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Ortho-K or CRT Lenses and Myopia Control: How does it work?

As a practice that specializes in Corneal Reshaping Therapy(CRT), I am often asked to explain how they work. This blog post will hopefully help explain the technology in the context of myopia control.

Orthokeratology (Ortho-k) or CRT lenses gently reshape the cornea overnight. The contacts are designed so that water pressure under the lens changes epithelial cells to temporarily alter the curvature of the cornea. Don't worry, it's painless. Most patients will only experience lens awareness the first few nights.

The curvature change in the cornea is controlled very carefully. The contacts are made to a degree of accuracy of 1 micron (a human hair is 100 microns)! The controlled gentle reshaping of the cornea ensures that the vision will be 20/20 during the day (without contacts or glasses)! The lenses must be worn every night to maintain this effect. Some specialists even refer to the lenses as "retainers" similar to how teeth alignment would be maintained at night.

The exciting benefit for children is that CRT lenses will slow or stop the progression of myopia. Many kids are developing myopia (nearsightedness) by age 7 or 8. Researchers are reporting a worldwide epidemic of myopia. Myopia typically continues to get worse every year until age 18 as the eyeball grows in length. In the past, we have always simply prescribed stronger glasses or contacts. Vision would be corrected to 20/20 and we would see the child again in 6 months or a year. In another year, we would then make the glasses stronger as the vision would continue to deteriorate. Now, we have the amazing ability to be proactive and slow down this progression. This is important from a public health perspective because we are also reducing the risk of serious eye problems:

So, how do CRT lenses slow myopia progression? This gets a little more complicated. Basically, when the cornea is reshaped with the CRT lens, a secondary ring of power is created around the edges of the pupil. In the picture above, you will see the red ring on the topography map. This secondary power changes how peripheral light lands on the retina. In a myopic eye, light rays from standard glasses and contacts combined with the light rays of our environment, land in the back of the eye out of focus. This phenomena is called peripheral hyperopic defocus. The defocused light rays send a signal to elongate the eyeball. An elongated eyeball is the cause of nearsightedness. Therefore, by changing this peripheral light ray defocus with the secondary ring in the topography map, we are able to slow or stop the signal to elongate the eye!

We are excited to offer this service to patients in the area! Dr. Rehak would be happy to discuss during a free consultation in either the Royersford or Phoenixville office. The initial fitting evaluation and all followups are only done in Royersford.

Want to read more?

A search on will reveal 95 journal articles on ortho-k and myopia control.

Read about the important research of the Brien Holden Vision Institute

The Singapore Government created a national program to fight the epidemic of school-aged nearsightedness. Ortho-k lenses are part of that fight.

University of California Berkeley College of Optometry has opened a myopia control clinic.

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