What is referred to as the sagittal depth of a lens?

The sagittal depth of a lens refers specifically to the distance from a flat reference surface, typically the plane of the lens frame or the point where the lens sits in the eye, to the most anterior point of the back surface of the lens. This measurement is crucial in determining how the lens will fit in the frame and how it interacts with the eye.

Understanding this concept is fundamental for ensuring proper lens positioning, which affects vision quality and comfort. The sagittal depth helps opticians assess how the lens aligns with the cornea and the overall ocular surface, which is important for prescription accuracy and fitting success.

By contrast, the choices that pertain to the distance from the front to the back surface, the thickness at the center, and the curvature of the lens edge focus on other aspects of lens construction or design, rather than the specific measurement defined as sagittal depth.