01 orthokeratology children chan


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01 orthokeratology children chan

  1. 1. 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.xBen Chan BSc (Hons) Optom Purposes: The aim of this study was to analyse clinical data of children undergoingPauline Cho PhD, FAAO orthokeratology (ortho-k) and to investigate patients’/parents’ perspective on ortho-kSin Wan Cheung MPhil, FAAO via telephone interviews.School of Optometry, The Hong Kong Methods: Clinical records of children undergoing ortho-k from a university optometryPolytechnic University, Hong Kong SAR, clinic were reviewed and the effects of ortho-k on refraction, vision and cornea wereChina 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. LensSubmitted: 27 February 2007 binding and ocular discharge were the most frequently reported problems during theRevised: 4 November 2007 treatment.Accepted for publication: 7 November Conclusion: Under close monitoring, overnight ortho-k is effective and safe for reducing2007 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 visionThe 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 inbeen 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 ContactLens Conference, Hong Kong, China, 14-15 Kong are children.1 Therefore, it is neces- 70 per cent among 17-year-olds.11,12 MostApril 2005 sary to investigate the efficacy of ortho-k ortho-k wearers in this region are children© 2008 The Authors Clinical and Experimental Optometry 2008Journal compilation © 2008 Optometrists Association Australia 1
  2. 2. 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) wasaiming at myopic control.13 Although a before the treatment, after the first night used to test for changes over the six-monthrecent non-randomised clinical study has of lens wear and at approximately one treatment period; paired t tests withshown that ortho-k is effective in slowing week, two weeks, one month, three Bonferroni correction were used to testthe 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 forortho-k will also be helpful to practitioners performed, with the ‘plus one blur test’ to unaided vision (five comparisons) p-valuesin better advising their patients/parents ensure relaxed accommodation. Corneal less than 0.01 (0.05/5) were considered asbefore 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 refractiveKong Polytechnic University has been ings, Q (asphericity, Q = -e2) at 9.8 mm cylinder and six-month residual refractiveproviding ortho-k service since 1997. Our chord (flat meridian) and apical radius of sphere were significantly different fromclinic 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 variablespractitioners joined our clinic. All practi- (version 3.90, Medmont Pty. Ltd., Cam- (for example, corneal staining), Friedmantioners 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 brandsthe care systems used for their patients. of lenses used, the recommended lensThe primary aim of this study was to care system and the number of lenses RESULTSconduct a retrospective review of the files required to achieve the optimum ortho-k Table 1 presents the demographical dataof 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 ageview, we also investigated the attitudes of a structured list of questions was con- of the wearers was nine years (range six topatients and parents and satisfaction ducted to obtain information on why the 15 years) and most of them were femaletowards 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 commonlythe treatment. encountered problem(s) with the proce- dure and their overall satisfaction with the Refraction and unaided vision The mean (ϮSD) pre-treatment refractiveMETHODS treatment. The general questions in the sphere was -3.56 Ϯ 1.49 D and the median questionnaire were to be answered byThe files of all children (younger than 16 refractive cylinder was -0.50 D (range zero parents, while questions involving visualyears of age) undergoing ortho-k and to -4.25 D). Only 27 patients had subjec- performance and satisfaction with thefitted 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 cylinderhad a pair of lenses used for at least six Treatment of data during the six-month treatment periodmonths and were still on ortho-k during As this was a retrospective study where are shown in Figure 1. The refractivethe surveyed period were included in this data were collected from clinic files, most sphere after ortho-k treatment wasstudy. One hundred and eight patients of the results were presented in num- significantly reduced when compared tomet these inclusion criteria. Demographi- bers and percentages. Some data may be the baseline data (repeated measurescal and clinical data were retrieved from missing due to omissions in the patient’s ANOVA, F (6, 21) = 60.32, p < 0.001) andtheir clinical files during the six-month record at some visits. Data were analysed the amount of reduction increased withtreatment period. These included data to determine the effect of overnight the time of treatment. The largest refrac-Clinical and Experimental Optometry 2008 © 2008 The Authors2 Journal compilation © 2008 Optometrists Association Australia
  3. 3. Orthokeratology in children Chan, Cho and Cheung 1.00 1.00 0.90 0.00 0.80 Unaided vision (decimal notation) -1.00 0.70Residual 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 monthsvisits 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 higherand 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 requiretests, 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-treatmenttests, p > 0.008). The mean (ϮSD) myopia and 0.73 Ϯ 0.28 decimal (0.12 logMAR or myopia (-3.50 D) also had significantreduced from -3.88 Ϯ 1.27 D (baseline) Snellen 6/7.5), respectively (Figure 2). residual refractive errors and required theto -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 responsessignificant 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 lensperiod (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 intion 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 simulatedand 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 lensrecorded at all visits (n = 29), the mean Spearman r = 0.53, p < 0.001; refractive wear, with stabilisation within two weeks ofunaided 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 perto improve (repeated measures ANOVA, with mean residual refractive sphere of cent of patients (44 out of 108) and 74 perF (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 theweeks of lens wear (paired t test, p < 0.01). tacles to obtain acceptable clear distance central three millimetres of the cornea.© 2008 The Authors Clinical and Experimental Optometry 2008Journal compilation © 2008 Optometrists Association Australia 3
  4. 4. Orthokeratology in children Chan, Cho and Cheung 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 valueTable 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 valueTable 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 one41 per cent after the first overnight lens DreimLens (Taiwan Macro Vision Group, per cent used Boston Simplus (Polymerwear 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 usegraded as mild (Grade 1 or less); 13 per eLens (E&E Optics Asia Ltd, Hong Kong) non-preserved saline for rinsing the lensescent 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 (894. Patients who had Grade 2 or higher level material used for all patients was Boston out of 108) were advised to use ocularof staining in the central cornea were XO (Polymer Technology Corporation, lubricants before lens removal in theadvised to cease lens wear until the condi- Rochester, NY, USA). morning, and about 58 per cent weretion 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 recommendedrecorded over the six-month treatment and disinfecting solution. Boston Advance single-dose ocular lubricant was Tearperiod. 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 perpre-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 patientsassociation was not very strong. prescribed multipurpose solution: 22.8 removed lenses with their fingers.Clinical and Experimental Optometry 2008 © 2008 The Authors4 Journal compilation © 2008 Optometrists Association Australia
  5. 5. Orthokeratology in children Chan, Cho and Cheung 80 100 No stain 90 1st overnight 70 Grade 1 80 1 week 60 2 weeks Grade 2 70 1 month 50 Grade 3 60Percentage 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 locationFigure 3. Corneal staining recorded at different visits during Figure 4. Corneal staining at different locations during sixsix 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 lastFor patients with myopia greater than Ninety-four patients agreed to a telephone two had discontinued lens wear (after4.00 D (n = 40), a ‘stepwise’ fitting proto- interview. The primary reason for under- more than six months) due to discomfortcol (see Discussion) was applied, so the going ortho-k was myopic control (87 per and unacceptable post-ortho-k vision evennumber 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 relativespatients with myopia equal to or lower who had children undergoing the treat- DISCUSSIONthan 4.00 D (n = 68), the first pair of ment. About 30 per cent learned aboutlenses 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 Demographicsper cent) achieved optimum ortho-k effect per cent from public seminars. This retrospective study collected anusing only one pair of lenses. All of these Almost 90 per cent of those interviewed extensive body of data of children whopatients had good lens centration, as reported good or very good post-ortho-k started ortho-k treatment in a universityshown in their topographical maps, and unaided distance vision. Fifty-seven per clinic during the first three years of thisthe mean myopic reduction was within cent of the patients reported that the century. In agreement with our previous0.25 D of the target. About 16 per cent of quality of unaided vision could be main- study,13 most wearers (more than 90 perthe patients required two pairs of lenses tained until the end of the day and the cent) were children, probably reflectingand 7.4 per cent required three pairs of rest reported noticeable deterioration of the prevalence and severity of myopialenses 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 Dunable to achieve satisfactory result with hours). or greater) and astigmatism (1.50 D orvision even after four pairs of lenses. The The most frequently reported non- greater), although conventional clinicalnumber of lenses required by patients visual problems were lens binding (44 per wisdom would suggest that such patientswith higher myopia (greater than 4.00 D) cent) and ocular discharge in the morning are likely to be relatively unsuccessful into achieve optimum myopic reduction (40 per cent), followed by tearing (21 per ortho-k, in terms of leaving significantwas significantly associated with the base- cent), redness (18 per cent) and dis- amounts of refractive error and poorline 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 requestedrefractive cylinder, corneal curvature, 94) ranked the treatment as good or very ortho-k for myopic control, even thoughRo and Q (Spearman -0.07 < r < 0.01, good, 8.5 per cent (8/94) ranked the they were informed of the necessity ofp > 0.05). treatment as acceptable and two per cent wearing spectacles to correct residual© 2008 The Authors Clinical and Experimental Optometry 2008Journal compilation © 2008 Optometrists Association Australia 5
  6. 6. Orthokeratology in children Chan, Cho and Cheungrefractive 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 theRefraction and unaided vision The safety of overnight ortho-k for majority of their subjects did not exhibitThe 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 theirorted.4–7,9 Our results also indicate that innovative lens designs, which allow children exhibited corneal staining in thealthough 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 notof 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. Wewear. At six months, the average unaided associated with ortho-k and most of these also noted that the incidence of cornealvision of our patients improved to the cases involved children.21–24 Corneal stain- staining tended to be higher whenmaximum 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-kthan the average 0.02 logMAR or better lens wear.25 Corneal staining in ortho-k Lens designs andreported in most studies.4–7 Among our may be due to thinning of the central care regimens usedpatients, 42 had pre-treatment refractive corneal epithelium, improper lens fitting, DreimLens was the most frequently usedsphere of more than 4.00 D and 11 corneal hypoxia, hyper-sensitivity to con- brand of lenses in our clinic in the earlypatients 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 overnightexcluded these patients, unaided vision back surface of the lens, lens binding and ortho-k therapy. The trend has changedwas 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 this6/7). 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 instructedsignificantly correlated with the amount of of ortho-k lens wear. The incidence of by their optometrists to use a separate lenspre-treatment and residual refractive staining decreased to 25 per cent at the care system, that is, daily cleaner witherrors, including spherical and cylindrical six-month visit. Although the incidence rubbing of lenses, saline for rinsing anderrors. 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 andfective in reducing refractive cylindrical corneal staining is of greater concern as more convenient to use, and are believedpower.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 thetive 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 canchanges in with-the-rule corneal astigma- level of central corneal staining that is cause irritation when they are in contacttism 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 possibleConsistent with previous studies,2,6–8,20 we as clinically insignificant (that is, lower and any chance of solution sensitivityfound 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 daily9.8 mm corneal chord after a single night Grade 2 or higher level of staining in the cleaner and rinsing the lenses with normalof 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 availabletween corneal shape changes, including condition subsided and none of them for rigid gas permeable lenses and thesimulated keratometry readings, apical required medical treatment. A few majority of these solutions are compatibleradius of curvatures and refractive studies have also reported the incidence with ortho-k lenses.Clinical and Experimental Optometry 2008 © 2008 The Authors6 Journal compilation © 2008 Optometrists Association Australia
  7. 7. Orthokeratology in children Chan, Cho and Cheung It should be noted that the brands of ortho-k lens wear and to increase safety by Mountford27 and Rah and co-workers.3lenses 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 foundover others. The preference for lenses or remove ortho-k lenses with their fingers. that the regression of apical corneal powerdisinfecting solutions to prescribe to the A suction holder is given for emergency over approximately an eight-hour periodpatients depends on the individual practi- use only. In cases where a suction holder was 0.50 to 0.75 D. Similarly, Rah andtioner and/or the availability in the stock is necessary, daily cleaning, proper co-workers3 also reported an amount ofof a particular brand in our clinic. Our storage, weekly disinfection and regular 0.25 to 0.50 D daytime regression inresults on the preferred solutions to be replacement of the suction holder should spherical equivalent manifest refractionprescribed 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 adulttioners in our clinic on the use of daily Number of lenses used subjects so it is uncertain whether thecleaner and normal saline in the care of Many of our patients (73.5 per cent) with regression rate in children would be theortho-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-koptional 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 mostbinding 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 withadvised 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 thewere instructed to apply an ocular lubri- target of reduction is increased progres- increase of tear viscosity during sleep withcant to mobilise the lens before removal, sively (usually in 1.00 D steps) until either the lenses, resulting in a fluid adhesionthereby 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 resolvedof hypersensitivity to the preservatives Therefore, the greater the amount of by improving the lens fit.28 Improperpresent in multi-dosage formulations, and myopia, the more lenses are required to removal of a bound lens can cause seriousto minimise contamination, however, only achieve optimum myopic reduction. Our damage to the cornea, especially if aabout 50 per cent of the patients used clinicians believe that a stepwise protocol suction holder is used. Proper patientsingle 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 nottaught to use a suction holder to aid lens of the cornea with a lower target lens only at the visit before lens delivery butremoval. This procedure is much easier before attempting a higher target. should be reinforced at each after-careto learn than using fingers, especially for visit.patients/parents who have no previous Telephone interview About 90 per cent of the interviewedexperience in rigid lens wear. A recent Generally, myopic control is the main patients ranked the treatment as goodstudy26 has shown a high contamination reason for parents enrolling their children or very good. Previous surveys using therate of suction holders in ortho-k lens for ortho-k treatment at our clinic. Most National Eye Institute Refractive Errorwearers. Dependency on suction holders of them learned of the treatment from Quality of Life (NEI-RQL 42) instrumentfor 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 thatknow how to remove the lenses properly Some were recommended from their there were either no differences31 orif they lose the suction holder. There is a optometrists. better25 quality-of-life indices in overnightdanger of serious corneal damage when a Most of the interviewed patients ortho-k compared to 30-day continuoussuction holder is used to remove a lens reported good post-ortho-k unaided vision wear silicone hydrogel lenses or dailythat 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 isand forcefully removing a bound lens can reported a deterioration of post-ortho-k well accepted as a means for myopiccause 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 tosuction holder is used to aid removal. To 16 hours) of no lens wear. The regressionreduce the risk of microbial infection in of the effect of ortho-k has been studied© 2008 The Authors Clinical and Experimental Optometry 2008Journal compilation © 2008 Optometrists Association Australia 7
  8. 8. Orthokeratology in children Chan, Cho and Cheung tology: preliminary results of the Lenses regular and irregular corneal astigmatismSUMMARY 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 inacteristics of the children undergoing changes. Eye Contact Lens 2003; 29: 137–145. corneal shape and refractive error inducedortho-k in a university clinic in Hong Kong 5. Sorbara L, Fonn D, Simpson T, Lu F, Kort by accelerated orthokeratology. ICLC 1997; 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 caseortho-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 microbialmyopia 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, Yehnot effective for the reduction of astigma- ogy. Optom Vis Sci 2000; 77: 252–259. LK, Tan HY, Huang SC, Lin KK. 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Quantitative evaluation ofClinical and Experimental Optometry 2008 © 2008 The Authors8 Journal compilation © 2008 Optometrists Association Australia