Changes in Stress-Strain Index in School-Aged Children: A 3-Year Longitudinal Study

Abstract

Purpose. To determine three-year change of the corneal biomechanical parameter stress-strain index (SSI) in schoolchildren aged 7– 9 years and their correlation with refractive error and axial length (AL). Methods. This is a prospective cohort study. Data of the AL, refractive error, and corneal biomechanical parameter SSI were collected at baseline and a 3-year follow-up for 217 schoolchildren. SSI, AL, and refractive error were measured via corneal visualization Scheimpflug technology (Corvis ST), IOLMaster biometry, and cycloplegic refraction. Three years of changes in SSI and its association with refractive error and AL were analyzed. Participants were divided into persistent nonmyopia (PNM), newly developed myopia (NDM), and persistent myopia (PM). The three-year difference in SSI among the three groups was analyzed. Results. After three years of follow-up, the corneal biomechanical parameter SSI decreased in all participants ( $P<0.01$ ). There was a negative correlation between the change in SSI and the change in AL (r = −0.205, $P=0.002$ ) and a positive correlation between the change in refractive error (r = 0.183, $P=0.007$ ). After three years of follow-up, there was a decrease in the SSI for the NDM, PM, and PNM participants, with a median change of −0.05 for PNM and −0.13 and −0.09 for the NDM and PM, respectively. There was a significant decrease in corneal biomechanical properties for NDM patients compared with PNM patients ( $P<0.01$ ). Conclusion. In 7- to 9-year-old schoolchildren, SSI decreased after three years of the longitudinal study, and the change in SSI was correlated with the change in AL and refractive error. There was a rapid decrease in corneal biomechanical properties among newly developed myopic patients.