| Author: | Zhang, Hanyu |
| Title: | The role of relative peripheral refraction in myopia control using myopic defocus |
| Advisors: | Lam, Carly (SO) |
| Degree: | Ph.D. |
| Year: | 2021 |
| Subject: | Myopia -- Treatment Low vision in children -- Treatment Ophthalmic lenses Hong Kong Polytechnic University -- Dissertations |
| Department: | School of Optometry |
| Pages: | 215 pages : color illustrations |
| Language: | English |
| Abstract: | The prevalence of myopia has increased substantially worldwide in the last two decades, especially in Asia. High myopia increases the risk of ocular pathologies, which could cause visual impairment and subsequent deterioration of quality of daily life. Myopia control is now targeting children at a young age in an attempt to reduce the risk of high myopia and preferably delay the onset or slow the myopia progression. The Defocus Incorporated Multiple Segments (DIMS) spectacle lens is a custom-made plastic spectacle lens. It includes a central optical zone (9.4 mm in diameter) for correcting distance refractive error and annular multi-focal zones with a relatively positive power (+3.50 D) and with multiple segments extending to the periphery (33 mm in diameter). This design simultaneously introduces myopic defocus and provides a clear vision for the wearer at all viewing distances. In a 2-year double-masked randomised controlled trial (RCT), children wearing the DIMS lens showed significantly slowed myopia progression and axial elongation by around 50 to 60%. Most studies reported myopia control efficacy as changes in refractive error and axial length (AL), with few describing the retinal shape changes. It has been suggested that retinal shape might be a determinant for developing myopia through biomechanical factors, and relative peripheral refraction (RPR) has been used to indirectly describe the retinal shape. However, few studies have reported changes of RPR after myopia control using myopic defocus in humans. Objectives of the study - There are three objectives: 1. To determine and describe the RPR among Hong Kong Chinse children who participated in the RCT. 2. To compare changes in RPR associated with myopia progression in myopic children wearing DIMS lenses and SV spectacle lenses over 2 years. 3. To compare changes in RPR associated with myopia progression in myopic children wearing DIMS lenses for the third year and children wearing SV lenses in the first 2 years who then switched to wear DIMS lenses for one year. Methods : In the first 2 years, a double-masked randomized clinical trial (RCT) was conducted between August 2014 and July 2017. The children were allocated randomly to wear either the DIMS lens (treatment group) or SV spectacle lens (control group). After completion of the RCT, participated children were offered a continuation of follow-up for 1 year. In the third year, the children who were in the DIMS group continued to wear the DIMS lenses (DIMS group), and those who were in the SV group were switched to wear the DIMS lenses (Control-to-DIMS group). We have also acquired a historical control group by searching clinical records from 2017 to 2019 of the Optometry Clinic in the Hong Kong Polytechnic University. A standardised eye examination was performed every 6 months over the 3-year study. Cycloplegic central and peripheral refraction across the horizontal retinal eccentricities were measured five times by using a Shin-Nippon NVision-K 5001 autorefractor (Ajinomoto Trading Inc., Tokyo, Japan) with the Maltese cross-target placed at the straight-ahead position (centre) and 10°, 20°, and 30° at nasal (10N, 20N, 30N) and temporal (10T, 20T, 30T) retinal eccentricity. AL was measured five times using the IOL Master 500 (Carl Zeiss, Oberkochen, Germany) and then averaged. The primary outcome included the changes in central spherical equivalent refraction (SER), and secondary outcomes included changes in AL, peripheral refraction, and relative peripheral refraction and comparison between the treatment and the control groups on these parameters. Results - Demography : Among 550 subjects recruited and assessed, 183 fulfilled inclusion and exclusion criteria and were also willing to participate in the RCT. They were randomised those 93 children were assigned to DIMS group, and 90 children were assigned to the SV group. There was no statistically significant difference in the baseline ocular parameters between the DIMS and SV groups (p>0.05). The mean age of the children were around 10 years old, and their mean SER were around -2.93±1.04D in the DIMS group and -2.70±0.98D in the SV group. Myopia progression and axial length changes in the 2-year RCT : One hundred sixty subjects completed the first 2-year measurements, with 79 subjects in DIMS group and 81 subjects in the SV group. Myopia progression was -0.38±0.06 D and -0.93±0.06 D in the DIMS and SV groups, and the axial elongation was 0.21±0.02 mm and 0.53±0.03 mm in DIMS and SV groups, respectively. Over 2 years, DIMS showed significantly less myopia progression (-0.55±0.09 D, p<0.0001) and less axial elongation (0.32±0.04 mm, p<0.0001) than the SV group. Changes in RPR associated with myopia progression in myopic children wearing DIMS lenses and SV spectacle lenses over 2 years. At baseline, the two groups presented no significant differences in peripheral refraction along the horizontal retina. Over the 2 years, the DIMS group showed myopic shifts in all retinal eccentricities, with a similar amount of myopic shifts between nasal and temporal retina. SV group had asymmetrical peripheral myopic shifts between the nasal and temporal retina, with more myopic shifts at 10T (-0.32±0.62 D, p=0.0001), at 20T (-0.69±0.95 D, p≤0.0001) and 30T (-0.85±1.52 D, p≤0.0001). There was no significant difference in peripheral J0 nor peripheral J45 between the two groups after 2 years. No significant changes in RPR were noted in the DIMS group, while significant hyperopic shifts in RPR were found at the nasal retina (10N: 0.27 ± 0.45 D; 20N: 0.75 ± 0.72 D; 30N: 0.98 ± 0.76 D, all p<0.0001) in the SV group. The RPR among Hong Kong Chinse children who participated in the RCT and its influences on myopia control. For children who completed the 2-year RCT, the mean central SER was -2.87 ± 0.97 D, and the mean age was 10.1 ±1.5 years. The two groups were combined for analysis as no significant difference in baseline peripheral refraction and RPR between DIMS and SV group. Hyperopic RPR was observed at most eccentricities across the horizontal retina, and it increased with more peripheral eccentricity. A broad range of hyperopic RPR was present at 30N, which ranged from 0 to 6 D. Compared to the RPR in the temporal retina, there was more hyperopic RPR at 10N (paired t-test, mean difference:0.17±0.63 D, p=0.001), 20N (mean difference: 0.65±1.21 D, p<0.0001) and 30N (mean difference: 0.84±1.68 D, p<0.0001).However, only a weak correlation between RPR and central SER was found in the baseline cross-sectional observation. Both relative J0 and relative J45 increased in magnitude with increasing eccentricity, and the magnitude of relative J45 was less than relative J0. An asymmetrical profile was also found in relative J0, with more negative of relative J0 at the 10T (paired t-test: mean difference: -0.28±0.36 D, p<0.0001), 20T (mean difference: -0.74±0.74 D, p<0.0001) and 30T (mean difference: -1.08±0.91 D, p<0.0001) compared with the corresponding eccentricity in the nasal retina. There was no significant difference in relative J45 between the nasal and temporal retina. In the DIMS group, baseline RPR in the nasal retina were positively associated with myopia progression (multiple linear regression,10N: r=0.36, p=0.001; 20N: r=0.35, p=0.001) and negatively associated with axial elongation (10N: r=-0.34, p=0.001; 20N: r=-0.29, p=0.006). In the SV group, baseline RPR at 10N (r=0.37, p=0.001) and 20N (r=0.36, p=0.001) and 30N (r=0.35, p=0.002) were positively associated with myopia progression but no statistically significant relationship between RPR axial elongation after Bonferroni correction (p>0.008). Subjects were subdivided into two subgroups according to baseline RPR: myopic RPR (10N,20N) and hyperopic RPR (10N,20N) group. Myopia progression and axial elongation were further compared between myopic RPR and hyperopic RPR group within the SV and DIMS group. In the SV group, there was no statistically significant difference in myopia progression (mean difference: -0.26±0.14 D, p=0.06) and axial elongation (mean difference:0.04±0.05 mm, p=0.48) between myopic RPR (n=27) and hyperopic RPR (n=54) at 10N. Also, no significant difference in myopia progression (mean difference: -0.25±0.20 D, p=0.19) and axial elongation (mean difference: 0.08±0.08 mm, p=0.27) between myopic RPR (n=11) and hyperopic RPR (n=70) at 20N. However, in the DIMS group, myopic RPR at 10N subgroup (n=27) showed statistically significant more myopia progression (mean difference: -0.36±0.14 D, p=0.009) and axial elongation (mean difference: 0.16±0.05 mm, p=0.001) than hyperopic PRR at 10N subgroup (n=52). And myopic RPR at 20N subgroup (n=12) showed statistically significant more myopia progression (mean difference: -0.40±0.16 D, p=0.01) and axial elongation (mean difference: 0.15±0.07 mm, p=0.02) than hyperopic PRR at 20N subgroup (n=67). Myopia progression and axial length changes in the third year : Among the 160 children who completed the 2-year RCT study, 128 children participated in the extended 1-year post-trial follow-up study, and 120 children completed the third-year visits. Children in the DIMS group (n=65) continually showed good myopia control effects. On average, the annual changes in myopia progression were -0.18 D, and this progression rate was almost linear over the 3 years. For the children who were in the original control group, the myopia control effect was significantly different over 3 years. In the first 2 years, the myopia progression rate ranged from -0.38D to -0.49D. After switching to DIMS lens, the annual myopia progression was reduced to only -0.05D for the third year. The annual axial elongation in the DIMS group was around 0.10 mm per year. A mean axial elongation of 0.08 mm in the third year was found in the Control-to-DIMS group (n=55), while it was 0.20 mm and 0.29 mm per year in the first and second years. The RPR changes in myopic children wearing DIMS lenses for the third year and children wearing SV wearers in the first 2 years who then switched to wear DIMS lenses. In the third year, DIMS group (n=65) showed myopic shifts in all the peripheral eccentricities and increased proportionally with the central myopia progression; therefore, it maintained a relatively constant RPR. When comparing the changes in RPR between the first 2 years and the third year, Control-to-DIMS (n=55) group showed a significant decrease in hyperopic RPR in the third year at nasal retina compared to the changes in RPR in the first 2 years (p<0.05, paired t-test). No significant difference in RPR changes between the nasal retina and temporal retina was found in the third year in the Control-to-DIMS group. In the Control-to-DIMS group, the RPR at 24-month was statistical significantly associated with myopia progression (multiple linear regression, 10N: r=0.40, p=0.004; 20N: r=0.48, p=0.001; 30N: r=0.43, p=0.001) after adjusting for the initial central SER at 24-month, age and sex. For the DIMS group, the baseline RPR was associated with the 3-year myopia progression (10N: r=0.38, p=0.002; 20N: r=0.35, p=0.007). Conclusion : DIMS lenses showed myopia control effects in retarding myopia progression and slowing down the changes in axial length in myopic children. As a spectacle lens, it has the advantage of being non-invasive and easily accepted by young children. No adverse effects were reported in the visual functions after wearing the lens for 2 years. Over 2 years, myopia control using myopic defocus in the mid-periphery impacted the changes in peripheral refraction and slowed central myopia progression by somehow altering the overall retinal shape. In addition, the asymmetrical changes in RPR in traditional spectacle lenses may infer a faster myopia progression. The determination in RPR among Hong Kong Chinse children who participated in the DIMS study suggested that among typical Chinese young myopes, there were asymmetrical hyperopic RPR at the horizontal retina, and the hyperopic RPR increased with increasing retinal eccentricities. DIMS lens was more effective in myopia control for children having hyperopic RPR but less effective in children with myopic RPR at the periphery. This could be related to the too much of myopic defocus that may not benefit the myopia retardation. Customised myopic defocus to fit individual subjects may optimise the myopia control effect. This study suggested that the myopia control effects of DIMS lenses was influenced by initial RPR. Initial RPR could be used as an indicator for the ordering lens and avoiding over-induce myopic defocus. RPR could be an important parameter to predict the changes in retinal shapes after myopia control. The mechanism of the signal detection and decoding of defocus required further investigation. |
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| Access: | open access |
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