Abstract
Purpose :
The sclera plays a key role in the maintenance of structural integrity and provides mechanical support to the eye. There is substantial evidence that myopic scleral remodeling contributes to biomechanical weakening, leading to further progression and associated pathologies. A precise characterization of regional ultrastructure is needed for a better understanding of scleral remodeling. The purpose of this study was to characterize the sclera ultrastructure from healthy rhesus monkeys.
Methods :
Transmission electron microscopy (TEM) images of the sclera from both eyes of two healthy rhesus monkeys were analyzed. Monkeys underwent normal emmetropization in a primate nursery illuminated with fluorescent lights of 480 lux on a 12-hr light/12-hr dark cycle. After 150 days, scleral tissue was collected in strips from equatorial nasal, equatorial temporal, and posterior regions and processed for TEM. Images were captured at three depths, outer, middle, and inner, for all regions. Fibroblast volume fraction, collagen fibril diameter, and volume fraction of fibrillin microfibrils were quantified using stereology and manual segmentation. Descriptive statistics (reported as mean ± sd) and ANOVAs were performed for metrics across all depths and regions.
Results :
Spherical equivalent refraction for the 4 eyes was +1.7 to +3.2 diopters. A total of 103 micrographs were analyzed to compute the volume fraction of fibroblasts and fibrillin microfibrils. The inner layer of the equatorial temporal region had the highest mean fibroblast volume fraction (15.4 ± 1.5%) while the outer layer of the posterior sclera had the lowest (3.2 ± 1.2%). For fibrillin microfibrils volume fraction, the outer layer of the equatorial nasal (2.8 ± 1.4%) and temporal regions (2.8 ± 0.9%) had the largest values while the outer layer of the posterior sclera had the smallest value (0.8 ± 0.4%). Analyzing a total of 3564 collagen fibrils by counting 396 per region and layer, revealed a mean diameter of
84 ± 28 nm (range: 61.6 nm to 113.9 nm). Mean fibril diameters in the outer layer were significantly smaller than middle and inner layers (P<0.001).
Conclusions :
In normal rhesus monkey eyes, scleral ultrastructure varies as a function of depth and region. These fundamental normative data are important for future studies investigating myopic scleral remodeling, where axial elongation and scleral thinning are known to show regional differences.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.