This study examined temporal ocular growth curves of a large cohort of Singaporean children who were 6 to 10 years of age at baseline and subsequently developed myopia. Their growth and rate of changes before and after the onset of
82 myopia were compared to matched-emmetropia values. We showed that the children with newly developed myopia had a more rapid shift of refraction towards myopia 2 to 3 years before the onset of myopia when compared to matched-emmetropia. These are clinically important results for personalised medicine as we could predict that children with SE between –0.4 to 0.4 D may have a high chance of developing myopia in the next few years. Similarly, children who had newly developed myopia had more rapid elongation of AL and VCD 3 years before myopia onset. In addition, we identified that the ACD of these children deepened at a faster rate than matched- emmetropia 3 years before myopia onset. Finally, we observed no differences in growth and rate of change curves for LT and CR between children with newly developed myopia and matched-emmetropia before and after the onset of myopia.
Our study suggests that the children with newly developed myopia were less hyperopic than their matched-emmetropia 3 years before the onset. This result agrees well with the finding of Ojai longitudinal study and the CLEERE study.(Hirsch, 1964;
Mutti, Hayes, Mitchell, et al., 2007) The Ojai longitudinal study of California school children aged 5 or 6 (n = 261 eyes) identified refractive error as a relevant predictor before the onset of myopia. They reported that the children with less hyperopia have higher risk of developing myopia during their elementary schools years. Our study found that the rate of change in SE was greater and more rapid from 3 years prior to the onset through 1 year after the onset for children who had developed myopia.
Their myopia progression was most rapid at 1 year after the onset. The CLEERE study, however, reported the time of most rapid refractive change was during the year before onset.
83 Our study also found that the mean SE of –0.5 D was only observed at approximate 0.5 years before the onset and this suggest that the window for predicting onset based on SE of –0.5 D is very limited. If the child’s SE is about 0.42 D, the child may develop myopia in the next 3 years based on our results. If the SE of child is between 0.2 D and 0.4 D, the child may develop myopia in the next 1 to 2 years.
Hence, this information is useful to eye care professionals to provide preventive advice for children with SE between –0.4 D and 0.4 D. For children with SE between –0.4D and 0.4 D with parental myopia, and other risk factors for myopia, interventions such as increased time outdoors may be implemented to prevent or slow the progression of myopia.
Our study shows a rapid elongation of AL, greater increase in VCD and ACD from 3 years before myopia onset for children with newly developed myopia.
Compared to the CLEERE study, we found that the AL was elongated in a similar fashion to our SCORM study. Their largest magnitude of change was observed between 1 year before onset and the year of onset, but the largest change observed in our children was during the year of onset. On the contrary, a longitudinal study conducted in China reported that the myopic and non-myopic eyes did not differ statistically in AL, VCD and ACD before the onset of myopia.(Mei & Rong, 1994) This study followed up 194 initially emmetropic eyes (SE between –0.25 D to +0.75 D) of 178 schoolchildren aged 9 to 12 years for a period of 1 to 2 years. Similar insignificant differences in these ocular components 1 year before the onset were also reported in a 3-year longitudinal study of 29 children who became myopic and 56 children who remained emmetropic in United States.(Goss & Jackson, 1995) These findings may be limited by the small sample size and relatively short period of follow up.
84 The growth and rate of change for LT and CR between 4 years before onset and 4 years after onset were minimal and no significant differences was observed in children who had newly developed myopia and those who had emmetropia. Our finding for LT is in agreement with the previous longitudinal studies which reported insignificant difference in the LT before onset of myopia.(Goss & Jackson, 1995; Mei
& Rong, 1994) Our results for CR are also consistent with previous findings that CR is relatively stable since it’s development is virtually complete by the age of 2 to 3 years.(Weale, 1982)
Our study is the first Asian longitudinal study to compare the refractive error and ocular components before and after the onset of myopia using fractional polynomial functions of yearly data between ages 6 to 13 years old among children with newly developed myopia and persistent emmetropia. Our study has a relatively large sample size with longitudinal biometry data and high follow-rate of 90% for children with at least 3 visits. One of the strengths of this study is the addition of VCD, ACD, LT and CR to the CLEERE study.(Mutti, Hayes, Mitchell, et al., 2007)
One limitation of our study is that we did not follow up a sufficient number of children with long follow-up time for us to study any long-term ocular biometric changes. Prospective studies could include a longer and standardised follow-up time from a younger age to adulthood to establish the overall pattern of eye growth before and after the myopia onset. The lack of lens power data is another study limitation.
Including such data will provide more insight on ocular biometric changes. Research studies with a larger number of Malay and Indian children to determine if there is any ethnic variation in the ocular growth patterns before and after the onset of myopia could be considered.
85 The changes in refraction and other ocular components such as AL and VCD prior to myopia onset are important to predict which child may develop myopia in the subsequent years. The interventions could also be personalised for individuals based on these changes. Our findings showed that the children with SE between –0.4 to 0.4 D may have a higher risk of developing myopia in the next 3 years. When the SE of the child falls within these ranges, education, interventions and risk factors modification could be initiated to prevent the development of myopia. As compared to Caucasian children, Asian children have earlier onset and higher rates of progression of myopia. However, our findings were generally similar to Western populations, and therefore further studies need to be carried out to determine other factors influencing prevalence rate.
In conclusion, our cohort study in Asian children showed that 3 years prior to myopia onset, these eyes had more myopic refraction, and tended to have more rapid growth in AL and more rapid increase in VCD and ACD. Our studies also suggest that SE and major ocular components including AL, VCD and ACD could potentially be used to predict the development of high myopia in children.