Complex sentence: The constant is a theoretical value that relates the lens power to AL and keratometry, it is not expressed in units and is specific to the design of the IOL and its intended location and orientation within the eye.
Split into simpler sentences: The constant is a theoretical value that relates the lens power to AL and keratometry. The A constant is not expressed in units and is specific to the design of the IOL and its intended location and orientation within the eye.