Orthokeratology (OK) concerns the fitting of specially designed contact lenses to reshape the corneal contour to temporarily modify refractive error. The most common clinical application of OK is the reduction of myopic error through corneal flattening.1 Although studies in the late 70s and early 80s did not find significant adverse events associated with the use of OK contact lenses, their application proved to be unpopular owing to incomplete treatment effects and transient, unpredictable reductions in refractive error.2–6 The subsequent development of innovative materials, lens designs, and instrumentation to depict changes in corneal topography has facilitated assessment of OK safety and efficacy in correcting low to moderate levels of myopia in adult individuals.7–9
Following an earlier retrospective study10 and case report,11 longitudinal studies have provided evidence for the efficacy of OK contact lens wear in slowing myopia progression in children, although prospective randomized clinical trials are required to ascertain this.12–15 Furthermore, it has been recently reported that orthokeratology represents a large proportion of all contact lens wear fits undertaken in children worldwide.16 Although OK in children has been associated with adverse ocular effects, including microbial keratitis,17 severe complications have generally been restricted to regions where regulation is limited such as east Asia and, in particular, countries such as China and Taiwan. The complications have been attributed to inadequately trained practitioners, lack of appropriate clinical equipment, the use of non–gas-permeable materials, and tap water as multipurpose contact lens care solution.18 Where regulation and monitoring are optimum, several studies have shown OK to be effective and safe in reducing low to moderate levels of myopia in children.19–21 However, all the latter studies have not been specifically designed to assess the incidence of adverse events and complications; have been carried out over short period; and have not employed adequate control groups. Although case reports and case series of observations of overnight OK have been presented for undefined populations, there are no formal prospective reports that have assessed the incidence of adverse events associated with the long-term use of OK for the treatment of myopia progression control in children.22 Furthermore, subject compliance with the treatment schedule is important when assessing the effectiveness of a treatment option: high discontinuation rates might suggest that the treatment is unlikely to be successful, irrespective of its clinical outcome. The relationship between the incidence of adverse events and discontinuation rates has been advocated as an alternative methodology for assessing the clinical success or failure of a visual correction method.23,24 The purpose of this study is therefore to compare the incidence of adverse events and discontinuations of orthokeratology contact lenses (OK) and distance single-vision spectacles (SV) in children during a 2-year period.
This study was part of the Myopia Control with Orthokeratology contact lenses study (MCOS) designed to assess the safety, efficacy, and subjective acceptance of OK vs. SV in white European myopic children during a 2-year period.15,25
Methods have been described in detail elsewhere.25 In brief, normal, healthy, white European subjects 6 to 12 years of age with moderate levels of myopia (− 0.75 to − 4.00D) and astigmatism (≤1.00D) and free of systemic or ocular disease affecting ocular health were recruited for the study and prospectively allocated OK or SV correction. Parent(s) or guardian(s) were allowed to choose one of two treatment modalities offered (i.e., SV or OK), after they were given a balanced account of their respective advantages and disadvantages.
Spectacles or contact lenses, contact lens care solutions (for the OK group only), and full ocular examinations were provided free of charge to all subjects throughout the study. Fully informed parental consent and child assent was obtained before the start of all experimental work and data collection. Patient participation in the study could be discontinued at the examiner's discretion should significant symptoms or slit-lamp findings occur. Subjects were instructed that they could withdraw from the study at any time. The study was conducted in accordance with the Tenets of the Declaration of Helsinki and approved by the Institutional Ethical Committee Review Board of Novovision Ophthalmology Clinic.
At the recruitment session, all subjects underwent a full anterior eye biomicroscopy, indirect fundus microscopy, binocular vision, and refractive evaluation to elucidate whether they were eligible to participate in the study; baseline study measurements were then recorded for eligible subjects.
Subjects in the SV group were prescribed distance single-vision spectacles having the highest positive spherical power consistent with optimum visual acuity and asked to wear the spectacles at all times. Subjects from the OK group were fitted with Menicon Z Night contact lenses using the Menicon Professional Easy Fit Software (Menicon Co., Ltd, Nagoya, Japan). After initial contact lens fitting, subjects were instructed on the first day on procedures for insertion, removal, and cleaning/disinfection, and instructions were reinforced at subsequent visits. Subjects were provided with MeniCare Plus multipurpose solution for the daily cleaning, rinsing, and disinfecting of their contact lenses, and Menicon Progent intensive cleaner for use once a week (Menicon Co., Ltd, Nagoya, Japan). Additionally, subjects were provided rewetting drops for instillation before lens removal during the first 2 weeks of lens wear (TheraTears, Advanced Vision Research, IL). At subsequent visits, subjects presenting with corneal staining ≥1 CCLRU unit were recommended to instill rewetting drops before lens removal.26
Subjects in the OK trial were informed that contact lenses should be inserted everyday just before going to sleep and removed immediately on waking the following morning. Subjects were requested to attend the clinic no later than 2 hours after lens removal on the morning following the first night of lens wear; the stipulation applied to all subsequent visits. A visit was scheduled 3 weeks later to ascertain whether the contact lens fitting was clinically acceptable; otherwise, new contact lens specifications were calculated and ordered. Subjective refraction was undertaken to check whether changes in contact lens' back surface contact lens design were required to correct a change in refraction. A successful OK fit was considered to be one which after 3 weeks of lens wear showed CCLRU anterior eye signs ≤1 unit,26 a “bulls eye” corneal topography pattern, and monocular and binocular spectacle visual acuities within ± 1 line of the best-corrected decimal acuity.
All OK subjects were informed that contact lenses should be removed if any problems were experienced. Subjects and their parent/guardians were instructed on steps to take in the event of an adverse reaction and on the importance of adherence to the study protocol; compliance was monitored closely by one of the authors (C.V.-C.). Subjects from both study groups were instructed to report to the clinic immediately should a reaction appear to be abnormal (e.g., red eye, pain, unusual discomfort, or eye secretions).
After initial enrollment, subjects were followed at 1, 6, 12, 18, and 24-month intervals. Follow-up visits were scheduled to fall within 2 hours of awakening. A decrease in one line of visual acuity accompanied by a change in subjective refraction27 at any of the follow-up visits was considered clinically significant and was remedied by supplying contact lenses or spectacles made to the new prescription.
The classification of adverse events and discontinuations was adapted from Morgan et al. (2005).23 Adverse events were classified into “serious,” “significant,” or “non-significant” according to Table 1.23,24 Although Table 1 shows most of the ocular adverse events that could occur as a result of contact and spectacle lens wear, all adverse events, additional to those shown in Table 1, were recorded. For obscure adverse reactions, the opinion of the ophthalmologist on duty at the clinic was sought and the condition treated in collaboration with the MCOS clinician. In all cases, an appropriate classification of an adverse reaction was determined. Recurrences of the same adverse event(s) in the same or fellow eye at any of the subsequent study visits were classified as separate events; bilateral events were counted as two separate events. For the purposes of comparison, the incidence of adverse events was calculated as a percentage of eyes per annum.23,24
The extent and depth of corneal staining were measured in both eyes of subjects wearing OK lenses using the CCLRU grading scales at baseline and after 1 night, 3 weeks, and 1, 6, 12, 18, and 24 months of wear.26 Additionally, the location (i.e., superior, inferior, nasal, temporal, and central) of the staining was recorded. A cobalt blue filter and a fluorescein enhancement filter (Kodak Wratten no. 12; Eastman Kodak, Rochester, NY) placed respectively in the illumination system and over the objective lens were used to facilitate assessment of corneal staining.28 Corneal staining was graded approximately 2 hours after lens removal, and staining with an extent and/or depth grade ≥2 was classified as an adverse event.
Discontinuation was defined as cessation of lens wear for the duration of the remainder of the study.23 Discontinuation may occur for a number of reasons: adverse events, ocular discomfort, visual problems, lack of motivation, failure to follow instructions, unacceptable visual acuity, and other logistic or personal reasons that may or may not have been directly related to lens wear. Temporary suspension of lens wear of up to 2 weeks was allowed (at the investigator's discretion) should significant symptoms or slit-lamp findings occur. Although temporarily discontinued, in these cases subjects were examined at frequent intervals until resolution of the condition, and attempts were made to limit the duration of discontinuation to as short a period as possible. Some subjects discontinued the study as result of “lost to follow-up”—defined as a situation whereby a subject did not present for the next follow-up visit (despite active efforts to encourage attendance). The incidence of discontinuations was calculated as a percentage of subjects per annum.23,24
The difference in incidence of adverse events and discontinuations between OK and SV was tested with Fisher exact test. The Friedman test was used to test differences in the extent and depth of corneal staining over time. Differences between single pairs of visits were further explored with the Wilcoxon signed rank test. The correlation between the extent of corneal staining and its depth was tested using the Spearman rho test. Statistical analyses were conducted using SPSS 15.0 (SPSS, Inc., Chicago, IL). The level of statistical significance was taken as 5%.
Between March 2007 and March 2008, 69 subjects enrolled in the study with 8 failing to meet the inclusion criterion for participation for the following reasons: corneal staining (1), high spherical refractive error (3), hypermetropic refractive error (1), and high cylindrical refractive error (3). Thirty-one children were subsequently and prospectively allocated OK and 30 SV lenses. The baseline demographics and refractive and biometric data of the two groups were found to be similar.25
A higher incidence of adverse events was found with OK compared with SV (p < 0.001). Nine OK subjects experienced 16 adverse events, whereas no adverse events were found in the SV group (Table 2). Two male subjects experienced 2 adverse events each at different time points (i.e., contact lens–induced peripheral ulcer, dimple veiling, corneal abrasion, and hordeolum) and 1 female subject experienced 3 adverse events (corneal abrasion, papillary conjunctivitis, and corneal staining). Two female and 1 male subjects experienced bilateral adverse events at the same time points (i.e., papillary conjunctivitis, blepharitis, and bacterial conjunctivitis). None of the adverse events resulted in a reduction of best-corrected visual acuity. Most adverse events were found between 6 and 12 months of lens wear, but 5 significant adverse events could not be solely attributable to OK lens wear (i.e., blepharitis , hordeolum , and bacterial conjunctivitis ) (Table 2, Fig. 1).
Considering both eyes of subjects across all time points, 101 eyes (22%) showed some degree of corneal staining. Some eyes (numbers in parenthesis) showed corneal staining at baseline (0), 1-night (5), 2-week (13), and 1- (5), 6- (8), 12- (3), 18- (3), and 24-month (8) visits. Significant differences in the extent of corneal staining were found over time (p = 0.008), and this was attributed to the significant increase in corneal staining from baseline to 1-night, 2-week, and 1- and 24-month visits, as well as the increase from the 1-night to 2-week visit (all p < 0.05).
The extent of corneal staining decreased significantly from 2 weeks to 12 and 18 months (all p < 0.05). No significant changes were found in the extent of corneal staining between any of the other pairs of visits (p > 0.05). Depth of corneal staining changed significantly over time (p = 0.009), owing to the significant increase in corneal staining observed between the baseline visit and all other visits and the increase at the 2-week visit in comparison with the 1-night and the 1-, 12-, and 18-month visits (all p < 0.05). No significant changes were found in depth of corneal staining between any of the other pairs of visits (p > 0.05).
The extent and depth of corneal staining across all time points as well as at 1-night, 2-week, and 6-, 12-, and 24-month visits were strongly correlated (all p < 0.001) (Fig. 2). No significant correlations were found between extent and depth of corneal staining at baseline and 1- and 18-month visits (p > 0.05).
Two and 6 subjects from the OK and SV groups, respectively, discontinued the study; this difference was not statistically significant (p = 0.15). Two discontinuations occurred between 3 and 6 months and the remaining between 12 and 24 months (see Table 2).
To the authors' knowledge, MCOS is the first prospective clinical study specifically designed to compare the relative clinical success of OK vs. SV in children in terms of incidence of adverse events and discontinuations during a 2-year period. Subjects and parents engaged enthusiastically in the study and responded well to the study protocols.
The greater incidence of adverse events found with OK vs. SV was expected as this has typically shown to be the case for all contact lens types (Table 3). The adverse events found with OK in this study are not considered to be serious, are similar to those reported with other contact lens types, and can be managed straightforwardly in clinical practice (Tables 2 and 3).23,24,29 Furthermore, although some of the adverse events found were anticipated they are not exclusively attributable to contact lens wear (Fig. 1).
That the adverse events found in this study were limited in severity is likely to be a consequence of how OK affects the morphology and biometry of the cornea. In thinning and reshaping the corneal epithelium, OK reduces epithelial cell size without affecting epithelial permeability and is therefore considered not to exert any changes in the corneal stroma or endothelium.30–32
In the present study, most adverse events were found between 6 and 12 months of lens wear, which is consistent with previous studies that have shown adverse events to peak at the beginning of contact lens wear and reduce thereafter.23,24,29
The incidence of corneal staining found in this study was lower19,20 and similar33 to previous reported studies, which might be attributed to differences in lens design, lens material, and lens surface properties. Some of the corneal staining found in this study might be partly attributable to subjects failing to instill rewetting drops before lens removal. Nevertheless, it should be noted that the levels of corneal staining found in this study are below what would be considered clinically significant.26
Corneal staining occurred most commonly in the central cornea, reaching a maximum extent within the first few weeks of lens wear and reducing thereafter, which again is in agreement with previous studies.19,20,33,34 This observation was to be expected because myopia reduction after OK treatment is achieved by flattening of the central cornea and redistribution of epithelial tissue from central to peripheral regions of the cornea.30 Therefore, practitioners undertaking OK treatments should be especially vigilant during the first few weeks of lens wear with regard to the risk of potential complications associated with corneal staining.
The lower incidence of discontinuations found with OK in comparison with SV agrees with that reported in a recent study (Table 4).14 Furthermore, the incidence of discontinuations with OK lens wear appears generally to be lower in comparison with other modalities of contact lens wear, including extended wear of gas-permeable,23 extended wear of silicone hydrogel contact lenses,23 and daily wear of hydrogel contact lenses29 (Table 4).
The rate of discontinuations found with OK in the present study was lower12,13 and similar14 to those previously reported (Table 4), whereas the incidence of discontinuations found with SV was intermediate to rates previously reported (Table 4).14,29
Comparisons of the incidence of adverse events and discontinuations between this study and historical controls shown in Tables 3 and 4 should be interpreted with caution. Nevertheless, all the studies used to make these comparisons used a similar study design to MCOS in that they were prospective trials undertaken for at least a 1-year period and were designed to assess the incidence rate of adverse events and/or discontinuations. It should also be taken into account that some studies recruited adults,24,29 whereas others recruited children,12–14 and it is possible that the incidence of adverse events and discontinuations might differ between adults and children.35
A limitation of this study is that it lacks an appropriate sample size to detect the absolute incidence rate of adverse events and discontinuations associated with OK and SV wear. However, the purpose of this study was to detect differences in the relative incidence of adverse events and discontinuations between OK and SV, rather than absolute incidence rates. Previous studies have used sample sizes similar to that used in the present study and were able to detect statistically significant differences in the incidence of adverse events and discontinuations between two different visual correction types.23,24
In summary, the relatively low incidence of adverse events and discontinuations found in MCOS is conducive to the correction of myopia in children with OK contact lenses. Good clinical practice in the fitting these lenses in children is, of course, imperative,36 and under these circumstances, OK appears to be a safe option for myopia correction in children.
Menicon Co., Ltd (Madrid Office)
Iglesia 9, Apartamento 106
Majadahonda, Madrid, Spain
The authors acknowledge the assistance of the clinical and technical staff at Novovision in the acquisition of the data for this study and EURO-OPTICA for help in recruiting subjects for the study. Jacinto Santodomingo-Rubido is a full-time employee of Menicon. This work was partly funded by Menicon Co., Ltd.
1. Swarbrick HA. Orthokeratology review and update. Clin Exp Optom 2006;89:124–43.
2. Kerns RL. Research in orthokeratology. Part VI: statistical and clinical analyses. J Am Optom Assoc 1977;48:1134–47.
3. Kerns RL. Research in orthokeratology. Part V: Results and observations–recovery aspects. J Am Optom Assoc 1977;48:345–59.
4. Binder PS, May CH, Grant SC. An evaluation of orthokeratology. Ophthalmology 1980;87:729–44.
5. Polse KA, Brand RJ, Keener RJ, Schwalbe JS, Vastine DW. The Berkeley Orthokeratology Study, part III: safety. Am J Optom Physiol Opt 1983;60:321–8.
6. Polse KA, Brand RJ, Schwalbe JS, Vastine DW, Keener RJ. The Berkeley Orthokeratology Study, part II: efficacy and duration. Am J Optom Physiol Opt 1983;60:187–98.
7. Mountford J. An analysis of the changes in corneal shape and refractive error induced by accelerated orthokeratology. Int Contact Lens Clin 1997;24:128–43.
8. Nichols JJ, Marsich MM, Nguyen M, Barr JT, Bullimore MA. Overnight orthokeratology. Optom Vis Sci 2000;77:252–9.
9. Rah MJ, Jackson JM, Jones LA, Marsden HJ, Bailey MD, Barr JT. Overnight orthokeratology: preliminary results of the Lenses and Overnight Orthokeratology (LOOK) study. Optom Vis Sci 2002;79:598–605.
10. Reim TR, Lund M, Wu R. Orthokeratology and adolescent myopia control. Contact Lens Spectrum 2003;18(3):40–2.
11. Cheung SW, Cho P, Fan D. Asymmetrical increase in axial length in the two eyes of a monocular orthokeratology patient. Optom Vis Sci 2004;81:653–6.
12. Cho P, Cheung SW, Edwards M. The longitudinal orthokeratology research in children (LORIC) in Hong Kong: a pilot study on refractive changes and myopic control. Curr Eye Res 2005;30:71–80.
13. Walline JJ, Jones LA, Sinnott LT. Corneal reshaping and myopia progression. Br J Ophthalmol 2009;93:1181–5.
14. Kakita T, Hiraoka T, Oshika T. Influence of overnight orthokeratology on axial elongation in childhood myopia. Invest Ophthalmol Vis Sci 2011;52:2170–4.
15. Santodomingo-Rubido J, Villa-Collar C, Gilmartin B, Gutiérrez-Ortéga R. Myopia control with orthokeratology contact lenses in Spain (MCOS): refractive and biometric changes. Invest Ophthalmol Vis Sci 2012:(e-pub June 22, 2012).
16. Efron N, Morgan PB, Woods CA, International Contact Lens Prescribing Consortium. Survey of contact lens prescribing to infants, children, and teenagers. Optom Vis Sci 2011;88:461–8.
17. Watt KG, Swarbrick HA. Trends in microbial keratitis associated with orthokeratology. Eye Contact Lens 2007;33:373–7.
18. DeWoolfson BH. Orthokeratology lens—related ulcers in children. Ophthalmology 2005;112:167.
19. Walline JJ, Rah MJ, Jones LA. The Children's Overnight Orthokeratology Investigation (COOKI) pilot study. Optom Vis Sci 2004;81:407–13.
20. Mika R, Morgan B, Cron M, Lotoczky J, Pole J. Safety and efficacy of overnight orthokeratology in myopic children. Optometry 2007;78:225–31.
21. Chan B, Cho P, Cheung SW. Orthokeratology practice in children in a university clinic in Hong Kong. Clin Exp Optom 2008;91:453–60.
22. Van Meter WS, Musch DC, Jacobs DS, Kaufman SC, Reinhart WJ, Udell IJ. Safety of overnight orthokeratology for myopia: a report by the American Academy of Ophthalmology. Ophthalmology 2008;115:2301–13.
23. Morgan PB, Efron N, Maldonado-Codina C, Efron S. Adverse events and discontinuations with rigid and soft hyper Dk contact lenses used for continuous wear. Optom Vis Sci 2005;82:528–35.
24. Santodomingo-Rubido J, Wolffsohn JS, Gilmartin B. Adverse events and discontinuations during 18 months of silicone hydrogel contact lens wear. Eye Contact Lens 2007;33:288–92.
25. Santodomingo-Rubido J, Villa-Collar C, Gilmartin B, Gutiérrez-Ortéga R. Myopia control with orthokeratology contact lenses in Spain (MCOS): study design and general baseline characteristics. J Optom 2009;2:215–22.
26. Terry RL, Schnider CM, Holden BA, Cornish R, Grant T, Sweeney D, La Hood D, Back A. CCLRU standards for success of daily and extended wear contact lenses. Optom Vis Sci 1993;70:234–43.
27. Lovie-Kitchin JE, Brown B. Repeatability and intercorrelations of standard vision tests as a function of age. Optom Vis Sci 2000;77:412–20.
28. Cox I, Fonn D. Interference filters to eliminate the surface reflex and improve contrasts during fluorescein photography. Int Contact Lens Clin 1991;18:178–81.
29. Sankaridurg PR, Sweeney DF, Holden BA, Naduvilath T, Velala I, Gora R, Krishnamachary M, Rao GN. Comparison of adverse events with daily disposable hydrogels and spectacle wear: results from a 12-month prospective clinical trial. Ophthalmology 2003;110:2327–34.
30. Swarbrick HA, Wong G, O'Leary DJ. Corneal response to orthokeratology. Optom Vis Sci 1998;75:791–9.
31. Nieto-Bona A, González-Mesa A, Nieto-Bona MP, Villa-Collar C, Lorente-Velazquez A. Short-term effects of overnight orthokeratology on corneal cell morphology and corneal thickness. Cornea 2011;30:646–54.
32. Savitsky DZ, Fan VC, Yildiz EH, Du TT, Asbell PA. Fluorophotometry to evaluate the corneal epithelium in eyes undergoing contact lens corneal reshaping to correct myopia. J Refract Surg 2009;25:366–70.
33. Lipson MJ, Sugar A, Musch DC. Overnight corneal reshaping versus soft daily wear: a visual quality of life study (interim results). Eye Contact Lens 2004;30:214–7.
34. Lipson MJ. Long-term clinical outcomes for overnight corneal reshaping in children and adults. Eye Contact Lens 2008;34:94–9.
35. Walline JJ, Holden BA, Bullimore MA, Rah MJ, Asbell PA, Barr JT, Caroline PJ, Cavanagh HD, Despotidis N, Desmond F, Koffler BH, Reeder K, Swarbrick HA, Wohl LG. The current state of corneal reshaping. Eye Contact Lens 2005;31:209–14.
36. Cho P, Cheung SW, Mountford J, White P. Good clinical practice in orthokeratology. Cont Lens Anterior Eye 2008;31:17–28.
myopia control; orthokeratology; adverse events; discontinuations; drop out; spectacles; rates