Effects Of Peripheral Myopic Defocus On Children And Chick Lens-induced Myopic Models

Purpose. To investigate the impact of pupil diameter on axial growth in myopic children following OK treatment.Methods. Fifty-two children aged9to14years were enrolled in the study. Subjects were free from any ocular disease; an apical corneal refractive power between41.50D and44.50D, refractive error between-1.00D and-4.50D, astigmatism less than1.50D, and monocular corrected distance visual acuity (CDVA) no worse than1.0. Subjects were divided into two groups,27for the OK group and25for the single vision spectacle lens (SV) group. Subjects in each lens group were further divided into two sub-categories according to their baseline scotopic pupil diameters:above average and below average. Axial length (AL) was measured at baseline and at every6-month visit through to24months. Linear mixed-effect model was used to determine AL changes from baseline. In this model, repeated visits were taken as within-subject effect, and treatment group as well as pupil size were taken as between-subject effects. The interaction of (treatment group*pupil size) was analyzed. Relationships between axial growth at24months and baseline pupil area were analyzed in both lens groups.Results. Twenty-five subjects in the OK group and22subjects in the SVL group completed the24-month study. Axial length increased significantly throughout the observed24-month period (F=32.09, p<0.001). Pupil size significantly affected axial growth (F=15.95, p<0.001) and different treatment modalities (OK vs SVL) interacted with the effect of pupil size on axial growth (F=24.66, p<0.001). To be more specific, axial growth was significantly slower in subjects with above average pupil sizes than those with below average pupil sizes in the OK group (F=25.04, p<0.001). Contrarily, pupil size didn’t affect axial growth in the SVL group (F=0.46, p=0.50). Baseline scotopic pupil area was significantly correlated to axial growth in the OK group (r2=0.405, p<0.001) but not in the SVL group (r2=0.171, p=0.056).Conclusions. Large pupil diameters facilitate the effect of OK to slow axial growth in myopia. We speculate that this is due to enhancement of the myopic shift in the peripheral retina. Chapter Two:Effects of peripheral myopic defocus and lighting intensity on lens-induced myopia chick modelsPurpose. To investigate the effects of peripheral myopic defocus and lighting intensity on refractive development and axial growth in lens-induced myopia (LIM) chick models.Methods. UC Davis White Leghorn chicks were used as myopia models. Chicks were free from any treatment in the first6days upon hatch. From day7on,74chicks were devided into8groups, namely, A1、B1、C1、D1and A2、B2、C2、D2. A1～D1remained untreated, and A2～D2were treated with-10D single vision lenses for a consecutely5days. All the chicks were raised in cages under ambient illuminance of8001ux in the first11days. They were transferred to chambers with illuminance of2001ux or80001ux on day12and further sub-grouped by wearing-10D single vision (SV) lenses or multi-focal (MF) lenses with-10D in the center and-5D in the periphery. A1and A2groups were2001ux+MF, B1and B2groups2001ux+SV, C1and C2groups8000lux+MF,D1and D2groups80001ux+SV. Streak retinoscopy was used to monitor refractive change, and A-scan ultrasonography with ultra-high resolution was appied to track biometrics. The effects of lighting intensity and peripheral myopic defocus on refractive development were studied. Measurements were taken on day1,3,5,7and10into lens treatment. Linear Mixed-effect Model was used for statistical analysis.Results. For the non-pre-treated chicks, the mean refractive errors reached-5.192D、-9.354D、-5.844D and-8.775D, and VCD grew by0.232mm、0.433mm、0.283mm and0.496mm for A1～D1group, respectively. Myopia progression were significantly slower in MF groups than in SV groups (F=24.19,p<0.001). Lighting intensity didn’t have a significant effect on myopia development (F=0.02,p=0.889). The-10SV pre-treated chicks developed a mean refractive error of-9.06D in5days. The refractions of A2and C2groups regressed from around-10D baseline level to-6D～-7D after being transferred to -10D/-5D MF lenses for5days and stabilized thereafter. Myopia continued to progress in chicks from B2and D2groups that continued to wear -10SV lenses. Vitreous chamber depth (VCD) stopped at baseline level in A2and C2groups that were transferred to MF lens wear but continued to grow in B2and D2groups. At the end of10-day treatments, the mean refractive errors were-5.906D、-8.813D.-7.094D and-9.786D for A2-D2groups, respectively. Peripheral myopic defocus had an inhibitory effect on further myopia progression (F=14.45,p<0.001), which was also reflected on VCD change (F=16.94,p<0.001). Lighting intensity didn’t have any effect on VCD growth in chicks that had already developed myopia (F=1.26,p=0.263).Conclusion. Peripheral myopic defocus significantly retarded myopia progression and axial growth in chick LIM models, while lighting intensity didn’t have a significant effect on refractive development in chick LIM models. Chapter Three:The role of artificial aniridia in the effects of peripheral myopic defocus and lighting intensity on lens-induced myopia chick modelsPurpose. To investigate the role of pupil size in the effects of peripheral myopic defocus and lighting intensity on refractive development and axial growth in lens-induced myopia chick models.Methods. Thirty White Leghorn chicks were raised treatment-free for6-7days before them underwent unilateral iridectomy. They were reared in chambers with illuminance level of80001ux or2001ux for10days since day12, and were sub-grouped by wearing-10D single vision (SV) or-10D-center/-5D-periphery multi-focal (MF) lenses. Streak retinoscopy was applied for refractive change monitoring and ultra-high resolution ultrasonography for tracking biometric data. The effects of lighting intensity, multi-focal lens and pupil size on refractive development were studied by incorporating data from Chapter1. Pupil areas under different ages and lighting intensities were tested and used to convert ambient lighting illuminance to retinal illuminance. Post-and pre-iridectomy retinal illuminances were compared.Results. Peripheral myopic defocus had a significant inhibitory effect on myopia progression (F=8.96,p=0.003), which was independent of pupil size (F=1.25,p=0.265). Lighting intensity didn’t affect refractive change (F=1.19,p=0.277). For iridectomized eyes, change in pupil size didn’t have an impact on myopia progression (F=0.68,p=0.409). Multi-focal lenses remarkably retarded vitreous chamber and axial length elongation (F=92.74,p<0.001;F=79.54,p<0.001), irrespective of pupil size (F=1.42,p=0.234). Lighting intensity didn’t affect VCD or AL growth (F=0.83,p=0.362;F=0.88, p=0.348). Pupil area increased with age and decreased with higher lighting intensity. However, the relationship between retinal illuminance and ambient lighting illuminance was unaffected by age. Retinal illuminance was6times higher in iridectomized eyes than in non-iridectomized eyes under80001ux illuminance level.Conclusion. Myopia progression in chick LIM models were not inhibited by higher retinal illuminance resulted from iridectomy, but were effectively prohibited by peripheral myopic defocus.