Chapter 31: Red eye

There are many causes of the red eye, but the most common cause is an infection of the conjunctiva (the clear membrane that covers the sclera) or an eye allergy. This section will look at some of the common causes and discuss them.

• Conjunctivitis is one of the most common causes of a red eye. Infection caused by a bacterium or virus commonly causes conjunctivitis. In infectious conjunctivitis there is eye discharge, no pain, no vision changes (except when eye discharge distorts vision) and no or mild sensitivity to light.
• Allergy is another common cause of conjunctivitis and red eye. It presents with clear watery discharge, a red eye and itching. It may be associated with a runny nose and sneezing.
• Subconjunctival hemorrhage is a focal red patch that typically affects one eye without any symptoms such as tearing or irritation. It is bleeding beneath the conjunctiva (outer layer of the eye). It often results from sneezing, coughing or physically straining.
• Episcleritis is similar to conjunctivitis but is typically without discharge (or a very small amount). It is associated with one eye being red with mild irritation. Episcleritis is a very focal irritation of the eye.
• The cornea can also become red. This can be a more serious form of red eye. It is generally differentiated from problems with the conjunctiva by more pain, significant light sensitivity and a visible lesion in the eye that the doctor notices when there is a staining substance put in the eye.
• A corneal abrasion or foreign body is a more serious cause of red eye. There is typically a history of injury and there is a break in the protective clear coat of the eye. It is usually caused from trauma, content lens use or foreign body.
• A red painful eye associated with blurred vision, headache and nausea may indicate acute narrow angle glaucoma and is a medical emergency.
• Anterior uveitis presents with light sensitivity, pain, decreased vision, and redness most pronounced around the iris (the colored part of the eye).