Orthokeratology
Orthokeratology (Ortho-K) is the use of rigid gas-permeable contact lenses, normally worn only at night, to improve vision through the reshaping of the cornea.  This method can be used as an alternative to eyeglasses, refractive surgery, or for those who prefer not to wear contact lenses during the day (for example, because lenses may become dislodged during sport.)

# History
The idea of correcting vision by reshaping the cornea has been around for a while. Doctors discovered the reshaping phenomena of glass lenses as early as the 1940s.
George Jessen created what was probably the first orthokeratology design in the 1960s made from PMMA material, which he marketed as "Orthofocus". These early designs had generally unpredictable results, leading to the belief that applied orthokeratology was more art or luck than science.
Not until new measuring instruments and computers were available was it possible to apply the theory to create designs with repeatable results.
Many groups and individuals claim to have been the first to develop modern orthokeratology solutions. But Dr. Richard Wlodyga, in particular, is generally credited with developing the first reverse zone lens design in the 1980s.
In the summer of 2000; at an educational meeting of Optometrists in Toronto, the Orthokeratology Academy of America was formed to support, promote and advance orthokeratology. By providing quality education and scientific information on the subject of ortho-k to all interested practitioners, the OAA provides an unbiased forum for the free exchange of ideas and concepts relating to all aspects of orthokeratology. Its membership has the opportunity to advance their role in the field by applying for and passing comprehensive exams in order to achieve Fellowship status in the Academy.
A significant milestone for the American market occurred in June 2002 when the FDA granted approval for overnight wear of a type of corneal reshaping called "Corneal Refractive Therapy" (CRT). This forms the basis of the "Paragon CRT" product backed by Paragon Vision Sciences Inc.
In 2004 the FDA approved a number of ortho-k designs for overnight wear, including designs from Contex ("Contex OK-E"), Euclid Systems ("Emerald"), and C&E GP Specialists ("Fargo"). 2005 saw additional FDA approvals, as manufacturers raced to bring orthokeratology to American consumers. However, nightwear ortho-k solutions were available to consumers in many countries outside the US much earlier as a result of different regulatory controls and bodies.
In 2005, Bausch & Lomb introduced the "Vision Shaping Treatment" (VST) program to collectively market a number of ortho-k products, using the "Boston" name.
In 2006 and 2007 papers presented at the British Contact Lens Association and the Global Ortho Keratology Symposium indicated the possiblility of orthokeratology slowing or stopping myopic progression. This was found to be effective in children in Hong Kong and is the subject of wider study to verify this data.

# Mechanism
It is presumed that the lenses used in orthokeratology reshape the cornea by moving the epithelial cells that cover the surface of the cornea.  Some studies indicate that the epithelial cells are compressed in some areas as well as relocated.

# Indications
In the United Kingdom, the treatment is currently offered for corrections from +3.00 to -6.00D, with possible treatment up to -8.50D. Some patients may not be suitable for treatment.
The US FDA approvals are for procedures up to -6.00D.  Some patients with higher degrees of myopia are successfully treated by specialty practitioners with "off-label" uses of these same lenses.

# Types of lenses
Orthokeratology lenses are made by several companies, using one of two FDA approved technologies.  All use special gas permeable lenses to reshape the cornea. The lens material is important for maintaining eye-health during the treatment.
Paragon Vision Sciences manufactures a lens trademarked "Paragon CRT" (Paragon Corneal Refractive Therapy) and marketed as "Accelerated Orthokeratology" (AOK). Bausch & Lomb's "Vision Shaping Treatment" offers the choice of four approved designs that may only be fit by certified practitioners. The four designs in the VST portfolio include (alphabetically)
- "BE Retainer" backed by BE Enterprises Inc
- "Contex OK-E System" backed by Contex Inc.
- "DreamLens" backed by Dreimlens Inc
- "Emerald" backed by Euclid Systems Corp
- "Fargo" backed by C&E GP Specialists.
Only a few other brands of ortho-k lenses have been approved by the FDA for overnight wear.  Currently no other studies are underway for any other lens designs.

# Cautions
Orthokeratology has occasionally had severe side-effects, even blinding complications.  These often occur due to the patient's failure to follow appropriate hygiene, and the use of tap water to rinse or store. Complications may also be due to relative corneal hypoxia (lack of oxygen) with prolonged or overnight contact lens wear in lenses made from the wrong material. The use of high or hyper oxygen-permeable materials significantly reduces hypoxia, and these are the materials that are normally used in orthokeratology.

# Footnotes
-  Eye-shaping contacts may repair vision - Cosmos Magazine. December 6, 2007.
-  Orthokeratology contact lenses cause permanent vision loss in children - American Academy of Ophthalmology media release, 1 March 2004
-  Acanthamoeba keratitis and overnight orthokeratology Case presentation: Canadian Adverse Reaction Newsletter Volume 16, Issue 2, April 2006
-  Eye Contact Lens. 2005 Sep;31(5):201-8
-  Ophthalmology. 2001 Aug;108(8):1389-99