Which of the following is true regarding the vertex distance in optical dispensing?

The correct statement regarding the vertex distance in optical dispensing is that it affects the effective power of the lens. Vertex distance refers to the space between the back surface of the lens and the front of the cornea. When this distance changes, it can alter the effective power of the lens perceived by the wearer.

For example, if a person has a high prescription, even a small increase in vertex distance can lead to a significant change in how the lens performs optically. This effect is particularly crucial for high prescription glasses, where even a few millimeters can impact clarity and visual comfort. Therefore, understanding vertex distance is essential for accurate lens fitting and ensuring optimal vision.

The other options do not accurately represent the significance of vertex distance. It's not unrelated to lens performance, as its variation directly influences how lenses function. Additionally, vertex distance is not limited to reading glasses but is a critical factor for all types of lenses, especially those used for distance vision. Lastly, while vertex distance is about the distance from the lens to the eye, it is not simply about the lens to frame distance; it particularly refers to the distance from the back of the lens to the eye's corneal surface.