Refractive error at birth and its relation to gestational age

The refractive status of premature infants is not well studied. This study was done to find the norms of refractive error in newborns at different gestational ages.

One thousand two hundred three (1203) eyes were examined for refractive error by streak retinoscopy within the first week of life between June 2001 and September 2002. Tropicamide eye drops (0.8%) with phenylephrine 0.5% were used to achieve cycloplegia and mydriasis. The refractive error was measured in the vertical and horizontal meridia in both eyes and was recorded to the nearest dioptre (D). The neonates were grouped in five gestational age groups ranging from 24 weeks to 43 weeks.

Extremely preterm babies were found to be myopic with a mean MSE (mean spherical equivalent) of -4.86 D. The MSE was found to progressively decrease (become less myopic) with increasing gestation and was +2.4 D at term. Astigmatism of more than 1 D spherical equivalent was seen in 67.8% of the eyes examined. Among newborns with > 1 D of astigmatism, the astigmatism was with-the-rule (vertical meridian having greater refractive power than horizontal) in 85% and against-the-rule in 15%. Anisometropia of more than 1 D spherical equivalent was seen in 31% babies.

Term babies are known to be hypermetropic, and preterm babies with retinopathy of prematurity (ROP) are known to have myopia. This study provides data on the mean spherical equivalent, the degree of astigmatism, and incidence of anisometropia at different gestational ages. This is the largest study in world literature looking at refractive errors at birth against gestational age. It should help understand the norms of refractive errors in preterm babies.