Final answer:
The ciliary body, part of the vascular tunic in the eye's middle layer, holds the lens in place via the suspensory ligaments and is essential for focusing light on the retina.
Step-by-step explanation:
The part of the middle layer of the eye that holds the lens in place via the suspensory ligaments is called the ciliary body. The ciliary body is a muscular structure that connects to the lens with suspensory ligaments, or zonule fibers. These structures work together to adjust the shape of the lens, which is essential for focusing light onto the retina at the back of the eye.
The ability to focus light correctly on the retina is crucial for clear vision. The ciliary body is part of the vascular tunic, which also includes the choroid and the iris. The ciliary body, along with the choroid, provides a blood supply to the eyeball and assists with controlling the shape and focal power of the lens.