Subfoveal Choroidal Thickness is Independently Associated with Axial Length and Myopia in Preschool Children: A Swept-Source Optical Coherence Tomography Study

The current study assessed subfoveal choroidal thickness (SFCT) in Chinese preschool children using swept-source optical coherence tomography (OCT) and evaluated its associations with age, sex, axial length, refractive status, family history of myopia, and corneal curvature. In this cross-sectional observational study, 303 eyes of 303 preschool children with no ocular diseases underwent comprehensive ophthalmic examinations, including cycloplegic refraction. SFCT was measured using swept-source OCT. Factors affecting changes in SFCT were analyzed using a general linear model. The mean SFCT was 326.33 ± 43.01 μm (range 198.67–438.33 μm) in children aged 3–6 years. The myopic group had significantly thinner SFCT than the emmetropic group (305.66 ± 41.18 μm vs. 347.41 ± 33.68 μm; p < 0.05). After adjusting for covariates, SFCT remained significantly lower in the myopic group (317.23 μm vs. 338.42 μm; mean difference: 21.19 μm, 95% confidence interval 7.09–35.28 μm). Myopia significantly affected SFCT (F = 8.75, p = 0.003, η2 = 0.029). SFCT was positively correlated with spherical equivalent refraction (β = 6.47, p = 0.036) and negatively associated with axial length, particularly in the myopic group (β = − 10.29, p = 0.023). There were no significant differences in SFCT associated with age group, sex, or family history of myopia (all p > 0.05). In preschool children, myopia is associated with significantly thinner SFCT, which is independently influenced by spherical equivalent refraction and axial length, but not by age, sex, or family history of myopia. These findings suggest that SFCT may serve as a responsive indicator of early myopic changes in preschoolers, though longitudinal studies are needed to determine its temporal relationship with axial elongation. Myopia (nearsightedness) is becoming more common in young children, but the early structural changes in the eye associated with it are not fully understood. Myopia occurs when the eyeball grows longer than normal, causing light to focus incorrectly in front of the retina instead of directly on it. This elongation of the eye affects structures such as the choroid, a thin layer of tissue that supplies blood to the retina. This study examined the choroid—a blood-rich layer in the posterior ocular wall that nourishes the retina—in 303 healthy Chinese children aged 3–6 years. Using a non-invasive imaging method called optical coherence tomography, researchers measured the thickness of the choroid under the center of the retina. Children with myopia had a thinner choroid (average 306 μm) than those with normal vision (average 347 μm). This difference remained after accounting for factors like the child’s age or sex. A thinner choroid was also linked to longer eyeballs and greater nearsightedness, particularly in myopic children. The association between a thin choroid and myopia was not affected by the child’s age, sex, or family history of myopia. These findings suggest that choroidal thinning may be an early sign of myopia development in preschool children. However, long-term studies are needed to clarify whether choroid changes happen before or after the eye starts to elongate.