What is the area between the two focal points of a spherocylindrical lens called?

The area between the two focal points of a spherocylindrical lens is referred to as the Conoid of Sturm. This term describes the specific geometric figure that represents the distribution of light rays coming from a point source as they pass through an astigmatic lens, such as a spherocylindrical lens. In essence, the Conoid of Sturm captures the lens's ability to focus light at two different focal points in two different meridians, which is characteristic of astigmatism.

The concept is critical in understanding how spherocylindrical lenses correct vision, as they address the variations in light refraction that occur due to the cylinder shape of the lens. Consequently, recognizing this area is essential for eye care professionals to formulate accurate prescriptions and provide effective visual correction for patients with astigmatism. Other terms available in the choices do not relate specifically to the concept of the area defined by the focal points in a spherocylindrical lens, making the Conoid of Sturm the most relevant and correct term in this context.