Mast cell in the cornea

Transmission electron micrograph showing a mast cell invading the central cornea of a patient with a corneal ulcer. The cell is surrounded by layers of collagen fibrils containing some lipid accumulation. The cell's nucleus is at the top of the cell and below are a number of heparin/histamine-containing cytoplasmic granules and mitochondria. The field is approximately 11 microns across.