Certified Ophthalmic Assistant Practice Exam

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

1. Conoid of light

2. Conoid of Sturm

3. Vertex of lens

4. Principal focus

The correct answer is: Conoid of Sturm

The area between the two principal points of a spherocylindrical lens is referred to as the "Conoid of Sturm." This term is significant in optics as it describes a specific area formed by the intersection of the optical paths from a spherocylindrical lens. The Conoid of Sturm represents the distribution of light rays that pass through the lens and focuses at different points depending on their orientation, producing astigmatism. Understanding the Conoid of Sturm is crucial in correcting astigmatism in patients, as it highlights how cylindrical lenses alter light paths to achieve a clear focus. This area is critical for prescriptive lenses as it helps practitioners realize the behavior of light when it transits through lenses with different curvature axes, aiding in accurate eye refraction and lens design. In contrast, the other terms provided describe different optical concepts. The Conoid of light pertains to a different geometrical shape that arises in lens systems not specifically related to astigmatism. The vertex of the lens refers to the highest point on the lens surface but isn't relevant to the area formed between principal points. The principal focus refers to the point where parallel rays of light converge after passing through the lens but does not denote the area between the principal points