prism ballast, truncation, and dynamic stabilization
Contact lenses may have rotational movement with blinking. In general, the inferior edge of the lens moves laterally and/or up with a blink.
In the fitting of a toric contact lens, this is not desirable, because the axis of the cylinder needs to remain in the same position.
There are various methods of stabilization.
1. Prism ballast:
The inferiorly thickened portion of the lens at the 6 o’clock position acts as a weight.
2. Truncation:
The inferior portion of the contact lens is cut off hori-zontally, forming a thicker edge that is supported by the inferior lidmargin.
3. Dynamic stabilization:
The superior and inferior borders of the con-tact lens are beveled so that the thinnest portion of the lens is posi-tioned under the lid margin, preventing rotation of the lens.
Tags:
Contact lens