Corneal neovascularization refers to the growth of blood vessels in the cornea, which normally lacks blood vessels. This most frequently results from corneal oxygen deprivation, or hypoxia. In response to this hypoxia, the body attempts to provide necessary nutrients and oxygen to the deprived corneal tissues by the creation of new blood vessels. During the early stages, this abnormal growth of blood vessels may produce no signs at all, or it may cause a variety of symptoms, including eye pain and excessive tearing, light sensitivity, redness, intolerance to contact lenses, and decreased vision.
Normally, the cornea is avascular, or lacking blood vessels, because it needs to be transparent to allow the passage of light for proper focus and sight. This lack of blood vessels means that the cornea must absorb oxygen from the air, and therefore any process that inhibits this absorption may cause corneal neovascularization. Most commonly, this pathology is caused by contact lens wear, with a greater incidence in prolonged contact lens wearers, considered anything over approximately 10 hours per day.
The reported prevalence varies from 1-30 percent among people who wear contact lenses, with a higher incidence in those wearing traditional soft plastic lenses than in those wearing newer, oxygen-permeable lenses. An increased risk is reported in contact lens wearers who have several underlying conditions, including high myopia, chronically dry eyes, or ocular surface disease, which generally defines a group of disease processes that affect the cornea and/or the conjunctiva. Other causes of corneal neovascularization include eye trauma, toxic chemical injuries, immunological diseases, infectious diseases such as keratitis, and cornea graft rejection.
In many cases, contact wearers experiencing only superficial neovascularization can promote healing by discontinuing contact wear, or by decreasing wearing time and switching to oxygen-permeable lenses. For cases of non-superficial neovascularization, more aggressive treatments may be required, such as the application of topical corticosteroids, hyperbaric oxygen treatment, or photodynamic therapy. Occasionally severe corneal neovascularization may cause corneal scarring, which leads to corneal opacity and serious vision problems, and in these cases corneal transplant may be necessary.
Corneal transplant, also known as corneal grafting or keratoplasty, is a surgical procedure that replaces a damaged cornea with corneal tissue from a recently deceased donor. These transplants often have a much lower rate of rejection than other transplant surgeries because the cornea normally lacks both blood and lymphatic vessels; therefore, the presence of these blood vessels prior to transplant is a risk factor for rejection. Also, even patients who did not have corneal neovascularization prior to surgery may develop this condition after undergoing a corneal transplant, leading to greater risk of rejection. For this reason, aggressive treatment of neovascularization may be necessary prior to corneal transplant surgery to ensure a lower chance of graft rejection.