Myoastrocytes in vitreous membrane in nontraumatic giant retinal tear

Ten cases with giant retinal tear and subsequent tractional retinal detachment were classified into three groups; 6 cases with nontraumatic origin, 2 cases due to blunt trauma and 2 cases due to posterior penetrating trauma. Open sky vitrectomy was performed and a total of 42 specimens of vitreous membranes were removed during surgery. The vitreous membranes of each group were studied by electron microscopy and the cellular elements were compared among these groups. In all three groups, five types of cells were observed, ie, retinal pigment epithelial cells, macrophages, fibroblasts, myofibroblasts and astrocytes. However, only in nontraumatic cases were found cells of another type which contained both glial filaments with the diameter of 9 nm and actin-like filaments with the diameter of 4 nm in their cytoplasm; they were called myoastrocytes from their cytoplasmic characteristics. Other cytoplasmic elements of the myoastrocytes were deeply indented nuclei, endoplasmic reticulum and pseudopodia with large cytoplasm. The myoastrocytes were considered to contribute to the contraction of the proliferative membrane in the eye with nontraumatic retinal tear, as the myofibroblasts do in the eye with traumatic retinal tears.