What Causes Eye Capillaries to Burst?

When a capillary in the white part of the eye bursts -- called a subconjunctival hemorrhage -- the appearance of blood can be rather dramatic and alarming. Often, there is no history of trauma to the eye -- the blood simply appears spontaneously. Subconjunctival hemorrhage is usually not indicative of any underlying disease. However, it can be associated with eye rubbing, infections, blood disorders, medication use and increased blood pressure to the head, as in coughing or vomiting.

An eye doctor examining a patient's eye. (Image: LuckyBusiness/iStock/Getty Images)

Pressure Buildup

Subconjunctival hemorrhage has a reported incidence of nearly 3 percent, which increases with age. This corresponds to the fragility of aging eye vessels, as with all the blood vessels of the body, increases with age. Certain activities, like lifting heavy objects, straining during a difficult bowel movement, sneezing, vomiting or even coughing to clear the throat can increase venous pressure to the head. This backup of pressure in the veins travels through to the tiniest vessels in the eye, sometimes causing the capillaries to burst.

Irritants on the Surface

If a person suffers from eye allergies, he may tend to rub the eyes to relieve the itch. This type of eye rubbing on the surface of the eye can cause a subconjunctival hemorrhage. Some people have growths on the conjunctiva – the white part of the eye -- known as pterygia, which make the eye susceptible to drying out. Dry eyes are often irritating and itchy, which can lead to frequent eye rubbing and hemorrhage. Foreign bodies and contact lens use have also been implicated. The simple act of taking a contact lens out of the eye with a long fingernail could scratch the conjunctiva and break a blood vessel.

Ocular and Systemic Infections

Viral conjunctivitis, also known as pinkeye, is a viral infection of the front surface of the eye. Many types of common cold viruses cause this infection, but virus types enterovirus, coxsackie and adenovirus are well known to cause a hemorrhagic conjunctivitis. This means that the infection includes both bleeding and inflammation in the conjunctiva. Illnesses that cause systemic fevers, such as the flu, measles, malaria or even chicken pox can lead to subconjunctival hemorrhage as well.

Blood Clotting and Medical Disorders

People with certain blood disorders are more likely to experience frequent subconjunctival hemorrhages. These include individuals with a low platelet count, known as thrombocytopenia, or those with anemia. People who are on anticoagulant medications, or blood thinners, like warfarin (Coumadin) or aspirin for heart conditions are at risk for easy bruising and bleeding. Certain types of cancer, such as leukemia, can cause bleeding of the conjunctival blood vessels. Less frequent causes of hemorrhage include diabetes mellitus and high blood pressure. Even when under good control, over the years these conditions can lead to fragility and easy breakage of the conjunctival blood vessels.

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