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Home > Health > Orthokeratology


Orthokeratology

Orthokeratology is a method used to help correct vision. So far it can only be used for myopia (nearsightedness). It does not involved surgery, but instead, the use of rigid gas permeable (RGP) contacts are used. It sometimes goes by other names, depending on the company that developed a specific method such as Corneal Refractive Therapy (CRT), Accelerated Orthokeratology (AOK), Corneal Corrective Contacts (CCC), Eccentricity Zero Molding (EZM), Gentle Vision Shaping System (GVSS) or Vision Shaping Treatment (VST).

Basic Concept of Orthokeratology

Nearsightedness (myopia) is caused by either having an eyeball that is longer - from the front of the eye to the back - than normal or when the cornea's curvature is too steep. Either way it results in images not being able to be focused on properly on the retina.

The goal of orthokeratology is to reshape the cornea - to flatten it a bit basically - so your eyes can focus light the way it should. With orthokeratology this is done by wearing specially made rigid gas permeable (RGP) contacts, usually at night while you sleep.

These contacts are made to fit very snugly to the surface of your eye - so your eyes have to be measured very precisely, in part with something call a corneal topographer. And they are made so that instead of having a uniformly curved surface, they are somewhat flatten on the center part (sometimes referred to as 'reverse geometry'). This applies pressure to the epithelium of your cornea, flattening it a bit.

The amount flattening of your cornea that is necessary is around 6 microns for every diopter of nearsightedness you have. (There are one million microns in a meter - to give you some idea of the scale involved.)

LASIK does a similar type of thing with surgery.

More About Orthokeratology

Since the contacts used are gas permeable - not soft - contacts, they are a bit rigid and take some getting used to to wear. At first you may only wear them for a short while during the day, until you can tolerate them for longer wear. This depends a bit on the method orthokeratology used however. The newer methods use more comfortable contacts and may have you start wearing the contacts overnight while you sleep right away. What generally happens, over time, is that you wear them at night, and can take them out during the day and be able to see without them.

However, this is not a permanent thing - you have to wear them each night for a period of time, depending upon the method used and how bad your eyes are. Then after a while you wear them on a sort of maintenance schedule (kind of like a retainer with braces) - if not your eyes will go back to the shape they were in before. I couldn't find a lot of information about how long or frequent the maintenance schedule is, it seems to depend upon the method used and the individual.

The way it used to be done, you would typically need more than one set of lenses over time to gradually correct your vision, but this is not always necessary anymore. And some methods have been approved for wearing the contacts overnight too:

Paragon CRT (Corneal Refractive Therapy)

The Paragon CRT system was developed by Paragon Vision Sciences. It was approved for overnight use by the FDA in June 2002. With their system only a single set of lenses is used and for a period of only 5 to 14 days. It can treat people with as much as -6.00 diopters of myopia! And also can be used for up to -1.75 diopters of astigmatism. For an eye doctor to be able to use Paragon CRT with patients they have to be trained, tested and certified by Paragon Vision Sciences.

According to Paragon, the technology they use is possible because of a number of advances including:

- Improvements in multicurve gas permeable contacts

- Better technology for fabricating the contacts in a complex and consistent fashion

- The existence of materials with a high oxygen permeability to allow overnight wear of contacts.

- Improvements in corneal mapping techniques

- A better understanding of how to reshape a cornea

They also have their white papers on their site which includes information about how the contacts are made. It explains that the center 6 millimeters of the contacts is the treatment zone, outside of that is a 1 mm return zone, and a non-curved landing zone around the edge. All sounds impressive to me, but I'm no eye doctor! (Just a woman with bad eyes looking for solutions!)

I recommend looking through their 'Eye Care Professionals' pages too if you think you might be interested in trying it - not just the 'Consumers' section - its too oversimplified and watered down to be able to actually learn how the process works. But be warned - their site has sound and video that plays automatically on many of the pages - apparently they don't know or care about web usability.

Bausch & Lomb Vision Shaping Treatment (VST)

Bausch & Lomb also has an overnight approved system for orthokeratology called Vision Shaping Treatment (VST). They didn't have very detailed information about it on their web site though, so not much I can say about it. On their site they do have a package insert on pdf, but when I tried to view it with my Gnome PDF viewer it was blank (maybe they don't support open source software?).


Additional Information


Another web site with information about orthokeratology is Ortho-K.net, this page has some good information - however - be warned! - the creators of this site either don't know or care about web usability either (or accessibilty for that matter)! It has sound that plays automatically when you go to the site - you have to shut it off if you don't want to hear it. Many of the pages seem to require the use javascript to view all the information too. And it uses frames!

Other articles in this series are: Contacts - An Introduction Part I: Eyes and Vision,
Contacts - An Introduction Part II: Contact Types and History,
Soft Contacts - Daily Wear and Disposable,
Rigid gas permeable (RGP) Contacts,
Daily Wear Contacts and
Extended Wear Contacts.






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