Corneal neovascularization is the abnormal growth of new blood vessels onto the cornea, the clear, dome-shaped outer layer at the front of the eye. This condition involves vessels invading tissue that is normally free of blood vessels. The presence of these new vessels can interfere with the cornea’s natural transparency, as the cornea relies on its avascular nature for clear vision.
What is Corneal Neovascularization?
The cornea is a transparent, dome-shaped membrane that covers the iris, pupil, and anterior chamber of the eye. It functions as the eye’s outermost protective layer and is responsible for most of the eye’s total focusing power. Unlike most tissues, the healthy cornea normally lacks blood vessels, which keeps it clear. It receives oxygen directly from the air, dissolved in tears, and nutrients through diffusion from tears and aqueous humor.
Corneal neovascularization disrupts this normal, avascular state by allowing new capillaries to grow from the limbus, the border between the cornea and the white sclera, into the corneal tissue. These new blood vessels obstruct the clear path light needs to enter the eye, affecting vision. The presence of these vessels can also lead to inflammation and scarring within the corneal tissue, further compromising its transparency.
Why Does it Occur?
Corneal neovascularization often arises from a disruption in the delicate balance of factors that promote or inhibit blood vessel growth within the cornea. When this balance shifts towards pro-angiogenic factors, such as vascular endothelial growth factor (VEGF), new vessel formation begins. Inflammation is a common trigger for this process, leading to the production of these growth factors by corneal cells, macrophages, and other inflammatory cells.
Various factors and conditions can instigate this imbalance. Chronic inflammation from conditions like dry eye, allergies, or ocular rosacea can stimulate new vessel growth. Infections (bacterial, viral, or fungal) can also cause significant inflammation that promotes neovascularization. Physical trauma or injury to the eye, including chemical burns, can directly damage the cornea and trigger a healing response that includes vessel formation.
Contact lens overwear or misuse is a frequent cause of superficial corneal neovascularization, primarily due to oxygen deprivation (hypoxia). Lenses that are too tight, decentered, or have heavy deposits can restrict oxygen delivery, prompting the cornea to grow new vessels. Wearing contact lenses while sleeping significantly increases this risk.
Certain underlying systemic diseases like diabetes and autoimmune disorders, as well as complications from corneal transplantation, can also predispose individuals to developing corneal neovascularization.
How Does it Affect Vision?
Blurred vision and reduced visual acuity are common, as the invading vessels disrupt the cornea’s transparency and interfere with light transmission. Patients may experience glare or halos around lights due to the scattering of light by these abnormal structures.
Light sensitivity (photophobia) is another frequent symptom, often stemming from the inflammation and irritation associated with neovascularization. Eye redness and a foreign body sensation can also occur. In some cases, the new blood vessels are fragile and can rupture, leading to bleeding within the cornea, which further impairs vision and can result in scarring. Over time, the ingrown vessels may also cause lipid deposition or swelling (edema) within the cornea, leading to increased cloudiness and potentially permanent vision loss if left unaddressed.
Management and Treatment Options
Diagnosing corneal neovascularization involves a comprehensive eye examination. An eye care professional can detect abnormal blood vessels using a slit-lamp examination. Advanced imaging techniques like optical coherence tomography angiography (OCTA) and fluorescein angiography provide detailed mapping and assessment of the vessels.
Treatment strategies aim to address the underlying cause, regress existing vessels, and prevent new growth. If contact lens wear is a factor, discontinuing or modifying lens use is a primary step. For inflammation or infection, medical therapies are prescribed. Topical corticosteroids reduce inflammation and can inhibit new blood vessel growth, though long-term use requires careful monitoring due to potential side effects like glaucoma.
Anti-VEGF (vascular endothelial growth factor) agents, such as bevacizumab, ranibizumab, and aflibercept, are also employed. These medications block VEGF, a key protein that promotes blood vessel formation, and can be administered as eye drops or injections around the eye. They are more effective on newly formed, immature vessels.
In severe or unresponsive cases, surgical interventions may be considered. Laser photocoagulation uses a laser to seal off or destroy the abnormal blood vessels. Photodynamic therapy involves injecting a light-sensitive dye into the bloodstream, which then accumulates in the vessels, making them susceptible to a specific laser light that causes them to close. In advanced cases with significant scarring or vision loss, a corneal transplant may be necessary to restore corneal clarity.