The Oblique Meridian Calculator is a specialized optical calculator used to determine the exact refractive power of a spherocylindrical lens at any specific, given angle. In other words, if you have a prescription with a certain sphere power, cylinder power, and axis, and you want to know how much total power that lens exerts along a different, "oblique" meridian—or precisely at the standard 90° or 180° axes—this calculator does precisely that.

Unlike an obliquely crossed cylinders calculator (which merges two different lenses), this tool analyzes a single existing lens prescription. Because a astigmatic (cylindrical) lens changes its power gradually as you rotate away from its principal axis, finding the exact power at an intermediate angle requires complex trigonometric calculations. This calculator automates that math, allowing opticians and lab technicians to plug in a patient's Rx alongside a "desired axis" to instantly see the total dioptric power acting along that specific meridian.