The Role of Orthokeratology in Myopia Control: A Review

Effect of 0.01% atropine eye drops combined with different optical treatments to control low myopia in Chinese children

PURPOSE

To investigate the efficacy and safety of 0.01% atropine (AT) in combination with different optical treatments for controlling myopia in Chinese children.

METHODS

This retrospective study analyzed 341 Chinese children aged 6-11 years with myopia between -0.50 D and -3.0 D between January 2022 and May 2023. The fast-progressing, myopic children received three optical treatments combined with 0.01 % atropine: 75 children with single-vision spectacles and atropine (SV + AT), 162 children with defocus-incorporated multi-segment spectacles and atropine (DIMS + AT), or 104 children with orthokeratology and atropine (OK + AT). The changes in spherical equivalent refraction (SER), axial length (AL), intraocular pressure (IOP), and amplitude of accommodation (AMP) were observed at 6-month and 1-year intervals.

RESULTS

After controlling for baseline variables, at 6 months, the increase in adjusted AL was significantly greater in the SV + AT group than in the DIMS + AT group (difference = 0.13 mm, 95 % CI: 0.07-0.20, P < 0.05) and in the OK + AT group (difference = 0.09 mm, 95 % CI: 0.09-0.17, P < 0.05). A more significant progression in adjusted SER was also observed in the SV + AT group than in the DIMS group (difference = -0.20D, 95 % CI: -0.29 to -0.11, P < 0.05). At 12 months, the greatest increase in adjusted AL was observed in the SV + AT group, with a statistically significant difference of 0.24 mm (95 % CI: 0.19-0.29, P < 0.05) compared with the DIMS group and a difference of 0.19 mm (95 % CI: 0.13-0.25, P < 0.05) compared with the OK + ST group. Similarly, a more significant progression in adjusted SER was observed in the SV + AT group than in the DIMS group (difference = -0.36 D, 95 % CI: -0.48 to -0.24, P < 0.05).

CONCLUSIONS

This study suggested that 0.01% atropine combined with DIMS or orthokeratology may be viable for controlling low myopia in fast-progressing, myopic children.

Development and evaluation of a deep neural network model for orthokeratology lens fitting

PURPOSE

To optimise the precision and efficacy of orthokeratology, this investigation evaluated a deep neural network (DNN) model for lens fitting. The objective was to refine the standardisation of fitting procedures and curtail subjective evaluations, thereby augmenting patient safety in the context of increasing global myopia.

METHODS

A retrospective study of successful orthokeratology treatment was conducted on 266 patients, with 449 eyes being analysed. A DNN model with an 80%-20% training-validation split predicted lens parameters (curvature, power and diameter) using corneal topography and refractive indices. The model featured two hidden layers for precision.

RESULTS

The DNN model achieved mean absolute errors of 0.21 D for alignment curvature (AC), 0.19 D for target power (TP) and 0.02 mm for lens diameter (LD), with R2 values of 0.97, 0.95 and 0.91, respectively. Accuracy decreased for myopia of less than 1.00 D, astigmatism exceeding 2.00 D and corneal curvatures >45.00 D. Approximately, 2% of cases with unique physiological characteristics showed notable prediction variances.

CONCLUSION

While exhibiting high accuracy, the DNN model's limitations in specifying myopia, cylinder power and corneal curvature cases highlight the need for algorithmic refinement and clinical validation in orthokeratology practice.

Novel Lenslet-ARray-Integrated Spectacle Lenses for Myopia Control: A 1-Year Randomized, Double-Masked, Controlled Trial

PURPOSE

To investigate the myopia control efficacy of novel Lenslet-ARray-Integrated (LARI) spectacle lenses with positive power lenslets (PLARI) and negative power lenslets (NLARI) worn for 1 year in myopic children.

DESIGN

Randomized, double-masked, controlled clinical trial.

PARTICIPANTS

A total of 240 children 6 to 12 years of age with spherical equivalent refraction (SER) between -4.00 and -1.00 diopters (D), astigmatism of ≤ 1.50 D, and anisometropia of ≤ 1.00 D.

METHODS

Participants were assigned randomly in a 1:1:1 ratio to PLARI, NLARI, and control (single-vision [SV]) groups. Cycloplegic autorefraction and axial length were measured at baseline and 6-month intervals after lens wear.

MAIN OUTCOME MEASURES

Changes in SER, axial elongation (AE), and differences between groups.

RESULTS

After 1 year, SER changes and AE in the PLARI and NLARI groups were significantly less than those in the SV group (SER: -0.30 ± 0.48 D, -0.21 ± 0.35 D, and -0.66 ± 0.40 D, respectively; AE: 0.19 ± 0.20 mm, 0.17 ± 0.14 mm, 0.34 ± 0.18 mm, respectively; all P < 0.001). No significant differences were found in SER changes and AE between PLARI and NLARI groups (P = 0.54 and P = 1.00, respectively). Younger age was associated with more rapid SER increase and larger AE in the SV group (r = 0.40 [P < 0.001] and r = -0.59 [P < 0.001], respectively) and PLARI group (r = 0.46 [P < 0.001] and r = -0.52 [P < 0.001], respectively), but not in the NLARI group (r = -0.002 [P = 0.98] and r = -0.08 [P = 0.48], respectively).

CONCLUSIONS

Compared with the SV group, both PLARI and NARI groups showed significantly slower myopia progression in terms of SER and AE. Faster myopia progression, in terms of both SER and AE, was associated with younger age in the SV and PLARI groups but not the NLARI group.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Utility of retinoscopy to examine peripheral refraction

PURPOSE

This study explored whether retinoscopy (RET) provides comparable results of relative peripheral refraction (RPR) to open-field autorefractometry (AR) in myopic subjects.

METHODS

Peripheral refraction was measured in 20 myopic and 20 control adult subjects. Both central and peripheral refraction (20° nasal and temporal eccentricity) were measured using RET and open-field AR. Differences in the median central spherical equivalent (SE), median RPR, and median J45/J180 power vectors between the RET and AR techniques were analyzed. Moreover, Bland - Altman plots were used to assess the agreement between RET and AR methods for RPR measurements in MG.

RESULTS

For MG, the median RPR values were positive (hyperopic shift), and no significant differences were observed between the RET and AR techniques with respect to RPR measurement. In addition, we did not observe any significant differences in the RPR values between the nasal and temporal eccentricities for either the RET or AR technique for myopic subjects. There was also a significant correlation and agreement between the RET and AR technique for RPR measurements. With respect to central refraction, the median SE was slightly more positive for the RET than for the AR technique. Inside the CG, we also found significant correlation between the RET and AR technique for RPR measurements, and we observed a myopic shift in peripheral eccentricities.

CONCLUSION

Our results show that retinoscopy may be a useful tool for objective measurements of RPR in myopic subjects and may be used interchangeably with the open-field AR method in everyday clinical practice.

Artificial Intelligence-Assisted Prescription Determination for Orthokeratology Lens Fitting: From Algorithm to Clinical Practice

OBJECTIVES

To explore the potential of artificial intelligence (AI) to assist prescription determination for orthokeratology (OK) lenses.

METHODS

Artificial intelligence algorithm development followed by a real-world trial. A total of 11,502 OK lenses fitting records collected from seven clinical environments covering major brands. Records were randomly divided in a three-way data split. Cross-validation was used to identify the most accurate algorithm, followed by an evaluation using an independent test data set. An online AI-assisted system was implemented and assessed in a real-world trial involving four junior and three senior clinicians.

RESULTS

The primary outcome measure was the algorithm's accuracy (ACC). The ACC of the best performance of algorithms to predict the targeted reduction amplitude, lens diameter, and alignment curve of the prescription was 0.80, 0.82, and 0.83, respectively. With the assistance of the AI system, the number of trials required to determine the final prescription significantly decreased for six of the seven participating clinicians (all P <0.01). This reduction was more significant among junior clinicians compared with consultants (0.76±0.60 vs. 0.32±0.60, P <0.001). Junior clinicians achieved clinical outcomes comparable to their seniors, as 93.96% (140/149) and 94.44% (119/126), respectively, of the eyes fitted achieved unaided visual acuity no worse than 0.8 ( P =0.864).

CONCLUSIONS

AI can improve prescription efficiency and reduce discrepancies in clinical outcomes among clinicians with differing levels of experience. Embedment of AI in practice should ultimately help lessen the medical burden and improve service quality for myopia boom emerging worldwide.

Is Spending More Time Outdoors Able to Prevent and Control Myopia in Children and Adolescents? A Meta-Analysis

INTRODUCTION

Spending more time outdoors was treated as a safe and cost-effective method to prevent and control myopia. While prior research has established an inverse association between outdoor time and the risk of myopia onset, the effect of increasing outdoor time in delaying the progression of myopia remains a subject of debate. The present meta-analysis aimed to assess the relationship between outdoor time and the myopia onset, and further examine whether there is a dose-response relationship between outdoor time and the risk of myopia onset. Meanwhile, perform whether the outdoor time is related to delaying the progression of myopia.

METHODS

Studies were retrieved from PubMed, Web of Science, Embase, Medline, and the Cochrane Database, spanning from their inception to February 2023. Three cohort studies and 5 prospective intervention studies were included, with a total of 12,922 participants aged 6-16 years.

RESULTS

Comparing the highest with the lowest exposure levels of time spent outdoors, the highest outdoor time was strongly associated with a reduced risk of myopia onset (odds ratio [OR]: 0.53; 95% confidence interval [CI]: 0.34, 0.82). A nonlinear dose-response relationship was found between outdoor time and myopia onset risk. Compared to 3.5 h of outdoor time per week, an increase to 7, 16.3, and 27 h per week corresponded with a respective reduction in the risk of myopia onset by 20%, 53%, and 69%. Among children and adolescents who were not myopic, spending more time outdoors significantly slowed down the speed of change in spherical equivalent refractive (weighted mean difference [WMD] = 0.10D, 95% CI: 0.07, 0.14) and axial length (WMD = -0.05 mm, 95% CI: -0.06, -0.03). Among children and adolescents who were already myopic, spending more time outdoors did not slow myopia progression.

CONCLUSIONS

Overall, spending more time outdoors can prevent the onset of myopia, but it does not seem to slow its progression. Further studies are needed to better understand these trends.

The effect of the back optic zone diameter on the treatment zone area and axial elongation in orthokeratology

PURPOSE

To investigate the influence of corneal parameters on the treatment zone area (TZA) after Corneal Refractive Therapy (CRT) with a 5.0-mm back optical zone diameter (BOZD) were worn and to compare changes in the axial length (AL) with traditional 6.0-mm BOZD lenses.

METHODS

This retrospective study involved 146 subjects (7-12 years) who wore orthokeratology (ortho-K) lenses for one year: 86 subjects were treated with CRT 5.0-mm lenses, and 60 subjects were treated with CRT 6.0-mm lenses. The TZA was measured after one year of ortho-K treatment. Both TZA and AL elongation after wearing the two kinds of lenses was compared. The parameters were recorded in the CRT 5.0 group: flat K, steep K, corneal toricity, e value, and anterior corneal elevation values at the 3-, 4-, and 5-mm chords along the principal meridians of the superior, inferior, nasal, and temporal sides. The relationships between these data and the TZA were analyzed.

RESULTS

The TZA was 12.90 ± 5.15 mm2 and 20.61 ± 4.54 mm2, and the AL elongation was 0.15 ± 0.18 mm and 0.26 ± 0.18 mm in the CRT 5.0 group and the CRT 6.0 group, respectively (all p < 0.001). The one-year AL elongation was significantly associated with initial age and the TZA (r =  - 0.394, 0.393; all p < 0.001) in the CRT 5.0 group. The following corneal parameters were found to have statistically significant correlations with the TZA: the e value, difference in corneal elevation (nasal-temporal at the 3-, 4-, and 5-mm chord), and the absolute value of elevation difference (nasal-temporal at the 3- and 4-mm chord and inferior-superior at the 3-, 4-, and 5-mm chord). The e value was the only relevant factor for the TZA by multiple regression analysis (unstandardized β = 14.219, p = 0.008). In the CRT 6.0 group, the one-year AL elongation was statistically significantly associated only with initial age (r =  - 0.605, p = 0.005), but not with the TZA (p = 0.161).

CONCLUSIONS

A smaller TZA induced by a smaller BOZD may be beneficial for retarding AL elongation in children undergoing ortho-K treatment. The morphology and eccentricity of the cornea may show effects on the TZA.

Assessing the rebound phenomenon in different myopia control treatments: A systematic review

PURPOSE

To review the rebound effect after cessation of different myopia control treatments.

METHODS

A systematic review that included full-length randomised controlled studies (RCTs), as well as post-hoc analyses of RCTs reporting new findings on myopia control treatments rebound effect in two databases, PubMed and Web of Science, was performed according to the PRISMA statement. The search period was between 15 June 2023 and 30 June 2023. The Cochrane risk of bias tool was used to analyse the quality of the selected studies.

RESULTS

A total of 11 studies were included in this systematic review. Unifying the rebound effects of all myopia control treatments, the mean rebound effect for axial length (AL) and spherical equivalent refraction (SER) were 0.10 ± 0.07 mm [-0.02 to 0.22] and -0.27 ± 0.2 D [-0.71 to -0.03] after 10.2 ± 7.4 months of washout, respectively. In addition, spectacles with highly aspherical lenslets or defocus incorporated multiple segments technology, soft multifocal contact lenses and orthokeratology showed lower rebound effects compared with atropine and low-level light therapy, with a mean rebound effect for AL and SER of 0.04 ± 0.04 mm [0 to 0.08] and -0.13 ± 0.07 D [-0.05 to -0.2], respectively.

CONCLUSIONS

It appears that the different treatments for myopia control produce a rebound effect after their cessation. Specifically, optical treatments seem to produce less rebound effect than pharmacological or light therapies. However, more studies are required to confirm these results.

SWOT analysis of ortho-K practice in India

PURPOSE

Orthokeratology (ortho-K) has been well established as a methodology for myopia correction and control its progression. A SWOT analysis serves as a strategic planning tool for intervention hence the purpose of this study to establish and implement ortho-K practice in India.

METHOD

The study was conducted between December 2020 and June 2021. A prospective questionnaire-based study was conducted to elicit the responses in the SWOT study. Based on focus group discussion a set of five statements under strengths, weaknesses, opportunities and threats were identified. These were closed ended questions were based on a 5-point likert scale. The Content Validation Index (CVI) was computed for each item taking those answers relevant with a score of three and four on the Likert scale and omitting those with a score of one and two on the Likert scale as non-relevant.

RESULTS

Strengths: 'Ortho-K is an excellent option for myopia control' was agreed by more than 50% of respondents. 67% of respondents agreed that advanced topographers has made ortho-K lens fitting easier. Weakness: More than 60% agreed that Ortho-K practice involves investment in instrumentation like topographers and trial lenses. 50% agreed that due to multiple follow up patients may be lost to follow up.

OPPORTUNITY

'Pandemic has necessitated the need for optometrists to explore myopia control options such as ortho-K' was agreed by more than 50%. Threats: 'Reluctance from adults and parents to try overnight contact lenses for myopia correction/control' was agreed by more than 50% of respondents. 62% agreed that atropine is perceived as an effective myopia control option by majority of the Indian ophthalmologists.

CONCLUSION

Ortho-K as an emerging modality for Myopia management in India through SWOT analysis, allows practitioners as well as CL industry to approach Ortho-K appropriately with novel designs and practice patterns that suits the market needs.

A snap-shot of orthokeratology lens rinsing habits: An online survey in a major eye hospital in Shanghai

PURPOSE

A hospital-based survey to explore lens rinsing habits of orthokeratology (ortho-k) patients, including the solution used for rinsing.

METHODS

An anonymous survey, via an online questionnaire, was administered to ortho-k lens wearers or their parents when they attended Fudan University Eye and ENT Hospital for routine follow-up visits. Three major issues were investigated: basic demographics, lens rinsing solution used, and specific rinsing habits. Relationships between demographics and rinsing solution used and rinsing behaviours were explored.

RESULTS

Of the total of 541 online questionnaires delivered, 296 were completed and returned. The respondents were the person responsible for lens care, either the ortho-k users themselves, or their parents. The median age of the lens wearers was 12.0 years (range: 8-22 years), and the median period of ortho-k lens wear was 18.0 months (range: 1-109 months). The most common rinsing solutions reported were a particular brand of multidose preserved saline (28.4%), cooled boiled water (23.3%), and non-preserved multidose saline (16.2%). Overall, the main reason for choice of rinsing solution was recommendation of eye care practitioners (90.2%). The respondents with a longer lens wear history tended to use commercially available bottled water, drinking water, or cooled boiled water rather than non-preserved saline (unidose or multidose) (p ≤ 0.009) and were more likely to use the rinsing solution to soak their lenses (p = 0.009). Lens wearers who rinsed the lenses themselves tended to use tap water compared to those whose lenses were handled by parents (p = 0.040).

CONCLUSION

Inappropriate choice and usage of rinsing solution appeared to be a common issue among ortho-k lens wearers in Shanghai, China. The problem was more pronounced in long-term wearers and in those who performed rinsing themselves.

Observation of the effect of posterior scleral reinforcement combined with orthokeratology and 0.01% atropine in the treatment of congenital myopia: a case report

BACKGROUND

Myopia has recently emerged as a significant threat to global public health. The high and pathological myopia in children and adolescents could result in irreversible damage to eye tissues and severe impairment of visual function without timely control. Posterior scleral reinforcement (PSR) can effectively control the progression of high myopia by limiting posterior scleral expansion, improving retrobulbar vascular perfusion, thereby stabilizing the axial length and refraction of the eye. Moreover, orthokeratology and low concentrations of atropine are also effective in slowing myopia progression.

CASE PRESENTATION

A female child was diagnosed with binocular congenital myopia and amblyopia at the age of 3 and the patient's vision had never been rectified with spectacles at the first consultation. The patient's ophthalmological findings suggested, high refractive error with low best corrected visual acuity, longer axial length beyond the standard level of her age, and fundus examination suggesting posterior scleral staphyloma with weakened hemodynamics of the posterior ciliary artery. Thereby, PSR was performed to improve fundus health and the combination of orthokeratology and 0.01% atropine were performed to control the development of myopia. Following up to 8 years of clinical treatment and observations, the progression of myopia could be well controlled and fundus health was stable.

CONCLUSION

In this report, 8-year of clinical observation indicated that PSR could improve choroidal thickness and hemodynamic parameters of the retrobulbar vessels, postoperative orthokeratology combined with 0.01% atropine treatment strategy may be a good choice for myopia control effectively.

Effect of COVID-19 home confinement on the efficacy of orthokeratology, 0.01% atropine and combined treatment

PURPOSE

To investigate the effect of COVID-19 home confinement on the efficacy of the interventions for controlling myopia, and to select effective therapies to control myopia during COVID-19 confinement.

METHOD

Children (n = 164) aged 8-12 years with spherical equivalent refraction of -1.00 to -6.00 diopters were stratified into two age subgroups and randomly allocated into the control, 0.01% atropine, orthokeratology (ortho-k) and atropine combined ortho-k (ACO) groups. Axial length (AL) was measured at baseline, 6-, 12-, 18- and 24-month visits. The follow-up spanned the period before the COVID-19 outbreak, the period of the home confinement, and the period of the school reopening. Hence, the AL change in different periods was collected and compared. Data analysis was performed following the criteria of intention to treat (ITT).

RESULTS

All 164 children were involved in the ITT analysis. Compared to control, all interventions can still reduce the AL elongation during the COVID-19 home confinement period (all p < 0.05). However, the efficacy was compromised: individuals experienced more AL elongation during the COVID-19 home confinement period in the control, 0.01% atropine and ACO groups (all p < 0.05). Interestingly, in the ortho-k group, the difference was insignificant (p = 0.178), and the interaction between the intervention type (control vs. ortho-k) and the confinement severity was significant (p for interaction = 0.041), which is different from the atropine (p for interaction = 0.248) or ACO group (p for interaction = 0.988). These results were stable after being adjusted by other variables based on the multivariable regression model.

CONCLUSION

Ortho-k was less affected by the COVID-19 home confinement, which is potentially a better therapy for children in this high-risk environment. Further investigations are warranted to validate this issue.

Machine learning models for orthokeratology lens fitting and axial length prediction

PURPOSE

In order to improve the efficiency of orthokeratology (OK) lens fitting and predict the axial length after 1 year of OK lens wear, machine learning models were proposed.

METHODS

Clinical data from 1302 myopic subjects were collected retrospectively, and two machine learning models were implemented. Demographic and corneal topographic data were collected as input variables. The output variables were the parameters of the OK lens and the axial length after 1 year. Eighty percent of input variables was used as the training set and the remaining 20% was used as the validation set. The first alignment curve (AC1) of the OK lenses, deduced using machine learning models and formula calculation, were compared. Multiple regression models (support vector machine, Gaussian process, decision tree and random forest) were used to predict the axial length after 1 year. In addition, we classified data based on lens brand, and carried out more detailed parameter fitting and analysis for spherical and toric OK lenses.

RESULTS

The OK lens fitting model showed higher (R2  = 0.93) and lower errors (mean absolute error [MAE] = 0.19, mean square error [MSE] = 0.09) when predicting AC1, compared with the formula calculation (R2  = 0.66, MAE = 0.44, MSE = 0.25). The machine learning model still had high R2 values ranging from 0.91 to 0.96 when considering the brand and design of the OK lenses. Further, the R2 value for the axial length prediction model was 0.94, which indicated that the machine learning model had high accuracy and good robustness.

CONCLUSION

The OK lens fitting model and the axial length prediction model played an important role in guiding OK lens fitting, with high accuracy and robustness in prediction performance.

The rate of orthokeratology lens use and associated factors in 33,280 children and adolescents with myopia: a cross-sectional study from Shanghai

OBJECTIVES

To investigate the rate of orthokeratology lens (ortho-k lens) use and its associated factors in children and adolescents with myopia.

METHODS

Cross-sectional study. Children from 104 primary and middle schools in Shanghai were enrolled by cluster sampling. Ophthalmic examinations were conducted and information was obtained using questionnaires for associated factors analysis.

RESULTS

A total of 72,920 children and adolescents were included, among which 32,259 were the potential population for ortho-k lens use. A total of 1021 participants used ortho-k lenses, equating to a use rate of 1.4% in the total population and 3.1% in the potential population. Age (OR 0.91, 95% CI: 0.88-0.95, p < 0.001), BMI (≥95th percentile: OR 0.48, 95% CI: 0.35-0.66, p < 0.001), age at initiation of refractive correction (≤12 years: OR 1.75, 95% CI: 1.31-2.33, p < 0.001), and parental myopia (either: OR 2.09, 95% CI: 1.58-2.75, p < 0.001; both: OR 3.94, 95% CI: 3.04-5.11, p < 0.001) were independently associated with ortho-k lens use. Of the ortho-k lenses users, 12.4% had a logMAR CVA of ≥0.3. A correction target (SE) of ≤-3.0 D (OR 2.05, 95% CI: 1.38-3.05, p < 0.001) and a sleeping duration of ≤6 h (OR 4.19, 95% CI: 2.03-8.64, p < 0.001) were factors independently associated with CVA ≥ 0.3.

CONCLUSIONS

A certain proportion of children and adolescents in Shanghai chose to wear ortho-k lenses, related to the situation of parents and children themselves. Health education and follow-ups should be strengthened to ensure orthokeratology application quality.

Long-Term Efficacy of Orthokeratology to Control Myopia Progression

OBJECTIVES

To assess the efficacy of orthokeratology in controlling the rate of myopia progression in children and investigate the factors associated with axial length (AL) growth rate with an average of 48 months of orthokeratology lens wear.

METHODS

As a retrospective study, 84 subjects underwent relatively complete ophthalmologic examinations. After initial lens wear, AL was measured on average every 12 months. The linear mixed-effects model (LMM) was used to compare the differences in AL growth rates at each time interval. The contribution of the independent variables to AL change was assessed using multiple linear regression.

RESULTS

In the LMM, there was a significant difference in the AL growth rate ( P <0.001) at each follow-up. The growth rate of AL was associated with initial AL, spherical equivalent refractive errors (SERs) and diameter of lens ( P =0.045, 0.003 and 0.037, respectively). When the baseline age was included as a factor, the influence of initial AL and SER became insignificant in the analysis, whereas age and diameter of lens were significantly correlated with the growth rate of AL ( P< 0.001 and P< 0.001, respectively). There were significant differences in growth rates among different age groups.

CONCLUSIONS

Results of the study demonstrated that the factors associated with lower growth rate in AL were older age and longer diameter of lens.

Optical Biometry Changes Throughout Childhood and Adolescence in Patients Wearing Ortho-K Lenses

Background

Orthokeratology has been shown to suppress progressive myopia in some children. We examine the changes in optical biometry parameters in orthokeratology (Ortho-K) patients, in a retrospective longitudinal study at a tertiary eye care center in Ann Arbor, MI, USA.

Methods

Optical biometry measurements obtained with the Lenstar LS 900 (Haag-Streit USA Inc, EyeSuite software version i9.1.0.0) were aggregated from 170 patients who had undergone Ortho-K for myopia correction between 5 and 20 years of age. Pre-intervention biometry measurements were compared with follow-up measurements done 6-18 months after initiation of Ortho-K. Linear mixed models were used to quantify associations in biometry changes with age of intervention allowing for correlation between measurements on two eyes of the same patient.

Results

A total of 91 patients were included in the study. Axial length increased through the age of 15.7 ± 0.84 years for Ortho-K patients at our center. The growth curve in our Ortho-K population was comparable to previously published normal growth curves in Wuhan and Germany populations. Corneal thickness and keratometry decreased at a stable rate regardless of age of intervention (-7.9 µm, 95% CI [-10.2, -5.7], p < 0.001).

Conclusion

In our population, Ortho-K did not appear to affect the overall trajectory of axial length progression when compared to normal growth curves, despite showing a previously described reduction in corneal thickness. As Ortho-K has been shown to have varying effects that differ from individual to individual, it continues to be important to reassess its effects on new populations to better understand its ideal uses.

TFOS Lifestyle: Impact of contact lenses on the ocular surface

Several lifestyle choices made by contact lens wearers can have adverse consequences on ocular health. These include being non-adherent to contact lens care, sleeping in lenses, ill-advised purchasing options, not seeing an eyecare professional for regular aftercare visits, wearing lenses when feeling unwell, wearing lenses too soon after various forms of ophthalmic surgery, and wearing lenses when engaged in risky behaviors (e.g., when using tobacco, alcohol or recreational drugs). Those with a pre-existing compromised ocular surface may find that contact lens wear exacerbates ocular disease morbidity. Conversely, contact lenses may have various therapeutic benefits. The coronavirus disease-2019 (COVID-19) pandemic impinged upon the lifestyle of contact lens wearers, introducing challenges such as mask-associated dry eye, contact lens discomfort with increased use of digital devices, inadvertent exposure to hand sanitizers, and reduced use of lenses. Wearing contact lenses in challenging environments, such as in the presence of dust and noxious chemicals, or where there is the possibility of ocular trauma (e.g., sport or working with tools) can be problematic, although in some instances lenses can be protective. Contact lenses can be worn for sport, theatre, at high altitude, driving at night, in the military and in space, and special considerations are required when prescribing in such situations to ensure successful outcomes. A systematic review and meta-analysis, incorporated within the review, identified that the influence of lifestyle factors on soft contact lens dropout remains poorly understood, and is an area in need of further research. Overall, this report investigated lifestyle-related choices made by clinicians and contact lens wearers and discovered that when appropriate lifestyle choices are made, contact lens wear can enhance the quality of life of wearers.

Is Orthokeratology Treatment Zone Decentration Effective and Safe in Controlling Myopic Progression?

OBJECTIVE

To compare the myopia control efficacy and safety of decentered versus centered positioning of orthokeratology.

METHODS

This is a retrospective intrasubject study, including 46 children with myopia (25 boys, 21 girls; age 11.12±0.33 years) treated for 1 year with OK decentration in one eye (group D) and central location in the other (Group C). Axial length was measured before and at 6 months and 12 months after the initial lens wear, respectively. Corneal topography was measured at baseline and at 1-month after lens wear. The corneal topography obtained from the 1-month visit was used to quantify treatment zone decentration (TZD) for each subject. Cycloplegic refraction was required for all children before fitting the orthokeratology lenses.

RESULTS

No differences were found between the groups in the biological ocular parameters ( P ≥0.05 for all). The axial elongation in group D and group C differed after 6 and 12 months ( P <0.001 for all). Similar corneal staining rates ( P =0.06) were noted during follow-up in groups D (n=20; 7.24%) and C (n=10; 3.62%), all of grade I. The uncorrected visual acuity (UCVA) in group D and C differed after 1, 6, and 12 months ( P =0.002, 0.010, 0.044), except 3 months ( P =0.146). Group D (n=32; 17.39%) was more likely to have glare or ghosting (chi-squared test, P <0.001) than group C (n=12; 6.52%) during follow-up visits. Axial elongation was significantly associated with baseline spherical equivalent (SE) in group C ( P =0.019). In group D, axial elongation was significantly associated with SE and TZD ( P <0.05 for all).

CONCLUSIONS

This intrasubject study showed that when the UCVA was acceptable and there were no apparent complications, orthokeratology decentration may be beneficial in controlling the progression of myopia. Axial elongation became slower in children with a higher SE and a larger TZD, because TZD ranged from 0.5 mm to 1.5 mm.

Health-related quality of life for children using orthokeratology (OK), peripheral lenslet designed (PLD) and single-vision (SV) spectacles: based on Child Health Utility 9 Dimensions (CHU9D)

PURPOSE

This study investigated the health-related quality of life (HRQoL) among children with myopia who used orthokeratology (OK), peripheral lenslet designed (PLD), and single-vision (SV) spectacles.

METHODS

This cross-sectional study was conducted between February of 2021 and August of 2022. It involved 211, 231, and 206 respondents with OK, PLD, and SV spectacle lenses, respectively. The HRQoL was presented as utility values using a general preference-based Child Health Utility-nine Dimensions (CHU9D) questionnaire. Descriptive statistical analysis and nonparametric hypothesis testing were used to compare the HRQoL in the OK, PLD, and SV groups.

RESULTS

Of the 648 respondents, the average utility scores was 0.936 (95 % confidence interval (CI): 0.929-0.943). Children who wore the PLD spectacles had a significantly higher utility scores (0.955, 95 % CI: 0.946-0.963) than those who wore the SV spectacles (0.926, 95 % CI: 0.913-0.939) and the OK lenses (0.925, 95 % CI: 0.913-0.937) (p < 0.01). The PLD spectacle wearers were less likely to be worried, sad, tired, or annoyed than those who wore OK and SV spectacles (P < 0.05). Self-reported improved eyesight and lessened eye pain and discomfort from myopia correction using PLD spectacles had higher utility values (P < 0.05).

CONCLUSIONS

The PLD spectacles had a significantly higher HRQoL than the OK and SV spectacles among children. Having better eyesight and less eye pain/discomfort from myopia correction could improve the HRQoL of children. This data indicates that PLD spectacles may be considered for myopia management in children and adolescents.

Low Dose Atropine in Preventing the Progression of Childhood Myopia: A Randomised Controlled Trial

PURPOSE

To study the efficacy of low dose atropine (0.01%) eye drops in preventing myopia progression in children by comparing the mean change in spherical equivalent (diopter) and axial length (mm) over a period of one year to a control group and study its effect on near vision, pupil size, keratometry and pachymetry.

METHODS

200 eyes of 100 myopic children were randomized into two groups based on a computer-generated random number table. The treatment group was administered 0.01% atropine eye drop once at bedtime and control group was administered a placebo. The follow up was done 3-monthly for 12 months by assessing the mean change in spherical equivalent and mean change in axial length. Other parameters like near vision, pupil size, keratometry and pachymetry were assessed at each follow up.

RESULT

The study was age and sex matched. The mean change in spherical equivalent refraction and axial length was significantly lower in the treatment group (0.31 ± 0.55 D; 0.11 ± 0.22 mm) than the placebo group (0.80 ± 1.65 D; 0.23 ± 0.44 D) (p-value: 0.003). Less steepening of the corneal curvature was observed in the treatment group (0.16 ± 0.28 D vs 0.29 ± 0.3 D; p < 0.001) and the mean change in pachymetry was comparable between the groups (0.00 ± 0.01) (p-value 0.489). No significant change was seen in near vision (96% of the eyes with atropine had no change in near vision; 2% of the eyes had a change of near vision by one line (p-value 0.500); 2% had a change by 3 lines (p-value: 0.07) or pupil size following treatment.

CONCLUSION

The use of 0.01% atropine eye drop reduced the progression of myopia over the study period of one year with no significant changes in near vision, pupil size. No patient reported any systemic and local side effects with administration of 0.01% atropine eye drop.

Factors Associated With Follow-Up Visits in Parents With Myopic Children Wearing Orthokeratology Lens

BACKGROUND

Orthokeratology (Ortho-k) is an effective method for slowing the progression of myopia and correcting refractive error in school children. Although parents of children aged < 10 years play a major role in Ortho-k lens care, they have a generally low level of compliance in performing regular follow-up visits.

PURPOSE

This study was developed to analyze the associations between follow-up visits by parents of Ortho-k lens wearers aged < 10 years and, respectively, the Ortho-k-related knowledge of these parents and information resources promoting Ortho-k use.

METHODS

A cross-sectional study design was used. Parents of children who wear Ortho-k lenses were recruited through a private Facebook group with 3,500 members in 2020 that was created in 2018 for information sharing and exchange among parents of these children. The following data were collected: demographics of the parents and their children, four-item Ortho-k-related knowledge, information resources that prompted the decision to use Ortho-k, and the regularity of follow-up visits. These data were presented in terms of means, standard deviations, and percentages. Logistic regression was performed to compute the odds ratios ( OR s) and 95% confidence intervals (CIs).

RESULTS

The study showed that 83.11% had regular follow-up visits. The correct response rate on Ortho-k-related knowledge was > 80%. However, 15.51% of the participants did not recognize axial length as an indicator for monitoring myopia progress, and 10.76% did not know that at least 6 hours of nighttime sleep is required for myopia control with Ortho-k. The most common information resource leading to Ortho-k use was self-acquisition from Internet sources. The spherical equivalent refraction of < -2.0 D was 2.58 times higher in participants with regular follow-up visits than in their peers with irregular follow-up visits ( OR = 2.58, 95% CI [0.22, 5.63]). In addition, acknowledgment of "There is no need to change the Ortho-k lenses regularly as long as there is no discomfort" was 7.19 times higher in participants with regular follow-up visits than in their peers with irregular follow-up visits ( OR = 7.19, 95% CI [1.26, 13.93]). However, participants with regular follow-up visits did not receive Internet ophthalmology advertisements prompting their decision to use Ortho-k 2.62 times higher than their peers with irregular follow-up visits ( OR = 2.62, 95% CI [0.04, 4.29]).

CONCLUSIONS

The results support that both information sources and knowledge of Ortho-k use influence the frequency of follow-up visits among parents of Ortho-k lens wearers aged < 10 years. Related support from health professionals in terms of providing appropriate information and guidance is recommended to promote higher rates of regular follow-up visit attendance.

Combination of orthokeratology lens with 0.01% atropine in slowing axial elongation in children with myopia: a randomized double-blinded clinical trial

BACKGROUND

To evaluate the additive effects of orthokeratology (OK) lenses and 0.01% atropine on slowing axial elongation in myopic children.

METHODS

A prospective, randomized, double-blinded, placebo-controlled trial was conducted over a 12-month period. Sixty children aged 8 to 12 years with spherical equivalent refraction from - 1.00 to -4.00 D who had been wearing OK lenses successfully for 2 months (as baseline) were randomly assigned in a 1:1 ratio to combination group (combination of OK lens and 0.01% atropine eye drops) and control group (combination of OK lens and placebo). The primary outcome was change in axial length, along with secondary outcomes including change in pupil diameter (PD) and accommodative amplitude (AMP) at 12 months (measured at 4-month intervals).

RESULTS

After 12 months, the overall axial elongation was 0.10 ± 0.14 mm and 0.20 ± 0.15 mm (p = 0.01) in the combination and control groups, respectively. The change in axial length in the two groups showed significant differences only in the first four months (median [Q1, Q3] (95% CI), -0.01 mm [-0.07, 0.05] (-0.06, 0.04) vs. 0.04 mm [0.00, 0.10] (0.02, 0.09); p = 0.04), but no difference thereafter. Multivariate linear regression analysis showed that the axial elongation was significantly slower in the combination group than in the control group (standard β = -0.10, p = 0.02). PD significantly increased by 0.45 mm [0.20, 0.68] at the 4th month visit (p < 0.001) and then remained stable in the combination group. The PD in the control group and AMP in the two groups remained stable from baseline to 12 months (all p > 0.05).

CONCLUSION

The combination therapy was more effective than the OK lens alone in slowing axial elongation after 12 months of treatment, and mainly in the first 4 months.

TRIAL REGISTRATION

The First Affiliated Hospital of Zhengzhou University, ChiCTR2000033904. Registered 16/06/2020, http://www.chictr.org.cn/login.aspx?referurl=%2flistbycreater.aspx.

Effect of the combined application of orthokeratology and single-vision spectacles on slowing the progression of high myopia: A systematic review and meta-analysis

PURPOSE

The purpose of the study was to conduct a meta-analysis about the effect of the combined application of orthokeratology and single-vision spectacles on slowing the progression of high myopia.

METHODS

The literature was searched in PubMed, EMBASE, the Cochrane Library, Wang Fang Data, CNKI and sinoMed. The Cochrane Handbook was used to evaluate the quality of the included randomized clinical trials, and the Newcastle-Ottawa Scale was used to evaluate the included case-control or cohort studies. The results were analyzed by Revman 5.3.

RESULTS

Five studies (2 randomized clinical trials, 2 case-controls, and 1 cohort study) with a total of 360 patients were included in this meta-analysis. The follow-up time was at least 1 year. Combined application of orthokeratology and single-vision spectacles were used in the experimental group. The control group used single-vision spectacles only. The pooled estimates indicated that the standardized mean difference between the 2 groups was -1.46 mm (95% confidence interval: -1.88 to -1.05; P < .05) for axial length elongation and -1.85D (95% confidence interval: -2.40 to -1.31; P < .05) for change in spherical equivalent refraction. No serious adverse events were reported in all studies.

CONCLUSION

The combined application of orthokeratology and single-vision spectacles is more effective than single-vision spectacles only on slowing the progression of high myopia.

Fitting of Orthokeratology in the United States: A Survey of the Current State of Orthokeratology

SIGNIFICANCE

The Fitting of Orthokeratology in the United States (FOKUS) survey provides information about the United States (US) OrthoK market. This independent survey is the first to attain detailed assessment of the OrthoK market.

PURPOSE

Develop and administer a survey to eye care providers (ECP's) in the US who are managing orthokeratology patients and those who are not to determine a profile of prescribers, patients and overall market.

METHODS

The FOKUS survey was administered and distributed online. Outcome measures of the FOKUS survey involved general categories of 1) practice and practitioner profiles, 2) clinical prescribing patterns, 3) patient profile, 4) products and marketing, 5) fees and 6) market size and growth.

RESULTS

The number of ECP's who are actively fitting and managing OrthoK patients in the US is approximately 3,000. 545 responded to the survey, 283 reported they were actively fitting orthokeratology. Orthokeratology is prescribed with the intent of managing myopia by 68% of respondents, 53% monitor axial length, and 61% start OrthoK patients at age 13 years old or under. The mean number of years a patient wears OrthoK is 7.8. A commonly reported complication with orthokeratology is corneal staining. Microbial keratitis (MK) is rarely or never seen by 86% of respondents. Of those currently fitting, 56% anticipate growth of orthokeratology fitting over the next twelve months. Of those not currently fitting orthokeratology, 46% plan to start within two years.

CONCLUSIONS

Orthokeratology represents a small but growing segment of the US contact lens market. The number of practitioners actively prescribing and fitting orthokeratology in the US is approximately 3,000 with high potential for growth within the next two years. Results of the FOKUS survey are relevant to practitioners currently fitting or considering orthokeratology, manufacturers, educators and researchers as baseline for future orthokeratology market assessment.

The effect of 0.01% atropine on ocular axial elongation for myopia children: A protocol for systematic review and meta-analysis

BACKGROUND

Orthokeratology (OK) has a significant effect on the control of myopia progression, and has been accepted by doctors and patients. A small number of studies have shown that the combination of OK and atropine can enhance myopia control. However, owing to individual differences, research groups, drug concentrations, and research design differences, the safety and effectiveness of the combined treatment still need to be verified. Therefore, the present meta-analysis aimed to determine the effect of 0.01% atropine on ocular axial elongation in myopic children.

METHODS

We searched the PubMed, Cochrane Library, and CBM databases from inception to March 1, 2022. Meta-analysis will be conducted using STATA version 14.0 and Review Manager version 5.3 softwares. We calculated the weighted mean differences (WMD) to analyze the change in ocular axial length (AL) between orthokeratology combined with 0.01% atropine (OKA) and OK alone. Cochran's Q-statistic and I2 test were used to evaluate the potential heterogeneity between studies. A sensitivity analysis was performed to evaluate the influence of single studies on the overall estimate. We will also perform subgroup and meta-regression analyses to investigate potential sources of heterogeneity. We will conduct Begger's funnel plots and Egger's linear regression tests to investigate the publication bias.

RESULTS

This systematic review aimed to determine the effect of 0.01% atropine on ocular axial elongation in children with myopia.

CONCLUSIONS

These findings provide helpful evidence for the effect of 0.01% atropine on ocular axial elongation in myopic children.

Clinical effect of rigid gas permeable (RGP) contact lens in improving vision and controlling myopia progression of unilateral high myopic children

BACKGROUND

The aim of this study was to explore the clinical effect of the RGP contact lens in improving vision and controlling myopia progression of the unilateral high myopic children.

METHODS

In this retrospective analysis case series study, we analyzed the clinical data for 23 subjects with unilateral high myopic children under 6 years old, with the spherical equivalent refractive error of the myopic eye from -5.0 D to -12.0 D, who were enrolled from the outpatient clinic at Beijing Tongren Hospital, China. Fourteen subjects could successfully fit the RGP contact lens, and nine subjects used the spectacle lens. Complete ocular examination was performed at the first visit at the clinic and every three months during the follow-up period.

RESULTS

In the RGP group, the change of axial length (AL) of the high myopic eye was from 25.62 ± 1.31 mm to 25.69 ± 1.31 mm after 12 months. The change of spherical equivalent (SE) was from -8.73 ± 2.54 D to -8.48 ± 2.77 D. The best corrected visual acuity (BCVA) improved from 0.24 ± 0.18 to 0.78 ± 0.26. In the spectacle group, the change of AL was from 24.76 ± 0.56 mm to 24.94 ± 0.71 mm. The change of SE was from -6.16 ± 2.86 D to -9.45 ± 2.06 D. The improvement of BCVA was from 0.52 ± 0.15 to 0.72 ± 0.23.

CONCLUSIONS

Wearing RGP lens in the children with unilateral high myopia is a safe, convenient and effective method to improve the best corrected vision and controlling myopia progression.

One-year analysis of the refractive stability, axial elongation and related factors in a high myopia population after Implantable Collamer Lens implantation

PURPOSE

To investigate the refractive stability, axial length (AL) changes and their related factors in a high myopia population after Implantable Collamer Lens (ICL) implantation.

METHODS

This prospective study included 116 eyes of 116 patients divided into several groups based on the spherical equivalent refractive error (SE)-SE > - 6 D, - 12 ≤ SE < - 6 D and SE < - 12 D groups-and AL-AL < 28 mm and AL ≥ 28 mm groups. The uncorrected and corrected distance visual acuity, refraction, AL and intraocular pressure were followed for 1 year.

RESULTS

SE changed from - 11.53 ± 5.25 D preoperatively to - 0.33 ± 0.70 D at 1 week, and further changed to - 0.48 ± 0.77 D at 1 year after ICL implantation, with average progression being - 0.15 ± 0.37 D from 1 week to 1 year after surgery. AL changed from 27.95 ± 2.33 mm preoperatively to 27.98 ± 2.36 mm 1 year after surgery, with an average axial elongation of 0.03 ± 0.12 mm. The mean axial elongation rate was 0.05 mm/year in the SE < - 12 D group, being significantly faster than the other refractive groups (P < 0.05); it was 0.06 mm/year in the AL ≥ 28 mm group, being significantly faster than the AL < 28 mm group (P < 0.05).

CONCLUSION

Patients with high myopia and long AL showed a continuous myopic progression and axial elongation at an adult age one year after ICL surgery, especially in those with myopia higher than - 12.00 D and AL longer than 28.00 mm.

The effect of 0.01% atropine and orthokeratology on ocular axial elongation for myopia children: A meta-analysis (a PRISMA-compliant article)

OBJECTIVES

This meta-analysis aimed to identify the therapeutic effect of 0.01% atropine with orthokeratology on ocular axial elongation for myopia children.

METHODS

We searched PubMed, Cochrane Library, and CBM databases from inception to July 1st, 2021. Meta-analysis was conducted using STATA version 14.0 and Review Manager version 5.3 softwares. We calculated the weighted mean differences to analyze the change of ocular axial length (AL) between orthokeratology combined with 0.01% atropine (OKA) and) alone. The Cochran's Q-statistic and I2 test were used to evaluate potential heterogeneity between studies. To evaluate the influence of single studies on the overall estimate, a sensitivity analysis was performed. We also performed sub group and meta-regression analyses to investigate potential sources of heterogeneity. We conducted Begger funnel plots and Egger linear regression tests to investigate publication bias.

RESULTS

Nine studies that met all inclusion criteria were included in this meta-analysis. A total of 191 children in OKA group and 196 children in orthokeratology (OK) group were assessed. The pooled summary weighted mean differences of AL change was -0.90 (95% CI = -1.25-0.55) with statistical significance (t = -5.03, P < .01), which indicated there was obvious difference between OKA and OK in myopic children. Subgroup analysis also showed that OKA treatment resulted in significantly less axial elongation compared to OK treatment alone according to SER. We found no evidence for publication bias.

CONCLUSIONS

Our meta-analysis indicates 0.01% atropine atropine is effective in slowing axial elongation in myopia children with orthokeratology.

Comparison of Two Main Orthokeratology Lens Designs in Efficacy and Safety for Myopia Control

Purpose

This study aimed to compare the efficacy and safety of corneal refractive therapy (CRT) lenses and vision shaping treatment (VST) lenses for myopia control in children.

Methods

Medical records of 1,001 children (2,002 eyes) who had been fitted with orthokeratology lenses for over 1.5 years were retrospectively reviewed. We collected the clinical data of four types of orthokeratology (OK) lenses available: one CRT lens (brand: CRT) and three VST lenses (brands: Euclid, Alpha, and Hiline) over 1.5 years. Results were compared and analyzed using a one-way ANOVA and Pearson's chi-square test.

Results

Axial length elongation in the CRT lens group was 0.13 ± 0.02 mm faster than that in the Euclid lens, 0.1 ± 0.02 mm faster in the Alpha lens, and 0.08 ± 0.02 mm faster in the Hiline lens over the 1.5-year period (all P < 0.05). Among the subjects, 37.3% of them using the CRT lens experienced more than 1 D of refractive growth, compared with 20.2–30.8% of subjects wearing the three groups of VST lenses (all P < 0.05). A lower incidence of total adverse events was found with the CRT lenses compared with the VST lenses (P < 0.05), especially corneal staining. No difference was found in axial length elongation, refraction growth, and incidence of adverse events among the three types of VST lenses (all P > 0.05).

Conclusions

Compared with the VST lenses, CRT lenses demonstrated a weaker effect on myopia control but with a better safety profile. Different types of VST lenses had similar efficacy and safety in the context of controlling myopia progression.

Efficacy, predictability and safety of long-term orthokeratology: An 18-year follow-up study

PURPOSE

To determine the efficacy, predictability and safety of long-term orthokeratology in children and adults.

METHODS

Case histories of 300 orthokeratology patients (596 eyes; 34.3% children; 65.7% adults) were reviewed to collect information on demographics, corneal and refractive parameters, visual acuity, residual refraction and adverse effects. Predictability was defined as the percentage of eyes with absolute values of spherical equivalent refraction ≤ 0.5 D of emmetropia, and efficacy as the ratio of post-orthokeratology uncorrected and pre-orthokeratology corrected distance visual acuity.

RESULTS

Median duration of treatment was 37 and 28.5 months in children and adults, respectively (p = 0.022). During the first year, 17.2% of children and 33% of adults ceased lens wear (p < 0.001). For children and adults with a successful ortho-k treatment of at least one year of duration, 88.7% and 95.9% of eyes had a predictable refractive outcome, and efficacy was 0.98 and 1.01, respectively. A larger percentage of children (65.7%) were free of complications than of adults (55.4%) (p = 0.015). One event of microbial keratitis occurred in adults (6.8 cases per 10,000 patient-years) and none in children. Corneal staining was the most frequent complication, with a higher incidence in adults (p = 0.007) and in higher myopia (p < 0.001), higher anterior corneal eccentricity (p = 0.019) and smaller anterior horizontal radius (p = 0.027).

CONCLUSION

Orthokeratology is a safe and predictable long-term procedure in children and adults, with a low incidence of serious adverse effects. Corneal staining episodes are relatively frequent throughout the course of the treatment, thus highlighting the relevance of education of experienced users.

Crystalline lens thickness change is associated with axial length elongation and myopia progression in orthokeratology

AIMS

Considering individual variability in regards to the effects of orthokeratology (ortho-k) on myopia progression and controversies regarding the precise underlying mechanism, the aim of this study was to investigate several ocular measurements associated with axial length (AL) growth in children wearing ortho-k lenses.

METHODS

In this retrospective chart review, medical records of 53 Chinese children who wore ortho-k lenses over the course of 12 months were reviewed. Baseline variables included age at initiation of ortho-k wear, refractive error (spherical equivalent, SE), central corneal thickness (CCT), and flat and steep keratometry of corneal principal meridians. The change of anterior chamber depth (ACD) and the change of crystalline lens thickness (CLT) between baseline and the 12-month follow-up were also analyzed. The contributions of all analyzed variables to AL change were assessed using univariate and multivariate regression analyses.

RESULTS

Initially, the results of paired t-test showed that CLT and AL were significantly increased after 12 months of ortho-k wear compared with that at baseline (P = 0.001 and < 0.001). The ACD did not change significantly after 12 months compared with that at baseline (P = 0.491). Subsequently, univariate analyses showed that a reduced rate of AL elongation was found in children who were older age at initiation of ortho-k wear (P = 0.028), had greater SE (higher degree of myopia) at baseline (p = 0.006), had thicker CCT at baseline (P = 0.04), and had greater increase of CLT (P = 0.001) in 12 months. At last, only greater SE (higher degree of myopia) and greater increase of CLT were associated with smaller increases of AL in multivariable analyses, (P = 0.003 and 0.001).

CONCLUSIONS

Both CLT and AL were significantly increased in children with overnight ortho-k wear after 12 months of follow-up. Greater baseline SE and greater increase of CLT were associated with less increase in AL during ortho-k wear in children with myopia.

The treatment zone size and its decentration influence axial elongation in children with orthokeratology treatment

BACKGROUND

To investigate whether the treatment zone size (TZS) and treatment zone decentration (TZD) will affect the axial elongation in myopic children undergoing orthokeratology treatment.

METHODS

A self-controlled retrospective study was conducted on 352 children who met the inclusion criteria. Axial length was measured before and at 12 months after the initial lens wear. Corneal topography was measured at baseline and at each follow-up after lens wear. The Corneal topography obtained from the 12-month visit was used to quantify TZS and TZD for each subject. Cycloplegic refraction was required for all children before fitting the orthokeratology lenses.

RESULTS

Axial elongation was significantly associated with age, baseline spherical equivalent (SE), TZS, and TZD with univariate linear regression. In groups with both small and large TZS, axial elongation was significantly decreased with large TZD (both P < 0.01). In groups with both small and large TZD, axial elongation was significantly decreased with small TZS (P = 0.03 for small TZD, P = 0.01 for large TZD). Age, SE, and TZD were significantly associated with axial elongation in multiple regression (all P < 0.01).

CONCLUSION

Relatively smaller TZS and larger TZD may be beneficial in slowing myopia progression in children with orthokeratology treatment.

Flitcroft's model of refractive development in childhood and the possible identification of children at risk of developing significant myopia

PURPOSE

To better understand juvenile myopia in the context of overall refractive development during childhood and to suggest more informative ways of analysing relevant data, particularly in relation to early identification of those children who are likely to become markedly myopic and would therefore benefit from myopia control.

METHODS

Examples of the frequency distributions of childhood mean spherical refractive errors (MSEs) at different ages, taken from previously-published longitudinal and cross-sectional studies, are analysed in terms of Flitcroft's model of a linear combination of two Gaussian distributions with different means and standard deviations. Flitcroft hypothesises that one, relatively-narrow, Gaussian (Mode 1) represents a "regulated" population which maintains normal emmetropisation and the other, broader, Gaussian (Mode 2) a "dysregulated" population.

RESULTS

Analysis confirms that Flitcroft's model successfully describes the major features of the frequency distribution of MSEs in randomly-selected populations of children of the same age. The narrow "regulated" Gaussian typically changes only slightly between the ages of about 6 and 15, whereas the mean of the broader "dysregulated" Gaussian changes with age more rapidly in the myopic direction and its standard deviation increases. These effects vary with the ethnicity, environment and other characteristics of the population involved. At all ages there is considerable overlap between the two Gaussians. This limits the utility of simple refractive cut-off values to identify those children likely to show marked myopic progression.

CONCLUSIONS

Analysing the frequency distributions for individual MSEs in terms of bi-Gaussian models can provide useful insights into childhood refractive change. A wider exploration of the methodology and its extension to include individual progression rates is warranted, using a range of populations of children exposed to different ethnic, environmental and other factors.

Update and guidance on management of myopia. European Society of Ophthalmology in cooperation with International Myopia Institute

The prevalence of myopia is increasing extensively worldwide. The number of people with myopia in 2020 is predicted to be 2.6 billion globally, which is expected to rise up to 4.9 billion by 2050, unless preventive actions and interventions are taken. The number of individuals with high myopia is also increasing substantially and pathological myopia is predicted to become the most common cause of irreversible vision impairment and blindness worldwide and also in Europe. These prevalence estimates indicate the importance of reducing the burden of myopia by means of myopia control interventions to prevent myopia onset and to slow down myopia progression. Due to the urgency of the situation, the European Society of Ophthalmology decided to publish this update of the current information and guidance on management of myopia. The pathogenesis and genetics of myopia are also summarized and epidemiology, risk factors, preventive and treatment options are discussed in details.

Atropine in topical formulations for the management of anterior and posterior segment ocular diseases

INTRODUCTION

Atropine is an old-known drug which is gaining increasing attention due to the myriad of therapeutic effects it may trigger on eye structures. Nevertheless, novel applications may require more adequate topical formulations.

AREAS COVERED

This review aims to gather the existing knowledge about atropine and its clinical applications in the ophthalmological field when administered topically. Atropine ocular pharmacokinetics is paid a special attention, including recent evidences of the capability of the drug to access to the posterior segment. Ocular bioavailability and systemic bioavailability are counterbalanced. Finally, limitations of traditional dosage forms and potential advantages of under investigation delivery systems are analyzed.

EXPERT OPINION

Mydriasis and cyclopegia have been widely exploited for eye examination, management of anterior segment diseases, and more recently as antidotes of chemical weapons. Improved knowledge on drug receptors and related pathways explains atropine repositioning as an outstanding tool to prevent myopia. The ease with which atropine penetrates ocular tissues is a double edged sword, that is, while it ensures therapeutic levels in the posterior segment, the unspecific distribution causes a wide variety of untoward effects. The design of formulations that can selectively deliver atropine to the target tissue for each specific application is an urgent unmet need.

Long-term progression of myopic maculopathy in degenerative myopia as imaged by SD-OCT and IR imaging

CLINICAL RELEVANCE

Clinicians can benefit from developing an understanding of the natural disease progression of myopic maculopathy in degenerative myopia using optical coherence tomography (OCT).

BACKGROUND

The prevalence of high myopia is constantly increasing. In this work, infrared imaging and OCT is used to study the natural course of the disease.

METHODS

This is a retrospective longitudinal study. Medical records of 72 patients with high myopia (< 6.00 D) and a minimum five-year follow-up period were analysed. Collected data on all enrolled patients included demographic characteristics and medical history, as well as recordings on best-corrected visual acuity, slitlamp examination, OCT, and fluorescein angiography in cases of suspected myopic choroidal neovascularisation. Images were independently marked by two graders.

RESULTS

The mean age of patients was 54.6 ± 14.4 years (59.72% female) with baseline logMAR best-corrected visual acuity of 0.22 ± 0.28. At baseline examination, 70.83% of the study group showed signs of maculopathy and 62.5% diffuse or patchy atrophy. During follow-up, 22.2% of patients with any type of atrophy showed enlarged affected areas. Two patients with baseline lacquer cracks developed new lesions. There was a weak correlation between patient age and maculopathy progression (r = 0.233; p = 0.03). While central retinal thickness was not associated with maculopathy progression (p = 0.203), a moderate correlation was found between choroidal thickness and maculopathy progression (r = -0.516; p < 0.001).

CONCLUSION

Lesion characteristics in myopic degeneration have been elucidated, taking advantage of the ongoing technological advances in retinal imaging. The understanding of disease patterns and progression is essential for appropriate management of patients, while discovering biomarkers which lead to choroidal neovascularisation development is of urgent importance to establish international diagnostic criteria and treatment protocols.

Stepwise candidate drug screening for myopia control by using zebrafish, mouse, and Golden Syrian Hamster myopia models

Background

We developed a preclinical protocol for the screening of candidate drugs able to control myopia and prevent its progression. The protocol uses zebrafish, C57BL/6 mice, and golden Syrian hamster models of myopia.

Methods

A morpholino (MO) targeting the zebrafish lumican gene (zlum) was injected into single-cell zebrafish embryos, causing excessive expansion of the sclera. A library of 640 compounds with 2 matrix metalloproteinase (MMP) inhibitors (marimastat and batimastat), which have the potential to modulate scleral remodelling, was screened to identify candidates for mitigating scleral diameter expansion in zlum-MO-injected embryos. The myopia-prevention ability of compounds discovered to have superior potency to inhibit scleral expansion was validated over 4 weeks in 4-week-old C57BL/6 mice and 3-week-old golden Syrian hamsters with form-deprivation myopia (FDM). Changes in the refractive error and axial length were investigated. Scleral thickness, morphology of collagen fibrils in the posterior sclera, messenger RNA (mRNA) expressions, and protein levels of transforming growth factor-β2 (TGF-β2), tissue inhibitor of metalloproteinase-2 (TIMP-2), MMP-2, MMP-7, MMP-9, and collagen, type I, alpha 1 (collagen Iα1) were investigated in C57BL/6 mice, and MMP-2, MMP-9, and MMP activity assays were conducted in these mice.

Findings

In the zebrafish experiment, atropine, marimastat, batimastat, doxycycline, and minocycline were the drugs that most effectively reduced expansion of scleral equatorial diameter. After 28-day treatment in diffuser-wearing mice and 21-day treatment in lid-sutured hamsters, myopic shift and axial elongation were significantly mitigated by eye drops containing 1% atropine, 50 µM marimastat, 5 µM batimastat, or 200 µM doxycycline. MMP-2 mRNA expression in mouse sclera was lower after treatment with atropine, marimastat, batimastat, or doxycycline. The protein levels and activity of MMP-2 and MMP-7 were significantly reduced after treatment with atropine, marimastat, batimastat, doxycycline, and minocycline. Furthermore, scleral thickness and collagen fibril diameter were not lower after treatment with atropine, marimastat, batimastat, or doxycycline than those of occluded eyes.

Interpretation

Stepwise drug screening in a range of models from zlum-MO-injected zebrafish to rodent FDM models identified effective compounds for preclinical myopia control or prevention. On the basis of the 640 compounds that were screened, MMP inhibitors may offer alternatives for clinical trials.

Funding

This research was supported by grants from Taiwan's Ministry of Science and Technology and Ministry of Health and Welfare.

Orthokeratology lens-related Acanthamoeba keratitis: case report and analytical review

Acanthamoeba keratitis (AK) is a rare but severe ocular infection with a significant risk of vision loss. Contact lens use is the main risk factor for AK. The orthokeratology (OK) lens, a specially designed contact lens, has been used worldwide as an effective method of myopia control. However, the OK lens is associated with an increased risk of Acanthamoeba infection. Many primary practitioners are concerned about this infection because of its relative rarity, the lack of promising therapeutic medications, and the need for referral. We herein report two cases of AK associated with OK lenses, present a systematic review of such cases, and discuss the possible reasons for the higher incidence rate of this infection in patients who wear OK lenses. We combined the clinical knowledge and skills of corneal specialists and lens experts with the sole objective of addressing these OK lens-related AK cases. We found that the most common risk factors were rinsing the lenses or lens cases with tap water. Prompt and accurate diagnosis along with adequate amoebicidal treatment are essential to ensure desirable outcomes for OK lens wearers who develop AK. Appropriate OK lens parameters and regular checkups are also important.

Compliance with orthokeratology care among parents of young children in Taiwan

OBJECTIVES

To evaluate compliance with orthokeratology (Ortho-K) care and its influencing factors among parents of 6-13-year-old myopic children in Taiwan.

METHODS

Parents who are responsible for the care of the Ortho-K lenses of their myopic children were recruited through a closed Facebook peer support group to answer an online compliance questionnaire, including the wear and care behaviours and follow-up visits of Ortho-K.

RESULTS

A total of 253 online questionnaires were analysed after excluding those with wrong information. Most participants (89.7%) were mothers and had university-level or higher education (72.3%); 67.6% of them could achieve a score equal or higher than 60% correct rate on knowledge items. In addition, 39.3% of participants had high myopia (spherical equivalent ≦ 6.0 diopters). The mean age at onset of myopia was 7.75 years for children, and 57.4% wore Ortho-K lenses for less than a year. Full compliance rate was 22.8%, as reported by fathers or mothers. The compliance rate for follow-up visits significantly increased with provision of axial length information in follow-up visits, knowledge of axial length changes as an effect of myopia control, and Ortho-K use for less than 6 months. The compliance rate for wear and care was significantly associated with high myopia in one of parents, high education level, early onset of myopia in children, knowledge of Ortho-K and myopia control, and Ortho-K use for less than 6 months.

CONCLUSION

These results indicate the need for a comprehensive education programme for parents with young myopic children to ensure strict adherence to fitting and wear protocols and good follow-up of Ortho-K lenses.

Near Infrared (NIR) Light Therapy of Eye Diseases: A Review

Near infrared (NIR) light therapy, or photobiomodulation therapy (PBMT), has gained persistent worldwide attention in recent years as a new novel scientific approach for therapeutic applications in ophthalmology. This ongoing therapeutic adoption of NIR therapy is largely propelled by significant advances in the fields of photobiology and bioenergetics, such as the discovery of photoneuromodulation by cytochrome c oxidase and the elucidation of therapeutic biochemical processes. Upon transcranial delivery, NIR light has been shown to significantly increase cytochrome oxidase and superoxide dismutase activities which suggests its role in inducing metabolic and antioxidant beneficial effects. Furthermore, NIR light may also boost cerebral blood flow and cognitive functions in humans without adverse effects. In this review, we highlight the value of NIR therapy as a novel paradigm for treatment of visual and neurological conditions, and provide scientific evidence to support the use of NIR therapy with emphasis on molecular and cellular mechanisms in eye diseases.

Efficacy in myopia control

There is rapidly expanding interest in interventions to slow myopia progression in children and teenagers, with the intent of reducing risk of myopia-associated complications later in life. Despite many publications dedicated to the topic, little attention has been devoted to understanding 'efficacy' in myopia control and its application. Treatment effect has been expressed in multiple ways, making comparison between therapies and prognosis for an individual patient difficult. Available efficacy data are generally limited to two to three years making long-term treatment effect uncertain. From an evidence-based perspective, efficacy projection should be conservative and not extend beyond that which has been empirically established. Using this principle, review of the literature, data from our own clinical studies, assessment of demonstrated myopia control treatments and allowance for the limitations and context of available data, we arrive at the following important interpretations: (i) axial elongation is the preferred endpoint for assessing myopic progression; (ii) there is insufficient evidence to suggest that faster progressors, or younger myopes, derive greater benefit from treatment; (iii) the initial rate of reduction of axial elongation by myopia control treatments is not sustained; (iv) consequently, using percentage reduction in progression as an index to describe treatment effect can be very misleading and (v) cumulative absolute reduction in axial elongation (CARE) emerges as a preferred efficacy metric; (vi) maximum CARE that has been measured for existing myopia control treatments is 0.44 mm (which equates to about 1 D); (vii) there is no apparent superior method of treatment, although commonly prescribed therapies such as 0.01% atropine and progressive addition spectacles lenses have not consistently provided clinically important effects; (viii) while different treatments have shown divergent efficacy in the first year, they have shown only small differences after this; (ix) rebound should be assumed until proven otherwise; (x) an illusion of inflated efficacy is created by measurement error in refraction, sample bias in only treating 'measured' fast progressors and regression to the mean; (xi) decision to treat should be based on age of onset (or refraction at a given age), not past progression; (xii) the decreased risk of complications later in life provided by even modest reductions in progression suggest treatment is advised for all young myopes and, because of limitations of available interventions, should be aggressive.

Effect of Defocus Incorporated Multiple Segments Spectacle Lens Wear on Visual Function in Myopic Chinese Children

Purpose

To compare visual function of myopic children who had worn either defocus incorporated multiple segment (DIMS) spectacle lenses or single vision (SV) spectacle lenses over two years.

Methods

We included 160 Chinese myopic (−1 diopter [D] to −5 D) children aged 8 to 13 years in a randomized clinical trial; they wore either DIMS lenses (DIMS; n = 79) or regular SV spectacles lenses (n = 81) full time for 2 years. Visual function, including high-contrast visual acuity (VA) and low-contrast VA at distance and near, binocular functions, and accommodation, before, during, and after 2 years of spectacle wear were assessed when both groups wore SV corrections. Changes of visual function between the two groups and within groups were compared.

Results

There were no statistically significant differences in the 2-year visual function changes between DIMS and SV groups (repeated measures analysis of variance with group as factor; P > 0.05). Statistically significant improvement in the best-corrected distance high-contrast VA (P < 0.001) and stereoacuity score (P < 0.001) were found after DIMS lens wear over 2 years. Similar findings were observed after SV spectacle lens wear. For both the DIMS and SV groups, there were statistically significant decreases in accommodative lag, monocular and binocular amplitude of accommodation after two years (P < 0.01), but not in the changes in distance low-contrast VA, near high-contrast VA, near low-contrast VA, or phoria.

Conclusions

Although changes in some visual function were shown during 2 years of DIMS lens wear, similar changes were found with SV lens wear. Wear of DIMS spectacle lenses for 2 years does not adversely affect major visual function when children return to SV corrections.

Translational Relevance

DIMS spectacle lenses did not cause any adverse effects on visual function.

Patterns of Use and Knowledge about Contact Lens Wear amongst Teenagers in Rural Areas in Malaysia

BACKGROUND

Contact lenses (CLs) are more popular than spectacles for vision correction amongst the youth. Knowledge about the risks of wearing CLs is critical especially for those with poor access to public health education. This study investigates the patterns of use and level of knowledge about CL wear amongst teenagers living in rural areas in Selangor, Malaysia using a set of validated questionnaires.

METHODS

A total of 8500 self-administered questionnaires were distributed in eight selected secondary schools. The results were analysed using descriptive statistics.

RESULTS

A total of 2474 (29%) completed questionnaires were collected. The mean age of the respondents was 14.8 ± 1.5 years, and approximately 7.2% were CL wearers. The majority of the wearers were females (76.0%) and wore soft CLs (92.2%). Cosmetic purposes (58.1%) and comfort (24.6%) were the main reasons for wearing CLs. Many of the respondents purchased their lenses from optical shops (50.1%) and beauty accessory shops (15.6%), and approximately 10% did not disinfect their lenses properly. Regarding knowledge about CL care, approximately 56% of the respondents responded correctly.

CONCLUSION

Half of the respondents do not have sufficient knowledge about the risks of wearing CLs. Thus, aggressive public health education aimed at teenagers is needed to prevent improper CL usage.

Contrast sensitivity and visual acuity in subjects wearing multifocal contact lenses with high additions designed for myopia progression control

OBJECTIVES

To assess the visual performance of multifocal contact lenses (MFCLs) with high addition powers designed for myopia control.

METHODS

Twenty-four non-presbyopic adults (mean age 24 years, range 18-36 years) were fitted with soft MFCLs with add powers of +2.0 D (Add2) and +4.0 D (Add4) (RELAX, SwissLens) and single vision lenses (SVCL; Add0) in a counterbalanced order. In this double-masked study, half of the participants were randomly fitted with 3 mm-distance central zone MFCLs while the other half received 4.5 mm-distance central zone MFCLs. Visual acuity was measured at distance (3.0 m) and at near (0.4 m). Central and peripheral contrast sensitivity was evaluated at distance using the Gabor patch test. The area under the logarithmic contrast sensitivity function curve (ALCSF) was calculated and compared between the groups (i.e. different additions powers used).

RESULTS

Near and distance visual acuities were not affected by the lenses, neither Add2 nor Add4, when compared to Add0, however, CZ3 significantly reduced distance visual acuity with Add4 when compared to CZ4.5 (-0.08 logMAR vs. for CZ3 and -0.18 logMAR for CZ4.5, p = 0.013). MFCLs impaired central ALCSF only when Add2 was used (15.99 logCS for Add2 and 16.36 logCS for SVCLs, p = 0.021). Peripheral ALCSF was statistically lower for both addition powers of the MFCLs when compared to SVCLs (12.70 for Add2 and Add4, 13.73 for SVCLs, p = 0.009). The above effects were the same for both central zones used.

CONCLUSIONS

MFCLs with CZ3 diameter and high add power (Add4) slightly reduced distance visual acuity when compared to CZ4.5 but no reduction in this parameter was found with medium add power (Add2). Central contrast sensitivity was impaired only by MFCLs with the lower add power (Add2). Both add powers in the MFCLs reduced peripheral contrast sensitivity to a similar extent.

Accommodation response and spherical aberration during orthokeratology

PURPOSE

To evaluate the changes in the accommodative response and in the corneal and internal spherical aberration during 3 months of wear of orthokeratology lenses from the baseline.

METHODS

Fifty children aged 8 to 17 were recruited for a prospective study and were fitted with orthokeratology lenses. Refraction without cycloplegia, high and low uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), accommodation lag, horizontal near phoria without correction, corneal topography, corneal, and total wavefront aberration were performed at baseline, 1 day, 1 week, 1 month, and 3 months. Data were analyzed by Student's t test for related samples, repeated measures ANOVA test, and Pearson correlation test.

RESULTS

The spherical equivalent (SE) before and after 3 months was - 3.33 ± 1.60 D and - 0.30 ± 0.46 D, respectively. Accommodation lag was 0.53 ± 0.38 D and 0.20 ± 0.33 D at baseline and at 3 months, respectively. A moderate correlation between lag at the baseline and its change between baseline and the 3-month visit was found (P < 0.05; R = 0.748). The spherical aberration (SA) increased for anterior corneal and total measurement, being statistically significant for all visits (P < 0.05). The internal SA decreased: - 0.105 ± 0.006 at baseline and - 0.196 ± 0.203 at 1 week (P < 0.05). No difference between baseline and the follow-up visits in posterior corneal SA was found (P > 0.05) CONCLUSION: The negative SA of the lens increases during OK treatment compensated for the increase of the anterior corneal surface positive SA, in addition to increasing the accommodative response.

Influence of Corneal Topographic Parameters in the Decentration of Orthokeratology

OBJECTIVE

To investigate the lens decentration (LD) of orthokeratology (ortho-k) and the association between pretreatment corneal topographic parameters and LD of the ortho-k.

METHODS

Fifty right eyes of 50 myopes wearing ortho-k lenses were included in the prospective study. Corneal topography was conducted pretreatment to get topographic corneal parameters, including flat-K (K1); steep-K (K2); corneal astigmatism (CA), CA at 0 to 3 mm (3 mm-CA), 3 to 5 mm (5 mm-CA), 5 to 7 mm (7 mm-CA); surface asymmetry index (SAI); surface regularity index; the curvature of best-fit sphere; the diameter of cornea (DC); the distance from the corneal center to the corneal vertex (CCCV); flat eccentricity (E1), steep eccentricity (E2), and E1/E2 (E ratio); and the corneal curvature differences between the nasal and temporal quadrants at 0 to 3 mm (3 mm-Knt), and the corneal curvature differences between the superior and inferior quadrants at 0 to 3 mm (3 mm-Ksi), 5 mm-Knt (at 3-5 mm), 5 mm-Ksi (at 3-5 mm), 7 mm-Knt (at 5-7 mm), and 7 mm-Ksi (at 5-7 mm). The relationship between these cornea topographic parameters and LD of the ortho-k was tested using stepwise multiple linear regression models.

RESULTS

The mean magnitude of LD was 0.51±0.23 mm (0.06-1.03 mm). According to the stepwise analysis, 4 factors were associated with the overall LD (P<0.01): SAI (β=0.252), CCCV (β=0.539), 5 mm-CA (β=-0.268), and 3 mm-Ksi (β=-0.374); 5 factors were associated with the horizontal LD (P<0.01): DC (β=0.205), CCCV (β=0.881), 3 mm-CA (β=-0.217), 5 mm-Knt (β=0.15), and 3 mm-Ksi (β=-0.18); and 3 factors were associated with the vertical LD (P<0.01): SAI (β=0.542), 5 mm-CA (β=-0.188), and 3 mm-Ksi (β=-0.213).

CONCLUSION

Lens decentration is most common, but in most cases, the amount of LD is moderate and acceptable. The magnitude of LD can be predetermined by topographic corneal parameters. Surface asymmetry index, CCCV, 5 mm-Knt, and 3 mm-Ksi may be more preferable parameters in terms of the assessment of LD of ortho-k.