Editing Keratoconus (section)

=== Lenses ===
[[Image:KC-lens.jpg|thumb|Rigid gas permeable (RGP) lens]]
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|rigid, gas-permeable]], (RGP) lenses. RGP lenses provide a good level of visual correction, but do not arrest progression of the condition.<ref>{{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}}</ref>

In people with keratoconus, rigid contact lenses improve vision by means of [[tears|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<ref name="grayson"/> and the fitter will endeavor to produce a lens with the optimal contact, stability and steepness. Some trial-and-error fitting may prove necessary.<ref name="Krachmer"/>

==== Hybrid lenses ====
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.<ref>{{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}}</ref> Early generation lenses have been discontinued.<ref>{{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}}</ref> 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.<ref>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 }}.</ref>

==== Scleral lenses ====
{{main|Scleral lens}}
[[File:Scleral lens worn on an eye.jpg|thumb|Scleral lens]]
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.<ref>{{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}}</ref> Easier handling can find favor with people with reduced [[dexterity]], such as the elderly.

==== Piggybacking ====
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.<ref>{{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}}</ref> 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.