| PurposeTo investigate the refractive states and longitudinal changes in Shanghai students in grades1-9, approach the process of nomal ocular refractive development and the mechanisms of myopia development and progression, provide bases for moypic preventing and controlling.Methods9086students aged6to15in12schools were selected using stratified clustered random sampling, the distance visual acuity, refractive error, ocular axial length, corneal curvatures, height and weight were measured, questionnaires about their age, sex and family history were completed,4651students in grade1-7were followed up for2years. The data were analyzed using SPSS.Results1. States of Refractive developmentThe cross-sectional study showed a61.0%prevalence of poor eyesight among students aged6-15years of Xuhui and Hongkou districts. The rate was63.5%for female and58.8%for male;54.5%for students aged6to12,79.7%for13to15years old。Myopic prevalence of age6to13was53.4%, female55.3%, male51.6%;45.2%for age6to12and76.7%for13to15.The mean spherical equivalent refraction (SER), axial length (AL) and corneal curvature (CC) were-1.96±0.02D,23.92±0.01mm and43.19±0.02D.2. Longitudinal changes of refractionThe refractive status had a myopic shift in the2-year follow-up, the prevalence of myopia increased from31.5%to55.7%, annual incidence was18.7%. The high myopia prevalence increased from2.1%to4.2%, annual incidence was1.1%。The rate of incidence was19.9%for female and17.6%for male;33.5%for students6-9years old and47.8%for age10to13.The annual changes of SER, AL and CC were-0.282±0.008D,0.307±0.003mm, and0.031±0.004DThe percentage of remained non-myopes was42.9%, newly developed and persistent myopes was25.6%and31.5%3. The process and correlation factors of myopic onset and progressionFemales were more likely to have myopia, while with the similar rate of progression. Students aged10to13had a higher risk of onset, but progressed less than6to9years old in myopes. The number of myopic parents and their degrees of myopia were positively associated with their chidren’s risk of onset and the rate of progression. The growth curves of height and AL had the tendencies somewhat similar; the higher rates of myopic onset and progression were concomitants of the bone growth.Before the onset of myopia, the elongation of AL was slow, the compensations by other refractive components, refraction had little change or emmetropized slowly. During the onset of myopia, the elongation of AL speeded up markedly, other refractive components tried their best to resist the myopic tendency but insufficiently. During the process, the driving force of genetic factors to refractive change increased, probably acted through the shared genetic mechanism between height and AL. After the onset of myopia, the effects of environmental factors on AL enhanced; genetic factors’influence weakened on AL, but with similar effects on SER, so they might begin to prompt the myopic tendencies of other refractive components; the effect-weakened genes weren’t the shared genes between height and AL. The more myopic the SER in baseline, the less the myopic changes which occurred in refrective parameters, perhaps related to the increasing myopic defocus.ConclusionsThe onset and progression of myopia appear to be a consistent, gradual process; was associated with sex, age, myopic family history and height change rate.Under the influence of genetic and environmental factors, the effects of AL elongation to myopic change of SER enhanced before, during, and after myopia’s onset, the compensations and resistance of other refractive components peaked during the onset, then tended to promote the myopic progression after the onset.The myopic tendency of the children and juveniles was obviously, the prevalence and incidence were high compared to other cities in China and the world, with greater effects of environmental factors than other cities. It’s necessary to pay close attentions, give actively prevention, control the onset and progression of myopia. |
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