Oscillations in the normal refractive development of young children

Abstract

Purpose : Since in infants both the optical power and axial length of the eye change rapidly, while receiving nearly no visual feedback before birth, it is almost impossible that they will immediately match each other at emmetropia. Instead, it seems more realistic that the growth rates of optical power and axial length gradually slow down and begin to oscillate, causing the resulting refraction to oscillate towards the target refraction in ever smaller steps. This work investigates the evidence for such oscillating behavior.

Methods : The mean refractive and biometry data of 46 previously published cross-sectional and longitudinal studies of children aged between 2 months preterm and 8 years postpartum were used in the analysis. These data were fitted with a damped harmonic oscillator, a well-known function in physics, as well as other functions published in the literature. For 3 longitudinal studies raw refractive data were also available, which allowed analyzing the refractive change rates.

Results : The damped harmonic oscillator function fits the data very well over the entire period considered (r² = 0.636), while from 0.25 – 8 years it outperforms an earlier regression by Mutti (r² = 0.517 vs. r² = 0.114, respectively). In the period from before birth until age 8 years ocular refraction begins at negative values (1 - 2 months preterm) and continues to increase until about 3 months postpartum, when it peaks at about +2.5D (see Figure). This is followed by a rapid power loss over the subsequent 9 - 12 months until the refraction reaches about +1D (emmetropization) and appears to “overshoot” this target, followed by a short positive trend and stabilization at +1D. This brief, but surprising refractive increase is also seen in three longitudinal studies (Ingram 1979, Abrahamsson 1988, Mutti 2018), as well as in the raw data of individual eyes in the form of a higher than expected number of individuals that showed a hypermetropization over 0.10D/month (20% vs. expected 1 - 2%).

Conclusions : Early refractive development appears to behave like a damped harmonic oscillator. Assuming the frequency and amplitude of these oscillations vary between individuals, this may be an alternative explanation for the tightening of the refractive distribution by the age of 6 years.

This is a 2020 ARVO Annual Meeting abstract.

 

Bubble plot of with the refractive data of 46 studies. Dashed line: cross-sectional studies; solid lines: longitudinal studies. Bubble size corresponds with the cohort size.