3D Bioprinting in Anterior Segment Ocular Tissue Engineering: Advances, Challenges, and Translational Pathways-A Systematic Review.

Bioprinting has been proposed for nearly every structure of the anterior eye, but the effort is unevenly spent. We systematically reviewed 71 experimental studies of bioprinting across the anterior segment: cornea, conjunctiva, sclera, lens, lacrimal gland and eyelid. Most work targets the corneal stroma. The endothelium, the layer most often replaced surgically and the first to reach a clinical trial, accounts for the fewest preclinical studies. Beyond the cornea, printed constructs are mostly disease models rather than implants, and the iris, trabecular meshwork and ciliary body remain untouched. Preclinical testing remains short-term and confined to small animals. Studies measure the same properties in different ways, so constructs cannot be compared across laboratories. We map what has been printed for each tissue and how far each construct stands from the clinic, and propose a minimum reporting set to make the next generation of studies comparable.