Abstract
Purpose:
Eye shape has been postulated to be a risk factor for refractive error. The purpose of this study is to determine if eye shape and size at birth are associated with refractive error and eye size 3 years later.
Methods:
A subset of 173 full-term newborn infants from the Growing Up in Singapore Towards healthy Outcomes (GUSTO) birth cohort underwent magnetic resonance imaging (MRI) to measure the axial length (AL), height, width, volume and surface area of the internal eye at birth. Eye shape was assessed by an index of oblateness, calculated as 1-(AL/width) or 1-(AL/height). Oblate eyes had oblateness >+0.01, spherical eyes had oblateness between +0.01 and -0.01, and prolate eyes had oblateness <-0.01. Cycloplegic autorefraction and optical biometry (IOLMaster) were performed 3 years later.
Results:
In total, 346 eyes of 173 children were analysed. The majority were male (94 children, 54%) and of Malay (43%) or Chinese (43%) origin. Most eyes were prolate at birth. At three years, the mean AL was 21.74±0.68mm (range 19.77-23.84), representing a mean increase from birth of 4.47±0.94mm (1.71-7.20). The mean spherical equivalent refraction(SER) was 0.91±0.80D (-2.40 to +3.47) and only a small proportion of eyes was myopic (8 eyes, 3.6%). After multivariate adjustment, eyes with longer AL at birth had smaller increases in AL at 3 years (p<0.001). Eyes with larger baseline volumes and surface areas had smaller increases in AL at 3 years (p<0.001 for both). Eyes which were more oblate at birth had greater increases in AL at 3 years (p<0.001). Using width to calculate oblateness, prolate eyes had smaller increases in AL at 3 years compared to oblate eyes (p<0.001), and, using height, prolate and spherical eyes had smaller increases in AL at 3 years compared to oblate eyes (p<0.001 for both). There were no significant associations between eye size and shape at birth and SER, corneal curvature or myopia at 3 years.
Conclusions:
Eyes that are longer, larger and have prolate or spherical shapes at birth exhibit smaller increases in AL over the first 3 years of life. Eye size and shape at birth influence subsequent eye growth but not the development of refractive error, suggesting adequate compensatory mechanisms to maintain emmetropia for at least the first 3 years of life.