What characteristic of the human cornea makes corneal transplantation possible?

The characteristic of the human cornea that makes corneal transplantation possible is the absence of blood vessels. This avascular nature is crucial because it significantly reduces the chances of rejection after a transplant. The cornea is nourished by the tear fluid and the aqueous humor rather than by blood vessels, which minimizes the immune response that would typically be triggered by the introduction of foreign tissue.

Furthermore, because the cornea does not have a direct blood supply, it lacks the immune cells found in blood, allowing transplanted tissue to integrate better without provoking a strong rejection response. This feature is essential for the success of corneal grafts, making transplantation a viable option for patients with corneal opacities or other conditions impairing vision.

While other choices, such as the high regenerative capacity, transparency, and presence of corneal epithelium, are important attributes of the cornea, they do not primarily relate to the unique advantage that facilitates successful corneal transplants. High regenerative capacity pertains to the maintenance and repair of the cornea, transparency is vital for vision, and corneal epithelium plays a role in protection and healing, but these aspects do not directly influence the transplant's acceptance or immediate success like the absence of blood vessels does