search
Contact Us
HOME

Journal Search Engine

to

Search Advanced Search Adode Reader(link)
Download PDF Export Citaion korean bibliography PMC previewer
ISSN : 1229-6457(Print)
ISSN : 2466-040X(Online)
The Korean Journal of Vision Science Vol.26 No.1 pp.65-73
DOI : https://doi.org/10.17337/JMBI.2024.26.1.65

Effectiveness and Safety of OK Lens in Controlling Myopia

Lu Yucheng1), Geun-Chang Ryu2)
1)Dept. of Optometry, Dongshin University, Student, Naju
2)Dept. of Optometry, Dongshin University, Professor, Naju
* Address reprint requests to Geun-Chang Ryu (https://orcid.crg/0000-0001-9100-3394) Dept. Optomtry and Vision Science, Dongshin University, Naju TEL: +82-61-330-3553, E-mail: gcryu@dsu.ac.kr
March 6, 2024 March 31, 2024 March 31, 2024

Abstract


Purpose : This study aimed to analyze the refractive errors profiles of myopic adolescents wearing orthokeratology (OK) lenses and conventional single-vision (SV) spectacles to examine the effect of OK lens on the progression of myopia.



Methods : The research method involved 100 adolescent patients who visited the Ophthalmology Department of Beihua University Affiliated Hospital in Jilin Province, China and 50 patients each were divided into an Orthokeratology (OK) lens group and a single-vision glasses group. Both groups of patients were followed up for one year, and changes in visual acuity (VA), spherical equivalent refraction (SE), axial length (AL), corneal endothelial cell count (CEC), central corneal thickness (CCT), intraocular pressure (IOP) were compared. Statistical analysis was performed using SPSS software and independent sample T-test, and p<0.050 was considered statistically significant.



Results : The differences in visual acuity between the two groups were statistically significant (p<0.010). The refractive results revealed a significant decrease in refractive errors after wearing orthokeratology lenses, whereas an increase in refractive errors was observed in patients wearing spectacle glasses. The difference between the two groups was statistically significant (p<0.010). Furthermore, the analysis of the axial length revealed that the axial length increased by 0.18±0.18 mm in of the OK group and 0.61±0.20 mm in the spectacle group. The differences between the two groups were statistically significant (p<0.001). Patients wearing OK lenses showed no significant changes in intraocular pressure, corneal endothelial cell count, and central corneal thickness compared to baseline (p>0.050).



Conclusion : The results showed that OK lenses were more effective in reducing spherical equivalent, improving visual acuity, and slowing down axial length elongation compared to single vision spectacles.


Myopia control , Myopia progression , Orthokeratology (OK) lenses

OK 렌즈의 근시 통제에 대한 효과와 안전성

루위청1), 유근창2)
1)동신대학교 안경광학과, 학생, 나주
2)동신대학교 안경광학과, 교수, 나주

    Ⅰ. Introduction

    Myopia, also known as nearsightedness, causes a decline in distant visual acuity. It results from the relaxation of the eye′s focusing mechanism, allowing light to enter through the pupil and converge in front of the retina's macular region, leading to the formation of diffuse light circles on the retina. Myopia occurs when the shape of the eye or the shape of certain parts of the eye causes light rays to bend (refract) inaccurately. Light rays that should be focused on nerve tissues at the back of the eye (retina) are focused in front of the retina.

    With an improvement in living standards, contemporary individuals not only require the ability to see but also place a greater emphasis on having comfortable and clear visual experiences. It is a globally recognized public health concern. Research data indicates that the prevalence of myopia among adolescents tends to increase with age.1,2) In a relaxed state of accommodation, parallel light rays converge in front of the retina, leading to myopia.3) Currently, approximately 28.3% of the global population is nearsighted, and it is estimated that the number of myopic individuals will reach 4.758 billion by 2050, accounting for 49.8% of the world's population and 9.8% will have high myopia.4,5) The World Health Organization (WHO) has included myopia prevention and control in its global initiative to combat blindness.6)

    The occurrence of myopia is primarily associated with close-up work. Prolonged use of both eyes at close distances can cause the eyes to converge, leading to axial elongation of the eyeballs under the pressure of the extra ocular muscles, ultimately resulting in myopia.7) Currently, a substantial body of literature reports that outdoor activities are an effective means of controlling the progression of myopia in adolescents.8) There are also several other factors contributing to myopia development. Such as family economic conditions, life styles, excessive use of electronic devices, diverse learning methods and high academic workloads9). And high myopia has become a leading cause of blindness and low vision in China.10,11)

    As a country with a large myopic population, China is witnessing a significant trend of myopia at younger ages, consistently holding the top position in myopia rates among children and adolescents globally. According to data from the "China Eye Health White Paper" released by the National Health Commission in 2020, the number of myopic individuals in China rapidly increased from 540 million in 2016 to 660 million in 2020.12) The national myopia incidence rate rose from 39.2% to 47.1%, with a continuous upward trend. According to statistics from Frost Sullivan, the number of individuals under 20 with myopia in China increased from 148 million in 2015 to 169 million in 2019, with an estimated reach of 191 million by 2030. According to data from the National Health Commission, the overall myopia rate among Chinese children and adolescents was 52.7% in 2020. Among them, 6-year-olds had a rate of 14.3%, primary school students 35.6%, junior high school students 71.1%, and high school students 80.5%, indicating a severe trend of myopia at younger ages.13)

    In fact, the rapid increase, younger onset, and severity of the myopic population have become significant characteristics and development trends in China. With the rising incidence of myopia in younger age groups and an increased awareness among consumers regarding myopia prevention and control, orthokeratology lenses have garnered widespread attention as an effective means to slow down the progression of myopia.

    In the past, most research on orthokeratology lenses in China has originated from economically developed regions such as the central and southern coastal areas. However, in the northeastern region, particularly in Jilin Province, relevant studies have been relatively rare. To effectively promote the application of orthokeratology lenses for controlling myopia among adolescents in economically underdeveloped areas like Jilin Province, it is crucial to conduct research with locally-based cases to produce more convincing and region-specific results.

    This study aims to analyze the refractive files of myopic adolescents who wore Orthokeratology (OK) lenses for one year and those who wore conventional single vision lens (SV) spectacles to explore the effects of OK lenses on myopia progression, visual acuity, axial length, corneal endothelial cells, central corneal thickness, intraocular pressure, and other parameters, as well as to compare the clinical efficacy differences in delaying the development of myopia in adolescents. This study aims to provide a more in-depth understanding and objective evaluation of the control effect and safety of orthokeratology lenses on myopia in adolescents, and to further supplement relevant clinical data in the Jilin Province, providing a clinical theoretical basis for the correct, scientific, healthy, and reasonable use of orthokeratology lenses.

    Ⅱ. Subjects and methods

    1. Study Subjects

    100 cases (200 eyes) of adolescent myopia patients who visited the Ophthalmology Clinic department of Beihua University Affiliated Hospital from January 2022 to January 2023 were selected as the study subjects. They were divided into two groups: the OK lens group and the single-vision lens spectacle group, with 50 cases (100 eyes) in each group. All patients' guardians were informed about this study and signed informed consent, and this study was approved by Beihua University Affiliated hospital's ethics committee (2023.No.58). All examinations of the patients were performed by the same fixed personnel.

    The inclusion and exclusion of subjects are shown in Table 1, as detailed in the following section.

    Orthokeratology (OK) lens, made of fluorosilicone acrylate polymer material (Boston Equalens II), with a diameter of 10.2~11.0mm, oxygen permeability coefficient of 127×10-11 cm2 ‧ mLO2/s ‧ mL ‧mmHg, and a central optical zone thickness of 0.24 mm. Euclid orthokeratology (OK) lens have 4 curves design: peripheral curve (0.5 mm), alignment curve1 (0.7 mm), alignment curve2 (0.5 mm), reverse curve (0.5mm)(Fig. 1). Purchased from Euclid Systems Corporation in the United States.

    2. Examination items and methods

    The examination flowchart is as follows Fig. 2.

    3. Research methods

    • Selecting of research subjects

    A total of 110 patients were selected for eligibility, and 50 patients in the OK lens group and 50 patients in the SV spectacle group respectively met the selection criteria for final data analysis (Fig. 3).

    4. Data processing and statistical analysis

    Data processing and statistical analysis were performed using SPSS 27.0.10 software (SPSS Inc., Chicago, IL, USA). For the comparison of various indicators between different time points within each group, repeated measures analysis of variance was used. The results were presented as mean± standard deviation for continuous variables. The comparison of differences in indicators between the two groups before and one year after wearing glasses was performed using a t-test, with p<0.050 considered statistically significant.

    Ⅲ. Results

    There were 50 patients in the OK lens group, including 24 males and 26 females, with an age range of 8 to 15 years and a mean age of (10.62±1.56) years. In the spectacle group, there were 50 patients, including 25 males and 25 females, with an age range of 8 to 15 years and a mean age of (10.78±1.75) years. The two groups of patients showed no significant statistical differences in gender and age (Table 2). Patients in the OK lens group wore lenses every night for 8~10 hours while sleeping, and patients in the spectacle group wore glasses regularly during tall the daytime.

    Before wearing glasses, there was no statistically significant difference in the comparison of each parameter between the two groups, indicating comparability (p>0.050) (Table 3).

    After 1 year of lens wearing, patients wearing OK lenses showed a gradual improvement in visual acuity. The visual acuity had a substantial improvement after one year. In contrast, patients wearing spectacle glasses exhibited a declining trend in visual acuity and a higher degree of reduction was observed after one year. The differences between the two groups were statistically significant (p<0.010, Table 4). The refractive results revealed a significant decrease in refraction after wearing orthokeratology lenses, whereas an increase in refraction was observed in patients wearing spectacle glasses. The difference between the two groups was statistically significant (p<0.010, Table 4). Furthermore, the analysis of the axial length revealed that the axial length increased by 0.18±0.18 mm in patients wearing orthokeratology lenses compared to baseline, and by 0.61±0.20 mm in patients wearing spectacle glasses compared to baseline. The differences between the two groups were statistically significant (p<0.001, Table 4).

    Patients wearing orthokeratology lenses showed no significant changes in intraocular pressure, corneal endothelial cell count, and central corneal thickness compared to baseline (p>0.050, Table 4).

    Ⅳ. Discussion and conclusion

    1. Effectiveness of OK lens

    1) Visual acuity

    At baseline, there was no statistically significant difference in visual acuity (VA) between the two groups of patients (p>0.050). And after 1 year the OK lens group showed significantly better VA compared to the spectacle group(OK group: 1.06± 0.09, spectacle group: 0.13±0.08, p＜0.010, Table 4).

    2) Spherical equivalent

    At baseline, there was no statistically significant difference in spherical equivalent refraction (SE) between the two groups of patients(p>0.050). And after 1 year the OK lens group showed significantly smaller SE compared to the spectacle group(OK group: -0.24±0.84, spectacle group: -3.92±1.34, p＜0.010, Table 4).

    3) Axial length

    At baseline, there was no statistically significant difference in axial length between the two groups of patients(p>0.050). However, after one year of lens wear, there was a significant statistical difference in axial length between the two groups, with the OK lens group showing significantly less axial length elongation compared to the spectacles group(OK group：0.18±0.18, spectacle group： 0.61±0.20, p＜0.001,Table 4).

    2. Safety of OK lens

    1) Intraocular pressure

    In this research, at baseline the mean value of intraocular pressure for the OK lens group patients was 15.78±1.94 mmHg. And one year later, the mean value of intraocular pressure for the OK lens group patients was 16.02±1.84 mmHg. The values showed a slight increase, but there was no significant statistical difference (p>0.050, Table 5).

    2) Corneal endothelial cell count

    In this research, at baseline the mean value of corneal endothelial cell count of the OK lens group patients was 3,229.45±196.89 cell/mm2. And one year later, the mean value of corneal endothelial cell count of the OK lens group patients was 3,216.39±195.91 cell/mm2. The values showed a slight decrease, but there was no significant statistical difference (p>0.050, Table 5).

    3) Central corneal thickness

    In this research, at baseline the mean value of central corneal thickness of the OK lens group patients was 548.59±29.51 μm. And one year later, the mean value of central corneal thickness of the OK lens group patients was 546.04±30.46 μm. The values showed a slight decrease, but there was no significant statistical difference (p>0.050, Table 5).

    In this study, we focused on the high incidence group of myopia in adolescents and compared the clinical effects of OK lenses and spectacle glasses on myopia control in two groups of patients. OK lens are more effective in reducing spherical equivalent, improving visual acuity, and slowing down axial elongation compared to single vision spectacle glasses. The safety of OK lenses was also confirmed through the comparison of intraocular pressure, corneal endothelial cell count, and corneal thickness in patients before and after the experiment. The impact of wearing OK lenses on these factors is nearly indistinguishable from that of wearing spectacles. Given that the fitting personnel have a comprehensive understanding of the fitting procedures and techniques of OK lenses and can use them scientifically and reasonably to control myopia progression in adolescents.

    Figure

    KJVS-26-1-65_F1.gif

    Design of Euclid orthokeratology (OK) lens.

    KJVS-26-1-65_F2.gif

    The examination flowchart.

    KJVS-26-1-65_F3.gif

    Patient selection flowchart.

    Table

    The inclusion and exclusion criteria of study subject

    Comparison of general information at baseline

    *mean±standard, t-value suggests a more significant difference between the means, <i>p</i>-value＜0.050 suggests difference is statistically significant.

    Comparison of various parameters between two groups at baseline

    *mean±standard, t-value suggests a more significant difference between the means, <i>p</i>-value＜0.050 suggests difference is statistically significant.

    Comparison of various parameters between two groups after 1 year

    *mean ± standard, t-value suggests a more significant difference between the means, <i>p</i>-value＜0.050 suggests difference is statistically significant

    Comparison of various parameters of OK lens group after 1 year

    *mean±standard, t-value suggests a more significant difference between the means, <i>p</i>-value＜0.050 suggests difference is statistically significant.

    Reference

    1. Wang Y, Chen DY et al.: Study on the influencing factors and prevention measures of myopia in Chinese adolescents. Pract Prevent Med. 23(3), 380-381, 2016.
    2. Si JK, Tang K et al.: Orthokeratology for myopia control: A meta-analysis. Optom Vis Sci. 92(3), 252-257, 2015.
    3. McCollim RJ: On the nature of myopia and the mechanism of accommodation. Med Hypotheses 28(3), 197-221, 1989.
    4. Rudnicka AR, Kapetanakis VV et al.: Global variations and time trends in the prevalence of childhood myopia, a systematic review and quantitative meta-analysis: Implications for aetiology and early prevention. Br J Ophthalmol. 100(7), 882-890, 2016.
    5. Holden BA, Fricke TR et al.: Global prevalence of myopia and high myopia andtemporal rends from 2000 through 2050. Ophthalmology 123(5), 1036-1042, 2016.
    6. Qu Jia: Adhere to the right way forward for the study of prevention and treatment for myopia. Zhonghua Yan Ke Za Zhi 39(6), 321-324, 2003.
    7. Sherwin JC, Reacher MH et al.: The association between time spent outdoors and myopia in children and adolescents: A systematic review and meta-analysis. Opthalmology 119(10), 2141-2151, 2012.
    8. Zhang H, Luo D: Study on the influencing factors and prevention measures of adolescent myopia. Psychological Doctor 40(5), 208-209, 2016.
    9. Ren X, Liu L et al.: Current status of myopia epidemiology surveys. Journal of Integrated Chinese Western Medicine 4, 195-196, 2018.
    10. Zadnik K, Sinnott LT et al.: Prediction of Juvenile-onset Myopia. JAMA Ophthalmol. 133(6), 683-689, 2015.
    11. Jun SY, Kim HK et al.: Long-term effect of orthokeratology lenses on axial length elongation in myopia: 2-3 years follow-up study. J Korean Ophthalmol Soc. 61(8), 897-904, 2020.
    12. Wei R, Lu D et al.: Interpretation of the international myopia institute white papers focusing on myopia prevention and control. Rec Adv Ophthalmol. 39(8), 701-713, 2019
    13. China Central Broadcasting Network: The overall myopia rate of children and adolescents in China is 52.7%, 2020, Available at https://baijiahao.baidu.com/s?id=1705221498753105658&wfr=spider&for=pc, Accessed February 1, 2024.
    Copyright © The Korean Society of Vision Science. All rights reserved.