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Orthokeratology (Ortho-K, also known under branded names like "dream lens" "Dreim Lens" and "dream vision") 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.)

Contents 1 History 2 Mechanism 3 Indications 4 Types of lenses 5 Cautions 6 Footnotes 7 References

[edit] History

The idea of correcting vision by reshaping the cornea has been around for some time. 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 some media said that, 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"). Each FDA approval has a PMA number. The PMA number of FDA approval for Paragon CRT is P870024; the PMA number of FDA approval for Euclid products is P010062. So far FDA database shows no PMA number for C&E 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 possibility 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.^[1]

[edit] 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.

A common misconception in design is that the lens "presses" on the cornea, thus flattening the eye. In fact, the belief is that the forces generated by the reverse curve cause the redistribution of the epithelial cells, and not pressure on the eye. Properly designed lenses do not touch the user's cornea.

[edit] 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.

[edit] 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 VST 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" designed and manufactured by Euclid Systems Corporation
• "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, but currently there are no other studies are underway for any other lens designs.

Doctors may also design their own lens shapes based on experience and the principles behind Ortho-K. To support such endevours Wave systems, Orthotool and other software packages assist in the design of lenses, while representing the expected change on the eye. Wave in particular uses a combination of corneal topography combined with a doctor's knowledge to create lenses designed for irregularly shaped eyes (qudrant based sloping), where the VST/CRT based solutions are based on traditional problem solving tecniques using standard spheric and aspheric designs.

[edit] Cautions

Orthokeratology has occasionally had severe side-effects, even blinding complications.^[2][3] These often occur due to the patient's failure to follow appropriate hygiene, and the use of tap water to rinse (although some systems allow for or suggest the use of "clean" tap water) or store.^[4] 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.^[5] The use of high or hyper oxygen-permeable materials significantly reduces hypoxia, and these are the materials that are normally used in orthokeratology. Some users may also experience vision issues such as ghosting, double vision, contrast problems and/or starbursting, especially at night. Causes for these experiences are not always known, but generally due to lack of centration and/or overly large pupil size (in light or dark).

[edit] Footnotes

[edit] References

• Research in Orthokeratology - University of New South Wales (Sydney, Australia).