The eye becomes "red" from a variety of causes, some are cause for concern and others are 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 the situation is. It is generally more important whether you also have eye pain or impaired vision in that case immediate attention is required. The advice of a medical practitioner, specifically an ophthalmologist is necessary to rule out any serious problem.
Causes of Red Eye
The red eye can occur for instance from dry eye, foreign body in the eye, allergies, infection (conjunctivitis or corneal ulcer), iritis, uveitis, inflammation, contact lens overwear and injury.
A bleed also called a subconjunctival haemorrhage is quite common and can occur from straining, sneezing and coughing. Sometimes this can occur with prolonged use of steroid eye drops, very high blood pressure and also where there may be a problem with the clotting mechanisms of the blood. A subconjunctival haemorrhage usually disappears in a couple of weeks.
Inflamation and Infection
Eye inflammation and infection cause red eye and classified according to the location of the infection.
Blepharitis - inflammation or infection of the lids, base of the lashes, lash follicles or oily secreting glands (meibomian glands). Redness of lid margins, crusty or oily secretions may be noticed.
Inflammation or infection of the mucous lining of the eyelids and surface of the eye. Red eye in this instance is commonly called "Pink Eye". Inflammation can be caused by an allergic reaction or irritation. Infections can be caused by a virus or bacteria and can be highly contagious.
Infection of the cornea causes an ulcer with white cells infiltrating along with redness, pain and sometimes a visible white or yellow spot. The cause of this is more commonly bacterial but in rare instances can be from a fungus. The most common cause of a corneal ulcer is contact lens wear. Contact lens wearers who develop a red eye must stop wearing lenses and be seen by an ophthalmologist without delay.
This is an important cause of red eye that occurs when the pressure in the eye suddenly increases. There can be associated reduction in vision and pain. This is a medical emergency.