01 orthokeratology children chan

C L I N I C A L A N D E X P E R I M E N T A L

OPTOMETRY

Orthokeratology practice in children in a
university clinic in Hong Kong*

Clin Exp Optom 2008 DOI:10.1111/j.1444-0938.2008.00259.x

Ben Chan BSc (Hons) Optom Purposes: The aim of this study was to analyse clinical data of children undergoing
Pauline Cho PhD, FAAO orthokeratology (ortho-k) and to investigate patients’/parents’ perspective on ortho-k
Sin Wan Cheung MPhil, FAAO via telephone interviews.
School of Optometry, The Hong Kong Methods: Clinical records of children undergoing ortho-k from a university optometry
Polytechnic University, Hong Kong SAR, clinic were reviewed and the effects of ortho-k on refraction, vision and cornea were
China investigated. A telephone interview was conducted to solicit patients’/parents’ perspec-
E-mail: soben@polyu.edu.hk tive of the treatment.
Results: One hundred and eight files were reviewed. Median age of the children was
nine years (range six to 15); mean (ϮSD) pre-treatment refractive sphere was
-3.56 Ϯ 1.49 D and the median refractive cylinder was -0.50 D (range zero to -4.25 D).
Significant refractive spherical reduction (58 per cent), improvement in unaided vision
and corneal topographical changes were noted after only one night of wear. No signifi-
cant change in astigmatism was found. Corneal staining was the most commonly observed
complication with ortho-k and more than 80 per cent of patients were advised to apply
ocular lubricants to loosen the lens before lens removal. Ortho-k was mainly undertaken
for myopic control and about 90 per cent of the respondents reported good/very good
unaided vision after ortho-k and ranked the treatment as satisfactory or very good. Lens
Submitted: 27 February 2007 binding and ocular discharge were the most frequently reported problems during the
Revised: 4 November 2007 treatment.
Accepted for publication: 7 November Conclusion: Under close monitoring, overnight ortho-k is effective and safe for reducing
2007 low to moderate myopia and the treatment is well accepted by the children.

Key words: corneal staining, corneal topographical changes, myopic reduction, ocular lubricants, orthokeratology, unaided vision

The effectiveness of overnight orthokera- myopic reduction is noted even after a for myopic reduction and vision correc-
tology (ortho-k) in flattening the cornea short period of lens wear,4–9 with more tion in children.
and temporarily reducing myopia has than 75 per cent of myopia being reduced Overnight ortho-k was introduced in
been widely documented.1–6 A significant within the first week4,5,7 in adult subjects. Hong Kong in 1997. In Hong Kong, the
Walline and co-workers10 reported similar prevalence of myopia is high, from 11
results in children wearing ortho-k lenses. per cent among seven-year-olds, up to
The majority of ortho-k wearers in Hong 57 per cent among 12-year-olds and over
*Presented at the 2nd Asia Cornea and Contact
Lens Conference, Hong Kong, China, 14-15 Kong are children.1 Therefore, it is neces- 70 per cent among 17-year-olds.11,12 Most
April 2005 sary to investigate the efficacy of ortho-k ortho-k wearers in this region are children

© 2008 The Authors Clinical and Experimental Optometry 2008
Journal compilation © 2008 Optometrists Association Australia 1

Orthokeratology in children Chan, Cho and Cheung

ortho-k on refractive, visual and cor-
Age range (median) (years) 6–15 (9) neal changes. The relationships between
Gender (male/female) 37/71 changes in consecutive visits were also
Mean Ϯ SD pre-treatment refractive sphere (range) (D) -3.56 Ϯ 1.49 (-0.75 to -8.75)
Pre-treatment refractive cylinder range (median) (D) 0 to -4.25 (-0.50) determined.
The distribution of refractive sphere,
unaided vision and topographical pa-
Table 1. Patient demographics (n = 108) rameters were not significantly different
from normal (Kolmogorov-Smirnov D
tests, p > 0.05), so parametric tests were
used for statistical analyses. Repeated mea-
sures analysis of variance (ANOVA) was
aiming at myopic control.13 Although a before the treatment, after the first night
used to test for changes over the six-month
recent non-randomised clinical study has of lens wear and at approximately one
treatment period; paired t tests with
shown that ortho-k is effective in slowing week, two weeks, one month, three
Bonferroni correction were used to test
the rate of myopic progression,14 there is a months and six months after wearing the
for differences between any two consecu-
need to conduct a randomised study to lenses. Only information from the right
tive visits. For refractive sphere and topo-
confirm this finding. Understanding the eye was used for analysis. At each visit, a
graphical parameters (six comparisons),
clinical profile of children undergoing non-cycloplegic subjective refraction was
p-values less than 0.008 (0.05/6) and for
ortho-k will also be helpful to practitioners performed, with the ‘plus one blur test’ to
unaided vision (five comparisons) p-values
in better advising their patients/parents ensure relaxed accommodation. Corneal
less than 0.01 (0.05/5) were considered as
before starting the treatment. topographical data, including the flattest
significant. The distributions of the data
The Optometry Clinic of The Hong and steepest simulated keratometry read-
for the baseline and six-month refractive
Kong Polytechnic University has been ings, Q (asphericity, Q = -e2) at 9.8 mm
cylinder and six-month residual refractive
providing ortho-k service since 1997. Our chord (flat meridian) and apical radius of
sphere were significantly different from
clinic employs full-time practitioners and curvature (Ro) were collected from the
normal (Kolmogorov-Smirnov D tests,
in the late 1990s, two experienced ortho-k Medmont E300 corneal topographer
p < 0.05). For these and ordinal variables
practitioners joined our clinic. All practi- (version 3.90, Medmont Pty. Ltd., Cam-
(for example, corneal staining), Friedman
tioners working in our clinic are indepen- berwell, Australia). Corneal staining with
test and Spearman’s correlation coeffi-
dent and our clinic does not impose any sodium fluorescein was recorded based on
cients were used for analysis.
constraints on the type of lenses fitted or Efron’s scale.15 Information on the brands
the care systems used for their patients. of lenses used, the recommended lens
The primary aim of this study was to care system and the number of lenses RESULTS
conduct a retrospective review of the files required to achieve the optimum ortho-k
Table 1 presents the demographical data
of children undergoing overnight ortho-k effect was also collected.
of 108 children whose files were reviewed.
in our clinic. Through a telephone inter- In addition, a telephone interview using
At the time of lens fitting, the median age
view, we also investigated the attitudes of a structured list of questions was con-
of the wearers was nine years (range six to
patients and parents and satisfaction ducted to obtain information on why the
15 years) and most of them were female
towards ortho-k, and identified the most patients/parents chose ortho-k, how they
(66 per cent).
commonly encountered problems during knew about ortho-k, their most commonly
the treatment. encountered problem(s) with the proce-
dure and their overall satisfaction with the
Refraction and unaided vision
The mean (ϮSD) pre-treatment refractive
METHODS treatment. The general questions in the
sphere was -3.56 Ϯ 1.49 D and the median
questionnaire were to be answered by
The files of all children (younger than 16 refractive cylinder was -0.50 D (range zero
parents, while questions involving visual
years of age) undergoing ortho-k and to -4.25 D). Only 27 patients had subjec-
performance and satisfaction with the
fitted between April 2000 and November tive refraction recorded at every visit.
treatment were addressed to the children.
2003 were reviewed. Only patients who Changes in refractive sphere and cylinder
had a pair of lenses used for at least six Treatment of data during the six-month treatment period
months and were still on ortho-k during As this was a retrospective study where are shown in Figure 1. The refractive
the surveyed period were included in this data were collected from clinic files, most sphere after ortho-k treatment was
study. One hundred and eight patients of the results were presented in num- significantly reduced when compared to
met these inclusion criteria. Demographi- bers and percentages. Some data may be the baseline data (repeated measures
cal and clinical data were retrieved from missing due to omissions in the patient’s ANOVA, F (6, 21) = 60.32, p < 0.001) and
their clinical files during the six-month record at some visits. Data were analysed the amount of reduction increased with
treatment period. These included data to determine the effect of overnight the time of treatment. The largest refrac-

Clinical and Experimental Optometry 2008 © 2008 The Authors
2 Journal compilation © 2008 Optometrists Association Australia


1.00
1.00

0.90
0.00
0.80

Unaided vision (decimal notation)
-1.00 0.70
Residual refraction (D)

* * 0.60
-2.00 *
0.50
-3.00
* 0.40

-4.00 0.30
Refractive sphere *
Refractive cylinder 0.20
-5.00
0.10
-6.00
1st
0.00
baseline 1 week 2 weeks 1 month 3 months 6 months 1st overnight 1 week 2 weeks 1 month 3 months 6 months
overnight

Period of lens wear Period of lens wear

*p < 0.001 (the residual spherical refraction is significantly different compared with previous visit) *p < 0.001 (the unaided vision is significantly different compared with previous visit)

Figure 1. Residual subjective refractive errors at different Figure 2. Unaided vision at different visits during six months
visits during six months of lens wear (each error bar indicates of lens wear (each error bar indicates one standard deviation)
one standard deviation) (n = 27) (n = 29)

tive spherical reduction (58 per cent) was No further improvement was observed vision during the daytime. On average,
observed after the first night of lens wear (p > 0.01) thereafter, that is, among sub- these patients also had significantly higher
and appeared to stabilise by the first sequent visits. The mean unaided vision pre-treatment refractive sphere and cylin-
month of wear (98 per cent) (paired t for this group of patients at the two-week der than patients who did not require
tests, p < 0.008). No further change was and six-month visits were 0.68 Ϯ 0.24 visual aids during the daytime (Table 2).
observed over subsequent visits (paired t decimal (0.18 logMAR or Snellen 6/9) Some patients with lower pre-treatment
tests, p > 0.008). The mean (ϮSD) myopia and 0.73 Ϯ 0.28 decimal (0.12 logMAR or myopia (-3.50 D) also had significant
reduced from -3.88 Ϯ 1.27 D (baseline) Snellen 6/7.5), respectively (Figure 2). residual refractive errors and required the
to -0.26 Ϯ 0.83 D (one month). At the For all patients who had unaided vision aid of spectacles after the procedure.
six-month visit, the mean residual re- recorded at the six-month visit (n = 103),
fractive sphere was -0.09 Ϯ 0.53 D. No 58 per cent had unaided vision of 0.80 Corneal responses
significant reduction in refractive cylinder decimal (0.10 logMAR or Snellen 6/7.5) Table 3 summarises the corneal topo-
was found over the six-month treatment or better and for four per cent of the graphical changes over the six-month lens
period (Friedman X2 = 8.24, p = 0.221) patients it was worse than 0.20 decimal wear (n = 73). There were significant flat-
(Figure 1). (0.70 logMAR or Snellen 6/30), which was tening in the simulated keratometry
For all patients with subjective refrac- mainly due to the significant residual reading and Ro and significant change in
tion recorded at the six-month visit refractive error and lens decentration. Q after commencing ortho-k treatment
(n = 108), the residual refractive sphere The mean unaided vision at the six- (repeated measured ANOVA: flattest sim-
and cylinder were significantly associated month visit was significantly correlated ulated keratometry reading: F (6, 67) =
with the pre-treatment refractive sphere to the residual refractive sphere (Spear- 72.08, p < 0.001; steepest simulated
and cylinder, respectively (refractive sph- man r = 0.55, p < 0.001) and cylinder keratometry reading: F (6, 67) = 57.89,
ere: Spearman r = 0.39, p < 0.001; refrac- (Spearman r = 0.48, p < 0.001). The mean p < 0.001; Ro: F (6, 67) = 184.34, p <
tive cylinder: Spearman r = 0.44, p < UVA was also correlated to the pre- 0.001; Q: F (6, 67) = 88.98, p < 0.001).
0.001). treatment refractive sphere and refractive Maximum changes in corneal parameters
For patients with unaided vision cylinder, respectively (refractive sphere: were observed after the first night of lens
recorded at all visits (n = 29), the mean Spearman r = 0.53, p < 0.001; refractive wear, with stabilisation within two weeks of
unaided vision after the first night of cylinder: Spearman r = 0.28, p = 0.004). lens wear (paired t test, p < 0.008).
lens wear was 0.41 Ϯ 0.23 decimal (0.40 After six months of ortho-k treatment, After the first overnight lens wear,
logMAR or Snellen 6/15) and continued 21 of the 108 patients (19 per cent), corneal staining was observed in 41 per
to improve (repeated measures ANOVA, with mean residual refractive sphere of cent of patients (44 out of 108) and 74 per
F (5, 24) = 13.57, p < 0.001) until after two -1.64 Ϯ 1.43 D required the aid of spec- cent of staining recorded was within the
weeks of lens wear (paired t test, p < 0.01). tacles to obtain acceptable clear distance central three millimetres of the cornea.



Visual aid required Visual aid not required p-value
(n = 21) (n = 87) Unpaired-t-test
mean Ϯ SD mean Ϯ SD
Baseline refractive sphere (D) -5.18 Ϯ 1.30 -3.16 Ϯ 1.26 <0.001
(range -3.50 to -8.75) (range –0.75 to –6.25)
Baseline Kf (mm) 7.79 Ϯ 0.15 7.81 Ϯ 0.28 >0.05
Baseline Ks (mm) 7.48 Ϯ 0.14 7.58 Ϯ 0.24 >0.05
Baseline Ro (mm) 7.71 Ϯ 0.40 7.73 Ϯ 0.22 >0.05
Baseline Q -0.43 Ϯ 0.15 -0.43 Ϯ 0.13 >0.05
Residual refractive sphere at 6 month (D) –1.64 Ϯ 1.43 -0.08 Ϯ 0.48 <0.001
Median (range) Median (range) Mann-Whitney U test
Baseline refractive cylinder (D) -1.00 (0.00 to -4.25) -0.50 (0.00 to -2.25) <0.001

Kf = Flattest simulated keratometry reading; Ks = Steepest simulated keratometry reading; Ro = Apical radius of curvature; Q = Asphericity value

Table 2. Ocular parameters of patients with or without need of visual aid during the daytime after orthokeratology

Baseline First overnight 1 week 2 weeks 1 month 3 months 6 months
Kf (mm) 43.38 Ϯ 1.52 42.18 Ϯ 1.35 42.01 Ϯ 1.42 41.72 Ϯ 1.47 41.71 Ϯ 1.61 41.55 Ϯ 1.56 41.61 Ϯ 1.55
Ks (mm) 44.79 Ϯ 1.65 43.80 Ϯ 1.58 43.40 Ϯ 1.63 43.11 Ϯ 1.67 43.10 Ϯ 1.71 43.09 Ϯ 1.68 43.14 Ϯ 1.67
Ro (mm) 7.70 Ϯ 0.26 8.06 Ϯ 0.37 8.12 Ϯ 0.29 8.14 Ϯ 0.32 8.19 Ϯ 0.33 8.20 Ϯ 0.32 8.20 Ϯ 0.35
Q -0.42 Ϯ 0.13 0.18 Ϯ 0.22 0.14 Ϯ 0.12 0.11 Ϯ 0.13 0.09 Ϯ 0.14 0.08 Ϯ 0.15 0.07 Ϯ 0.17

Kf = Flattest simulated keratometry reading; Ks = Steepest simulated keratometry reading; Ro = Apical radius of curvature; Q = Asphericity value

Table 3. Summary of corneal changes (mean Ϯ SD) at different visits over 6 months of ortho-k lens wear (n = 73)

The incidence of corneal staining de- Lens designs and per cent used Unique pH (Alcon Labora-
creased over the course of treatment from care regimen used tories Inc, Fort Worth, TX, USA) and one
41 per cent after the first overnight lens DreimLens (Taiwan Macro Vision Group, per cent used Boston Simplus (Polymer
wear to 25 per cent at the six-month visit. Taiwan) was the most commonly used lens Technology Corporation, Rochester, NY,
Most staining (84 per cent) at all visits was design (80 per cent), followed by the USA). All patients were instructed to use
graded as mild (Grade 1 or less); 13 per eLens (E&E Optics Asia Ltd, Hong Kong) non-preserved saline for rinsing the lenses
cent were graded as Grade 2 and only three (14 per cent). Only 1.4 per cent of patients after cleaning.
per cent were graded as Grade 3 or Grade used a custom-made lens design. The lens More than 80 per cent of patients (89
4. Patients who had Grade 2 or higher level material used for all patients was Boston out of 108) were advised to use ocular
of staining in the central cornea were XO (Polymer Technology Corporation, lubricants before lens removal in the
advised to cease lens wear until the condi- Rochester, NY, USA). morning, and about 58 per cent were
tion subsided. Figures 3 and 4 summarise Most patients (76 per cent) were advised to use a single-dose formulation.
the levels and locations of staining advised to use a separate daily cleaner The most commonly recommended
recorded over the six-month treatment and disinfecting solution. Boston Advance single-dose ocular lubricant was Tear
period. None of the patients had corneal Cleaner and Boston Advance Condition- Naturale Free (Alcon Laboratories Inc,
staining at every visit. The frequency of ing Solution (Polymer Technology Corpo- Fort Worth, TX, USA).
staining was significantly associated with ration, Rochester, NY, USA) were the most Almost all reviewed patients (97 per
pre-treatment spherical refractive error commonly recommended care solutions. cent) used a suction holder to aid lens
(Spearman r = -0.25, p = 0.01), though the The remaining patients (24 per cent) were removal. Only three per cent of patients
association was not very strong. prescribed multipurpose solution: 22.8 removed lenses with their fingers.



80 100
No stain 90 1st overnight
70
Grade 1 80 1 week
60 2 weeks
Grade 2
70
1 month
50 Grade 3
60
Percentage

Percentage
3 months
Grade 4 6 months
40 50

40
30
30
20
20
10
10

0 0
1st 1 week 2 weeks 1 month 3 months 6 months Central Superior Inferior Peripheral
overnight
Period of lens wear Corneal location

Figure 3. Corneal staining recorded at different visits during Figure 4. Corneal staining at different locations during six
six months of lens wear (first overnight, n = 107; 1 week, months of lens wear (first overnight, n = 107; 1 week, n = 102;
n = 102; 2 weeks, n = 106; 1 month, n = 86; 3 months, n = 91; 2 weeks, n = 106; 1 month, n = 86; 3 months, n = 91; 6 months,
6 months, n = 108) n = 108)

Number of lenses Telephone survey ranked the treatment as poor. The last
For patients with myopia greater than Ninety-four patients agreed to a telephone two had discontinued lens wear (after
4.00 D (n = 40), a ‘stepwise’ fitting proto- interview. The primary reason for under- more than six months) due to discomfort
col (see Discussion) was applied, so the going ortho-k was myopic control (87 per and unacceptable post-ortho-k vision even
number of lenses used was dependent on cent). More than 50 per cent heard about after modifications to lens fittings.
the amount of pre-treatment myopia. For ortho-k from their friends and relatives
patients with myopia equal to or lower who had children undergoing the treat-
DISCUSSION
than 4.00 D (n = 68), the first pair of ment. About 30 per cent learned about
lenses prescribed aimed for full correc- the treatment from their optometrists,
tion. The majority of these patients (73.5 12 per cent from newspapers and one Demographics
per cent) achieved optimum ortho-k effect per cent from public seminars. This retrospective study collected an
using only one pair of lenses. All of these Almost 90 per cent of those interviewed extensive body of data of children who
patients had good lens centration, as reported good or very good post-ortho-k started ortho-k treatment in a university
shown in their topographical maps, and unaided distance vision. Fifty-seven per clinic during the first three years of this
the mean myopic reduction was within cent of the patients reported that the century. In agreement with our previous
0.25 D of the target. About 16 per cent of quality of unaided vision could be main- study,13 most wearers (more than 90 per
the patients required two pairs of lenses tained until the end of the day and the cent) were children, probably reflecting
and 7.4 per cent required three pairs of rest reported noticeable deterioration of the prevalence and severity of myopia
lenses to achieve the optimum ortho-k distance vision about 12 hours (median) in Chinese children. Our patients incl-
effect. Two patients (three per cent) were after lens removal (range: four to 16 uded children with high myopia (6.00 D
unable to achieve satisfactory result with hours). or greater) and astigmatism (1.50 D or
vision even after four pairs of lenses. The The most frequently reported non- greater), although conventional clinical
number of lenses required by patients visual problems were lens binding (44 per wisdom would suggest that such patients
with higher myopia (greater than 4.00 D) cent) and ocular discharge in the morning are likely to be relatively unsuccessful in
to achieve optimum myopic reduction (40 per cent), followed by tearing (21 per ortho-k, in terms of leaving significant
was significantly associated with the base- cent), redness (18 per cent) and dis- amounts of refractive error and poor
line refractive sphere (Spearman r = -0.33, comfort (12 per cent). unaided vision after the treatment.
p = 0.005) but was not associated with Of the respondents, 89 per cent (84/ The parents of these patients requested
refractive cylinder, corneal curvature, 94) ranked the treatment as good or very ortho-k for myopic control, even though
Ro and Q (Spearman -0.07 < r < 0.01, good, 8.5 per cent (8/94) ranked the they were informed of the necessity of
p > 0.05). treatment as acceptable and two per cent wearing spectacles to correct residual



refractive errors to achieve satisfactory changes. Several authors have reported of corneal staining after the commence-
distance vision after the procedure. similar clinical findings in overnight ment of overnight ortho-k treatment.3,10
ortho-k.4,7,14,20 Rah and co-workers3 found that the
Refraction and unaided vision The safety of overnight ortho-k for majority of their subjects did not exhibit
The greatest change in refractive sphere myopic reduction is still a controversial significant corneal staining at the morn-
was observed after the first night of issue despite the development of hyper- ing visits. Walline and co-workers10 re-
lens wear. Similar results have been rep- oxygen permeable lens materials and ported that more than one half of their
orted.4–7,9 Our results also indicate that innovative lens designs, which allow children exhibited corneal staining in the
although there was a continued reduction greater myopic reduction and more morning immediately after lens removal.
in refractive sphere until after one month predictable results.7,20 Safety is a major As the severity of the staining was not
of lens wear, visual improvement reached concern, as there have been several clinically significant, they did not recom-
optimum level after two weeks of lens reports of serious corneal complications mend discontinuation of lens wear. We
wear. At six months, the average unaided associated with ortho-k and most of these also noted that the incidence of corneal
vision of our patients improved to the cases involved children.21–24 Corneal stain- staining tended to be higher when
maximum level of 0.74 decimal (equiva- ing is a common complication in any aiming for a higher target.
lent to 0.13 logMAR or Snellen 6/8), type of contact lens wear and the inci-
however, this finding is relatively poorer dence of staining is increased in ortho-k
than the average 0.02 logMAR or better lens wear.25 Corneal staining in ortho-k Lens designs and
reported in most studies.4–7 Among our may be due to thinning of the central care regimens used
patients, 42 had pre-treatment refractive corneal epithelium, improper lens fitting, DreimLens was the most frequently used
sphere of more than 4.00 D and 11 corneal hypoxia, hyper-sensitivity to con- brand of lenses in our clinic in the early
patients had pre-treatment refractive tact lens solution, mechanical abrasion 2000s, as it was the first lens design intro-
cylinder of more than 1.50 D. If we due to the build-up of deposits on the duced into Hong Kong for overnight
excluded these patients, unaided vision back surface of the lens, lens binding and ortho-k therapy. The trend has changed
was improved to a mean of 0.88 decimal incorrect removal of a bound lens on with time as many different lens designs
(equivalent to 0.06 logMAR or Snellen waking. Our results show that almost one have since been introduced into this
6/7). Consistent with previous re- half of the patients (41 per cent) exhib- region.
ports,3,4,7,16 unaided vision after ortho-k is ited corneal staining after the first night The majority of patients were instructed
significantly correlated with the amount of of ortho-k lens wear. The incidence of by their optometrists to use a separate lens
pre-treatment and residual refractive staining decreased to 25 per cent at the care system, that is, daily cleaner with
errors, including spherical and cylindrical six-month visit. Although the incidence rubbing of lenses, saline for rinsing and
errors. These subjects were advised to use of corneal staining decreased with the disinfecting solution for storing the lenses,
spectacles to achieve good distance vision period of lens wear, most of the staining instead of a bottle of multi-purpose solu-
after the procedure. (74 per cent) was in the central cornea. tion for cleaning, rinsing and disinfecting.
Ortho-k has been reported to be inef- Central (as opposed to peripheral) Single bottle systems are less complex and
fective in reducing refractive cylindrical corneal staining is of greater concern as more convenient to use, and are believed
power.3–6,16 The present survey agrees the disruption of central corneal integrity to facilitate compliance. In terms of effi-
with these reports. No significant refrac- is more likely to lead to sight-threatening cacy, a single bottle solution serving the
tive cylindrical change was noted during complications, if accompanied by im- functions of cleaning, rinsing and disin-
the six-month ortho-k treatment, how- proper use and care of lenses and acces- fecting is essentially a compromise solu-
ever, some researchers have reported sories. Hence in ortho-k practice, the tion and some multipurpose solutions can
changes in with-the-rule corneal astigma- level of central corneal staining that is cause irritation when they are in contact
tism in their ortho-k subjects.17–19 regarded as clinically significant should with the eye. Ortho-k involves sleeping
be more stringent. In the present study, with high Dk lenses and hence, it is desir-
Corneal responses most staining (84 per cent) were graded able to have the lenses as clean as possible
Consistent with previous studies,2,6–8,20 we as clinically insignificant (that is, lower and any chance of solution sensitivity
found that on average, the corneal shape than Grade 2) and no clinical action was should be avoided. In our clinic, we rec-
changed from prolate to oblate over a taken for these patients. Patients who had ommend rubbing the lenses with a daily
9.8 mm corneal chord after a single night Grade 2 or higher level of staining in the cleaner and rinsing the lenses with normal
of lens wear. Therefore, it is not surpris- central three millimetres of the cornea saline after cleaning and before insertion.
ing to find significant correlations be- were advised to cease lens wear until the Several disinfecting solutions are available
tween corneal shape changes, including condition subsided and none of them for rigid gas permeable lenses and the
simulated keratometry readings, apical required medical treatment. A few majority of these solutions are compatible
radius of curvatures and refractive studies have also reported the incidence with ortho-k lenses.



It should be noted that the brands of ortho-k lens wear and to increase safety by Mountford27 and Rah and co-workers.3
lenses and solutions used do not necessar- during removal, our clinic has com- Mountford27 conducted a 90-day retro-
ily reflect the effectiveness of these brands menced teaching parents/patients to spective study on 48 subjects and found
over others. The preference for lenses or remove ortho-k lenses with their fingers. that the regression of apical corneal power
disinfecting solutions to prescribe to the A suction holder is given for emergency over approximately an eight-hour period
patients depends on the individual practi- use only. In cases where a suction holder was 0.50 to 0.75 D. Similarly, Rah and
tioner and/or the availability in the stock is necessary, daily cleaning, proper co-workers3 also reported an amount of
of a particular brand in our clinic. Our storage, weekly disinfection and regular 0.25 to 0.50 D daytime regression in
results on the preferred solutions to be replacement of the suction holder should spherical equivalent manifest refraction
prescribed to patients only highlighted be emphasised. after one-month overnight ortho-k treat-
the importance placed by ortho-k practi- ment. These two studies used adult
tioners in our clinic on the use of daily Number of lenses used subjects so it is uncertain whether the
cleaner and normal saline in the care of Many of our patients (73.5 per cent) with regression rate in children would be the
ortho-k lenses. pre-treatment myopia equal to or lower same. Further work in Hong Kong is inves-
The use of an ocular lubricant is than 4.00 D (n = 68) required only one tigating the daytime regression of ortho-k
optional in overnight ortho-k treatment, pair of lenses to achieve the optimum effect in children.
as dryness is not a problem during sleep, ortho-k effect. In our clinic, for patients More than 40 per cent of the respon-
however, due to the high incidence of lens with myopia greater than 4.00 D, a ‘step- dents ranked lens binding as the most
binding associated with overnight ortho-k, wise’ fitting protocol is used, that is, the common non-visual problem they ex-
more than 80 per cent of patients were first pair of lenses target a myopic reduc- perienced. Lens binding associated with
advised to apply an ocular lubricant to aid tion of 4.00 D, and provided the corneal overnight ortho-k has been reported pre-
lens removal in the morning. Patients health and lens centration are good, the viously,6,28 and the suggested cause was the
were instructed to apply an ocular lubri- target of reduction is increased progres- increase of tear viscosity during sleep with
cant to mobilise the lens before removal, sively (usually in 1.00 D steps) until either the lenses, resulting in a fluid adhesion
thereby ensuring safety. Most patients the desired refractive change is achieved force between the lens and the cornea.
were advised to use single dosage (usually within one month) or the cornea Therefore, the level of binding is patient-
formulations, to avoid possible problems does not respond to further changes. dependent29,30 and may not be resolved
of hypersensitivity to the preservatives Therefore, the greater the amount of by improving the lens fit.28 Improper
present in multi-dosage formulations, and myopia, the more lenses are required to removal of a bound lens can cause serious
to minimise contamination, however, only achieve optimum myopic reduction. Our damage to the cornea, especially if a
about 50 per cent of the patients used clinicians believe that a stepwise protocol suction holder is used. Proper patient
single dosage ocular lubricants. for higher myopic reduction is prudent, as education on how to free a bound lens
The majority of patients/parents were it is less aggressive and allows monitoring before removal is of vital importance not
taught to use a suction holder to aid lens of the cornea with a lower target lens only at the visit before lens delivery but
removal. This procedure is much easier before attempting a higher target. should be reinforced at each after-care
to learn than using fingers, especially for visit.
patients/parents who have no previous Telephone interview About 90 per cent of the interviewed
experience in rigid lens wear. A recent Generally, myopic control is the main patients ranked the treatment as good
study26 has shown a high contamination reason for parents enrolling their children or very good. Previous surveys using the
rate of suction holders in ortho-k lens for ortho-k treatment at our clinic. Most National Eye Institute Refractive Error
wearers. Dependency on suction holders of them learned of the treatment from Quality of Life (NEI-RQL 42) instrument
for removal of ortho-k lenses is not to be other parents, friends or relatives whose to evaluate the levels of patient satisfac-
encouraged as patients/parents may not children had received the treatment. tion with overnight ortho-k showed that
know how to remove the lenses properly Some were recommended from their there were either no differences31 or
if they lose the suction holder. There is a optometrists. better25 quality-of-life indices in overnight
danger of serious corneal damage when a Most of the interviewed patients ortho-k compared to 30-day continuous
suction holder is used to remove a lens reported good post-ortho-k unaided vision wear silicone hydrogel lenses or daily
that is not on the cornea. Also, lens and no visual problems during waking disposable hydrogel lenses, respectively.
binding is common in overnight ortho-k hours. About one half of the patients This indicates that overnight ortho-k is
and forcefully removing a bound lens can reported a deterioration of post-ortho-k well accepted as a means for myopic
cause severe injuries to the cornea and vision towards the end of day, mostly after correction.
the situation may be exacerbated if a about 12 hours (median) (range: four to
suction holder is used to aid removal. To 16 hours) of no lens wear. The regression
reduce the risk of microbial infection in of the effect of ortho-k has been studied



tology: preliminary results of the Lenses regular and irregular corneal astigmatism
SUMMARY and Overnight Orthokeratology (LOOK) in patients having overnight orthokeratol-
study. Optom Vis Sci 2002; 79: 598–605. ogy. J Cataract Refract Surg 2004; 30: 1425–
This study provides comprehensive infor- 4. Soni PS, Nguyen TT, Bonanno JA. Over- 1429.
mation and a quick overview on the char- night orthokeratology: visual and corneal 20. Mountford J. An analysis of the changes in
acteristics of the children undergoing changes. Eye Contact Lens 2003; 29: 137–145. corneal shape and refractive error induced
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R. Reduction of myopia from corneal 24: 128–144.
during the first three years of this century.
refractive therapy. Optom Vis Sci 2005; 82: 21. Young AL, Leung AT, Cheng LL, Law RW,
In general, most children were undergo- 512–518. Wong AK, Lam DS. Orthokeratology lens-
ing ortho-k for myopic control. Overnight 6. Tahhan N, Du Toit R, Papas E, Chung H, related corneal ulcers in children: a case
ortho-k using modern reverse geometry La Hood D, Holden BA. Comparison of series. Ophthalmology 2004; 111: 590–595.
lens designs is an effective non-surgical reverse-geometry lens designs for overnight 22. Tseng CH, Fong CF, Chen WL, Hou YC,
way for the reduction of low to moderate orthokeratology. Optom Vis Sci 2003; 80: Wang IJ, Hu FR. Overnight
796–804. orthokeratology-associated microbial
myopia and improvement in unaided 7. Nichols JJ, Marsich MM, Nguyen M, Barr keratitis. Cornea 2005; 24: 778–782.
vision. Spherical ortho-k lens designs are JT, Bullimore MA. Overnight orthokeratol- 23. Hsiao CH, Lin HC, Chen YF, Ma DH, Yeh
not effective for the reduction of astigma- ogy. Optom Vis Sci 2000; 77: 252–259. LK, Tan HY, Huang SC, Lin KK. Infectious
tism. Most ortho-k effects occur within the 8. Sridharan R, Swarbrick H. Corneal keratitis related to overnight orthokeratol-
first week of lens wear with the greatest response to short-term orthokeratology ogy. Cornea 2005; 24: 783–788.
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staining, we had no record of significant dren’s Overnight Orthokeratology Investi- corneal reshaping versus soft disposable
gation (COOKI) pilot study. Optom Vis Sci contact lenses: vision-related quality-of-life
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to achieve an optimum effect. Referral of myopia in Hong Kong. Ann Acad Med 26. Boost MV, Cho P. Microbial flora of tears
from friends was the major source of intro- Singapore 2004; 33: 34–38. of orthokeratology patients, and microbial
duction to ortho-k. Most of the surveyed 12. Lam CS, Goh WS. The incidence of refrac- contamination of contact lenses and
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of a suction holder to remove their lenses. nal Orthokeratology Research In Children permeable lens adherence: a patient-
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Ben Chan
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Okamoto F, Sakata N, Hiratsuka K, Kakita
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