Optomechanical mouse
The optical-mechanical or Optomechanical mouse consists of a ball that rolls one of two wheels inside the mouse. This wheel contains a circle of holes
or notches that allow a LED light to be shined through and detected by a sensor, as each wheel spins they represent the X or Y axis for the mouse pointer. This mouse is much more accurate than the traditional mechanical mouse that used only wheels and rollers, however is not as good as an optical mouse.
Also see: Mechanical mouse, Mouse definitions, Optical mouse