Effectiveness of peripheral defocus spectacle lenses in myopia control: a Meta-analysis and systematic review

AIM: To evaluate the effectiveness of peripheral defocus spectacle lenses(PDLs) in myopia control. METHODS: Literature retrieval on Pub Med, Cochrane Library, Embase, and Web of Science databases, and the search time limit was from the establishment of each database to December 29, 2021 were conducted. Change of spherical equivalent refraction(SER) and axial change(AL) were extracted from the literatures that met the inclusion criteria, and Rev Man5.3 software was used for Meta-analysis. RESULTS: A total of 4 randomized controlled trials(RCTs) were included in this Meta-analysis, involving 770 myopic children. The results showed that PDLs could delay the progression of myopia in children with myopia compared with single vision spectacle lenses(SVLs;WMD=0.21 D, 95%CI: 0.01, 0.41, P=0.04). However, there was no significant difference in controlling the growth of axial length(AL) in myopic children(WMD=-0.10 mm, 95%CI:-0.21, 0.01, P=0.07). The results of the effectiveness of myopia control between the two spectacle lenses showed that PDLs were more effective in controlling the progression of myopia(OR=5.73, 95%CI: 2.58, 12.70, P<0.001) and delaying the growth of AL(OR=44.25, 95%CI: 8.84, 221.58, P<0.001) than SVLs, and the differences were statistically significant. CONCLUSION: PDLs can control the progression of myopia compared with SVLs, but cannot delay the growth of AL, and the effectiveness of PDLs in myopia control better than SVLs.

ZERNIKE ASTIGMATISM AND VISUAL PERFORMANCE IN MYOPIC EYES BY RIGID GAS PERMEABLE CONTACT LENSES WEAR

To investigate the effects of rigid-gas-permeable contact lens(RGP-CL)wear on Zernike astigmatism and visual performance in myopic eyes.Methods:A wavefront sensor was used to evaluate Zernike astigmatism for 21 eyes with minimum astigmatism and 18 eyes with moderate astigmatism under three different modes of refractive correction:the RGP-CL,spectacle lens correcting spherical equivalent(SL)and spectacle lens fully correcting spherical error and astigmatism(fSL).Contrast visual acuity was assessed with a VA tester at four contrast levels and two luminance backgrounds.Results:Compared to the SL wear,RGP-CL wear changed the main axis astigmatism(Z_(2)^(2))from
0:09-0:34 to 0.34-0.22 for the minimum astigmatism group,while the contrast VA was improved about 0.05 LogMAR(F=8:06,p<0:01).For the group with moderate astigmatism,significant reduction in Z_(2)^(2)was found for both fSL wear(t=4:78,p<0:001)and RGP-CL wear(t=6:29,p<0:0001).The changes in astigmatism were significantly correlated between the fSL and RGP-CL wears(r=0:897,p<0:0001 for Z_(2)^(-2);and r=0:643,p=0:004 for Z_(2)^(2)).Contrast VA was significantly improved for both fSL and RGP-CL wears and the improvements were significantly correlated between each other for all four contrast levels and two backgrounds.Conclusion:RGP-CL wear induces astigmatism for the eyes with minor astigmatism probably due to a correction of corneal astigmatism and thus a manifesting of the lens astigmatism.For the astigmatic eyes,RGP-CL wear has similar effect on correcting astigmatism as the spectacle lens wear with spherical-cylinder correction and also produces similar visual improvement.

Measurement Error of Refractive Index for Spectacle Lens

As an important optical constant of optical properties for spectacle lens,the refractive index measurement is studied using V prism refractometer. In the experiment,according to various factors inducing measurement error,the experimental results are analyzed,which include right angle deviation,contact liquid,curvature,and focusing accuracy. The study results show that focusing accuracy is the most important factor of influence for measurement,consists of contact liquid wettability,sample shape,and effective width of light transmission. In addition,the refractive index measurement is less affected by angle deviation of sample and the refractive index deviation of contact liquid. On the basis of the experimental data analysis,it is possible to relax the deviation of right angle of the sample to 1' or 2'.