Corneal neovascularization (CNV) is the in-growth of new blood vessels from the pericorneal plexus into avascular corneal tissue as a result of oxygen deprivation. Maintaining avascularity of the corneal stroma is an important aspect of healthy corneal physiology as it is required for corneal transparency and optimal vision. A decrease in corneal transparency causes visual acuity deterioration. Corneal tissue is avascular in nature and the presence of vascularization, which can be deep or superficial, is always pathologically related.

Corneal neovascularization is a sight-threatening condition that can be caused by inflammation related to infection, chemical injury, autoimmune conditions, immune hypersensitivity, post-corneal transplantation, and traumatic conditions among other ocular pathologies. Common causes of CNV within the cornea include trachoma, corneal ulcers, phlyctenular keratoconjunctivitis, rosacea keratitis, interstitial keratitis, sclerosing keratitis, chemical burns, and wearing contact lenses for over-extended periods of time. Superficial presentations of CNV are usually associated with contact lens wear, while deep presentations may be caused by chronic inflammatory and anterior segment ocular diseases.

Corneal neovascularization has become more common worldwide with an estimated incidence rate of 1.4 million cases per year, according to a 1998 study by the Massachusetts Eye and Ear Infirmary. The same study found that the tissue from twenty percent of corneas examined during corneal transplantations had some degree of neovascularization, negatively impacting the prognosis for individuals undergoing keratoplasty procedures.

In advanced stages, corneal neovascularization can threaten eyesight, which is why routine (annual) eye exams are recommended for contact lens patients.

CNV causes may be congenital in nature—such as with aniridia—or acquired. Frequently, inflammatory, infectious, degenerative, traumatic, or iatrogenic (e.g., contact lenses) conditions can be responsible for acquired CNV.

Some major acquired inflammatory conditions include graft rejection following keratoplasty, graft or host diseases of the new tissue, atopic conjunctivitis, rosacea, ocular pemphigoid, Lyell's syndrome, and Stevens–Johnson syndrome.

Infections responsible for CNV range from the bacterial (chlamydia, syphilis, pseudomonas) and viral (e.g., herpes simplex & herpes zoster viruses) to the fungal (candida, aspergillus, fusarium) and parasitic (onchocerca volvolus).

Degenerative diseases such as pterygiums and Terrien's marginal degeneration may also be responsible.