Relative peripheral refraction and its role in myopia onset in teenage students

INTRODUCTION

Myopia is an important and widespread public health problem, especially in Asia

. Although myopia is known to be caused by both genetic and environmental factors,the ocular components, such as the axial length, cornea, and crystalline lens, are regarded as the primary determinants of refractive error and are also related to myopia incidence and progression

. Our previous studies show that the incidence of myopia in high school students remains high and is related to low outdoor time and high near-work time

. It is necessary to predict the incidence of myopia in advance; however, reliable indicators of this condition are lacking.

Currently, the role of peripheral refraction in incident myopia and myopic progression has been the focus of much research

, and myopic eyes have been found to exhibit relative peripheral hyperopia when compared with nonmyopic eyes

. Several animal studies have supported the role of peripheral refraction in myopia incidence. The studies in monkeys by Smith

found that the peripheral retina contributed to emmetropization and myopia onset; even when the central retina was blocked or ablated by a laser,emmetropization was able to progress in young monkeys, but if a lens was applied to induce relative peripheral hyperopia,central myopia occurred. However, contradictory findings to those of the above animal studies have been reported by studies about the relationship between peripheral refraction and myopia development in humans. Atchison

claimed that there was no significant difference in the initial peripheral hyperopia between eyes that developed myopia and those that remained non-myopic after 2y in 7-year-old and 14-yearold Chinese children. The authors concluded that relative peripheral hyperopia does not predict the progression of myopia. Mutti

found that relative peripheral hyperopia at the 30° nasal visual field angle had little effect on the risk of myopia onset during the next 5y in 9-year-old children. A study conducted by Sng

in 7-year-old Singaporean Chinese children revealed that emmetropic children who did not develop myopia during the next 15mo had relative peripheral myopia. Furthermore, a similar study in 6- to 9-year-old Chinese children found that the baseline relative peripheral refraction had no significant correlation with myopic central refractive changes during 12mo of follow-up

.

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At the baseline, the relative peripheral refraction in the myopic group did not significantly differ from that in the E0-E2, H0-E2, and H0-H2 groups (

＞0.05; Figure 2C). At the follow-up examination, the relative peripheral refraction at 20° N was significantly more hyperopic in the myopic group than in the E0-E2, H0-E2, and H0-H2 groups (

＜0.01), while the relative peripheral refraction at 10° N was significantly more hyperopic in the myopic group than in the H0-H2 group (

＜0.01; Figure 2D). The relative peripheral refraction at ±10° and ±20° did not significantly differ among the E0-E2, H0-E2, and H0-H2 groups (

＞0.05).

SUBJECTS AND METHODS

Ethical Approval The study protocol was approved by the Ethics Committee of Air Force Medical Center and adhered to the provisions of the Declaration of Helsinki. The purpose and content of the study were explained to the students and their parents and written and oral consent was obtained from the students and their parents.

Study Population We randomly enrolled 85 participants aged 14-16y from a selected group of male teenage Chinese students in the Experimental Class of the Air Force

in November 2017 and followed them up for 2y until November 2019. The inclusion criteria were as follows: uncorrected Snellen visual acuity 20/20 or better in both eyes and spherical equivalent refraction (SER) between -0.25 and +2.00 D and cylindrical refraction not more than 1.00 D in both eyes. The SER was calculated as the spherical power plus half of the cylindrical power after cycloplegia. The exclusion criteria were a history of ocular surgery, ocular trauma, or an ocular disease that affected the vision.

Changes in Peripheral and Central Refraction and Their Related Factors Relative peripheral refraction and central refraction changes of four subgroups in 2y were shown in Table 5. In general, the changes in relative peripheral refraction at different visual field angles increased as the changes in central refraction increased (Figure 3). The amplitudes of central refractive changes in the myopia and H0-E2 groups were significantly higher than those in the E0-E2 and H0-H2 groups (

＜0.05); however, the differences between these changes in the myopia and H0-E2 groups were not significant (

＞0.05). The amplitude of relative peripheral refraction change at 20° N was significantly higher in the myopia group than in the E0-E2 group (

=0.001) and the H0-H2 group (

=0.0001). The amplitude of relative peripheral refraction change at 20° T was significantly higher in the myopia group than in the H0-H2 group (

=0.0001), while that at 10° T was significantly higher in the myopia group than in the E0-E2 group (

=0.039). The amplitudes of relative peripheral refraction changes at ±20° were significantly higher in the H0-E2 group than in the H0-H2 group (

=0.006 and 0.0001, respectively).

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Measurements In this longitudinal study, all participants were examined at the baseline and at a follow-up visit 2y later. Peripheral refraction was measured with an open-field autorefractor (WAM5500; Grand Seiko, Hiroshima,Japan)

. The pupils were dilated by instilling one drop of 0.5% tropicamide-phenylephrine ophthalmic solution(Mydrin-P; Santen, Osaka, Japan) every 5min for 20min in both eyes

. The peripheral refraction examination was performed 20min after the drug administration. Peripheral refraction was measured in the horizontal meridian at 0°, ±10°,and ±20°; central refraction was tested first, followed by nasal and temporal peripheral refraction. Only the right eyes of the participants were included in the analysis.

Classification Myopia was defined as a central SER of -0.50 D or less, while -0.50 D＜SER＜+0.50 D indicated emmetropia,and SER≥+0.50 D indicated hyperopia. At the baseline, 30 students were hyperopic, and 55 students were emmetropic.Students were considered to have incident myopia if they were found to have developed myopia at the follow-up examination;non-myopic students were those who remained non-myopic at the follow-up examination.

Despite the strong evidence for the role of peripheral refraction in myopia onset in animal experiments, clinical studies have revealed only a weak effect of the peripheral retina. Moreover,few studies have explored the peripheral refractive status in non-myopic children over the age of 14y, by which time it is believed that the progression of myopia will be slower.Therefore, the purpose of this study was to identify the peripheral refraction characteristics and determine the role of peripheral refraction in myopia development in a group of selected male senior high school children aged 14 to 16y over a 2-year follow-up period.

For further analysis, the participants were divided into four subgroups: students who were hyperopic or emmetropic at the baseline but were myopic at 2y (incident myopia), students who were hyperopic at the baseline but were emmetropic at 2y(H0-E2), students who remained hyperopic at 2y (H0-H2), and students who remained emmetropic at 2y (E0-E2).

由以上兩組對比可知，在最優路線的求解上，本文算法相比較于文獻[12]中的算法具有一定優勢，驗證了本文算法的優勢性。

Statistical Analysis Statistical analyses were performed using the Statistical Package for the Social Sciences for Windows software, version 24.0 (SPSS Inc., Chicago, IL,USA). Continuous variables were presented as mean±standard deviation (SD) or 95% confidence intervals (95%CI).Peripheral refraction and relative peripheral refraction values were compared using repeated-measures analysis of variance,followed by Bonferroni post hoc tests. The Spearman rank test was performed to analyze the correlation between the changes in relative peripheral refraction and the changes in central refraction. Multiple linear regression analyses were conducted to investigate the association between the changes in relative peripheral refraction and the changes in central refraction. Multivariate Logistic regression analysis was performed to assess the correlation of incident myopia with the baseline central refraction and the baseline relative peripheral refraction. All

values were two-sided and were considered statistically significant when less than 0.05.

RESULTS

General Information We enrolled 89 participants aged 14-16y in November 2017. Four students did not complete the peripheral refraction examination at the 2-year follow-up. Thus,a total of 85 male students with a mean age of 15.47±0.57y were included in this study. The average central refraction of the students was 0.23±0.36 D at the baseline and 0.08±0.45 D at the 2-year follow-up, and there was no significant differencein cylindrical refraction between baseline (0.39±0.30 D) and 2-year follow-up (0.42±0.28 D,

=0.44). Of the 85 students,13 were found to have developed myopia at the follow-up examination.

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所有數據以x±s表示，應用SPSS17.0軟件，兩均數比較用t檢驗，多組間比較用單因素方差分析，P<0.05有統計學意義。

Differences Among the Four Subgroups Non-myopic students were divided into the following three subgroups: H0-H2 (

=17), H0-E2 (

=13), and E0-E2 (

=42). Tables 3 and 4 show the peripheral refraction and relative peripheral refraction in these three subgroups at the baseline and the 2-year followup. In the H0-H2 group, neither the peripheral refraction nor the relative peripheral refraction significantly differed between the baseline and follow-up (

＞0.05). In the E0-E2 group,the peripheral refraction and relative peripheral refraction significantly differed between the baseline and follow-up only at 20° N (

＜0.01). In the H0-E2 group, however, peripheral refraction changed significantly from the baseline to the follow-up at 0°, ±10°, and 20° T (

＜0.05), while the relative peripheral refraction changed significantly at ±20° and 10° N(

＜0.05).

This study explored the characteristics of peripheral refraction and relative peripheral refraction in a group of selected male Chinese children aged 14 to 16 years old and tested the hypothesis that relative peripheral hyperopia predicts myopia onset. Our results showed that there was no significant difference in relative peripheral refraction between myopic eyes and non-myopic eyes at the baseline. After 2y, the relative peripheral refractions of students who became myopic turned hyperopic and those of non-myopic students remained relatively myopic or emmetropic. The relative peripheral refraction at 10° T, 10° N, and 20° N significantly differed between the myopic and non-myopic groups. These results are consistent with previously reported data

, which showed that relative peripheral hyperopia might correlate with myopia onset; however, it is unclear if this relationship is causal or merely a correlation, at least in our 2-year follow-up study.

局部應用前列腺素類似物滴眼液對原發性開角型青光眼患者角膜厚度影響的Meta分析 ………………… 蔣鵬飛等（24）：3431

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