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The global prevalence of myopia is increasing year by year, leading to many ocular health issues and social problems. In recent years, it has been confirmed that peripheral defocus is closely related to the occurrence and development of myopia. Alteration of the state of peripheral defocus can significantly influence the progression of myopia and emmetropization, but the exact mechanisms are still unclear. At present, there is no method that can completely control myopia. Nowadays, the main controlling methods, including orthokeratology lens, peripheral defocus lens and multi-focal soft lens, have been confirmed to be closely related to peripheral defocus. In this paper, we will review and summarize the development and effect of these peripheral defocus relating control methods. In addition, the researches on the related mechanisms of peripheral retinal defocus and myopia prevention and control at home and abroad are reviewed, as well as the potential mechanisms of peripheral defocus, with a view to further improving the controlling effects of existing methods, developing new prevention and control methods and reducing the incidence and progression of myopia.
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AIM: To observe and compare the changes in retinal peripheral refraction and aberrations after femtosecond laser-assisted laser in situ keratomileusis(FS-LASIK)versus small incision lenticule extraction(SMILE)for myopia correction.METHODS: A total of 71 patients(71 eyes)with myopia who underwent FS-LASIK from October 2022 to April 2023 in our hospital were selected as the FS-LASIK group, and 80 patients(80 eyes)with myopia who underwent SMILE were selected as the SMILE group. All patients underwent corneal wavefront aberration measurement and multispectral refractive topography preoperatively and 3mo postoperatively, as well as refraction difference value(RDV)in the range of 0°～10°, 10°～20°, 20°～30°, 30°～40°, and 40°～53° in the annulus of the retina, which were recorded as RDV-(0°～10°), RDV-(10°～20°), RDV-(20°～30°), RDV-(30°～40°), and RDV-(40°～53°). The results of two groups of patients were compared.RESULTS: No significant differences were observed in RDV-(0°～10°), RDV-(10°～20°), RDV-(20°～30°), RDV-(30°～40°), RDV-(40°～53°)between the two groups at 3mo post-operation(all P>0.05). Furthermore, the RDV-(20°～30°), RDV-(30°～40°)and RDV-(40°～53°)of the two groups at 3mo postoperatively were all significantly lower than those preoperatively(all P<0.05). The changes in coma(horizontal)and spherical aberration(SA)at 3mo postoperatively were smaller in the SMILE group [0.106(0.056, 0.171)and 0.115(0.081, 0.182)μm] than in the FS-LASIK group [0.206(0.104, 0.355)and 0.197(0.128, 0.254)μm](Z=-4.170, -5.016, all P<0.05). A negative correlation was found between postoperative SA and postoperative RDV-(10°～53°)(rs=-0.205, -0.181, -0.226, -0.244, all P<0.05).CONCLUSION: Both FS-LASIK and SMILE reduced retinal hyperopic defocus in the peripapillary macular range of 20°～53° eccentricity, and the postoperative changes in coma(horizontal)and SA were smaller with SMILE than with FS-LASIK. There was a certain correlation between postoperative SA and postoperative retinal peripheral defocus.
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@#AIM: To observe the changes of relative peripheral refraction(RPR)after wearing orthokeratology(OK)lens, and to explore the relationship between the changes of RPR and the axial length(AL).<p>METHODS: Totally 104 cases of adolescent myopia(-1.00D to -6.00D)were selected from May 2016 to Nov. 2018. Then they were randomly divided into the experimental group and the control group. The experimental group wore OK lens, and the control group wore frame glasses. Their AL, RPR(N30°-T30°)were observed for 1a.<p>RESULTS:The RPR of the experimental group showed myopic drift at each time point after wearing OK lens(<i>P</i><0.05), and the change was most obvious in 1mo(<i>P</i><0.05). After 1mo, the RPR basically tended to be stable(<i>P</i>>0.05). The RPR of the control group showed an increase in hyperopia. One year later, there were statistical differences in the changes of AL and RPR between the two groups(<i>P</i><0.001). There was a positive correlation between the changes of AL and RPR in the experimental group(<i>P</i><0.001).<p>CONCLUSION: After wearing OK lens, the AL growth slowed down, while the RPR showed myopic drift and it was most obvious in 1mo. There was a correlation between the changes of AL and RPR.
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@#AIM:To observe the different effect of controlling myopia by orthokeratopraxis with different width between defocus circle and the rim around the cornea.<p>METHODS: A retrospective case-control study. A total of 45 patients(85 eyes)who came to our hospital for orthokeratopraxis lens fitting during January 2014 to December 2015 were selected. The diameter of the orthokeratopraxis lens was 90%-95% of the diameter of the cornea. So the patients were divided into three groups according to the different diameter of the orthokeratopraxis lens. The diameter of the orthokeratopraxis lens for the patients whose corneal diameter was between 12.1 to 13.00mm was 11.0-11.2mm(Group A). The diameter of the orthokeratopraxis lens for the patients whose corneal diameter was between 11.1-12.00mm was 10.5-10.9mm(Group B). The diameter of the orthokeratopraxis lens for the patients whose corneal diameter was between 10.0-11.00mm was 10.0-10.4mm(Group C). The change of the spherical equivalent(SE)and axial length(AL)were analyzed after wearing the lens for 1a and 2a.<p>RESULTS: Before wearing lens, the age, SE(D)and AL(mm)was not statistically significant in the three groups(<i>P</i>>0.05). After wearing lens for 1a and 2a, the change of SE(D)and AL(mm)was not statistically significant in Group A and Group B(<i>P</i>>0.05)and the change was statistically significant in Group C(<i>P</i><0.05). The change of the SE and AL was also significantly different between Group A and Group C after wearing orthokeratopraxis lens for 2a(<i>P</i><0.05). A similar result was found between Group B and Group C(<i>P</i><0.05).<p>CONCLUSION: The effect of controlling myopia by orthokeratopraxis with different position of defocus circle on cornea is different. The position of defocus circle is more close to the corneal limbus, the effect is weaker.
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Background It has been reported that orthokeratology has the effects of slowing down myopia progression and axial elongation.However,the affecting mechanism of orthokeratology wearing on ocular peripheral refraction is still not elucidated.Objective This study was to observe and compare the changes of ocular peripheral refraction and relative peripheral refraction (RPR) in low to moderate myopic eyes of children after wearing orthokeratology lens and spectacles for 6 months.Methods A randomized controlled clinical trial was carried out after approval of Ethic Committee of Beijing Tongren Hospital and informed consent of guardians of the children.One hundred myopic children aged (ll.0±1.9) years were recruited in Beijing Tongren Hospital from June 2014 to January 2015,with the diopter of-0.50 to-6.00 D.The subjects were randomized into orthokeratology group and spectacles group by the process PLAN PROC of software SAS 9.1.3,50 for each group.The subjects in the orthokeratology group wore orthokeratology lens for 6 months and those in the spectacles group wore spectacles for the same period.An infrared open-field autorefractor was employed to measure the refraction at central 0°,temporal 15°,temporal 30°,nasal 15°and nasal 30° radial lines before and after wearing lens for the assessment and comparison of the changes of peripheral refraction and RPR.Results There was no significant difference in spherical equivalent between the orthokeratology group and the spectacles group before wearing lens ([-3.35±1.31] D versus [-3.01± 1.15] D,P =0.20).The peripheral refraction values in the orthokeratology group were (-2.28 ± 1.60),(-3.28±1.41),(-3.40±1.23),(-3.38±1.12) and (-2.09±1.29)D at nasal 15°and nasal30°,central,temporal 15° and temporal 30°radial lines before wearing lens,and reduced by (0.29±1.67),(0.85±1.66),(0.92±1.76) and (0.66±1.66) D at nasal 30°,nasal 15°,central and temporal 15° after wearing lens,respectively,with significant differences at nasal 15°,central and temporal 15°(all at P＜0.05).The peripheral refraction values in the spectacles group were (-1.88±1.30),(-2.66±1.18),(-2.89±1.27) and (-1.94±1.31)D at nasal 15°,nasal 30°,temporal 15 ° and temporal 30°,radial lines before wearing lens and increased by (-0.25±0.80),(-0.43 ±0.67),(-0.32±0.64) and (-0.22±0.75)D after wearing lens,respectively,with significant differences between before and after wearing lens (all at P＜0.05).The RPR shifted from hyperopia defocus to myopia defocus before and after wearing lens in temporal 15° and 30° radial lines in the orthokeratology group,and at various radial lines in the spectacles group,the RPR showed gradually worsening of hyperopia defocus.Conclusions Long-term wearing of orthokeratology results in a hyperopia shifting in myopic children by exposing the peripheral retina towards relative myopia defocus,whereas wearing spectacles leads to a relative hyperopia defocus on retina.Thus,orthokeratology may slow down the myopia progression.