Which of the following are two methods of stabilizing the rotation of rigid bifocal contact lenses?

Truncation and prism ballast are effective methods used to stabilize the rotation of rigid bifocal contact lenses.

Truncation involves cutting a portion of the lens at the bottom, which helps the lens to sit correctly on the eye by allowing it to align with the lower eyelid. This design helps reduce the lens's tendency to rotate, ensuring that the optical zones remain properly positioned for effective vision correction.

Prism ballast, on the other hand, incorporates a heavier area at the bottom of the lens. This lower weight helps to counteract any shifts that may occur due to eye movements or blinking. The additional weight directs the lens to settle in a consistent, stable position, enhancing wearer's comfort and vision because the bifocal segment remains centered over the pupil.

Both methods work together to enhance the stability of the lens on the eye, crucial for the effectiveness of bifocal corrections, where precise positioning can significantly impact visual performance and comfort.

The other methods mentioned do not specifically address the stabilization of rotation in bifocal lenses as effectively. For example, weight distribution and edge contouring may enhance comfort and fit but do not specifically target the stabilization of rotation.