Biomaterials for refractive correction: corneal onlays and inlays

Corneal inlays and onlays represent a means of providing patients with permanent refractive error correction. As an alternative to conventional spectacles and contact lens, these techniques are less invasive compared with laser-based refractive surgery and are reversible. In this review, we provide a brief overview of the anatomic microstructure of the human cornea, indicating the primary physiological function for each component. Next, the wide range of biomaterials used as corneal inlays and onlays are considered, from synthetic polymers to biological components derived from the extracellular matrix. The limitations and challenges associated with the most common materials are discussed as is the need to improve their properties to achieve long-term, complication-free intraocular implantation. Finally, the prospect of applying tissue engineering strategies is noted for its potential to generate autologous corneal tissue that could be implanted as the optimal inlay or onlay materials.