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Encyclopedia > 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 desiring to not wear contact lenses during the day. A pair of contact lenses, positioned with the concave side facing upward. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... Glasses, spectacles, or eyeglasses are frames bearing lenses worn in front of the eyes, sometimes for purely aesthetic reasons but normally for vision correction or eye protection. ... Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease dependency on glasses or contact lenses. ...

Contents

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. The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ...


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. George Jessen was an optometrist who was an early pioneer of the contact lens. ...


Not until new measuring instruments and computers were available was it possible to apply the theory to create designs with repeatable results. The tower of a personal computer. ...


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. Paragon Vision Sciences Paragon Vision Sciences manufactures Paragon CRT lenses. ...


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. The United States Food and Drug Administration is the government agency responsible for regulating food, dietary supplements, drugs, cosmetics, medical devices, biologics and blood products in the United States. ...


In 2005, Bausch & Lomb introduced the "Vision Shaping Treatment" (VST) program to collectively market a number of ortho-k products, using the "Boston" name. Bausch and Lomb (German pronunciation BOWsh and LAWM) is an American company based in Rochester, New York, specialized in medical optics like contact lenses and surgical instruments. ...


In 2006 and 2007 papers presented at the British Contact Lens Association and the Global Ortho Keratology Symposium indicated the possiblility of orthok slowing or stopping myopic progression. This was found to be effective in children in Hong Kong and is the supject 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. In zootomy, epithelium is a tissue composed of a layer of cells. ...


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. Off-label use is the practice of prescribing drugs for a purpose outside the scope of the drugs approved label, most often concerning the drugs indication. ...


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. A soft contact lens A contact lens (also known as contact, for short) is a corrective or cosmetic lens placed on the cornea of the eye atop the iris. ...


Paragon Vision Sciences manufactures a lens trademarked the CRT (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) Paragon Vision Sciences Paragon Vision Sciences manufactures Paragon CRT lenses. ...

  • "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 [1][2]. These often occur due to the patient's failure to follow appropriate hygiene, and the use of tap water to rinse or store [Eye Contact Lens. 2005 Sep;31(5):201-8]. 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 [Ophthalmology. 2001 Aug;108(8):1389-99]. The use of high or hyper oxygen permeable materials significantly reduces hypoxia, and are usually the materials used in Orthokeratology.


References

  1. ^ http://www.medicalnewstoday.com/medicalnews.php?newsid=6245
  2. ^ http://www.hc-sc.gc.ca/dhp-mps/medeff/bulletin/carn-bcei_v16n2_e.html#4

  Results from FactBites:
 
Orthokeratology - Wikipedia, the free encyclopedia (742 words)
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.
It is presumed that the lenses used in orthokeratology reshape the cornea by moving the epithelial cells that cover the surface of the cornea.
Orthokeratology lenses are made by several companies, using one of two FDA approved technologies.
Eyesight Associates - Medical Info (1046 words)
Orthokeratology may be able to provide you with vision that is independent of glasses or contact lenses until you are old enough to undergo refractive surgery.
Orthokeratology lenses are worn during sleep and removed in the morning.
The orthokeratology lenses flatten the central 6 to 7 millimeters of the cornea.
  More results at FactBites »

 
 

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