Oedema of some cells of the corneal endothelium which bulge towards the aqueous humour. With specular microscopy or with high magnification biomicroscopy the cells appear as black areas as they do not reflect light towards the observer. Blebs occur within minutes of inserting a contact lens on the eye and disappear within hours after insertion. They may result from a local acidic pH shift at the endothelium. See endothelial bedewing; corneal endo-thelium; specular reflection illumination.