Vitreous asteroid bodies. Ultrastructural characteristics and composition
B. W. Streeten
Ultrastructural studies were performed on five cases of asteroid hyalosis
of the human vitreous. The large asteroid bodies were composed if
intertwined ribbons of multilaminar membranes with a 6-nm periodicity
characteristic of complex lipids, especially phospholipids, lying in a
homogeneous background matrix. Clumps of dense material were interspersed
throughout the asteroids, and swirls of thin membranous strands often
surrounded them. The structure of small asteroid bodies suggested that the
lipid ribbons resulted from deposition of successive lipid layers on the
thin membranes, so that bodies with variable degrees of lipidization occur.
By energy-dispersive x-ray analysis, calcium and phosphorus were the main
elements detectable in asteroid bodies of all sizes. Electron-diffraction
structural analysis showed that calcium hydroxyapatite and, possibly, other
forms of calcium phosphate crystals were present in the focal densities.
Calcium may also be bound to phosphate groups in the phospholipids. The
large quantity of complex lipids and calcium in asteroids bodies suggests a
derivation from sources exogenous to the vitreous.
