Abstract
Purpose:
To establish the relationship of change in refraction over a period of 5-6 years with changes in ocular biometric and anthropometric measures.
Methods:
Sydney Myopia Study participants aged 6 and 12 years were re-examined 5-6 years later in the Sydney Adolescent and Vascular Eye Disease Study (SAVES). Axial length (AL), anterior chamber depth (ACD) and corneal radius (CR) were measured using the IOLMaster (Carl Zeiss, Germany). Spherical equivalent refraction (SER) in dioptres (D) was calculated from cycloplegic autorefraction (cyclopentolate 1%; Canon RK-F1) and myopia was defined SER ≤-0.50D. All measures, including height and weight, were established at baseline and follow-up using the same methodology. Ethnicity was defined by self identified origin of both parents.
Results:
Complete longitudinal refractive data was available for 2059 children; 863 with an average age of 12.8 years at follow-up and 1196, mean age 17.2 years. There was significant change in SER from baseline to follow-up for both cohorts and for all biometric measures, including AL/CR (p<0.0001). Change in height was not correlated with shift in SER in either cohort when stratified by ethnicity. In a multivariate model adjusted for height and ethnicity, change in SER was significantly associated with change in AL and AL/CR (p <0.0001) in both the younger and older cohorts. CR marginally flattened (0.05, 0.02mm, younger and older cohorts respectively). The power of the cylindrical component of SER marginally decreased (0.02D, p = 0.039) in the younger but not older cohort, however, for those with myopia compared to those without, there was an increase in the cylindrical power for those with baseline (p=0.001) and incident myopia (p<0.0001) in the older cohort and only baseline myopia in the younger cohort (p=0.017). In both cohorts, myopia remained significantly associated with change in cylindrical power on multivariate analysis (p<0.0001).
Conclusions:
Change in refraction was significant associated with change in AL and AL/CR, while the change in CR though statistically significant was clinically insignificant. General growth including height was not associated with change in SER. An increase in the cylindrical component of refraction was significantly associated with existing myopia at all ages and with incident myopia in the older cohort.
Keywords: 677 refractive error development •
461 clinical (human) or epidemiologic studies: natural history •
605 myopia