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Common
Q&A About CRT and Ortho-K
Questions:
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.
Can CRT control the
progression of myopia?
10. Research Proves that
Ortho-K can Effectively Control Myopia Progression in Children
Answers:
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.
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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.
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3.
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.
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4.
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.)
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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.
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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.
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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.
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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
seven such cases.
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.
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.
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9. 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
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10. 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.
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