Birth weight cannot be used as an indicator for refractive status at least in children 40 months or older. Photo: Getty Images.

As children with retinopathy of prematurity (ROP) often have myopia, it’s been hypothesized that size and weight at birth could potentially be linked to refractive error. Birth weight and refraction have proven to be related immediately after birth; however, this relationship tends to wane rather quickly. After recent observation of a group of children at 40 months of age, researchers detected no significant correlation between birth weight and spherical equivalent (SE).

Participants of the study underwent medical examinations between 2018 and 2019 at 40 months old (n=411). None had eye diseases such as ROP. Non-cycloplegic refraction testing was performed using a Spot Vision Screener, and birth weight was identified from each patient’s medical record. Children were then split into three groups based on birth weight: normal (2,500g to 3,500g), high (>3,500g) or low birth weight (<2,500g).

The data revealed no correlation between birth weight and SE for the right eye (which was used for analysis since the left and right eye showed no significant difference in SE). The mean SE was the same across all three groups based on a one-way analysis of variance.

The researchers suggested the current weight of a child may have more to do with refractive error than birth weight or size.

“Children aged seven to nine years who were heavier or had a higher BMI tended to have more hyperopic refractions,” the researchers explained in their study. “It appears that while refraction in a child’s eye is affected by birth weight and by gestational age immediately after birth, as the child grows up, only the current weight of the child perhaps affects SE since we have shown that birth weight and gestational age are not related to refraction at 40 months of age.”

While birth weight may correlate with refractive status for a newborn infant, the parameter cannot be relied on as a means of predicting SE as the child grows older.

Tatara S, Ishii M, Nogami R. Birth weight and refractive state measured by Spot Vision Screener in children aged 40 months. BMJ Open Ophthalmol. November 23, 2021. [Epub ahead of print].