Common Q&A About CRT and Ortho-K


1. What are the differences between CRT and Ortho-K?

2. What is Cornea Refractive Therapy (CRT)?

3. How does CRT work?

4. Can everyone wear CRT?

5. How long does it take to reach good vision with CRT?

6. How often will I have to replace my Paragon CRT lenses?

7. Is CRT a safe procedure?

8. What are the upper limits of CRT treatment? Any examples?

9. Myopia Control in Children through Refractive Therapy Gas Permeable Contact Lenses: Is it for Real? New!!

10. Can CRT control the progression of myopia?  

11. Research Proves that Ortho-K can Effectively Control Myopia Progression in Children


1. What are the differences between CRT and Ortho-K?

CRT and Ortho-K are becoming a very popular vision correction procedure in the recent years.  Yet one of the most common questions that people ask is what are CRT and Ortho-K, and what are their differences.

Orthokeratology, or Ortho-K, is a non-surgical process which reshapes (flattens) the cornea of the eye using contact lenses. Ortho-K is not a new method; it has been practiced by some eye doctors for 40 years. So this technology has been matured. In the past, Ortho-k produced mixed results and wasn't FDA-approved for overnight wear, so the procedure had limited appeal.

Then in June 2002, the FDA granted overnight wear approval to a type of corneal reshaping called Corneal Refractive Therapy (CRT).  Paragon Co. owns the patent of CRT, so only one company, Paragon, can make the CRT lens.  CRT technology is based on the same theory as Ortho-K, however, it has a big improvement on design and material of the lenses. That is why CRT works a lot better than Ortho-K: Ortho-K only works for people who have nearsightedness less than -4.00D, astigmatism less than 0.75D, even within the range, the result can vary a lot.  But CRT can work very efficiently for nearsightedness up to –6.00, astigmatism up to 1.75D. The CRT lens use high oxygen permeability material, so it is safe for overnight wear.  A lot of data has shown that CRT causes no permanent side effect to patients. That is why FDA approves it.

For non-FDA approved Ortho-K lens, most labs can make them, and doctors do not need certification to fit Ortho-K lens. For CRT, only Paragon produces such lenses, and only very small percentage of eye doctors are rigorously trained and certified for fitting CRT lens.  There are only about 20 eyes doctors in San Diego that hold CRT certification and are qualified for fitting CRT lenses.  That is less than 10% of eyes doctors in San Diego.

(Back to questions...)

2. What is Cornea Refractive Therapy (CRT)?

Cornea refractive therapy (CRT) is a non-surgical process clinically developed to reshape the cornea while you sleep. The result is the temporary correction of myopia with or without moderate astigmatism.

Similar in appearance to standard contact lenses, CRT therapeutic lenses (FDA approved) gently reshape the corneal surface during sleep and provide clear, natural vision when the lenses are removed upon waking.

Because CRT offer 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.  

(Back to questions...)

How does CRT work?

In the myopic (near-sighted) eye, the focusing power is too great. Light focuses in front of the retina, making distant objects appear blurry. CRT lenses correct myopia, with or without low or moderate astigmatism, by gently reshaping the cornea while you sleep. When the CRT lenses are removed in the morning, the treated cornea allows light to focus on the retina. The result is clear, natural vision for all or most of your waking hours.

(Back to questions...)

Can everyone wear CRT?

Not everyone can wear CRT.  The lens are designed for individuals with low to moderate myopia (nearsightedness up to –6.00 diopters) with or without astigmatism (up to –1.75 diopters).  By September of 2008, our record at Excel Eyecare has been -9.75D (nearsightedness) or -2.50D (astigmatism). However, since there are variations in patient physiology and visual needs, the decision for CRT, at any age, can only be made after a thorough eye exam and the recommendations of the eye care professional.  At this time, hyperopia (farsightedness) is not correctable with CRT.

Dr. Gan is a certified CRT specialist with years of experience. You are welcome to to schedule an appointment for free consultation exam to see if you or your child is a good candidate for this procedure. (Click here to check the certified Paragon CRT Practitioners.) 

(Back to questions...)

5. How long does it take to reach good vision with CRT?

Most patients have rapid improvement in the first few days of treatment and achieve nearly their optimum vision in 10 to 14 days.

(Back to questions...)

6. How often will I have to replace my Paragon CRT lenses?

Generally speaking the CRT lenses have to be replaced once a year.  However, depending on factors such as protein build-up, how well the lenses are taken care of, etc., the lenses may have to be replaced more frequently.

(Back to questions...)

7. Is CRT a safe procedure?

The Paragon CRT lens we use are specially designed oxygen permeable therapeutic contact lens used in Corneal Refractive Therapy. It is a safe and reversible procedure.

There is a small risk involved when any contact lens is worn.  It is not expected that the Paragon CRT lenses for contact lens Corneal Refractive Therapy will provide a risk that is greater than other contact lenses.  There were no serious adverse events reported in the Paragon CRT FDA clinical study.

(Back to questions...)

8. What are the upper limit of CRT treatment? Any examples?

Generally, CRT can work effectively for nearsightedness up to –6.00, and astigmatism up to 1.75D. Beyond that limit, the case is considered difficult, and many patients may be rejected due to the high refractive error.  Another common case in which CRT is not advisable is when patients have very flat corneas because it leaves little room for CRT lenses to reshape them.

Can CRT treat such difficult cases (nearsightedness higher than –6.00D, and astigmatism higher than –1.75D)?  It is true that the higher the refractive error, the more it requires the doctor’s meticulous skill, experience and dedication, as well as the precision of the instruments.  However, Excel Eyecare Optometry has been treating patients in CRT that were either rejected by or failed in other optometry offices.  We have achieved a great success in these cases. By September of 2008, our record has been -9.75D (nearsightedness) or -2.50D (astigmatism). The following is a brief summary of nine such cases.

Sabrina became nearsighted since she was 6 years old, and her myopia progressed very rapidly then. Her mom consulted several optometric offices, and she was rejected because of her high myopia, high astigmatism and flat cornea. In May of 2006, Dr. Gan started CRT treatment for her.  Her prescription was:  R: -5.00-2.00x 180, L: -5.00-1.75x 180. After being treated with a pair of special designed CRT lens, Sabrina’s vision recovered to R: 20/25, L: 20/20 after one week. However, about two years later, Sabrina started to complain that her vision was blurry at the end of the day. Dr. Gan changed the design of the CRT lens, it did make the improvement, but after about a year, her night time vision was poor again. Dr. Gan changed the design of her lens, and her vision was only OK in the morning but still poor in the evening. Sabrina’s workload increased at school, she also got less and less sleep, which could be one of the reasons why her night time vision got worse, but her vision demand is getting higher and higher. Sabrina decided to give up CRT wear in Jan. of 2010, and her prescription went back to: R: 5.25-1.75X 180, L: 5.00-1.75X180. It’s apparent that her myopia was controlled very successfully over the past 4 years, even though her vision was not satisfactory in the last two years.

In Jan. 2011, Sabrina came to Dr. Gan’s office for annual eye exam after one year of wearing soft contact lens. It’s found that Sabrina’s prescription went up to: R: 8.25-2.25X 180, L: 8.00-2.00X180. Sabrina’s parents were extremely worried, and requested her to use CRT lens again.  Dr. Gan realized that the traditional CRT lens have reached the limitation and they no more work for this case. She decided to try the latest advanced cornea refractive therapy design lens. With the newly designed lens, Sabrina’s vision recovered to 20/20 both eyes within one week, her vision remains 20/20 throughout the day, and her eyes remain very healthy. Sabrina is very happy with her perfect 20/20 night time vision.

David, a 6 year old boy who lives in New York,  has a rapid progression of myopia: his nearsighted prescription tripled within one year (his prescription was: -1.25 OU one year before, now his prescription : R: -4.00-0.75x175, L: -4.00-1.00x180). His dad is a high myopia (over -10.00 both eyes). David's parents were very worried, and looked for methods of slowing down the progression of his nearsightedness. They did a lot of research, and found out that CRT is the only way to slow down or stop the progression of the nearsightedness. They looked for CRT doctors in New York, and found some doctors who have CRT certificate. They visited these doctors, and found that they do not have that much experience or knowledge about the CRT. They called Paragon (the manufacturer of CRT lens) and asked the top CRT doctors. Paragon recommended Dr. Michelle Gan because the volume of her CRT patients is the highest, and she has done a lot of very difficult cases of the CRT that most of CRT doctors could not handle. Later they found out that patients from the all over the world fly to Dr. Gan’s office for CRT treatment:  Dr. Gan has treated CRT patients from Canada, Switzerland, Taiwan, mainland China, Florida, San Francisco, Los Angeles, Orange county and so on.

So David’s parents decided to fly to San Diego to seek for CRT treatment from Dr. Gan. They arrived on April 14, 2011.  After all the measurements, Dr. Gan designed a pair of CRT lens.  After wearing them for two days, David’s vision went up to 20/20 OU. Dr. Gan said David’s eyes responded to the treatment very well, but she saw some signs of dryness, and decided to change to a little looser lens. After using them for two days, David’s vision was still 20/20 without dryness.

David’s dad also had an eye exam with Dr. Gan, with all the hi-tech instruments, Dr. Gan found that he had some visual field loss in the right eye.  After a dilation check, Dr. Gan found that he has retinal tear and suggested him to get a laser treatment to prevent retinal detachment after they go back to New York. David’s dad said he got eye exam every year, but he was most impressed by Dr Gan’s thoroughness and her instruments. One week later, the family went back to New York happily.

Mary Kang, a 12-year-old girl, started Ortho-K treatment in another office two years ago when her refractive error were R: -3.50-0.75X180, L: -3.00X-1.00X180, which were not too high. However her cornea was very flat (R: 39.12D, OS: 39.75D). She was first prescribed to wear Ortho-K lenses at night time, which did not work well for her and she still had very poor day time vision. Then she was prescribed to wear daytime contact lenses or glasses (-2.00DS) in order to see better.  She was told that her case was too difficult because her corneas were too flat. She gave up the Ortho-K treatment half a year ago because of the pain and irritability of wearing contact lenses 24 hours a day.  She went to a few other offices popular in CRT treatment, but was told that her case was very difficult, and that the success rate was practically naught. 

Referred by friends, who were CRT patients of Dr. Gan, Mary Kang visited Excel Eyecare Optometry on Oct. 12, 2006.  At that time, her refractive error was much worse: R: -5.75-1.25X 175, L: -5.25-1.00X165, and her corneas were still very flat: R: 39.12D, L 39.75D in K values (the average patients have K values of 43.50 for both eyes).  Dr. Gan accepted her and started the treatment on Oct. 15. After going through two pairs of CRT lenses in three weeks, Mary was able to see 20/20 with both eyes. She finally rid herself of her glasses and daytime contact lenses. To her, it was a miracle to have clear vision once again.

Iris Lang, a 9-year-old girl, had been experiencing rapid progression of myopia (nearsightedness). Her parents were very worried at the rate her eyes were deteriorating.  Referred by one CRT patient of Dr. Gan, Iris visited Excel Eyecare Optometry on Oct. 2, 2006 when her refractive error was R: -7.25-1.25X155 and L: -5.50-2.50X180.  Moreover, her corneas were very flat: R: 41.75D, L: 41.75D in K values.  Dr. Gan discussed this case with Dr. Ken Kopp, Manager-Clinical & Professional Services of Paragon,  and he commented: “This case will definitely be a great adventure for you, Dr. Gan.  If you succeed in this case, you will be the queen of CRT!”  Dr. Gan started the treatment on Oct. 10.  After one week of treatment, Iris’s refractive error was reduced to R: -2.00DS, L: -0.75-0.25X150.  Based on the current shape of her corneas, Dr. Gan prescribed a different pair of CRT for her, and one week later her vision improved dramatically to R: 20/25, L: 20/20. Three weeks into her treatment, she was able to see 20/20 with both eyes, and her ocular health remained intact.

Douglas Bi, a 12-year-old boy, had been experiencing rapid progression of myopia.  Douglas went to a very prestigious optometry office for consultation a couple of years ago, and was told that his case was much too difficult and the successful rate was much too low.  They quickly dismissed any plans of a CRT treatment.  However, after Douglas’s sister had a successful CRT treatment from Dr. Gan, he was encouraged to have Dr. Gan treat him as well. His refractive error was: R: -6.50-2.25X 065, L: -6.25-2.75X145.  Dr. Gan started the CRT treatment on August 29, 2006.  After one week of treatment, his vision improved immensely to R: 20/30, L: 20/20. After just two weeks, his vision became 20/20 with both eyes.

Kelly, a 17 year old girl with very high nearsightedness. One year ago they had consulted about the CRT technology at another clinic, but were told that her prescription was already too high (around -7.00 right, -8.00 left) for CRT correction. In August ’07, she visited Dr. Gan’s office. The exam showed that her prescription had progressed: Right: -8.50-0.50X020, Left: -9.75-0.75X167. Retinas of both eyes were very thin; if her prescription keeps going up, she will have a higher risk of getting retinal detachment. Her mom was so worried that she begged Dr Gan to try whatever method to prevent further progression of her nearsightedness.  Although no one had even tried to correct such a high prescription in the history of CRT, Dr. Gan decided to take this adventure. After a series of careful measurements, calculations and modification based on her experience, Dr. Gan designed a pair of CRT lens for Kelly. On the second day, Kelly's vision was already miraculously improved to 20/40 (right) and 20/80 (left). One week later, her vision was 20/30 (right) and 20/50 (left). One month later, her vision was already perfect: 20/20 for both eyes.

Sam, an outgoing 12 year old girl, loves sports and really wanted to get rid of her glasses. The eye exam and CRT pretests showed that Sam’s subjective refraction errors were: Right eye: -1.25-2.25X085, left eye: -1.75X2.50X090; K values (corneal curvature): right: 48.00, left: 48.50. Although her nearsightedness (-1.25 and –1.75) was not high, her astigmatism (-2.25 and –2.50) was very high, which made this case more difficult. The axis of her astigmatism was the so-called "against-the–rule" type (around 90°) instead of the "with-the–rule" type (around 180°). Against-the-rule astigmatism is usually very hard to treat; and against-the-rule astigmatism higher that 1.00 is generally considered to be untreatable by CRT. To make things worse, her K values and topography results showed that her cornea were very steep and irregular, which would make it hard to center the lens on the cornea. Dr. Gan discussed about this case with Dr. Ken Kopp again. He thought that it was an extremely difficult case with such a low successful rate that it was not even worth to try.

Dr. Gan explained the situation to Sam and her mom. Although very disappointed, they still insisted to give it a try. After a series of precise measurements and calculations with modifications based on Dr. Gan's own experience, Dr. Gan designed a pair of lens and had them special ordered from Paragon CRT. These lens perfectly centered on Sam's cornea when put on. The second day follow-up showed that Sam was able to see 20/25 both eyes. One week follow-up showed that Sam was able to see 20/20 both eyes with no refractive error! The very excited Sam can enjoy her sports freely now. “What an amazing case,” Dr. Ken Kopp commented, “You broke the record of the CRT difficult cases again!”

Rahul is a 7 yrs old boy who lives in Ottawa, Canada. In the recently years, his eyes have suffered from rapid progression of nearsightedness. In earlier 2008, his prescription was:  right: -7.25 -1.25X060; left: -7.00 -1.75X160. The very worried parents heard that CRT could slow down the progression of nearsightedness, and had consulted almost all the CRT doctors in Canada and even some in the US cities near Ottawa. Unfortunately, his cornea shape is irregular and very flat (K=41 OU, average K is 43-44), his nearsightedness is very high, and although his astigmatism prescription is not very high, the axis is at an oblique direction, which makes the cornea shape irregular. All of these factors makes it extremely hard to correct his vision using CRT. All the doctors rejected Rahul as a difficult CRT candidate.  

Then they heard about Dr. Gan from one of her CRT patients, and the whole family of 4 (mom, dad and brother) flew from Ottawa to San Diego on July 4th, 2008. They booked a hotel for one month for Rahul’s CRT treatment and follow-ups. Dr. Gan talked to Dr Ken Kopp about this case again. He said that this case only had 10% of successful rate.  But Dr. Gan still decided to take the adventure.

On July 5th, Dr. Gan did a full eye exam for Rahul. Based on the detailed data and her experience, Dr. Gan designed and ordered a pair of special CRT lens from Paragon.  On the 2nd day follow-up,  his vision improved to 20/80 (right) and 20/70 (left) and his prescription decreased remarkably to: right: -3.00-0.50x075; left: -2.50-0.50x175. One week later, his vision was 20/30 (right) and 20/30+ (left), and his prescription became -0.75DS (right) and -0.50DS (left). The family was very pleased with the result and decided to go back to Canada earlier than planned. Before they left San Diego (10 days after Rahul started to wear CRT lens), they had another check up, and it showed that Rahul’s vision was even better: R: 20/25, L: 20/25, both eyes were very healthy. The family went back to Canada happily on July 17th.

Gloria and Angela are very cute 10 year old twin sisters. They came to Excel Eyecare for eye exam on 5/3/2007. They complained of blurry vision, and had hard time to see the board at school. They were wearing CRT lens fitted by a very experienced and well-known CRT doctor. They had started to wear CRT lens from the beginning of 2006, but their vision were not satisfactorily corrected. They had to go to follow up almost every week, had changed CRT lens almost every time for about one year, and there was very little improvement.

Dr. Gan did detailed exams for both of them. Gloria's vision was R: 20/60, L: 20/40. Refraction results showed that Gloria were farsighted with a lot of astigmatism. Topographer showed that both CRT lens were de-centered and both corneas were distorted, which induced a lot of astigmatism. That was the main reason that Gloria's vision was poor. Angela's vision was R:20/80, L:20/40. Refraction result showed that Angela was nearsighted with a lot of astigmatism.  Topographer result showed that the CRT lens were decentered, and the corneas were distorted. Dr. Gan did another exam for them after letting the two twin sisters stop wearing CRT lens for one month. She found that both of their corneas had irregular shape, which made the CRT lens very difficult to center on their corneas and hence hard to correct the vision successfully.

Their mom asked if Dr. Gan can take over and fix the twin's cases. Considering that they were fitted by such an experienced and well-known CRT doctor who tried so hard to make them work but was not successful, Dr. Gan suggested them to wear day time contact lens. So the sisters started to wear daytime contact lens from June 2007, and quit the CRT therapy.

In July of 2008, their mom called Dr. Gan from Orange County (The whole family moved to Orange County because of job change), and told Dr. Gan that the two sisters had rapid nearsightedness progression in the past year, and both of them missed CRT contact lens. They wanted to try CRT lens again no matter how low of the success rate would be. Dr. Gan decided to give a try on Gloria first because she had higher prescription, and more irregular cornea shape. Dr. Gan carefully studied the data she collected and her previous CRT history, figured out why all the CRT lens the previous doctor had tried did not work. She specially designed a pair of lens that could overcome the irregular shape of her cornea, so that the CRT lens would not slip to the side and cause distortion.

On 8/2/2008, the whole family drove to San Diego from Orange County, and Gloria started to wear her new CRT lens. During the one week follow up, her vision were found to be: Right: 20/20, Left: 20/30. One month later, her vision was Right: 20/20, Left: 20/20.  Angela also started CRT fitting on 9/1/2008. One week later, her vision improved to: Right: 20/25, Left: 20/30. One month later, her vision were 20/20 for both eyes.

The whole family was very happy about it, and would love to share their amazing experience with you.


Joanna, a 15 yrs old girl, had a follow up appointment with Dr. Gan at Excel Eyecare Optometry at 5pm on July 26, 2011. Joanna was able to read 20/20 with either eyes without hesitation. She has worn with this pair of advance new design of Cornea Refractive Therapy lens for one week, and now her vision was perfect all day long. She was so happy and excited!

Joanna started CRT treatment on June 6, 2006. She had a rapid progression of nearsightedness. At an age of 10, Joanna’s prescription was: R: -5.75-0.75X048, L: -5.50-0.75X165. Her corneas were flat, which made it very difficult to correct with CRT. Dr. Gan predicted that her response to CRT might not be very good, her night time vision might be worse than her vision in the morning, but CRT could still prevent her prescription from getting worse. It took Joanna about one month to get morning vision: R: 20/25, L: 20/30, but her night time vision was always a little worse, but was sufficient for her daily vision demand.

As Joanna grew, her school load was getting heavier and heavier, she slept less and less in the evenings.  So the CRT wearing time got less too, and her vision without CRT got so worse that, at one point, she found her vision was not sufficient for her school work. Joanna still did not want to quit CRT, one reason is that she knew that her prescription will increase if she discontinued wearing CRT, also she did not want to wear glasses.

In our experience, CRT does have its limitations, especially for a small group of kids who have high nearsightedness and flat and irregular corneas. Recently there is a brand new type of Cornea Refractive Therapy lens that are reported to work better for this group of kids. So Dr. Gan designed a new pair of lens with this new technology for Joanna.  Within one week, Joanna’s vision was brought back to 20/20, and her 20/20 vision stayed all day long. We were very happy to find a promising solution for the group of kids with difficult cases.


On August 21, 2012, an anxious mom and a 12 years girl, Megan, from Thousand Oaks came to our office to seek for night time Cornea Refractive Therapy. She was referred by our existing CRT patient who also lives in Thousand Oaks. Megan’s mom was very worried because Megan’s prescription increased so fast, at a young age of 12, her prescription was: R: -9.25-1.25X180, OS: -9.75-1.50X010. They had visited many offices that do CRT in Thousand Oaks, Los Angeles, and Irvine in past three years since she was only -6.00, and she was told that her nearsighted was too high to be treated with CRT. On August 20, the mom heard that her neighbor’s daughter had high nearsighted and was successfully treated by Dr. Gan. The next day, the mom called Excel Eyecare and requested to be seen on the same day, and drove to San Diego immediately after she hung up the phone.

Dr. Gan examed Megan’s eyes and designed a pair of lens for Megan. After 5 days of wearing the lens, Megan’s vision were: 20/30 OU without lens in the morning, her prescription reduced to: OD: -0.75-0.50X 170, OS: -0.75-0.75X180. After two weeks of wearing it, Megan complained that she was able to see well in the morning, but her night time vision got worse.  At 6:00pm, her vision was R: 20/40, L: 20/60, and her mom was not fully satisfied.  So Dr. Gan adjusted the lens. After wearing the new lens for another two weeks, Megan was able to see 20/20 in the morning and 20/25 in the evening, both patient and mom was very satisfied. Megan has worn the lens for 6 months since then, and every time Megan came to Excel Eyecare for a follow up, they cannot tell Dr. Gan and staff enough how excited they are, and wish they hadmet Dr. Gan sooner, so her prescription would not be so high.


On 4/1/2013, a worried mother brought her three daughters to our clinic for eye exam. The exam results showed that all the girls' nearsightedness prescriptions doubled from a year before. Valerie, 9 year old, had -9.25 nearsightedness with 3.25 diopter of astigmatism on her right eye, and -9.50D nearsightedness with 4.50 diopter of astigmatism on her left eye. Her twin sister, Vickie, has -5.50 nearsightedness with 2.25 D of astigmatism on the right, and -5.57D of nearsightedness with 1.50D of astigmatism on the left. Their older sister, Vivian, has -6.00D nearsightedness with2.5D of astigmatism on the right, and -6.50D nearsightedness with 1.75D astigmatism on the left. Their retinal images all showed significant distortion and thinning, especially for Valerie, which indicated a high risk of retinal detachment.

The worried mom had brought them to several optometry offices and hoped that those doctors could stop the progression of their nearsightedness by wearing night time contact lens, but they were rejected because their nearsightedness and astigmatism were too high. They eventually came to Excel Eyecare since she heard from her friends that Dr. Gan is a national leader of Corneal Refractive Therapy (CRT) and has successfully treated many difficult cases that had broken world records.  Dr. Gan started to do all the measurements for the girls, and designed three pairs of night time corrective lens for them. At one week follow up appointment, the mother was so happy that she could not stop tearing: The three girls all had 20/20 vision on both eyes. Miraculously, Valerie could only see 20/30 with regular glasses before, and now she is seeing 20/20 after one week of wearing the CRT lens that Dr. Gan designed for her.


Dr. Gan’s rich experience in CRT treatment, her clinic’s state-of-the-art instruments, and her passion and love for her patients contributed to her exceptional success rate in CRT treatment. The grateful parents of these patients have authorized us to give out their phone numbers at our discretion. If you would like to talk to them, please call us at 858-780-9889.

(Back to questions...)

9. Myopia Control in Children through Refractive Therapy Gas Permeable Contact Lenses: Is it for Real?  New!!

The 2013 paper on American Journal of Ophtalmology shows another research study on whether CRT can effectively control the progression of myopia (Click the following to read two relevant scientific articles):

"Myopia Control in Children through Refractive Therapy Gas Permeable Contact Lenses: Is it for Real?"
Bruce Koffler and James Sears, American Journal of Ophthalmology, 2013; 156: 1076–1081

The authors drew the following conclusion:

"The initial practice of Orthokeratology proved to be ineffective, but with new development of lens material and designs especially for overnight wear, orthokeratology has developed into a viable and effective treatment for myopia. Studies suggest that current techniques are highly effective at treatingmyopia of up to 6.00Dand astigmatism of up to 1.75 D. Orthokeratology is an effective option in slowing the progression of myopia by redirecting the image shell onto both the central and mid-peripheral retina, thereby producing emmetropization. Improved training, better lens hygiene, and patient compliance have promoted
the safety of orthokeratology to make it as safe as other overnight methods. The future will bring further applications of orthokeratology to treat other refractive errors. Orthokeratology is a very useful tool in combating refractive errors in
myopic children and, with further studies, should prove to be useful in a wide range of other refractive disorders."

(Back to questions...)

10. Can CRT control the progression of myopia? 

The results of several recent research studies showed that CRT can effectively control the progression of myopia. Click the following to read two relevant scientific articles:

"The Children’s Overnight Orthokeratology Investigation (COOKI) Pilot Study" in Optometry and Vision Science, 81:407-413, 2004
Jeffery J. Walline, Marjorie J. Rah, and Lisa A. Jones, The Ohio State University College of Optometry, Columbus, Ohio (JJW, LAJ) and New England College of Optometry, Boston, Massachusetts (MJR)

"The Longitudinal Orthokeratology Research in Children (LORIC) in Hong Kong: A Pilot Study on Refractive Changes and Myopic Control" in Current Eye Research, 30:71–80, 2005
Pauline Cho, Sin Wan Cheung, and Marion Edwards, Department of Optometry & Radiography, The Hong Kong Polytechnic University, HongKong, SAR, China 

(Back to questions...)

11. Research Proves that Ortho-K can Effectively Control Myopia Progression in Children

Ortho-K (and its more advanced kind, CRT) is a popular, non-surgical myopia correction procedure that flattens the cornea using contact lenses at sleep. Can Ortho-K also prevent the progression of myopia in children? The following is the abstract of a study on this by a Hong Kong research group (Pualine Cho et al., The Longitudinal Orthokeratology Research in Children (LORIC) in Hong Kong: A Pilot Study on Refractive Changes and Myopic Control Current Eye Research, 30:71–80, 2005).

Purpose: Myopia is a common ocular disorder, and progression of myopia in children is of increasing concern. Modern overnight orthokeratology (ortho-k) is effective for myopic reduction and has been claimed to be effective in slowing the progression of myopia (myopic control) in children, although scientific evidence for this has been lacking. This 2 year pilot study was conducted to determine whether ortho-k can effectively reduce and control myopia in children.

Methods: We monitored the growth of axial length (AL) and vitreous chamber depth (VCD) in 35 children (7–12 years of age), undergoing ortho-k treatment and compared the rates of change with 35 children wearing single-vision spectacles from an earlier study (control). For the ortho-k subjects, we also determined the changes in corneal curvature and the relationships with changes of refractive errors, AL and VCD.

Results: The baseline spherical equivalent refractive errors (SER), the AL, and VCD of the ortho-k and control subjects were not statistically different. All the ortho-k subjects found post-ortho-k unaided vision acceptable in the daytime. The residual SER at the end of the study was −0.18 ± 0.69 D (dioptre) and the reduction (less myopic) in SER was 2.09 ± 1.34 D (all values are mean ± SD). At the end of 24 months, the increases in AL were 0.29 ± 0.27 mm and 0.54 ± 0.27 mm for the ortho-k and control groups, respectively (unpaired t test; p = 0.012); the increases in VCD were 0.23 ± 0.25 mm and 0.48 ± 0.26 mm for the ortho-k and control groups, respectively (p = 0.005). There was significant initial corneal flattening in the ortho-k group but no significant relationships were found between changes in corneal power and changes in AL and VCD.

Conclusion: Ortho-k can have both a corrective and preventive/control effect in childhood myopia. However, there are substantial variations in changes in eye length among children and there is no way to predict the effect for individual subjects.

(Back to questions...)


Copyright (C)2005-10 Excel Eyecare Optometry. All rights reserved. See Terms of Use for details.