This retrospective cohort included premature children (less than 37 weeks gestational age) born between 10/2011 and 8/2013 with ≥ two cycloplegic refractions. Cycloplegic refractions were converted into power vectors: (spherical equivalent), [positive for with-the-rule (WTR) and negative for against-the-rule (ATR) astigmatism], and (oblique astigmatism). Each power vector component was fitted by multilevel mixed-effects linear regression models; the mean change over time was analyzed.
Mean was 0.59 (95% CI 0.53-0.66) at six months and 0.29 (95% CI 0.19-0.39) at 18 months; afterward, the change was <0.1 per year. decreased -0.32 (0.64 diopters) over three years. When analyzed in one-year increments, the mean change in and was lowest at 24 months. decreased 1.13 diopters over three years.
WTR astigmatism and spherical equivalent decreased over the first three years of life. WTR astigmatism accounted for the majority of amblyopogenic refractive errors. The change in leveled after 18 months and the lowest rate of change was at 24 months in and , thus it may be appropriate to screen this high-risk population around 18-24 months.