The measuring magnifier may be used to measure which of the following GP parameters?

The measuring magnifier is a specialized tool used in the fitting and evaluation of gas permeable (GP) contact lenses. It allows practitioners to obtain precise measurements of various lens parameters, which is essential for ensuring proper fit and comfort for the wearer.

The correct answer identifies that the measuring magnifier can be used to measure the posterior optic zone diameter and the overall diameter of GP lenses. The posterior optic zone diameter refers to the curvature of the back surface of the lens that directly interfaces with the cornea, while the overall diameter is the complete lateral measurement of the lens from edge to edge.

These measurements are crucial during the fitting process since they directly influence the lens's effectiveness and the wearer's comfort. Accurate determination of these dimensions helps practitioners customize lenses based on individual anatomical variations and visual needs.

In contrast, while options might mention other parameters like thickness, base curve, or secondary curve radii, the measuring magnifier is specifically suited for the two parameters highlighted in the correct answer. The posterior optic zone diameter and overall diameter are fundamental to assessing the lens shape and its suitability for the patient’s eye.