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Identification of the baseline chracteristics for children undergoing orthokeratology with relatively fast myopia progression can allow a more accurate determination of the risk/benefit ratio. This study aimed to investigate if baseline corneal biomechanics can classify relatively slow and fast myopia progression in children. Children aged six to 12 years with low myopia (0.50 to 4.00 D) and astigmatism (less than or equal to 1.25 D), were recruited. Participants were randomised to be fitted with orthokeratology contact lenses with a conventional compression factor (0.75 D, n = 29) or an increased compression factor (1.75 D, n = 33). Relatively fast progressors were defined as participants who had axial elongation of 0.34 mm or above per 2 years. A binomial logistic regression analysis and a classification and regression tree model were used in the data analysis. The corneal biomechanics were measured with a bidirectional applanation device. The axial length was measured by a masked examiner. As there were no significant between-group differences in the baseline data (all p > 0.05), data were combined for analysis. The mean ± SD axial elongation for relatively slow (n = 27) and fast (n = 35) progressors were 0.18 ± 0.14 mm and 0.64 ± 0.23 mm per 2 years, respectively. The area under the curve (p2area1) was significantly higher in relatively fast progressors (p = 0.018). The binomial logistic regression and classification and regression tree model analysis showed that baseline age and p2area1 could differentiate between slow and fast progressors over 2 years. Corneal biomechanics could be a potential predictor of axial elongation in orthokeratology contact lens-wearing children. [ABSTRACT FROM AUTHOR]

Oxygen transmissibility required to avoid corneal oedema during closed-eye soft lens wear is estimated to be 125.0 × 10 SP -9 sp barrer.[7] However, orthokeratology lenses do not cover the entire cornea, so the critical oxygen transmissibility required to avoid corneal oedema during overnight orthokeratology lens wear is unknown. Keywords: COVID-19; microcystic oedema; microcysts; orthokeratology EN COVID-19 microcystic oedema microcysts orthokeratology 736 740 5 08/03/21 20211101 NES 211101 Introduction The presence of small (15-50 µm), irregular-shaped microcysts with defined borders in the corneal epithelial layer indicates chronic corneal hypoxia during extended contact lens wear,[1] but may also be observed in non-contact lens wearers with less severity.[2] They usually cause mild or no visual impairment. The significant lens decentration observed at the 18-month visit could have changed the lens-cornea relationship. [Extracted from the article]

Background: To investigate the influence of compression factor upon changes in ocular higher‐order aberrations (HOAs) in young myopic children undergoing orthokeratology treatment. Methods: Subjects aged between six and < 11 years, with low myopia (0.50–4.00 D inclusive), low astigmatism (≤ 1.25 D), and anisometropia (≤ 1.00 D), were randomly assigned to wear orthokeratology lenses of different compression factors in each eye (one eye 0.75 D and the fellow eye 1.75 D). HOAs were measured weekly over one month of lens wear. Wavefront analysis was conducted over a 5‐mm pupil using a sixth order Zernike polynomial expansion. Linear mixed models were used to examine the individual Zernike co‐efficients and specific root‐mean‐square (RMS) error (spherical, comatic, total HOAs) metrics and their changes between the two eyes during the study period. Results: Twenty‐eight myopic (mean manifest spherical equivalent refraction: −2.10 ± 0.58 D) children (median [range] age: 9.3 [7.8–11.0] years) were analysed. Significant interocular differences in HOAs at baseline were observed for Z6−6 and Z6−4 only (both p < 0.05). During the lens wear period, eyes fitted with the increased compression factor showed greater changes in primary spherical aberration (Z40, p = 0.04) and RMS values for spherical and total HOAs (both p < 0.01). Considering data from both eyes together, after adjusting for the paired nature of the data, some other Zernike terms (Z31 and Z60, both p < 0.01) and the RMS value of comatic aberrations (p < 0.001) significantly increased after one month of orthokeratology treatment. The increase in primary spherical aberration (Z40) was positively correlated with the reduction in spherical equivalent refractive error, but only in eyes fitted with the increased compression factor (r = 0.69, p < 0.001). Conclusions: Increasing the orthokeratology compression factor by 1.00 D significantly altered some HOAs, particularly spherical aberration. Given the association between positive spherical aberration and eye growth in children, further research investigating the influence of orthokeratology compression factor on axial eye growth is warranted. [ABSTRACT FROM AUTHOR]

The prevalence of myopia in children is increasing worldwide and is viewed as a major public health concern. This increase has driven interest in research into myopia prevention and control in children. Although there is still uncertainty in the risk factors underlying differences in myopia prevalence between ethnic groups, rates in children of East Asian descent are typically higher regardless of where they live. Mounting evidence also suggests that myopia prevalence in children increases with age. Earlier commencement and more rigorous education systems in these countries, resulting in more time spent on near-work activities and less time on outdoor activities, may be responsible for the earlier age of myopia onset. However, to date, the mechanisms regulating myopia onset and progression are still poorly understood. Findings from several studies have shown orthokeratology to be effective in slowing axial elongation and it is a well-accepted treatment, particularly in East Asian regions. While our understanding of this treatment has increased in the last decade, more work is required to answer questions, including: How long should the treatment be continued? Is there a rebound effect? Should the amount of myopia control be increased? To whom and when should the treatment be offered? Practitioners are now faced with the need to carefully guide and advise parents on whether and when to undertake a long somewhat complex intervention, which is costly, both in time and money. In the near future, a greater demand for effective prophylaxis against childhood myopia is envisaged. Other than orthokeratology, atropine therapy has been shown to be effective in slowing myopia progression. While its mechanism of control is also not fully understood, it is likely that it acts via a different mechanism from orthokeratology. Thus, a combined treatment of orthokeratology and atropine may have great potential to maximise the effectiveness of myopia control interventions. [ABSTRACT FROM AUTHOR]

Contact lens wear is a popular, convenient and effective method for vision correction. In recent years, contact lens practice has expanded to include new paradigms, including orthokeratology; however, their use is not entirely without risk, as the incidence of infection has consistently been reported to be higher in contact lens wearers. The explanations for this increased susceptibility have largely focused on physical damage, especially to the cornea, due to a combination of hypoxia, mechanical trauma, deposits and solution cytotoxicity, as well as poor compliance with care routines leading to introduction of pathogens into the ocular environment. However, in recent years, with the increasing availability and reduced cost of molecular techniques, the ocular environment has received greater attention with in-depth studies of proteins and other components. Numerous proteins were found to be present in the tears and their functions and interactions indicate that the tears are far more complex than formerly presumed. In addition, the concept of a sterile or limited microbial population on the ocular surface has been challenged by analysis of the microbiome. Ocular microbiome was not considered as one of the key sites for the Human Microbiome Project, as it was thought to be limited compared to other body sites. This was proven to be fallacious, as a wide variety of micro-organisms were identified in the analyses of human tears. Thus, the ocular environment is now recognised to be more complicated and interference with this ecological balance may lead to adverse effects. The use of contact lenses clearly changes the situation at the ocular surface, which may result in consequences which disturb the balance in the healthy eye. [ABSTRACT FROM AUTHOR]

Purpose The aim was to assess the consistency of corneal epithelial cell viability of an ex vivo porcine eye model. Method Six porcine eye models (four test and two control) were prepared for each experiment. The model has a computer-controlled mechanical arm, which could move the eyelid of the porcine eye and apply phosphate buffered saline to simulate blinking and lacrimation. The four test eyes were set up to simulate evaporative dry eyes with simulated lacrimation and blinking (one blink and one drop of buffered saline per minute) over three hours. Control A models were set up to collect pre-experimental baseline data, while those of control B were the same as the test eyes but without lacrimation and blinking simulation. All porcine eyes were kept in a closed chamber with temperature and humidity well controlled. After three hours, the cells of all eyes (except control A, which were assessed immediately before commencement of the experiment) were assessed. The eyes were first dipped into 0.4 per cent trypan blue solution. Following the dissection and separation of the cells, the number of dead cells were then counted under the microscope with a field size of 0.25 mm2. The experiment was repeated 11 times. Results No significant differences were found in the number of dead cells among the four test eyes in both the central and peripheral cornea. There were significantly more dead cells in the test eyes compared to control A but significantly less when compared to control B. More dead cells were found in the central cornea than the peripheral cornea in the test eyes but the difference was not observed in controls A and B. Conclusion Epithelial cell viabilities among the four porcine eye models with simulated lacrimation and blinking were consistent. The majority of cells were viable before the experiment and simulated lacrimation and blinking maintained more viable cells over time. [ABSTRACT FROM AUTHOR]

Purpose Reports on cytotoxic effects of rigid gas-permeable lens multipurpose solutions, which remain important because of increasing popularity of orthokeratology, are limited. This study determined cytotoxic effects of rigid gas-permeable lens multipurpose solutions on human corneal epithelial cells and assessed the proliferation rate at different levels of cell membrane damage. Methods The human corneal epithelial cells were exposed to multipurpose solutions containing chlorhexidine gluconate (0.003%) and polyaminopropyl biguanide ( PHMB) (0.0005%) ( MPS- A), PHMB (0.0005%) ( MPS- B) and PHMB (0.0001%) ( MPS- C) for one, five and 10 minutes. Following staining with Annexin V- FITC/7- AAD, cell viability and membrane integrity were assessed by flow cytometry. Effects of exposure to concentrations of 10 to 40 per cent multipurpose solutions for 12 hours on the metabolic rate of human corneal epithelial cells were assessed by 3-(4-,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide ( MTT) cell proliferation assay. Recovery rates were assessed after re-culture for 96 hours at 37° C. Results MPS- A exposure caused the highest percentage of early and late necrotic cells for all exposure times and was significantly higher than other multipurpose solutions (p < 0.0001). After 10 minutes exposure, almost 40 per cent of cells in MPS- A but less than five per cent in MPS- B or MPS- C, were in late necrotic stage. After 12 hours of exposure, cell activity was significantly reduced in a dose-response manner for MPS- A treated cells only (p > 0.05). After 96 hours of re-culture, all exposed cells showed some reduction in viability but the effects of exposure to 30 and 40 per cent MPS- A resulted in loss of viability. Conclusion The presence of chlorhexidine appeared to increase cytotoxicity of multipurpose solutions for rigid gas-permeable lenses. This was apparent in both increased levels of necrotic cells on initial exposure and reductions in viability after prolonged exposures at lower dilutions. Multipurpose solutions containing PHMB as a preservative, while not causing acute cytotoxicity, did affect cell viability following exposure to diluted solutions. This indicated it is inadvisable to expose the cornea to multipurpose solutions but rather to rinse lenses with saline before insertion and use artificial tears for rewetting. [ABSTRACT FROM AUTHOR]

Purpose: The aim was to determine the cytotoxic effects of three multipurpose solutions (MPS) on human corneal epithelial cells (HCEC) and to assess the metabolic rates of recovering cells at different levels of cell membrane damage. Method: The effects of one to 15 minutes exposure to multipurpose solutions containing polyquaternium-1 (MPS-A), polyaminopropyl biguanide (MPS-B) and polyhexanide (MPS-C) on HCEC were determined. Recovery rates at different levels of cell membrane damage were assessed after re-culture for two hours at 37°C. Cell viability and membrane integrity were assessed using Annexin V-FITC/7-AAD staining and flow cytometry. Effects of concentrations of 10 to 40 per cent multipurpose solutions on the metabolic rate of recovering HCEC were assessed using a Vybrant MTT cell proliferation assay kit. Results: The highest percentage of late necrotic cells resulted after exposure to MPS-A compared with other solutions and the control (p < 0.001). The percentages of early necrotic cells after 10 and 15 minutes of soaking in MPS-B were significantly higher than the control and other multipurpose solutions (p < 0.001). Although MPS-C exposure also resulted in statistically significant higher percentages of early necrotic cells than the control (p < 0.005), these differences were small. No recovery was noted when HCEC treated with multipurpose solutions were re-cultured, with numbers of dead cells in MPS-B-treated cultures increasing fourfold. The MTT assay showed significant dose-response decreases of 500 nm absorbance for all MPS-treated cells. In 40 per cent MPS-A-treated HCEC, lack of activity indicated the cells were non-viable. Conclusions: Multipurpose solutions induced varying levels of irreversible tissue sensitivity reactions, with MPS-A showing the greatest effects. The solutions damaged cell integrity and reduced metabolic rates suggesting delayed healing ability. The formulations of multipurpose solutions need to balance antimicrobial effectiveness with low cytotoxicity, which might not be currently possible to achieve. In light of our results, we suggest that contact lens wearers should be advised to rinse the soaked lenses with saline before lens insertion. [ABSTRACT FROM AUTHOR]

Purpose: The aim was to determine the corneal parameters in low to moderate myopic Chinese children and to investigate the differences in these corneal parameters between male and female subjects. Methods: Refractive errors and corneal parameters were retrieved from subjects who had participated in studies on myopia and astigmatism in 2008 and 2009. Corneal parameters including simulated K (Sim K) and asphericity (Q) at 9.0 mm chord and horizontal visible iris diameter (HVID) were determined for 217 children (112 males and 105 females aged from six to 12 years) using the Medmont E300 topographer. Results: The Q of the corneas was -0.44 ± 0.12 along the flat meridian and -0.22 (-0.70 to 0.63) along the steep meridian. The HVID and Sim K of male subjects were larger and flatter than female subjects. The mean HVID of male and female subjects was 11.3 ± 0.3 mm and 11.1 ± 0.30 mm, respectively. The mean Sim K value in male and female subjects was 7.91 ± 0.24 mm and 7.79 ± 0.21 mm, respectively, along the flat meridian, and was 7.65 ± 0.26 mm and 7.53 ± 0.24 mm, respectively, along the steep meridian. Conclusions: All corneas were prolate elliptical in shape along the flat meridian and the peripheral flattening rate was found to be greater along the flat meridian. A greater flattening rate was observed in the corneas of Chinese children when compared to that of Caucasian children. The Q between male and female subjects was not significantly different. Male subjects tended to have larger HVID and flatter corneas than female subjects. [ABSTRACT FROM AUTHOR]

The article offers information on toric orthokeratology (ortho-K) that helps in controlling myopia. It offers information on spherical reverse geometry lens (RGL) used in orthokeratology for correcting myopia. It mentions that ortho-K can lead to induced astigmatism and poor vision. It mentions that Medmont E300 corneal topographer is used for corneal topography.

Purpose: To compare the visual outcome of Soflens Daily Disposables and Soflens Daily Disposable for Astigmatism (Bausch & Lomb, Rochester, NY, USA) when worn by subjects with low astigmatism. Methods: Forty-one subjects (aged 19 to 40 years) with myopia between 0.50 D to 6.00 D and astigmatism not more than -1.25 D in at least one eye were recruited and fitted with spherical and toric soft contact lenses in this double-masked, non-dispensing cross-over study. High and low contrast logMAR visual acuities were measured over the lenses. At the end of the study, each subject was asked to complete a questionnaire on vision, initial comfort and ease of handling of the two lens types. Results: Monocular and binocular high and low contrast logMAR visual acuities were significantly better with the toric lenses compared with the spherical lenses (p < 0.01). Results from the questionnaire showed a significantly higher grade for vision with the toric lenses than with the spherical lenses (p = 0.003) but no significant differences in initial comfort and ease of handling between spherical and toric lenses (p > 0.21). Conclusions: The results of the present study show that both subjective and objective vision in myopic subjects with low astigmatism improves significantly when corrected with toric lenses compared with spherical lenses. [ABSTRACT FROM AUTHOR]

Background: Cycloplegia has been shown to have no effect on axial length measurement made with the IOLMaster in adults. The current study aimed at evaluating the effect of cycloplegia on axial length and anterior chamber depth (ACD) measurements made with the IOLMaster and an ultrasonic biometer in children. Methods: Pre- and post-cycloplegic axial length and ACD were measured with the IOLMaster followed by the Sonomed A-5500 in 31 children aged from seven to 15 years by the same examiner. The 95% limits of agreement (LoA) were determined, if there were no significant correlations found between the mean differences and their means. Results: Seven subjects were excluded. Results from the remaining 24 subjects show that the effects of cycloplegia, instruments, and interaction between cycloplegia and instrument on axial length measurement were insignificant (repeated measure ANOVA F1,23 < 2.19, p > 0.15). The 95% LoA in cycloplegia were better with the IOLMaster (-0.04 to 0.04 mm) than with the Sonomed A-5500 (-0.13 to 0.14 mm). The 95% LoA between the two instruments were similar with and without cycloplegia (pre-cycloplegia: -0.20 to 0.27 mm; post-cycloplegia: -0.17 to 0.22 mm). There was no significant interaction between cycloplegia and instrument in ACD measurement (repeated measure ANOVA F1,23= 0.85, p = 0.37), however, ACD was 0.05 to 0.06 mm shorter before cycloplegia (repeated measure ANOVA F1,23= 44.70, p < 0.001) and was 0.06 to 0.08 shorter measured with the IOLMaster (repeated measure ANOVA F1,23= 28.81, p < 0.001). Conclusion: Effects of cycloplegia on axial length measurement in children made with IOLMaster and Sonomed A-5500 were insignificant. In contrast, ACD measurement was significantly affected by cycloplegia and different instruments. [ABSTRACT FROM AUTHOR]

Contact lens hygiene has long been recognised as key to the prevention of contact-lens associated infection and inflammation. Microbial keratitis (MK) is the only serious and potentially sight-threatening contact lens adverse event. International studies including recent research in Asia Pacific show that MK is rare but, as the consequences can be severe, it is important to minimise the risk factors. Studies continue to show that one of the key risk factors is lens and lens case hygiene. Therefore, it is also useful to review the behaviour of our patients, to see how closely they follow the recommended hygiene practices. Recent studies in various regions have shown that patients’ lens care habits do not meet a required standard. Patients can become complacent and thus non-compliant with lens care instructions. Furthermore, they do not understand the high risk of some behaviour and they are not hearing the practitioner when instructions and reminders are given. Further education is important to improve patient compliance and safety. The Asia Pacific Contact Lens Care Summit held in Singapore urged the industry and practitioners to restore the emphasis of proper lens care, including the ‘rub and rinse’ technique, and developed a new set of guidelines to help eye-care professionals educate their patients on the importance of proper contact lens care to avoid eye infections. The summit also presented the latest research on how to avoid corneal staining, another important element of contact lens care. This review provides a summary of the summit presentations and the science behind these guidelines. [ABSTRACT FROM AUTHOR]

Purposes: The aim of this study was to analyse clinical data of children undergoing orthokeratology (ortho-k) and to investigate patients’/parents’ perspective on ortho-k via telephone interviews. Methods: Clinical records of children undergoing ortho-k from a university optometry clinic were reviewed and the effects of ortho-k on refraction, vision and cornea were investigated. A telephone interview was conducted to solicit patients’/parents’ perspective of the treatment. Results: One hundred and eight files were reviewed. Median age of the children was nine years (range six to 15); mean (±SD) pre-treatment refractive sphere was -3.56 ± 1.49 D and the median refractive cylinder was -0.50 D (range zero to -4.25 D). Significant refractive spherical reduction (58 per cent), improvement in unaided vision and corneal topographical changes were noted after only one night of wear. No significant change in astigmatism was found. Corneal staining was the most commonly observed complication with ortho-k and more than 80 per cent of patients were advised to apply ocular lubricants to loosen the lens before lens removal. Ortho-k was mainly undertaken for myopic control and about 90 per cent of the respondents reported good/very good unaided vision after ortho-k and ranked the treatment as satisfactory or very good. Lens binding and ocular discharge were the most frequently reported problems during the treatment. Conclusion: Under close monitoring, overnight ortho-k is effective and safe for reducing low to moderate myopia and the treatment is well accepted by the children. [ABSTRACT FROM AUTHOR]

Purpose: The aims were to determine the level of compliance of contact lens wearers, to identify which procedures have highest levels of non-compliance and to study the effectiveness of a compliance enhancement strategy on the level of compliance. Methods: The level of compliance for each subject was evaluated with a self-administered questionnaire together with microbiological examination of their contact lenses, lens cases and lens care solutions. The effect of an intervention to improve the level of compliance was determined by a controlled trial. A regular self-review exercise on proper lens handling was given to the test group once every three months for 12 months. The levels of compliance and contamination of contact lenses and lens care accessories between test and control groups were compared at the end of the 12-month period to evaluate the effect of the intervention. Results: Sixty-five subjects who were experienced contact lens wearers were recruited and 60 completed the study. All showed some degree of non-compliance in the care of their contact lenses and lens accessories. Most (about 60 per cent) were non-compliant with at least six of a total of 15 lens care procedures. The most common non-compliant behaviour among contact lens wearers was associated with the care of the lens case. By the end of the study period, our compliance enhancement strategy did not appear to have had a significant effect on the behaviour of our subjects, except for improvement in the care of lens cases. Compliance for other procedures improved in both test and control groups. Conclusion: All subjects showed some degree of non-compliance and the spectrum of non-compliance was wide. The poorest levels of compliance were associated with care of the lens case, which was also the most frequently contaminated item. Our compliance enhancement strategy showed a significant difference in improvement in compliance between the intervention and control groups only in the care of lens cases. [ABSTRACT FROM AUTHOR]

Background: Our aim was to compare the clinical performance of a biweekly (second generation) silicone hydrogel lens and a biweekly hydrogel lens worn for daily wear modality. Methods: We used a double-masked study, in which non-presbyopic, asymptomatic and adapted soft lens wearers were recruited. Subjects wore a silicone hydrogel lens in one eye and a hydrogel lens in the other (lens types and eyes were randomly assigned) for one month. Lenses were replaced every two weeks. Contact lens fitting, pre-lens tear film thinning time, vision, corneal integrity and lens deposits were assessed before and every fortnight after delivery of new lenses. A questionnaire was used to compare the subjective performance of the two lens types. Results: Thirty of the 33 subjects completed the study. There were no significant differences in lens fitting (centration and movement), pre-lens tear film thinning time, vision or corneal integrity between the two lens types. Statistically, there was no significant difference in lens deposits between the two lens types but silicone hydrogel lenses tended to have more Grade 3 to 4 lipid deposits than hydrogel lenses. Subjects found no significant differences between the two lens types in terms of vision and comfort. Preference for silicone hydrogel lenses increased from 33 at the first after-care visit to 50 per cent at the second after-care visit. Conclusion: This short-term study demonstrates that the performance of silicone hydrogel and hydrogel lenses is comparable but the former tends to build up more lipid deposits than the latter. We did not find better performance in terms of ocular integrity of silicone hydrogel lenses compared to the hydrogel lenses, probably because the subjects were adapted asymptomatic contact lens wearers before commencing the study. Contact lens wearers having hypoxia-related problems are likely to benefit from using silicone hydrogel lenses, as these lenses provide at least three times more oxygen than conventional hydrogel lenses. [ABSTRACT FROM AUTHOR]

Purpose: Our aim was to determine the repeatability of measurements of axial length (AL) and anterior chamber depth (ACD) made with two ultrasonic biometers and the IOLMaster in a group of non-orthokeratology (ortho-k) adult subjects and to investigate the agreement among instruments in children undergoing ortho-k therapy and in children wearing spectacles. Methods: To determine repeatability, AL and ACD were measured twice in 22 non-ortho-k young adults using two A-scan ultrasonic biometers (A-5500 and A-2500) and the IOLMaster. To determine agreement, AL and ACD were measured with the same instruments in 30 children undergoing ortho-k therapy and 30 spectacle-wearing children. Results: In the adult subjects, there were no significant differences in ACD and AL measurements obtained from the three instruments (repeated measures ANOVAs, p > 0.05). There was also no significant between-measurement difference for each instrument. The between-measurement agreement was better for the IOLMaster (95% limits of agreement (LA): -0.04 and +0.05 mm for both AL and ACD) than for the two A-scan ultrasonic biometers (95% LA: -0.12 and +0.11 mm for AL; -0.22 and +0.27 mm for ACD). Among the children, AL measurements with all three instruments were not significantly different from each other for both the children undergoing ortho-k therapy and those wearing spectacles (repeated measures ANOVAs, p > 0.05). The 95% LA of differences obtained from any two instruments were also comparable for both groups of subjects (within -0.20 mm and +0.20 mm). ACD measurements of the children were significantly different among the three instruments (repeated measures ANOVAs, p < 0.05). No significant differences in ACD measurements were found between A-5500 and A-2500 for both groups of children (paired t tests, p > 0.017). Conclusions: The repeatability of AL and ACD measurements with the IOLMaster was very good, and was better than with the A-scan ultrasonic biometers. The agreements in AL measurements between A-scan ultrasonic biometers and IOLMaster were comparable in both the ortho-k and the spectacle-wearing subjects, and were comparable to the repeatability of the A-scan ultrasonic biometers. ACD measurements between A-scan ultrasonic biometry and the IOLMaster were not comparable. AL measurements with the IOLMaster can replace the measurements from the two A-scan ultrasonic biometers used, however, the reverse is not true. AL and ACD measurements with all three instruments were unaffected by the flattened cornea following ortho-k lens wear. [ABSTRACT FROM AUTHOR]

Background: To investigate the influence of compression factor upon changes in ocular higher-order aberrations (HOAs) in young myopic children undergoing orthokeratology treatment.Methods: Subjects aged between six and < 11 years, with low myopia (0.50-4.00 D inclusive), low astigmatism (≤ 1.25 D), and anisometropia (≤ 1.00 D), were randomly assigned to wear orthokeratology lenses of different compression factors in each eye (one eye 0.75 D and the fellow eye 1.75 D). HOAs were measured weekly over one month of lens wear. Wavefront analysis was conducted over a 5-mm pupil using a sixth order Zernike polynomial expansion. Linear mixed models were used to examine the individual Zernike co-efficients and specific root-mean-square (RMS) error (spherical, comatic, total HOAs) metrics and their changes between the two eyes during the study period.Results: Twenty-eight myopic (mean manifest spherical equivalent refraction: -2.10 ± 0.58 D) children (median [range] age: 9.3 [7.8-11.0] years) were analysed. Significant interocular differences in HOAs at baseline were observed for Z6-6 and Z6-4 only (both p < 0.05). During the lens wear period, eyes fitted with the increased compression factor showed greater changes in primary spherical aberration ( Z40 , p = 0.04) and RMS values for spherical and total HOAs (both p < 0.01). Considering data from both eyes together, after adjusting for the paired nature of the data, some other Zernike terms ( Z31 and Z60 , both p < 0.01) and the RMS value of comatic aberrations (p < 0.001) significantly increased after one month of orthokeratology treatment. The increase in primary spherical aberration ( Z40 ) was positively correlated with the reduction in spherical equivalent refractive error, but only in eyes fitted with the increased compression factor (r = 0.69, p < 0.001).Conclusions: Increasing the orthokeratology compression factor by 1.00 D significantly altered some HOAs, particularly spherical aberration. Given the association between positive spherical aberration and eye growth in children, further research investigating the influence of orthokeratology compression factor on axial eye growth is warranted. [ABSTRACT FROM AUTHOR]