The eye becomes “red” when blood vessels dilate and get larger or if a vessel has a bleed (Subconjunctival Haemorrhage). Redness of the eye can occur from a variety of causes some of which can be serious.

Please note

There are many possible causes of a red eye or eyes. 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. Sometimes the level of redness does not correlate with the how serious the problem might be however associated eye pain and/or poor or decreased vision are very serious and immediate attention is required. The advice of a medical practitioner, specifically an ophthalmologist is necessary to rule out any serious problem.

Red eyes occur from either the eye vessels enlarge on the surface of the eye and becoming bloodshot or if a vessel breaks and there is a bleed.

Fig 1. Enlarged Vessels

Enlarged vessels (fig 1) 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.

Redness of the eye

Fig 2. Subconjunctival Bleed

A bleed (Fig 2) also called a subconjunctival haemorrhage is quite common.

It 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.

Subconjunctival bleed eye – redness of the eye

Inflammation 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.

Corneal ulcer

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.

Acute Glaucoma

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.

If you are unsure about your loss of vision contact one of our Patient Co-ordinators who can arrange an appointment for you to see one of our surgeons. Call 0800 0112882 or email us here.

Author Information

Authored by Sheraz Daya MD FACP FACS FRCS(Ed) FRCOphth, Consultant Ophthalmic Surgeon & Medical Director, June 2019.

Next review due June 2024.