A method of illumination used in slit lamp biomicroscopy, in which the source and the microscope are placed at equal angles from the normal to the corneal surface, so that the surface observed will be illuminated by the image of the source.
The reflection of sound waves from the surface of an internal structure, which can be used to produce a picture of the surface as an echogram. A specular reflection contrasts with vaguer diffuse echoes produced by minor differences in tissue density.