Final answer:
The first ADD segment in a trifocal lens improves the user's vision for intermediate distances, commonly for tasks at arm's length such as computer work.
Step-by-step explanation:
The first ADD segment of a trifocal lens helps with seeing objects at an intermediate range, which is typically between 18-24 inches away from the eyes. These lenses are primarily designed for individuals who require correction for multiple distances. The lens essentially has three focal points: one for distance at the top, the intermediate ADD segment in the middle, and one at the bottom for close-up tasks like reading.
Trifocals are especially useful for tasks such as working on a computer or viewing objects on a desk, providing a smoother transition between near and far vision compared to bifocals. The first ADD segment allows for more comfortable vision at arm's length, which is essential for intermediate tasks that are too close for the distance portion of the lens and too far for the near portion.