Corneal Reshaping Therapy (CRT)-
Ortho Keratology (Ortho-K)
Now you can be free of wearing contact lenses and/or glasses during the day and see clearly while performing your daily activities without undergoing surgery! Recent clinical research combined with the latest corneal surface mapping technology, computerized manufacturing and space age oxygen-breathing materials have brought new science to corneal reshaping.
Corneal Refractive Therapy or Ortho-K is a non-surgical process developed to reshape the cornea. The cornea is gently flattened, while you sleep, resulting in the temporary correction of myopia (nearsightedness
) even with or moderate astigmatism (egg shaped cornea).
Similar in appearance to standard gas permable contact lenses these therapeutic lenses are designed differently to gently reshape the corneal surface while you sleep. They provide clear, natural vision when the lenses are removed upon waking.
Because ortho-k offers freedom from glasses and the hassle of wearing contact lenses during the day, this leading-edge technology can enhance the lifestyle of those requiring vision correction. Active individuals can freely participate in sports without the interference of glasses or bother of contacts. Eye irritation or dryness sometimes associated with contact lens wear due to outside dust and pollutants is eliminated.
Can Everyone Wear CRT?
Not everyone can wear CRT. This lens are intended for individuals with low to moderate myopia (nearsightedness up to -6 diopters) and moderate astigmatism. The larger the amount of myopia the harder it is to completely eliminate the nearsighted error. We have been very successful using corneal shaping in patients demonstrating-1.00 to -3.00 diopters of error. 90% of our patients with these myopic prescriptions acheive 20/20 with both eyes open. As your prescription increases the molding effect takes longer, but still works. We are beginning to work with hyperopia and presbyopia.
Myopia and Orthokeratology
Two factors have changed our thinking in the last decade. Myopia has become epidemic in the United States and Asia. Researchers have reported that the prevalence of myopia has increased from 20% to 40% in the United States (Vitale et al, 2009). In Asia the number of myopic children has exceeded 80% percent in some areas of the world such as Taiwan (Lin et al, 1999). This dramatic increase provides proof of the enviormental influence on the increase in myopia.
Figure1
The second major myopia development comes from corneal reshaping therapy (CRT) with contact lenses or ortho- keratology. For decades, eye doctors fitting these reshaping lenses reported that myopia appeared to develop at a much slower rate than children wearing traditonal soft lenses or glasses. For years many of us did not believe the claims of these orthokeratologists , however, numerous recent studies have demonstrated that there is significant slowing of progressive myopia or elongation of the eyes in kids wearing overnight orthokeratology versus other correction methods.
The studies, demonstrating the effect of CRT are from totally different parts of the world—the United States, Hong Kong, and Australia. All of the studies show fairly similar results: a 50% reduction in the progression of myopia (Cho et al, 2005; Swarbrick et al, 2010; Walline et al, 2009). Two of the studies compared the change in the length of eye ball with patients fit with and wearing CRT lens vs a control groups of spectacle wearers (Cho et al, 2005) or soft contact lens wearers (Walline et al, 2009). After more than two years, these studies found approximately a 50 percent reduction in axial elongation in the eyes wearing CRT. Recent data reported by Swarbrick et al (2010) showed slowed eye growth for eyes wearing CRT lenses compared to the other eye in patients eyes wearing traditional gas permable contact lenses.
Why Do These Lenses Work to Control Myopia?
Through a process known as emmetropization, the length of the eye changes through self-regulation to eliminate any potential optical error, i.e., 20/20 vision without glasses.(See Fig. 1)The eye grows slower in response to blur from nearsightness and faster in response to blur from farsighted in an attempt to obtain clear vision. Emmetropization results in a properly shaped eyeball and is more active in the first few years of life.
Previously, the central retina, or macula was thought to be responsible for this process of emmetropization, but recent animal studies demonstrate that the peripheral retina is much more responsible for emmetropization than previously thought.(see Fig.1) Recent research suggests that myopic progression appears to be controlled by the focus of light on the peripheral retina.. In the 1970s, a Dutch army ophthalmologist, Hoogerheide, noted that when eyes became myopic that the eyes increased in length asymmetrically, ie. that is they became longer, not wider. When this happens the peripheral and central focus become different, i.e., egg shaped growth pattern.With traditional glasses or contact lenses you obtain good central acuity but peripheral defocus.(See Fig. 2)
The development of myopia or elongation of the eye occurs when the peripheral retina is blurred.This peripheral de-focused image becomes the signal for the eyeball to grow or become myopic,In animal studies if the peripheral blur is removed, the eye alters its length and becomes smaller to eliminate the error, This occurs in animals even if the macula (fovea) is destroyed and no longer functioning (Smith et al, 2005). (Smith et al, 2009). This explains why bifocal spectacles may not be as effective as was once thought in slowing myopia, since central blur is not as strong of a signal to control eye growth as was previously believed.
Figure 2
Unlike glasses or traditonal contact lenses, CRT or Ortho-K lenses correct both the central and peripheral refractive error and, thus, eliminate the future stimulus for myopia progression. When the peripheral retina is corrected there is no blur or retinal signal for the eyeball to elongate, i.e., become more myopic. (See Fig. 3)
Figure 3
What is in the future of Ortho Keratology and or CRT?
Advanced Corneal Systems is developing an alternative to LASIK — Corneaplasty, a non-surgical procedure that permanently changes the shape of the cornea. A three-step process using ortho-k lenses similar to CRT molds the cornea. First the cornea is made softer and more malleable with a derivative of hyaluronidase. The cornea is then molded into the desired shape with custom-fitted ortho-K contact lenses. Lastly, a cross-linking “fixative” agent sets the cornea in its optimum shape. Sandoz, a pharmacologic company, is partnering with Advanced Corneal Systems in the FDA clinicals. Advanced Corneal Systems expects approval of this non-surgical, reversible procedure within one to two years.
How do I care for my lenses?
Your lenses should be chemically disinfected after every use (not heat). Our staff will instruct you about what care system is best for you. Your lenses should be replaced as your eye care practitioner sees fit.
How likely is it that CRT will work for me?
In the FDA trials in 2001, of the 159 eyes targeted for 20/20 vision (who had this acuity with their best spectacles), 59% obtained 20/20 or better without other correction and 92% obtained 20/40 or better at 9 months (20/40 vision is the acuity required in most states to drive without glasses). 67% of the subjects obtained 20/20 vision in at least one eye (their better seeing eye) and 94% achieved 20/40. Our personel experience is much better due to improved fitting technology.
How long does it take to reach good vision?
Most patients have rapid improvement with accelerated CRT within the first few days of treatment they achieve 20/40 vision and achieve their optimum vision in 10 to 14 days. A small percentage of patients will not improve enough to function under all conditions without additional correction.
Is Corneal Refractive Therapy Permanent?
No, it is temporary. If you stop wearing the lenses regularly while you sleep your lens-free vision will return to its original state in as little as 72 hours.
What are some important things for me to remember?
If you feel like you are having a problem with your vision or contact lenses, immediately remove your lenses and call our office. Always follow the instructions given to you about lens wear, follow-up and care systems.
What are the risks of wearing CRT?
There is a small risk involved when any contact lens is worn. It is not expected that the CRT Contact Lenses for Corneal Refractive Therapy will provide a risk that is greater than other rigid gas permeable contact lenses. Because this procedure is reversible some patients may notice changes in their vision late in the day.
The two most common side effects that occur in rigid contact lens wearers are corneal edema and corneal staining. It is anticipated that the same side effects will also occur in some wearers of CRT. Other side effects that sometimes occur in all contact lens wearers are pain, redness, tearing, irritation, discharge, abrasion of the eye or distortion of vision. These are usually temporary conditions if the contact lenses are removed promptly.
In very rare instances, infections of the eye, corneal ulcer, iritis, or neovascularization, corneal scarring, permanent decreased vision may occur. The occurrence of these side effects should be minimized or completely eliminated if proper lens care is exercised.
What do I do in the period of time between when I start CRT and when I achieve treatment?
It is important to understand that for a time after you have begun initial treatment but before sufficient treatment is realized, your old glasses will no longer be the appropriate prescription. We usually prescribe 1D contact lenses to get you through the adaptation period.
What if I have questions about CRT?
It is essential that you discuss any issues you may have about your eye health or contact lens wear with usl. If you need any further information about CRT lenses, please contact us.
Find out more. Call for a free consultation today.
