The posterior sclera of a highly myopic eye doesn’t follow normal fibrillar organization, according to a recent study. Compared with non-myopic eyes, myopic specimens exhibited notable alterations in the peripapillary sclera, including a partial loss of circumferential collagen alignment and a redistribution of the normally observed regional pattern of collagen anisotropic proportion.
Researchers used wide-angle x-ray scattering mapping to determine bulk collagen orientation changes in seven non-myopic eyes and three eyes with high myopia (>6D of refractive error). The high myopia group showed a statistically significant increase in fiber angle deviation away from the normal circumferential arrangement with more radially oriented fibers present in the peripapillary sclera overall.
While the reported structural changes could be a consequence of scleral remodeling during axial lengthening, researchers proposed that the changes may represent a mechanical adaptation to increased tissue stresses in the enlarged eye. The elongated eyeball would increase the optic nerve traction force, causing a higher amount of optic nerve straightening for the optic nerve head to travel the same distance as that in a healthy eye. If that were to occur, then collagen remodeling might become more important than intraocular pressure or cerebrospinal fluid pressure, and collagen fibers would try to orient along the direction of higher stress, according to the study.
The researchers are currently building growth and remodeling models to help determine the most relevant forces responsible for a change in the collagen fiber orientation. The study concluded that structural changes in the peripapillary region may link to the increased susceptibility of myopic eyes to glaucoma development, as its data could help enhance future modeling studies of ocular biomechanical changes in myopia and glaucoma.
|Markov PP, Eliasy A, Pijanka JK, et al. Bulk changes in posterior scleral collagen microstructure in human high myopia. Mol Vis. 2018;24:818-33.|