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ONE RED EYE shutterstock_728030470_edited.jpg

There are many causes of red eyes, but sometimes just one eye can appear very red, and this can be potentially very serious. The serious causes of one red eye usually, but not always, also cause pain and or blurred vision. If you develop one red eye, it

needs to be attended to and treated promptly.

Most commonly, when we develop red eyes, both eyes become red, if the condition is infectious like conjunctivitis and spreads from one eye to the other, or if it is due to something that can affect the whole body including the eyes, like allergies .

Such conditions include:

  1. Allergies (including reaction to eye drops)

  2. Blepharitis (eyelid inflammation)

  3. Dry eyes (decreased production of tears)

  4. Conjunctivitis (inflammation of the surface layer of the eye)

Sometimes one eye can suddenly become red if a small blood vessel on the surface of the eye bursts. This is called a subconjunctival haemorrhage. It is usually painless, does not affect the vision, resolves on its own and is not serious.

If one eye becomes red, particularly if there is also pain or blurred vision, it can be potentially serious and needs to be attended to promptly.

Causes of one red eye

Contact lens related corneal abrasion, infection or ulcer

You may develop an infection on the cornea, which is the clear front surface of the eye, especially if you are a contact lens wearer. These infections can be very nasty and spread rapidly into the eye, potentially causing scarring and blindness.


If you are a contact lens wearer and develop ANY eye symptoms, TAKE THE LENS OUT straight away. It is very important to have a current pair of glasses that you can wear instead of contact lenses, so you can rest the eyes while still being able to see, if your lenses are causing problems. Sometimes it is just a scratch which will quickly heal once the lenses are removed, but it is best to get it checked by your doctor, optometrist or at your local hospital in case the problem is more serious. You may need special tests and treatment.


Eye infections may be caused by bacteria, viruses (including herpes virus) or fungi. Whilst there are some clinical features that may suggest one or another, the only way to be sure what is causing your infection is to have the eye examined and swabs taken and the material sent for testing, which means first going to see your doctor or the hospital for examination and testing before getting treatment.

Eye pain

Eye pain may have many causes, including trauma, abrasion, infection, inflammation (episcleritis, scleritis or uveitis) or high pressure (glaucoma).

Not all eye pain is serious, and not all serious conditions are painful, but if you have eye pain, it needs to be attended to.


Inflammation can affect all the coats of the eye from

  • the central clear cornea (keratitis)

  • the surface clear conjunctiva that covers the white of the eyeball and lines the eyelids (conjunctivitis)

  • the superficial episclera (episcleritis)

  • the deeper sclera (scleritis)

  • the uveal tract (uveitis) which is the anterior coloured part of the eye (iritis or anterior uveitis) and the posterior pigmented part of the eye (posterior uveitis)

In general, the deeper in the eye the inflammation is, the more painful it is and the more serious it is.  The sooner you are diagnosed and treated, the quicker it will heal, so if your red eye comes with pain and particularly with blurred vision, please see your doctor promptly.

High pressure causing pain (acute glaucoma)

There is a rare form of glaucoma called acute glaucoma in which the drainage outflow of the eye blocks off acutely and the pressure rises very high, very quickly, causing pain and blurred vision. This is a medical emergency and needs to be attended to promptly to reduce the pressure before it causes permanent damage to the optic nerve and blindness.

The tendency to this condition may be picked up on your regular eye check and treated with laser to prevent the high pressure emergency occurring.

It is important to understand that most types of glaucoma cause no symptoms at all in the early stages and this is why it is so important to have our eyes checked regularly, particularly after the age of 40 and even earlier if you have a family history, as glaucoma can run in families.

Eyelid conditions

Sometimes one red eye is due to an underlying eyelid condition.

  • Blepharitis (inflammation of the eyelids) makes the eyelids look red and can also cause redness and inflammation of the underlying eye.

  • A stye is a blocked gland in the eyelid which can become inflamed or even infected, causing redness and swelling of the eyelid and sometimes irritation or inflammation of the underlying eye.

  • An infection of the skin of the eyelid (periorbital cellulitis) can sometimes spread into the deeper tissues, causing orbital cellulitis. This is a serious condition that can affect the vision and spread deeper into the sinuses and needs prompt admission to hospital and treatment with antibiotics.

  • Ectropion is a chronic condition in which the lower eyelid droops and turns out, exposing the delicate inner lining of the eyelid which then becomes red and inflamed. The eye itself can also become inflamed because it is no longer being protected by the eyelid.

  • Entropion is a chronic condition in which the lower eyelid turns in, and the eyelashes can then rub on the eye, causing irritation, abrasion and even ulceration and infection of the cornea.

What is the treatment of one red eye?

As you can see, the causes of one red eye are many and varied and most required a medical doctor to diagnose and treat them.


The treatment depends on the cause and it is important to seek medical attention promptly to make sure your red eye is not something serious and to treat it quickly and appropriately if it is, so that no permanent damage is done.

Our eyes are precious. Have them seen to at once if they don't look or feel right, particularly if you have pain or your vision is blurred.


Please Contact the Clinic if you would like to know more.

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