Corneal reshaping and myopia progression

Abstract

Anecdotal evidence indicates that corneal reshaping contact lenses may slow myopia progression in children. The purpose of this investigation is to determine whether corneal reshaping contact lenses slow eye growth.
Forty subjects were fitted with corneal reshaping contact lenses. All subjects were 8 to 11 years and had between -0.75 D and -4.00 D myopia with less than 1.00 D astigmatism. Subjects were age-matched to a soft contact lens wearer from another myopia control study. A-scan ultrasound was performed at baseline and annually for 2 years.
Twenty-eight of 40 (70%) subjects wore corneal reshaping contact lenses for 2 years. The refractive error and axial length were similar between the two groups at baseline. The corneal reshaping group had an annual rate of change in axial lengths that was significantly less than the soft contact lens wearers (mean difference in annual change = 0.16 mm, p = 0.0004). Vitreous chamber depth experienced similar changes (mean difference in annual change = 0.10 mm, p = 0.006).
Results confirm previous reports of slowed eye growth following corneal reshaping contact lens wear.

Full text

Corneal reshaping and myopia progression
J J Walline, L A Jones, L T Sinnott
The Ohio State University
College of Optometry,
Columbus, Ohio, USA
Correspondence to:
Dr J J Walline, 338 West Tenth
Avenue, Columbus, OH 43210-
1240, USA; walline.1@osu.edu
Accepted 25 February 2009
Published Online First 4 May 2009
ABSTRACT
Background/aims: Anecdotal evidence indicates that
corneal reshaping contact lenses may slow myopia
progression in children. The purpose of this investigation
is to determine whether corneal reshaping contact lenses
slow eye growth.
Methods: Forty subjects were fitted with corneal
reshaping contact lenses. All subjects were 8 to 11 years
and had between 20.75 D and 24.00 D myopia with
less than 1.00 D astigmatism. Subjects were age-
matched to a soft contact lens wearer from another
myopia control study. A-scan ultrasound was performed
at baseline and annually for 2 years.
Results: Twenty-eight of 40 (70%) subjects wore corneal
reshaping contact lenses for 2 years. The refractive error
and axial length were similar between the two groups at
baseline. The corneal reshaping group had an annual rate
of change in axial lengths that was significantly less than
the soft contact lens wearers (mean difference in annual
change = 0.16 mm, p = 0.0004). Vitreous chamber
depth experienced similar changes (mean difference in
annual change = 0.10 mm, p = 0.006).
Conclusion: Results confirm previous reports of slowed
eye growth following corneal reshaping contact lens
wear.
Approximately 100 million people in the USA are
myopic,
1
and the majority of these patients became
short-sighted during childhood.
2
Patients with low
myopia are able to wear thinner spectacle lenses
that are more comfortable and cosmetically more
appealing, they have more predictable refractive
surgery results,
3
and they have a lower risk of
retinal detachment,
4
glaucoma and chorioretinal
degeneration
5
than patients with high myopia.
Therefore, slowing the progression of myopia
during childhood could have a positive effect on a
large number of people.
Orthokeratology contact lenses were originally
fitted in the late 1960s and continued through the
1980s. Results with the orthokeratology contact
lenses were often incomplete and unpredictable,
6
so orthokeratology was rarely performed until the
new millennium. New materials with higher
oxygen permeability and reverse geometry contact
lens designs allowed short-sighted patients to wear
orthokeratology (now commonly called corneal
reshaping) contact lenses during sleep to tempora-
rily flatten the cornea and provide consistently
clear vision throughout the day without wearing
glasses or contact lenses. Several studies have
shown that adults
7–9
and children
10 11
can experi-
ence clear vision throughout the day if they wear
the corneal reshaping contact lenses during sleep.
Watt and Swarbrick summarised all of the cases of
microbial keratitis related to orthokeratology that
have been reported in the literature.
12
They found
that approximately half of the cases occurred in
children younger than 16 years, and three-quarters
of the cases were reported in East Asia. However,
the number of people wearing orthokeratology
contact lenses is unknown, so the rates of
microbial keratitis associated with orthokeratology
cannot be calculated for comparison to soft or gas-
permeable contact lens wear.
Preliminary data indicate that corneal reshaping
contact lenses may slow myopia progression. The
first report of corneal reshaping contact lenses
slowing myopia progression was published by
Reim and colleagues.
13
In a retrospective chart
review of 253 eyes examined 1 year after initiating
corneal reshaping contact lens wear and 164 eyes
examined after 3 years of corneal reshaping contact
lens wear, the authors included changes in refrac-
tive error and base curve of the contact lens to
measure myopia progression. Over a period of
1 year, the refractive error progressed an average of
20.06 D, and the refractive error progressed
20.37 D over 3 years. Both values represent slower
myopia progression than has been reported for
single vision spectacle wearers, approximately
20.50 D per year,
14 15
but there were no control
subjects to provide comparative data.
A case report published by Cheung et al
measured the axial growth from one child who
wore a corneal reshaping contact lens in one eye
and no contact lens in the other eye because it was
essentially emmetropic.
16
Over a period of 2 years,
the uncorrected eye grew 0.34 mm axially, and the
eye with a corneal reshaping contact lens grew
0.13 mm. Although this was the first direct
measure of slowed eye growth following corneal
reshaping contact lens wear, the evidence was
anecdotal.
The first controlled trial comparing axial growth
of subjects fitted with corneal reshaping contact
lenses to a retrospective cohort of single vision
spectacle wearers was reported by Cho and
colleagues.
17
Over a 2-year period, the corneal
reshaping contact lens wearers’ eyes grew an
average of 0.29 (SD 0.27) mm, and the spectacle
wearers’ eye grew 0.54 (0.27) mm (p = 0.01). This
study provided the first evidence from a controlled
trial that indicated corneal reshaping contact lenses
slow the growth of the eye, but the subjects were
not fitted using a standardised protocol.
All three of these studies indicate that corneal
reshaping contact lenses may slow the growth of the
eye, but they suffer from limitations that make
interpretation of the results difficult, such as lack of
an adequate control group,
13 16
indirect measurement
of refractive error progression
13
and being fitted by a
variety of eye care practitioners from the commu-
nity.
17
However, confirmation of the study by Cho
and colleagues may provide sufficient evidence to
Clinical science
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warrant a randomised clinical trial to investigate the effect of
corneal reshaping contact lens wear on myopia progression in
children. We conducted the Corneal Reshaping and Yearly
Observation of Nearsightedness (CRAYON) Pilot Study to
investigate the effect of corneal reshaping contact lens wear on
eye growth of 8- to 11-year-old myopic children over 2 years.
MATERIALS AND METHODS
The CRAYON Pilot Study followed the tenets of the Declaration
of Helsinki and was approved by The Ohio State University
Biomedical Institutional Review Board. All parents provided
informed consent, and child assent was attained from all subjects.
All subjects were 8 to 11 years old at the baseline visit. They
had between 20.75 D and 24.00 D spherical component
myopia and less than 21.00 D astigmatism by cycloplegic
autorefraction. Cycloplegia was achieved by administering one
drop of 0.5% proparacaine, followed by two drops of 1%
tropicamide administered 5 min apart. All subjects had 20/20 or
better visual acuity in each eye and good ocular and systemic
health. They had not previously worn gas-permeable contact
lenses, they were not taking medications that might affect
contact lens wear, they were not participating in other eye or
vision studies, and they had no previous eye surgeries.
Eligible subjects were matched by age category (8 or 9 years
vs 10 or 11 years) to a historical control subject who was
randomly assigned to wear soft contact lenses during the
Contact Lens and Myopia Progression (CLAMP) Study.
18
After
participating in a run-in period of gas-permeable contact lens
wear for an average of 2 months, CLAMP Study subjects were
randomly assigned to wear gas-permeable or soft contact lenses
for the remainder of the study. This randomisation visit was
considered the basis for determining the timing of all
subsequent visits and served as the baseline for measuring
changes during the CLAMP Study. Only subjects randomly
assigned to wear soft contact lenses were matched to a corneal
reshaping contact lens wearer.
The primary outcome of the CRAYON Pilot Study was the
difference in the 2-year change in axial length, measured by a-
scan ultrasound, between corneal reshaping and soft contact
lens wearers. Secondary outcomes included comparisons of
anterior chamber depth, lens thickness and vitreous chamber
depth between corneal reshaping and soft contact lens
wearers. Refractive error and corneal curvature are temporarily
altered by orthokeratology, so they are not compared in this
investigation.
A-scan ultrasound
The IOLMaster was not available at the beginning of the
CLAMP Study, so no baseline measurements were available for
comparison with the IOLMaster. Therefore, A-scan ultrasound
measurements were performed and edited until five readings
with high, equal lens peaks and a distinct, anterior scleral peak
were recorded using identical protocols. The measurements
were performed while the subject viewed a distant target under
cycloplegia using one drop of 0.5% proparacaine, followed by
two drops of 1% tropicamide administered 5 min apart. The
examiner lightly touched the cornea with a hand-held probe
until a reading was automatically recorded in the automatic
mode. The vitreous chamber depth was calculated by subtract-
ing the anterior chamber depth and the lens thickness from the
axial length. The baseline measurements were performed at the
initial visit for the CRAYON Pilot Study subjects and at the
randomisation visit for the CLAMP Study subjects.
Contact lenses
Corneal reshaping contact lens wearers were fitted with
Corneal Refractive Therapy (Paragon Vision Sciences, Mesa,
Arizona) contact lenses, using HDS-100 materials, according to
the manufacturer’s directions. In summary, the spherical
component of the manifest refraction and the flat keratometry
meridian were used to determine the initial trial lens, which was
placed on the eye and evaluated for a proper fit. Subjects were
also provided with Unique-pH Multi-Purpose Solution (Alcon,
Ft Worth, Texas) and their contact lenses were occasionally
cleaned in-office with Progent (Menicon USA, San Mateo,
California). Subjects fitted with soft contact lenses wore Focus
2-week disposable contact lenses, and they were given SOLO
Care multi-purpose solutions (CIBA Vision Care, Duluth,
Georgia). All subjects received free contact lenses, solutions
and eye care throughout both studies.
Statistics
The analyses include only the 28 subjects who completed the
entire study and the control subjects to which they were
initially matched. Repeated measures over time were collected.
For the analysis, data were treated as eyes nested within
subjects nested within pairs. A subject with no missing data
could have six measures of each outcome, one from each eye in
each year. We used multilevel modelling, a generalisation of
multiple regression that handles clustered observations, to
model each outcome.
For each outcome, a linear growth model was fitted. The
model used random effects for pair, subject within pair, and eye
within subject which adjusted the mean growth curve intercept
and the mean growth curve slope. The effects of treatment, visit
and their interaction were then evaluated for each of the ocular
components of interest. All analyses were conducted using
Statistical Analysis Software (SAS) version 9.1 (SAS Institute,
Cary, North Carolina).
Table 1 Baseline demographic and ocular characteristics of subjects who completed (n = 28) and subjects
who did not complete (n = 12) the Corneal Reshaping and Yearly Observation of Nearsightedness Pilot Study
Variable Completed Not completed p Value
Age (years) 10.5 (1.1) 10.2 (1.0) 0.44
Female (%) 46.4 58.3 0.49
White (%) 85.7 75.0 0.41
Axial dimensions of average eye (mm)
Anterior chamber depth 3.84 (0.21) 3.89 (0.29) 0.57
Lens thickness 3.35 (0.13) 3.42 (0.17) 0.13
Vitreous chamber depth 17.11 (0.77) 16.58 (0.83) 0.06
Axial length 24.30 (0.73) 23.83 (0.85) 0.09
Variables are mean (SD) unless otherwise indicated.
Clinical science
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RESULTS
Forty subjects were enrolled in the CRAYON Study between 30
September 2004 and 2 March 2005. Twenty-eight of the 40
(70%) completed the 2-year study. Subjects dropped out of the
study before attending the 1-day (n = 4), 10-day (n = 4), 6-
month (n = 2), 1-year (n = 1) and 2-year (n = 1) visits. None of
the drop-outs were due to complications; the vast majority was
due to lack of interest in contact lens wear after the initial
experience. The baseline demographic and ocular characteristics
are similar between the subjects who completed the study and
the subjects who did not complete the study (table 1), and also
between the corneal reshaping who remained in the study for
2 years and the age-matched soft contact lens wearers (table 2).
Table 3 shows the mean (SD) ocular components for each
treatment group, and table 4 shows the differences between the
groups at each visit. The eyes of both treatment groups grew
(both p = 0.0001); however, the annual rate of change in axial
length was on average 0.16 mm per year less (p = 0.0004) for
corneal reshaping contact lens wearers than soft contact lens
wearers (fig 1).
Vitreous chamber depth change was similar to that of axial
length. There was a statistically significant positive rate of
change in vitreous chamber depth in both groups (p,0.0001).
Vitreous chamber depth grew 0.10 mm per year faster for soft
contact lens wearers than corneal reshaping contact lens
wearers (treatment6visit interaction p = 0.006).
The annual rate of change in anterior chamber depth of
corneal reshaping contact lens wearers was not statistically
significant (mean change = 20.01 mm, p = 0.63), but the rate of
change in anterior chamber depth of soft contact lens wearers
was statistically significant (mean change = 0.05 mm,
p = 0.0005). On average, the anterior chamber depth of the
soft contact lens wearers increased 0.06 mm per year more than
the anterior chamber depth of the corneal reshaping contact
lens wearers (treatment6visit interaction p = 0.004).
Lens thickness did not exhibit any statistically significant
annual change for either group (p.0.43); nor was there a
statistically significant difference in rate of change between the
treatment groups (p = 0.47).
DISCUSSION
Corneal reshaping contact lenses provide short-sighted patients
with clear vision without requiring vision correction to be worn
during the day.
7–11
Results of this study confirm results from
prior investigations that indicated that corneal reshaping
contact lenses also slow the progression of myopia in
children.
13 16 17
How these contact lenses may control myopic
eye growth is still debatable.
Recent animal studies indicate that the peripheral retina is
more responsible for regulation of eye growth than previously
thought.
19 20
In infant monkeys, form deprivation limited to the
peripheral retina produced myopic eye growth, and all monkeys
recovered from the induced refractive error, regardless of
whether their fovea was ablated with an argon laser.
20
Furthermore, ablation of the fovea at an early age did not
prevent emmetropisation typically experienced by infant
monkeys; nor did it prevent refractive error development
induced by form deprivation.
19
In humans, myopic eyes experience relative hyperopia in the
periphery that hyperopic and emmetropic eyes do not,
21
and
children who become myopic have more relative hyperopic
peripheral blur than emmetropic children 2 years before the
onset of myopia.
22
Patients with peripheral hyperopic defocus
are also more likely to develop myopia.
23
Therefore, peripheral
hyperopia may act as a signal for increased eye growth.
The focus of light posterior to the peripheral retina may act as
a signal for continued myopic eye growth. The current theory of
myopia control with corneal reshaping contact lens wear is that
the oblate shape of the cornea and the ‘‘knee’’ where the oblate
portion of the cornea returns to its original curvature cause
peripheral light rays to focus anterior to the peripheral retina.
This results in an image shell that provides focused light
centrally at the fovea, while the peripheral retina experiences
myopic defocus that results in slowed axial growth. There is still
Table 2 Baseline demographic and ocular characteristics of corneal reshaping and soft contact lenses
wearers participating in the Corneal Reshaping and Yearly Observation of Nearsightedness Pilot Study
Variable Corneal reshaping Soft p Value
Age (years) 10.5 (1.1) 10.5 (1.0) 0.93
Female (%) 46.4 39.3 0.59
White (%) 85.7 89.3 1.0
Axial dimensions of average eye (mm)
Anterior chamber depth 3.84 (0.21) 3.81 (0.30) 0.74
Lens thickness 3.35 (0.13) 3.38 (0.16) 0.47
Vitreous chamber depth 17.11 (0.77) 17.02 (0.65) 0.61
Axial length 24.30 (0.73) 24.20 (0.63) 0.63
Variables are mean (SD) unless otherwise indicated.
Table 3 Mean (SD) axial dimensions for corneal reshaping and soft contact lens wearers at each visit
Outcome Treatment Baseline Year 1 Year 2
Anterior chamber depth (mm) Corneal reshaping 3.84 (0.21) 3.86 (0.22) 3.83 (0.22)
Soft 3.81 (0.30) 3.91 (0.24) 3.91 (0.27)
Lens thickness (mm) Corneal reshaping 3.35 (0.13) 3.35 (0.11) 3.34 (0.12)
Soft 3.38 (0.16) 3.37 (0.18) 3.39 (0.18)
Vitreous chamber depth (mm) Corneal reshaping 17.11 (0.77) 17.24 (0.74) 17.37 (0.79)
Soft 17.02 (0.65) 17.26 (0.72) 17.48 (0.78)
Axial length (mm) Corneal reshaping 24.30 (0.73) 24.45 (0.70) 24.55 (0.72)
Soft 24.20 (0.69) 24.50 (0.69) 24.77 (0.80)
Clinical science
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much to learn about the role of the peripheral optical profile in
regulation of eye growth, but peripheral myopic defocus
currently is the leading theory to explain the potential myopia
control effect of corneal reshaping contact lenses.
The results of our study indicate that eye growth is slowed by
55%, which is similar to the 46% slowed axial elongation
reported by Cho and colleagues.
17
Corneal reshaping contact
lenses provide clear vision by flattening the cornea, which in
theory would shorten the axial length of the eye and could
explain the observed treatment effect. In fact, our study found
that the anterior chamber depth increased significantly more for
soft contact lens wearers than corneal reshaping contact lens
wearers. However, when our study and the study by Cho and
colleagues eliminated the effects of the anterior chamber by
measuring the growth of only the vitreous chamber depth, a
significant treatment effect was still present.
17
This indicates
that some signal must act to slow the myopic eye growth.
Limitations of the current study
Nearly one-third of the subjects withdrew from the study prior
to the conclusion. If poor adaptation to corneal reshaping
contact lens wear was related to the treatment response
(perhaps flatter corneas make it more difficult to adapt and
decrease the treatment response), the results would appear to
show significant myopia control when in reality the results
were skewed because the treatment effects were only measured
for the subjects who benefitted most. However, there were no
significant differences in baseline demographic or biometric
measures between the subjects who were lost to follow-up and
those who remained in the study, decreasing the risk of bias.
The examiners were not masked to the treatment group of the
subjects because only the corneal reshaping contact lens wearers
were actively enrolled in the study. The control subjects were
matched to the corneal reshaping subjects following participation
in a different study. Although the examiners were not masked by
treatment group, it is unlikely that their knowledge could have
influenced the outcome dramatically. The same procedures were
used for both studies, and the outcome was change over time. In
order to affect the outcome, a difference in procedures would have
had to taken place after the baseline visit, but the same procedures
were used throughout the study.
Some believe that use of soft contact lens wearers as the control
group may artificially inflate the treatment effect experienced by
corneal reshaping contact lens wearers due to ‘‘myopic creep’’ that
has been reported following initiation of soft contact lens wear.
However, studies of adolescents with at least 1 year of follow-up
have shown that soft contact lens wear does not increase myopia
progression.
24 25
Soft contact lenses do not increase myopia
progression or eye growth compared with spectacles, so soft
contact lens wearers are an appropriate control group.
Conclusion
Despite the fact that several studies have investigated myopia
control over the past few years, an effective treatment with few
side effects is still to be discovered. Corneal reshaping contact lens
wear holds promise for myopia control. It has now been shown by
two separate controlled trials to slow the axial growth of the eye.
However, further investigations must apply the gold standard
study design, a randomised clinical trial, to definitively determine
whether or not corneal reshaping contact lenses slow the growth
of the eye. Investigations must also attempt to determine the
mechanism of the treatment effect and why the treatment effect
may continue beyond the first year.
Acknowledgements: Supported by materials from Paragon Vision Sciences, CIBA
Vision Corporation, Alcon Laboratories, and Menicon.
Competing interests: None.
Ethics approval: Ethics approval was provided by The Ohio State University
Biomedical Institutional Review Board.
Patient consent: Obtained from the parents.
Provenance and peer review: Not commissioned; externally peer reviewed.
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Lens thickness (mm) +0.03 (0.21) +0.02 (0.20) +0.04 (0.22)
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ANSWERS
From questions on page 1141
1. Describe the OCT RNFL thickness profile and clock-hour
analysis (figs 1C, 2C)
The RNFL thickness profile revealed depressions in the
inferotemporal region OU and in the superotemporal region
OS. OCT demonstrated borderline thinning compared with the
normative database at 7 o’clock and normal thickness in all
other clock-hour and quadrants OD. In OS, the clock-hour
analysis showed the 1 and 5 o’clock positions and the inferior
quadrant to be borderline thin.
2. Describe the cross-sectional scans (figs 1D, 2D)
The cross-sectional scans showed localised thin RNFL within
the normally thick superior and inferior areas. The areas of thin
RNFL were smoothed out by the software algorithm and were
not detected or detected as borderline.
3. How would you interpret OCT results in the future?
The OCT data require careful and critical analysis in order to
interpret the information complementary to and in context of the
conventional clinical and functional examination. Localised RNFL
defects might be missed or underestimated by OCT analysis due
to failure of the RNFL defect to thin to such an extent that it falls
below the first percentile for the population represented by the
device’s normative database. It is important to critically analyse
the graphic representation and OCT images. The averaging
algorithm may ‘‘wash out’’ the data from the defect by averaging
them with the data of the adjacent thicker areas. This is most
pronounced when the localised defect occurs in an area with thick
RNFL such as the superior and inferior regions.
DISCUSSION
The StratusOCT software uses a normative database that
allows excellent discrimination between healthy and glaucoma-
tous eyes.
1
There are some patients, however, who may have
thinning of the RNFL, yet remain within the normal range. In
these patients, RNFL defects and even VF loss may be present,
yet the OCT may give readings that do not fall into the
borderline or abnormal zones in the clock-hours scheme. It is
clear from the RNFL thickness profile that the shape of the
RNFL curve is not normal in these patients. That is, instead of
having the four elevations ordinarily seen, two superior and two
inferior, an area of expected elevation may be flat or even
depressed. Because the curve still lies within the boundaries of
the normal or borderline range, this RNFL thinning is not
flagged or flagged only as borderline. The clinician must identify
the abnormal shape of the curve, which indeed deviates from
the expected without dropping below the floor of ‘‘normal.’’
StratusOCT uses cross-correlation for alignment of adjacent
A-scans and smoothing image processing procedures in order to
provide homogenous scans and consistent results. The RNFL is
differentiated from other retinal layers using an edge detection
algorithm. Using this software, the OCT has been shown to
provide reproducible quantitative RNFL data
2
and to enable
good discrimination between healthy and glaucomatous eyes.
3
However, this approach, in concert with the limitations of the
normative database, is also vulnerable to missing well-estab-
lished localised RNFL defects as we demonstrated in this study.
When narrow and deep RNFL defects are present, the
smoothing algorithm may fail to recognise them and bridge
the gaps, thus overestimating thinner RNFL area as seen in our
cases. This is most pronounced in places where the RNFL is
thickest (superior and inferior regions). Furthermore, the
quadrant and clock-hour sectors are arbitrarily defined and do
not follow the actual anatomical distribution of the ganglion
cell axons which might further affect the analysis output and
obscure or underestimate thinning areas.
We therefore recommend that the routine OCT evaluation by
the clinician should include careful attention to the thickness
profile that might reveal RNFL thinning that is not flagged as
borderline or outside normal limits in the quadrant and clock-
hour analyses. In cases where there is a discrepancy between the
clinical findings and OCT, further insight may also be gained by
viewing the actual cross-sectional images, taking into account
the limitations of the software as outlined above.
Br J Ophthalmol 2009;93:1185. doi:10.1136/bjo.2007.131854a
REFERENCES
1. Budenz DL, Michael A, Chang RT, et al. Sensitivity and specificity of the StratusOCT
for perimetric glaucoma. Ophthalmology 2005;112:3–9.
2. Paunescu LA, Schuman JS, Price LL, et al. Reproducibility of nerve fiber thickness,
macular thickness, and optic nerve head measurements using StratusOCT. Invest
Ophthalmol Vis Sci 2004;45:1716–24.
3. Wollstein G, Ishikawa H, Wang J, et al. Comparison of three OCT scanning areas for
detection of glaucomatous damage. Am J of Ophthalmol 2005;139:39–43.
Education
Clinical science
Br J Ophthalmol September 2009 Vol 93 No 9 1185
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doi: 10.1136/bjo.2008.151365
2009 2009 93: 1181-1185 originally published online May 4,Br J Ophthalmol
J J Walline, L A Jones and L T Sinnott
Corneal reshaping and myopia progression
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