Blood shot eyes are caused by enlarged, dilated blood vessels leading to the appearance of redness on the surface of the eye. It can also be called as Red eyes, Scleral injection, and Conjunctival injection. There are many possible causes o a red eye. Some are quite concerning, even they may require medical emergencies. Others are of no consequence or concern at all. The degree of redness or appearance of blood usually does not correlate to how serious it is. It is important whether you have an eye pain or impaired vision or not.

Causes of bloodshot eyes

Bloodshot eyes appear red because the vessels in the surface of the white portion of the eye get enlarged and irritated. This often results from extremely dry air, sun exposure, dust, foreign body, an allergic reaction, infection, trauma, or any other conditions which does not suit you and your eyes. Other reason of a red eye is straining or coughing. This may lead to a bright red, uniformly dense bloody area on the sclera. In medical terms it is called as Subconjunctival hemorrhage. Although this bloody area may appear alarming, it is fairly common occurrence and of little significance.

Location of occurrence

Eye infections or inflammation can occur in different locations. They cause redness as well as possible itching, discharge, pain, or vision problems:
1) Blepharitis- Inflammation of the eyelash follicles along the eyelid. It is caused by skin bacteria. Itching is common and your eyelids may appear greasy or crusty.
2) Conjunctivitis- Inflammation or infection of the membrane that lines the eyelids and coats the surface of the eye (the conjunctiva). This condition is often referred to as "pink eye". It may be caused by a virus, bacteria, allergy, or irritation. If caused by an organism, this is highly contagious.
3) Corneal ulcers- Often caused by a bacterial or viral infection. (The cornea is the outer covering of the eye.)
4) Uveitis- Inflammation of the uvea, which includes the iris, ciliary body, and choroid. This is often related to an autoimmune disorder, infection, or exposure to toxins. Often, only the iris is inflammed, which is called iritis.

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