Orthokeratology (Ortho-K, CRT) Information

Info from Orthokeratology of America:



COOKI (Children's Overnight Orthokeratology Investigation)

The purpose of this study was to determine the safety and efficacy of overnight Orthokeratology in eight to eleven year old children. The conclusion of this study showed that CRT contact lenses worn during sleep provide adequate vision for myopic children to be able to function throughout the day without wearing glasses or contact lenses. 78.4% of children age eight to eleven years are able to successfully adapt to rigid gas permeable contact lens wear. There were no adverse ocular effects.


COMET (The Correction of Myopia Evaluation Trial)

This study evaluated whether Varilux progressive addition lenses slows down the rate of juvenile onset myopia versus single vision lenses. This was a five year study, six to eleven year olds, 48% male/52% female, ranging 1.25 diopters to 4.50 diopters of myopia. The use of the progressive addition lenses compared with the single vision lenses slowed down the progression of myopia by a small amount during the first year and the difference was maintained over the next two years. It was concluded however that this small decrease in the rate of progression of myopia does not warrant a change in the clinical management of myopia.


CLAMP (Contact Lens And Myopia Progression)

This study had several goals. To evaluate the effect of rigid lenses on myopia progression in children. To determine the mechanism of effect if one exists. To examine the efficacy of rigid contact lenses for the treatment of myopia in young children. To compare vision and comfort issues between rigid and soft contact lens wearers. The conclusions of this study are as follows: Rigid gas permeable  lens produce a slower rate of progression of myopia in children than soft contact lenses. Although corneal curvature changed, the axial growth was not significantly different between the groups. The decreased refractive error progression is not accompanied by slowed axial growth. The corneal curvature changes during corneal reshaping contact lens wear are reversible. The treatment effect experienced in the CLAMP study may not be permanent. Most of the effect on refractive error was limited to the first year of the trial. The study did not indicate that rigid gas permeable lens should be prescribed primarily for the intent of myopia control.


MYOPIA CONTROL (Houston Study)

This study examined the control of myopia progression comparing rigid gas permeable contact lens versus spectacles. The results showed that the mean increase in myopia for the gas permeable lens was 0.42 diopters per year versus a mean increase in myopia for the spectacle wearers of 0.78 diopters per year. The mean increase in axial length for the gas permeable lens was 0.22 mm per year versus a mean increase in axial length for the spectacle wearers of 0.31 mm per year. The study showed that the decrease in progression of myopia using gas permeable lenses is attributable to mix of axial length growth reduction and corneal flattening. 


LORIC (The Longitudinal Ortho-k Research In Children)

This study looked at several factors. It was to determine whether Orthokeratology can effectively reduce and control myopia in children. It also compared Orthokeratology treatment with single vision spectacles. It monitored the growth of axial length and the vitreous chamber depth. It also monitored corneal curvature and the relationships with changes of refractive errors. The conclusions of the study found that the subjects found post Orthokeratology unaided vision acceptable in the daytime. The mean increase in axial length for the Orthokeratology group was 0.14 mm per year compared with the mean increase in axial length for the spectacle lens wearers of 0.27 mm per year. In the spectacle wearing group, the eye elongation is faster in those with higher baseline prescriptions. Orthokeratology would benefit higher baseline prescriptions as eye elongation is slower in these subjects. Higher myopia showed greater slowing of progression in the Orthokeratology group. 


SMART (Stabilizing Myopia by Accelerating Reshaping Technique)

This study is to determine if wearing Orthokeratology lenses on an overnight basis stops or slows the progression of myopia in children. The group being studied is eight to eleven years old. This group will be compared to spherical soft lens wearers. This study is currently underway so no data is yet available. 


New 2011 Reseach, Ortho K has good safety profile on the corneal epithelium   

Abstract: Fluorophotometry to Evaluate the Corneal Epithelium in Eyes Undergoing Contact Lens Corneal Reshaping

Researchers set out to determine whether use of Corneal Refractive Therapy (CRT, Paragon Vision Sciences) lenses has an adverse effect on the health of corneal epithelium by monitoring epithelial permeability by fluorophotometry. 
The researchers concluded that reshaping of the cornea through the use of orthokeratology does not have adverse effects on corneal epithelium as evaluated by changes in corneal epithelial permeability.
Savitsky DZ, Fan VC, Yildiz EH, Du TT, Asbell PA. Fluorophotometry to evaluate the corneal epithelium in eyes undergoing contact lens corneal reshaping to correct myopia. J Refract Surg 2009;25:366-70.

Visit the Orthokeratology Academy of America site for more information:



And to find an Ortho-K doctor:



ORTHO-K CRT Info in Chinese

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