Which part of the bifocal lens facilitates near vision?

The correct answer is Lower part with convex lens.

Let us understand the design and working of a bifocal lens step-by-step:

1. What is a Bifocal Lens?
A bifocal lens is a corrective lens that contains two distinct optical powers. It is most commonly prescribed for people with presbyopia (a condition where the eye exhibits a progressively diminished ability to focus on near objects, usually due to aging) who also require correction for myopia (nearsightedness) or hyperopia (farsightedness).

2. Division of the Lens:
To accommodate both distance and near vision, a bifocal lens is divided into two sections:
• Upper Part: This portion is used for distance vision (looking straight ahead or far away). It typically contains a concave lens if the person has myopia, or a lens suited for distance correction.
• Lower Part: This portion is used for reading and viewing close-up objects. Since reading or performing close-up work requires looking downwards, the reading segment is placed at the bottom.

3. Lens Type for Near Vision:
Near-vision correction (for presbyopia or farsightedness) requires converging light rays before they enter the eye, so that they focus correctly on the retina rather than behind it. A convex lens (converging lens) is used to achieve this.

Therefore, the part of the bifocal lens that facilitates near vision is the lower part containing a convex lens.