Anterior scleral thickness is negatively correlated with axial length and positively correlated with age. Photo: Jie Zhou/BMC Ophthalmology. Click image to enlarge.

Many studies have confirmed changes in scleral composition, structure, biomechanics and remodeling during myopia progression, but few have been conducted on the connection between myopia and the anterior sclera. To help clarify this correlation, researchers aimed to compare anterior scleral thickness (AST) in people with emmetropia and myopia to explore its relationship with myopia. The team found that AST is negatively correlated with axial length (AL) and positively correlated with age.

A total of 93 participants (56 females, 37 males) aged 20 through 50 with emmetropia and myopia underwent ocular imaging through anterior segment OCT. Raw B-scan OCT images were acquired along each of the four meridians (superior, inferior, nasal and temporal). AST was estimated from the limbus to a distance of 6mm.

Study results revealed that scleral thickness varied significantly with AL and measurement location and found AST to be negatively correlated with AL and positively correlated with age. Compared with emmetropic eyes, the anterior sclera in highly myopic eyes was thinner.

Age turned out to be a significant influencing factor on AST. Previous studies have shown that the structure and composition of the sclera change with age and that the cross-sectional area of scleral collagen fibrils increases with age. “Moreover, the mean collagen fibril radius and intermolecular lateral spacing in the sclera also increase with age,” the authors wrote in their paper.

The results of this study match previous ones that found older age is associated with a thicker sclera. “However, an examination of Chinese cadaveric eyes showed no correlation between scleral thickness and age/sex,” the authors noted. “The different distances from the limbus at which the measurements were obtained and the different technology and devices used for the AST measurements may partly explain the different results.”

The superior meridians were the thinnest, which was consistent with previous studies as well. “The difference was that our study did not find the inferior meridians to be the thickest,” the authors explained. “One possible reason for this is when looking upward to the fully exposed inferior sclera, the inferior scleral thickness of the distal AST is easily affected by the ciliary body and the choroid.”

“Myopia affects not only posterior scleral thickness but also AST,” the authors concluded. “Accordingly, AST may be useful for monitoring the progression of myopia.”

Zhou J, He H, Yang Q, et al. Comparison of anterior sclera thickness in emmetropes and myopes. BMC Ophthalmol. February 14, 2023. [Epub ahead of print].