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Home » Contact Lenses Plus » All About Contacts » Types of Contact Lenses » Corneal Reshaping Therapy (Ortho-K, CRT)

Corneal Reshaping Therapy (Ortho-K, CRT)

What is Corneal Refractive Therapy?

Simply stated, corneal refractive therapy is a sophisticated, non-surgical process which reshapes the cornea during sleep. The individual wearing CRT lenses removes the lenses upon awaking and is able to go throughout the day without needing vision correction such as spectacles or contact lenses.

Is Corneal Refractive Therapy the Same as Orthokeratology?

Orthokeratology is defined as the reshaping of the cornea to reduce myopia through the use of rigid contact lenses. So technically, CRT is a type of orthokeratology. However, earlier corneal reshaping designs were limited by the available technology of the time. The newly developed corneal refractive therapy utilizes recent advancements in three highly technical areas: computerized corneal mapping, computerized manufacturing, and oxygen permeable contact lens materials. Each of these produce a therapeutic contact lens design that is unique. This has allowed CRT to become the first corneal reshaping modality to earn FDA approval for nighttime corneal refractive therapy.

CRT is an FDA approved contact lens corneal reshaping system used to reduce or temporarily correct myopia. The method was approved in June, 2002 by the FDA for correction of up to –6.00 D of myopia with up to –1.75 D of cylinder. The term Corneal Refractive Therapy is an FDA approved indication and is in the public domain, whereas, the acronym CRT is a registered trademark of Paragon Vision Sciences. CRT describes a method of correction for myopia by use of overnight wear of specially designed gas permeable lenses that redistribute and compress the corneal epithelium such that central epithelial thickness is decreased while peripheral epithelial thickness is increased. The reconfiguration of the epithelium results in redistribution of the refractive power of the cornea. The process is reversible when contact lens wear is discontinued. Lens selection is guided by the patient refraction, corneal curvature measurements, and confirmation of lens fit by evaluation of the fluorescein pattern beneath the contact lens.

What are the benefits of Corneal Refractive Therapy?

Corneal Refractive Therapy offers freedom from glasses and the need of wearing contact lenses during the day. Active individuals can freely participate in sports without the interference of glasses or need of contact lenses. Furthermore, since the lenses are only worn during the night, eye irritation or dryness, sometimes associated with contact lens wear due to outside dust and pollutants, is eliminated. Lastly, the process is completely reversible.

How Long Does It Take to Achieve Good Vision?

Some individuals report good vision the first day. Most, however, find improvement in the first few days of treatment. Individual optimum vision is usually achieved in 10 to 14 days. It may be that for a time after you have begun CRT treatment, your spectacles or contacts will no longer be the appropriate prescription. You may need to utilize your CRT lenses for part of the day or possibly use temporary soft lenses in different prescriptions as an interim option. Your eye care practitioner will discuss your options for visual correction during the transitional period.

What Will My Vision Be Like While Wearing CRT Lenses?

Your vision should be excellent. One of the positive features of CRT, is that if you have to get up in the middle of the night, you will be able to see and not need to put on your spectacles. Also, if during the treatment phase, you find that you require vision correction, you can wear your CRT lenses to see clearly.

How Long Does Corneal Refractive Therapy Last?

This therapy is only temporary. If you stop wearing the lenses regularly while you sleep, your vision will return to its original state in as little as 72 hours. This makes the therapy completely reversible.

Who is Eligible for Corneal Refractive Therapy?

CRT is designed for individuals with low to moderate myopia (nearsightedness up to –6.00 diopters) with or without astigmatism (up to –1.75 diopters). At the present time, hyperopia (farsightedness) is not correctable with CRT. Also, CRT does not correct for presbyopia (requiring reading glasses or bifocals). Each individual's eyes have differences in physiology and visual requirements. Therefore, the decision for corneal refractive therapy, at any age, can only be made after a thorough eye exam and the recommendation of your eye doctor.

What Are the Risks Involved With Wearing CRT Lenses?

Wearing any contact lens involves a small risk. Infection of the cornea is a possible risk. Initial data to date indicate that contact lenses for corneal refractive therapy do not provide a risk that is greater than other contact lenses. Studies are ongoing in this regard.

What is the Care and Replacement Schedule for CRT Lenses?

Typically these lenses will be replaced on an annual basis. However, individual factors such as protein build-up, how well the lenses are taken care of, etc., impact the frequency of lens replacement. Be certain to follow the instruction of your eye doctor.

These lenses should be chemically disinfected after every use (do not use any form of heat disinfection). Your eye doctor will instruct you about which care system is best for you.

Can Children have Corneal Refractive Therapy?

At this time, the FDA has placed no age restrictions on candidates for Corneal Refractive Therapy. The therapy is being successfully performed on children 12 years old and younger and may be a good option for children and teens that are involved in sports. Visual requirements due to age or activities can only be assessed after a thorough eye exam. Your eye doctor will recommend what is best.

What Should I Do if I Lose or Damage a CRT Lens During Therapy?

Corneal Refractive Therapy is not just wearing contact lenses, it is a therapy and system. If you discontinue wear, even for only one night, your vision may be impaired the next day. Previously worn glasses or contact lenses may not help, so immediate replacement is necessary. Having a spare pair of CRT lenses is strongly recommended. Discuss this with your eye doctor.


Pamphlet advisors were David W. Lamberts, MD and John S. Massare, PhD. Copyright 2004, Contact Lens Association of Ophthalmologists, Inc. Thanks to Contact Lens Docs for content used in the creation of this website. All rights reserved.  Reproduction other than for one-time personal use is strictly prohibited.

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