of irregular [[Astigmatism (eye)|astigmatism]] suggesting a possibility of keratoconus. Severe cases can exceed the instrument's measuring ability.<ref name="epstein"/> 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]].<ref name="epstein"/><ref>{{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}}</ref>

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.<ref name="rabonitz">{{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}}</ref> 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.<ref name="Edrington">{{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}}</ref> 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.<ref name="epstein"/> Similarly, around 50% of subjects exhibit Vogt's [[striae]], fine stress lines within the cornea caused by stretching and thinning.<ref name="Edrington"/> The striae temporarily disappear while slight pressure is applied to the eyeball.<ref name="epstein"/> 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]].<ref name="feder"/> Other [[clinical sign]]s of keratoconus will normally have presented themselves long before Munson's sign becomes apparent,<ref name="Krachmer">{{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}}</ref> 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 [[Non-invasive (medical)|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.<ref name="puco"/> 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.<ref>{{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}}</ref>

=== Stages ===
[[File:Corneal topography, stage II keratoconus (Elise A. Slim et al.).svg|thumb|Corneal topography showing stage II keratoconus]]
Once keratoconus has been diagnosed, its degree may be classified by several metrics:<ref name="Gupta">{{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}}</ref>
* The steepness of greatest curvature from 'mild' (< 45 [[dioptre|D]]), 'advanced' (up to 52 [[dioptre|D]]) or 'severe' (> 52 [[dioptre|D]]);
* The morphology of the cone: 'nipple' (small: 5&nbsp;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.<ref name="Gupta"/>

{| class="wikitable"
|-
!Stage
!Characteristics<ref>{{cite journal | vauthors = Krumeich JH, Kezirian GM| date = April 2009 | title = Circular keratotomy to reduce astigmatism and improve vision in stage I and II keratoconus | pmid = 19431926 | journal = J. Refract. Surg. | volume = 25 | issue = 4| pages = 357–65 | doi=10.3928/1081597x-20090401-07}}</ref><ref>{{cite journal | vauthors = Krumeich JH, Daniel J| date = August 1997 | title =Lebend-Epikeratophakie und Tiefe Lamelläre Keratoplastik zur Stadiengerechten chirurgischen Behandlung des Keratokonus (KK) I-III|language=de |trans-title=Live epikeratophakia and deep lamellar keratoplasty for I-III stage-specific surgical treatment of keratoconus| pmid=9379645 | journal = Klin. Monbl. Augenheilkd. | volume = 211 | issue = 2| pages = 94–100 | doi=10.1055/s-2008-1035103| s2cid = 72600086 }}</ref>
|-
|Stage 1
|
* Eccentric steepening Induced myopia and/or astigmatism of ≤ 5.0 D
* K-reading ≤ 48.00 D
* Vogt's lines,<ref>[http://webeye.ophth.uiowa.edu/eyeforum/atlas/pages/vogts-striae.htm Vogt's striae in keratoconus, University of Iowa Health Care, Ophthalmology and Visual Sciences] {{webarchive|url=https://web.archive.org/web/20160813124346/http://webeye.ophth.uiowa.edu/eyeforum/atlas/pages/vogts-striae.htm |date=13 August 2016 }}</ref> typical topography
|-
|Stage 2
|
* Induced myopia and/or astigmatism between 5.00 and 8.00 D
* K-reading ≤ 53.00 D
* Pachymetry ≥ 400&nbsp;μm
|-
|Stage 3
|
* Induced myopia and/or astigmatism between 8.01 and 10.00 D
* K-reading > 53.00 D
* Pachymetry 200 to 400&nbsp;μm
|-
|Stage 4
|
* Refraction not measurable
* K-reading > 55.00 D
* Central scars
* Pachymetry  ≤ 200&nbsp;μm
|-
| colspan="2" | Stage is determined if one of the characteristics applies.<br>
Corneal thickness is the thinnest measured spot of the cornea.
|}