What is the usual truncation size for a contact lens?

The usual truncation size for a contact lens being in the range of 0.5 to 1.5 mm is aligned with the common practices in fitting lenses, particularly those designed for specific visual corrections or to enhance comfort and stability on the ocular surface. Truncation refers to a method where a portion of the lens is removed or flattened, typically at the bottom edge, to help with centration and stability during blinking.

This particular range is optimal for ensuring that the lens can sit properly on the eye without causing undue pressure or discomfort. In the context of eye anatomy and how lenses interact with natural tears and the eyelids during movement, a smaller truncation helps maintain proper alignment while minimizing the chances of lens displacement.

Other sizes either exceed this range or may not provide the necessary stability for effective use, which makes 0.5 to 1.5 mm the preferred choice for most contact lenses requiring truncation.