Editing Keratoconus (section)

== Signs and symptoms ==
[[Image:Kc simulation.jpg|right|thumb|Simulation of the [[diplopia|multiple images]] seen by a person with keratoconus.<br /> "...&nbsp;a candle, when looked at, appears like a number of lights, confusedly running into one another" — Nottingham<ref name="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.<ref name="feder">{{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}}</ref><ref name="epstein">{{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}}</ref> At early stages, the [[symptom]]s of keratoconus may be no different from those of any other [[Refractive error|refractive defect]] of the eye. As the disease progresses, vision deteriorates, sometimes rapidly due to irregular [[astigmatism]].<ref name="CRFA" /> [[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 [[itch]]ing in the eye,<ref name="feder"/> 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|left|thumb|Multiple images made by extremely high contrast light sources as seen by a person with keratoconus]]

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 (vision)|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 [[Lens flare|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 (optics)|coma]].<ref name="pmid17553566">{{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}}</ref><ref name="pmid19029032">{{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= }}</ref> 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.