What is the longest vertical dimension of the lens segment referred to?

The term that describes the longest vertical dimension of the lens segment is known as segment depth. This dimension is crucial for understanding how a multifocal lens segment fits within the overall design of the lens and how it interacts with the wearer's visual needs. Segment depth refers specifically to the vertical measurement from the top to the bottom of the segment, thus playing a significant role in ensuring optimal viewing comfort.

In multifocal lenses, the segment depth is particularly important because it affects how the different sections of the lens are aligned with the wearer's line of sight. A proper segment depth ensures that the wearer can easily transition between different visual zones, such as from distance vision to near vision.

The other terms don't align with the definition as closely. Profile height generally refers to the overall contour of the lens profile rather than strictly the vertical segment dimension. Thickness pertains to the density or width of the lens itself rather than its vertical depth. Vertical length, while it may seem similar, does not specifically denote the part of the lens segment that is used for bifocal or multifocal purposes.