What causes blood vessels to burst in the eye?

This sounds like a subconjunctival hemorrhage, with is the rupture of a small blood vessel within the white part of the eye. Fortunately, subconjunctival hemorrhages are rarely serious, although they often look quite alarming due to their bright red color, and they generally resolve on their own without difficulty. The most common causes of subconjunctival hemorrhage are things that increase pressure in the body, which leads to strain in the small blood vessels. Common things that do this include sneezing, coughing, vomiting, lifting weights, and the like. However, sometimes the vessels can burst on their own without any obvious strain, and rubbing or itching the eyes can also sometimes cause the vessels to rupture. The usual treatment for subconjunctival hemorrhage is simply observation. If there is any discomfort, you can take a mild over the counter pain killer. Rarely, a subconjuntival hemorrhage can be a sign of an underlying medical problem. For example, if you are on blood thinning medications and suddenly develop this finding, it may be a sign that your blood is too thin. Likewise, if you have high blood pressure or diabetes, these can predispose to subconjunctival hemorrhage. These would all be reasons to talk to your primary care doctor sooner rather than later.