Ortho-k Group Research Articles

Repeatability of choroidal thickness measurements with Spectralis OCT images

ObjectiveTo investigate the repeatability of choroidal thickness measurements determined from enhanced depth imaging optical coherence tomography (EDI-OCT) images of eyes after wearing single-vision spectacles (SV) and orthokeratology (ortho-k) lenses.Methods and...

Effect of Orthokeratology on Axial Length Elongation in Anisomyopic Children.

Anisomyopia is a natural experimental paradigm that compares dose response between fellow eyes. This study is the first to explore whether orthokeratology (ortho-k) has a dose-response effect on axial length growth and reduces the interocular difference in axial length in anisomyopic children. The purpose of this study was to compare the effect of ortho-k on axial length elongation between the fellow eyes of anisomyopic children. In this retrospective study, 49 anisomyopic children who wore ortho-k lenses were assigned to the anisomyopic ortho-k group. Based on the one-to-one match principle (same age and proximate spherical equivalent), high-isomyopic and low-isomyopic groups each enrolled 49 isomyopic children who wore ortho-k lenses with spherical equivalent similar to that of the more myopic eye and the less myopic eye in the anisomyopic ortho-k group, respectively. Forty-nine anisomyopic children who wore spectacles were enrolled in the anisomyopic spectacle group. At baseline and at 1- and 2-year visits, axial length was measured. Axial length elongation and interocular difference in axial length were compared. In the anisomyopic ortho-k group, the less myopic eyes exhibited more axial length elongation than did the more myopic eyes during 1- and 2-year treatment periods (P < .01). However, there was no significant difference in axial length elongation between the fellow eyes in the isomyopic groups and anisomyopic spectacle group. At the 2-year visit, the interocular difference in axial length of children in the anisomyopic ortho-k group significantly decreased from 0.72 ± 0.34 to 0.56 ± 0.38 mm (P < .05). In contrast, ortho-k lens-wearing isomyopic children or spectacle-wearing anisomyopic children did not show a significant change in interocular difference in axial length. Orthokeratology could reduce the amount of anisomyopia in children primarily through stronger myopia control in the more myopic eye.

Role of corneal biomechanical properties in predicting of speed of myopic progression in children wearing orthokeratology lenses or single-vision spectacles

ObjectiveTo determine the characteristics of children who were likely to progress rapidly and gain the greatest benefit from orthokeratology (ortho-k) treatment.Methods and analysisThe files of 113 children who participated in...

Increased Corneal Toricity after Long-Term Orthokeratology Lens Wear.

Purpose To investigate the change in corneal toricity and associated refractive astigmatism after discontinuation of long-term orthokeratology (ortho-k) lens wear. Methods This study investigated 136 subjects aged between 6 and 14 (9.1 ± 1.5) years old at the commencement of ortho-k treatment, who had been undergoing overnight ortho-k treatment for 24 to 72 (37.4 ± 11.9) months. Corneal refractive power and manifest refraction were measured and compared before ortho-k and 1 month after discontinuation of ortho-k lens wear. Changes in corneal curvature were analyzed. Corneal curvature data from a historical longitudinal study were used as control. Results Compared to pre-ortho-k values, the corneal curvature became significantly flatter in the flatter meridian (−0.22 ± 0.27 D, P < 0.001) and steeper in the steeper meridian (0.06 ± 0.34 D, P=0.032) after cessation of ortho-k lens wear, resulting in a significant increase in corneal toricity (0.28 ± 0.43 D, P < 0.001), which is associated with an increase in refractive astigmatism (0.57 ± 0.57 D, r=0.465, P < 0.001). The amount of residual corneal flattening in the flatter meridian is significantly affected by the length of ortho-k treatment (t=−2.965, P=0.004) and the baseline age of subject (t=−2.841, P=0.005), but not by the baseline spherical or cylindrical refractive error (both P > 0.05). In the historical control group, there is no significant change in the corneal curvature over two years in children wearing spectacle lenses (both meridians, P > 0.05). Change of corneal toricity was more significant in the ortho-k group than in the spectacle control group (P=0.001). Conclusions Long-term ortho-k lens wear increases corneal toricity after discontinuation of the treatment, which is associated with an increase in refractive astigmatism. A more pronounced change in corneal toricity was found in subjects who were younger to start ortho-k and have been in a longer period of treatment. This trial is registered with http://www.chictr.org.cn (ChiCTR-TNRC-11001210).

Change in subfoveal choroidal thickness secondary to orthokeratology and its cessation: a predictor for the change in axial length.

To investigate changes in subfoveal choroidal thickness (SFChT) during orthokeratology (Ortho-K) lens wear and after its cessation and the association of short-term change in SFChT with the long-term eye elongation in Ortho-K subjects. A prospective clinical trial. Fifty myopic children aged between 9 and 14years were enrolled. Twenty-nine subjects continuously wore Ortho-K lens for 12months and discontinued for 1month. Twenty-one subjects wearing single vision distance spectacles for 12months were included as the control group. SFChT was assessed using optical coherence tomography. Ocular parameters, including axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT) and apical corneal power (ACP), were also measured. After 12months of follow-up, AL elongation was larger and SFChT change was smaller in the control group compared to the Ortho-K group (both p<0.001). In the Ortho-K group, SFChT increased by 16μm from baseline at the 1-month visit (p<0.001), and the magnitude of choroidal thickening remained unchanged at the 6- and 12-month visit (p=0.289). One month after discontinuation of Ortho-K lens, SFChT and ocular parameters of the anterior segment, including ACP, CCT and ACD recovered to baseline level (All p>0.05), and AL increased by 0.23±0.18mm compared to baseline (p=0.018). SFChT change at 1-month was negatively associated with AL change at 13-month (standard β, -0.581, p=0.001) after adjusting for other influencing factors, including baseline age and the ocular parameters. Subfoveal ChT (SFChT) significantly increased after short-term Ortho-K lens treatment and the increase maintained throughout the period of treatment. One month after Ortho-K lens cessation, SFChT, ACP, CCT and ACD returned to baseline. Short-term response in SFChT is associated with long-term change in AL in children undergoing Ortho-K lens and may be a predictor for the effectiveness of the treatment.

Accommodation function comparison following use of contact lens for orthokeratology and spectacle use in myopic children: a prospective controlled trial.

To study effects of orthokeratology (Ortho-k) on accommodation function in myopic children. A prospective, non-randomized, case-control study was performed from September to October 2016. Eighty-three children with myopia were divided into two groups. One group was treated with the rigid contact lens for overnight Ortho-k, and the other was treated with single-vision spectacle lens (SVL). Accommodation function were assessed by accommodative amplitude (AA), accommodative sensitivity (AS), accommodative lag (Lag), negative relative accommodation (NRA), and positive relative accommodation (PRA) before and 1, 3, 6 and 12mo after treated. Totally 72 myopic children were finished the follow-up: 37 in Ortho-k group and 35 in SVL group. Wearing time had a significant effect on AA, AS, Lag, and NRA of myopic children in two groups (all P<0.05). Meanwhile, there was an interaction effect between wearing time and wearing types (FAA=5.3, FAS=45.5, FLag=7.0, FNRA=3.7, all P<0.05). However, the between-group difference of AA (F=0.1), AS (F=3.2), Lag (F=1.1), NRA (F=0.3), and PRA (F=0.1) showed no significance. AA, AS, NRA, Lag and PRA were improved significantly in Ortho-k group within 1 to 6mo after wearing. Wearing Ortho-k can improve the accommodation function of myopic children, which might be one of the mechanisms for myopia control.

Choroidal thickness and axial length changes in myopic children treated with orthokeratology.

To analyze the change in subfoveal choroidal thickness (SFChT) and its relationship with changes in axial length (AL) in myopic children treated with Orthokeratology (Ortho-k). Fifty myopic children participated in this study: 29 subjects were treated with Ortho-k lenses and 21 with single vision distance spectacles. The SFChT and ocular biometrics, including AL, were measured at baseline, one month, and six months after lens wear in both groups. AL significantly increased in both groups over time. In the Ortho-k group, SFChT also increased; however, there was no significant change in SFChT in the control group over time. At the six-month visit, the magnitude of eye growth was significantly reduced in the Ortho-k group compared to the control group (0.06±0.10mm vs. 0.17±0.10mm, P<0.001). SFChT was significantly thicker in the Ortho-k group compared to the control group at the one-month and six-month visits (15.78±11.37μm vs. -2.98±8.96μm, P<0.001 (one-month visit); 21.03±12.74μm vs. -2.50±14.43μm, P<0.001 (six-month visit)), although there was no significant difference between the two follow-up visits (P=0.102 for the Ortho-k group; P=0.898 for the control group). Changes in the large choroidal vascular layer (LCVL) accounted for the majority of subfoveal choroidal thickening (approximately 77% and 80% at one-month and six-month visits, respectively). Ortho-k treatment induced significant choroidal thickening and a slowing of eye growth. LCVL thickening accounted for the majority of SFChT thickening. However, its potential mechanism in myopia control requires further investigation.

Effects of orthokeratology on the progression of low to moderate myopia in Chinese children.

BackgroundTo investigate the effectiveness of orthokeratology (ortho-k) in reducing the development of myopia in Chinese children with low to moderate myopia.MethodsThis was a retrospective study. In the ortho-k group, there were141 subjects, and the average age was (9.43 ± 1.10) years. The average spherical equivalent refractive error (SER) was (−2.74 ± 1.15)D, with examinations performed 1, 7, 30, and 90 days and 12 months after the patients started wearing ortho-k lenses. In the control group, there were 130 subjects, and the average age was (9.37 ± 1.00) years. The average SER was (−2.88 ± 1.39)D, with examinations performed every 6 months. Axial elongation, which is an important parameter reflecting the progression of myopia, was measured at baseline from the same IOLMaster each time by the same masked examiner and was compared between the groups after 1 year. The subjects were divided into two sub-groups according to age to further study the development of myopia at different ages. An unpaired t-test, paired t-test, Chi-square test and Spearman test were performed to analyze the data.ResultsAfter 1 year, the average axial elongation was (0.27 ± 0.17) mm in the ortho-k lens group and (0.38 ± 0.13) mm in the control group, with a significant difference between the groups (P < 0.001). Axial elongation was not correlated with SER but had a negative correlation with initial age (ortho-k group: rs = −0.309, p < 0.01; control group: rs = −0.472, p < 0.01). The percentages of individuals with fast myopic progression (axial elongation > 0.36 mm per year) were 38.0 % among younger children (7.00 to 9.40 years) and 24.3 % among older children (9.40 to 12.00 years), whereas the respective percentages were 76.5 and 12.9 % in the control group. When SER ranged from -5.0D to −6.0D, the axial elongation in the ortho-k group was 57.1 % slower than that in the control group.ConclusionsOrtho-k lenses are effective in controlling myopic progression in Chinese children, particularly in younger children and in children with higher myopia.

Long-term effect of orthokeratology on the anterior segment length.

To compare the effects of normal growth and longer term use of orthokeratology (ortho-k) on ocular biometric parameters in the anterior segment, including central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (CLT), and anterior segment length (ASL). Baseline and six monthly data were retrieved from 78 subjects (aged 7-10 years, with myopia≤4.00D and astigmatism≤1.25D) who had completed a two-year randomized clinical trial using ortho-k for myopia control. They were randomly assigned to wear ortho-k lenses or single-vision spectacles (control). Anterior segment parameters were measured with the Pentacam after cycloplegia. No significant changes in CLT and ASL over time were observed in either group of subjects (37 ortho-k; 38 control). In the control group, CCT remained unchanged during the study period but in the ortho-k group, it was significantly reduced by an average of 0.009mm by the 6-month visit (p<0.001) and remained unchanged thereafter. No significant changes in ACD was found in the ortho-k group but it was significantly increased by an average of 0.04mm (p=0.001) in the control group. CLT nor ASL did not change over time in either control or ortho-k subjects. Although ACD significantly increased in the control subjects and CCT significantly reduced in the first six months of ortho-k lens wear, these changes were small and did not affect the overall ASL.

Orthokeratology to control myopia progression: a meta-analysis.

ObjectiveTo evaluate the clinical treatment effects of orthokeratology to slow the progression of myopia.MethodsSeveral well-designed controlled studies have investigated the effects of orthokeratology in school-aged children. We conducted this meta-analysis to better evaluate the existing evidence. Relevant studies were identified in the Medline and Embase database without language limitations. The main outcomes included axial length and vitreous chamber depth reported as the mean ± standard deviation. The results were pooled and assessed with a fixed-effects model analysis. Subgroup analyses were performed according to geographical location and study design.ResultsOf the seven eligible studies, all reported axial length changes after 2 years, while two studies reported vitreous chamber depth changes. The pooled estimates indicated that change in axial length in the ortho-k group was 0.27 mm (95% confidence interval [CI]: 0.22, 0.32) less than the control group. Myopic progression was reduced by approximately 45%. The combined results revealed that the difference in vitreous chamber depth between the two groups was 0.22 mm (95% confidence interval [CI]: 0.14, 0.31). None of the studies reported severe adverse events.ConclusionThe overall findings suggest that ortho-k can slow myopia progression in school-aged children.

Parents' knowledge and perspective of optical methods for myopia control in children.

To solicit parents' knowledge on myopia control strategies available; to investigate their attitudes toward the use of orthokeratology (ortho-k), daily wear soft lenses, and spectacles for myopia control, assuming all three optical strategies were equally effective for myopia control; and to collect their opinion on the age at which children can commence contact lens wear for vision correction. Telephone interviews were conducted on parents who responded to the advertisement for two myopia control studies, one on ortho-k and one on soft lenses. Most of the 196 respondents (ortho-k group, 56%; soft lens group, 44%) were mothers, aged 36 to 45 years. Ortho-k was the most commonly known myopia control strategy (86%). Parents in the ortho-k group selected ortho-k (49%) and spectacles (45%) (p < 0.001) as their preferred myopia control strategy, whereas parents in the soft lens group had no preference (p = 0.57). Decision was affected by prior knowledge of myopia control strategy. Major considerations were convenience and safety among parents selecting contact lenses and spectacles, respectively, as their preferred options. Overall, because of the lack of confidence in safety in contact lens wear, most parents (75%) were of the opinion that contact lenses for vision correction were only for children older than 14 years (53%) and not indicated for children younger than 8 years. Parents in Hong Kong were open to the use of contact lenses for myopia control in young children and they appeared to regard myopia control contact lenses as "treatment" and not as visual aids. They were more conservative in the use of contact lenses for vision correction in children. Parents' decision in selecting a myopia control strategy, assuming all three strategies to be equally effective, was affected by an individual's concerns of safety and additional benefits as well as influenced by positive evidence on myopia control effects.

High Myopia–Partial Reduction Ortho-k

To investigate if the combination of partial reduction (PR) orthokeratology (ortho-k) and spectacles for residual refractive errors in the daytime was effective to slow myopic progression in high myopic children. High myopic children (aged 8 to 11 years) with spherical equivalent refraction at least -5.75 diopters (D) and myopia -5.00 D or more myopic were recruited and randomly assigned into PR ortho-k and control groups. Subjects in the PR ortho-k group were fitted with custom made four-zone ortho-k lenses with target reduction of 4.00 D for both eyes, and the residual refractive errors were corrected with single-vision spectacles for clear vision in the daytime. Control subjects were fully corrected with single-vision spectacles. Axial length of each eye of all subjects was measured with the IOLMaster at 6-month intervals by a masked examiner. This study was registered at www.clinicaltrial.gov with the identifier NCT00977236. Fifty-two subjects were recruited and randomized to the PR ortho-k and control groups. Twelve PR ortho-k and 16 control subjects completed the study. Compared with the residual refractive errors at the 1-month visit (after stabilization of ortho-k treatment), the median increase in noncycloplegic residual myopia at the 24-month visit was 0.13 D. In the control group, the median increase in myopia was 1.00 D at the end of the study. The mean ± SD increases in axial length were 0.19 ± 0.21 mm in the PR ortho-k group and 0.51 ± 0.32 mm in the control group (95% confidence interval, -0.55 to -0.12; unpaired t test, p = 0.005). This single-masked randomized study showed that PR ortho-k effectively slowed myopic progression in high myopes. Axial length elongation was 63% slower in PR ortho-k-treated children compared with children wearing spectacles.

High myopia-partial reduction orthokeratology (HM-PRO): Study design

To report the study design and preliminary results of a pilot study, High Myopia-Partial Reduction Orthokeratology study. Children with myopia of 6.00D or above and who satisfied the recruitment criteria were randomly assigned to partial reduction orthokeratology (PR ortho-k) and spectacle-wearing control groups. The myopia of the PR ortho-k children were partially reduced using custom made 4-zone ortho-k lenses of target 4.00D. Residual refractive errors were corrected with single vision spectacles. Control subjects were fully corrected with single vision spectacles. PR ortho-k subjects were also required to return for assessment after the first overnight lens wear, and one week and one month after lens wear. Fifty-two eligible subjects were randomly assigned to PR ortho-k group (n=26) and control group (n=26). The median age of each group was 10.00 years. The median (range) subjective myopia of the right eye at baseline was 6.41D (5.00-8.00D) and 6.22D (6.00-8.00D) for PR ortho-k and spectacle groups, respectively (p>0.05). Nineteen (79%) PR ortho-k subjects achieved successful lens fit at the one month visit and the median myopic reduction was 3.75D in the right eye. The incidence of (mild) corneal staining in PR ortho-k subjects reduced from 30% at the first overnight lens wear to 16% at the 1-month visit. Corneal pigmented arc was observed in 32% of PR ortho-k subjects at the 1-month visit. PR ortho-k was successfully applied to high myopic children with no significant changes in ocular health/best corrected visual acuity after one month of lens wear.

Multizentrische Studie zur Fahreignungsbegutachtung von LASIK- und Orthokeratologie-Patienten im Vergleich zu konventionell korrigierten Personen

Corneal optical zone induced by LASIK and orthokeratology (Ortho-K) treatment modifies the refraction of the incoming light bundle in its border area in situations of dawn and darkness. Considering the legal regulations of the driver's license and the recommendations of the German Society of Ophthalmology (DOG) and the American Academy of Ophthalmology (AAO), the vision for driving suitability of ortho-K patients is tested and compared with that of LASIK patients and a reference group (juvenile: < 30 years, adult: > 40 years) under different criterions. The examination of the visual acuity, contrast sensitivity under mesopic conditions and glare contrast sensitivity are main topics of the study. This multicentre retrospective study includes 333 eyes of 167 subjects. 65 subjects were habitual wearers of reverse-geometry contact lenses, 60 subjects were treated by LASIK. 42 subjects use glasses, contact lenses or none of them. The follow-up time was 22.8 ± 11.9 months. The measurement of the visual acuity was based on DIN Standard 58220 part 3 and the ISO Standard 8596. The Mesotest II (Oculus Inc.) was used for testing contrast sensitivity under mesopic conditions and glare contrast sensitivity. Detecting the personal evaluation of vision and satisfaction, subjects were instructed to complete a questionnaire (NEI-RQL-42). Relating to the legal requirements in Germany, sufficient visual acuity was found in 76.7 % of the LASIK group, in 73.9 % of the Ortho-K users and in 85.7 % of the reference group (72.7 % in the adult group, 100 % in the juvenile group). Considering the DOG recommendations under inclusion of mesopic vision and glare sensitivity, 71.7 % of the LASIK subjects and 95.7 % of the Ortho-K subjects are suitable for driving a motor vehicle of the German classes A, A1, B, BE, M, S, L and T. With regard to the legal situation in the USA, 100 % of the Ortho-K users, 93.2 % of the LASIK group, 86.4 % of the adult reference group and 100 % of the juvenile reference group are fit to drive. The evaluation of the subjective questionnaire showed very high ratings in the Ortho-K (mean 85 of 100 points) and the LASIK (mean 86 of 100 points) group with no statistically significant differences. Considering the legal regulations, the volume of the subjects of Ortho-K and LASIK showed no significant difference of individuals considered fit to drive in comparison to a reference group. Neither LASIK nor Ortho-K patients have any restriction in the ability to drive a vehicle. The requirements of the DOG with regard to contrast sensitivity under mesopic conditions and glare contrast sensitivity for driving a vehicle are better fulfilled in the Ortho-K group compared to the group of LASIK patients. According to the DOG recommendations there are fewer subjects that are suitable for driving a motor vehicle as in the reference group. This fact must be discussed preoperatively.

Validity of Axial Length Measurements for Monitoring Myopic Progression in Orthokeratology

To investigate the short-term effect of orthokeratology (ortho-k) lens wear on the anterior segment length for validating the use of axial length for monitoring myopic progression after ortho-k treatment. THIRTY-SEVEN AND 39 SUBJECTS (AGES: 7-10 years) were randomly assigned to wear ortho-k and single-vision spectacles, respectively. Central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (LT), and anterior segment length (ASL: summation of CCT, ACD, and LT) were measured before and 6 months after the treatment under cycloplegia. Changes in these parameters were evaluated and compared between the two groups of subjects. There were no significant between-group differences in the baseline data (P > 0.37). After 6 months of lens wear, in the ortho-k group, CCT was significantly reduced by 0.009 ± 0.009 mm (P < 0.001), whereas ACD and LT remained unchanged (P > 0.15). In the spectacle group, ACD was significantly increased by 0.01 ± 0.03 mm (P = 0.008), whereas CCT and LT remained unchanged (P > 0.06). In both groups of subjects, ASL did not appreciably change but axial length was significantly increased by 0.10 ± 0.10 mm and 0.20 ± 0.11 mm in the ortho-k and the spectacle groups, respectively (P < 0.001). Eyeball elongation occurred in children wearing both ortho-k and single-vision spectacles. Since ASL was not affected by ortho-k treatment, axial length measured reflects the true growth of the eyeball and is a valid parameter for monitoring myopic progression in ortho-k treated eyes.

Retardation of Myopia in Orthokeratology (ROMIO) Study: A 2-Year Randomized Clinical Trial

This single-masked randomized clinical trial aimed to evaluate the effectiveness of orthokeratology (ortho-k) for myopic control. A total of 102 eligible subjects, ranging in age from 6 to 10 years, with myopia between 0.50 and 4.00 diopters (D) and astigmatism not more than 1.25D, were randomly assigned to wear ortho-k lenses or single-vision glasses for a period of 2 years. Axial length was measured by intraocular lens calculation by a masked examiner and was performed at the baseline and every 6 months. This study was registered at ClinicalTrials.gov, number NCT00962208. In all, 78 subjects (37 in ortho-k group and 41 in control group) completed the study. The average axial elongation, at the end of 2 years, were 0.36 ± 0.24 and 0.63 ± 0.26 mm in the ortho-k and control groups, respectively, and were significantly slower in the ortho-k group (P < 0.01). Axial elongation was not correlated with the initial myopia (P > 0.54) but was correlated with the initial age of the subjects (P < 0.001). The percentages of subjects with fast myopic progression (>1.00D per year) were 65% and 13% in younger (age range: 7-8 years) and older (age range: 9-10 years) children, respectively, in the control group and were 20% and 9%, respectively, in the ortho-k group. Five subjects discontinued ortho-k treatment due to adverse events. On average, subjects wearing ortho-k lenses had a slower increase in axial elongation by 43% compared with that of subjects wearing single-vision glasses. Younger children tended to have faster axial elongation and may benefit from early ortho-k treatment. (ClinicalTrials.gov number, NCT00962208.).

Repeatability of corneal biomechanical measurements in children wearing spectacles and orthokeratology lenses

To determine the repeatability of corneal hysteresis (CH) and corneal resistance factor (CRF) measurements in children wearing spectacles and children under orthokeratology (ortho-k) therapy using the Ocular Response Analyzer (ORA). CH and CRF were measured twice at a 10-min interval using ORA on the same day in both eyes of 25 children (mean age = 10.6 ± 1.2 years) wearing spectacles and 34 children (mean age = 10.9 ± 1.0 years) wearing ortho-k lenses. Four measurements were obtained from each eye in each set of measurements. Only data from the right eyes were analyzed. No significant between-measurement differences in CH and CRF were found in either group of subjects (paired t-tests, p > 0.05) and no correlations were found between the mean differences and their means (Pearson's correlations, -0.09 < r < 0.21, 0.24 < p < 0.85). The 95% limits of agreement (LA) were -1.87 mmHg to +2.59 mmHg and -1.53 mmHg to +1.41 mmHg for CH and -1.86 mmHg to +2.22 mmHg and -1.45 mmHg to +1.57 mmHg for CRF in the spectacle and ortho-k groups, respectively. A significant between-group difference in CRF was found (unpaired t-tests, p = 0.02). Repeatability of CH and CRF measurements using the ORA is within ± 2 mmHg in children wearing spectacles or ortho-k lenses. We suggest that the ORA can be used to monitor long-term corneal biomechanical changes during ortho-k treatment.

The Longitudinal Orthokeratology Research in Children (LORIC) in Hong Kong: A Pilot Study on Refractive Changes and Myopic Control

Purpose: Myopia is a common ocular disorder, and progressionof myopia in children is of increasing concern. Modern overnight orthokeratology(ortho-k) is effective for myopic reduction and has been claimed to beeffective in slowing the progression of myopia (myopic control) in children,although scientific evidence for this has been lacking. This 2 year pilot studywas conducted to determine whether ortho-k can effectively reduce and controlmyopia in children. Methods: We monitored the growth of axial length (AL)and vitreous chamber depth (VCD) in 35 children (7–12 years of age), undergoingortho-k treatment and compared the rates of change with 35 childrenwearing single-vision spectacles from an earlier study (control). For the ortho-ksubjects, we also determined the changes in corneal curvature and the relationshipswith changes of refractive errors, AL and VCD. Results: The baselinespherical equivalent refractive errors (SER), the AL, and VCD of the ortho-kand control subjects were not statistically different. All the ortho-k subjectsfound post-ortho-k unaided vision acceptable in the daytime. The residual SERat the end of the study was –0.18 ± 0.69 D (dioptre) and the reduction (lessmyopic) in SER was 2.09 ± 1.34 D (all values are mean ± SD). At the endof 24 months, the increases in AL were 0.29 ± 0.27 mm and 0.54 ± 0.27 mmfor the ortho-k and control groups, respectively (unpaired t test; p = 0.012);the increases in VCD were 0.23 ± 0.25 mm and 0.48 ± 0.26 mm for theortho-k and control groups, respectively (p = 0.005). There was significantinitial corneal flattening in the ortho-k group but no significant relationshipswere found between changes in corneal power and changes in AL and VCD.Conclusion: Ortho-k can have both a corrective and preventive/control effect inchildhood myopia. However, there are substantial variations in changes in eyelength among children and there is no way to predict the effect for individualsubjects.

Orthokeratology in low myopia. Part 1: efficacy and predictability

Aims Modern orthokeratology (ortho-k) using reverse geometry lens designs is being widely used for myopia reduction world-wide although there has been no well-controlled clinical trial of this procedure. This paper reports on the efficacy and predictability of an ortho-k procedure using the OK-74 lens design (now known as OK-704). Methods. We carried out a 100-day, controlled, randomised clinical trial in which 14 subjects underwent ortho-k and a further 14 were fitted with aligned rigid contact lenses. Results The mean reduction in myopia was 1.50 (SD 0.45) D in the ortho-k group and 0.01 (SD 0.20) D in the control group. Unaided vision improved by −0.64 (SD 0.22) logMAR units in the ortho-k group, compared with −0.09 (SD 0.11) units in the control group. Variables which correlated with refractive change were corneal thickness, p-value of the nasal semi-meridian and the difference between central and peripheral corneal powers. A multiple factors model can account for 72% of the refractive change. Conclusions Ortho-k using the OK-74 lens design achieved an average myopia reduction of 1.50 D. The model developed can provide an estimate of the refractive change likely to occur in ortho-k, a matter of importance to both clinician and patient.

A study of the central and peripheral refractive power of the cornea with orthokeratology treatment

The central and peripheral refracting power of the cornea after orthokeratology treatment was studied by a cross-sectional method. Three Asian subject groups were recruited. Group 1 consisted of 31 normal non-contact lens wearers, group 2 consisted of 14 subjects who wore orthoK contact lenses for 10–20 months, and group 3 consisted of 14 subjects who wore orthoK contact lenses for more than 20 months. Our results showed that the corneal refracting power (central 3.3 mm) in both of the groups with orthoK contact lens treatment did not differ significantly from the average cornea. The group that wore orthoK lenses for more than 20 months had a flatter temporal peripheral cornea than did the normal group at approximately 2.95 mm from the corneal apex. Because the temporal cornea is steeper than the nasal cornea in normal eyes, a relatively flatter temporal cornea in the orthoK group produces a more symmetrical peripheral cornea.