What does the term axis refer to in a spherocylindrical lens?

The term "axis" in a spherocylindrical lens specifically refers to the meridian of no cylinder power. In the context of a cylindrical lens, the axis indicates the orientation of the cylinder correction, which is essential for correcting astigmatism. The axis is measured in degrees, ranging from 0 to 180, and it designates the specific meridian that does not have any additional cylindrical power applied to it. This means that along this axis, the lens provides spherical power only, while the cylindrical power is present in the perpendicular meridian.

Understanding this concept is crucial for optometric technicians as they prepare lenses for patients who require astigmatic correction. The correct placement of the axis ensures that the cylindrical correction aligns properly with the patient's visual needs. Furthermore, this knowledge aids in accurately interpreting prescriptions and ensuring that the lenses manufactured or recommended will help the patient achieve optimal vision.