The basic properties of toric (spherocylindrical) lenses were introduced in the Quick-Start Guide. Unlike a rotationally symmetric lens (eg, sphere), which produces a point image of a point object, a toric lens always produces 2 linear “images” of a single point. As we have seen, the 2 focal lines are perpendicular to each other—one parallel to the cylinder axis, the other perpendicular to the cylinder axis. The focal lines are found at different distances from the lens, according to the vergence equation for the maximal and minimal powers of the principal meridians of the lens.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.