What causes red eye?

If your red eye is painless, it is most likely caused by a minor eye problem, such as conjunctivitis or a burst blood vessel. These conditions don’t tend to affect your vision and many often get better within a week or two with minimal intervention.Your Specsavers optometrist will identify your symptoms and suggest treatments.

Common causes

  • Conjunctivitis
  • Burst blood vessel
  • Iritis
  • Acute glaucoma
  • Corneal ulcer
  • Scratch to the cornea or grit in the eye

Common causes of red eye


Conjunctivitis is inflammation of the thin layer of tissue covering the eyeball and inner surfaces of the eyelids. Blood vessels swell, making one or both eyes look bloodshot and feel gritty. Other symptoms can include itchiness, watering eyes and sticky eyelashes.

It can be caused by an infection, an allergy (for example, to pollen), or an irritant, such as chlorine or dust. Treatment will depend on what is causing the condition. Sometimes no treatment is needed, because it may get better on its own.

Burst blood vessel

Burst blood vessels on the eye surface are sometimes caused by straining, coughing or injuring your eye, resulting in a bright red blotch.

It can look alarming, especially if you’re taking medication such as aspirin or warfarin, but it’s not usually serious and should clear up on its own within a few weeks.

What if your red eye is painful?If your red eye is painful or you have other symptoms such as reduced vision, the cause could be one of the conditions below.


Iritis is inflammation of the iris, the coloured part of the eye. You may have a red eye, sensitivity to light, blurred vision and/or a headache. Iritis usually responds quickly to treatment with steroid medication to reduce the inflammation. It rarely leads to severe problems.

Acute glaucoma

Acute glaucoma is an increase in pressure inside your eye. Your eye may be very red and painful, and you may feel sick and see haloes around lights. Your vision may be blurred or cloudy. This is a serious condition and could lead to permanent loss of vision if not treated quickly.

Corneal ulcer

An ulcer on the cornea can cause the eye to become red and sensitive to light and it can feel like there’s something in your eye. Bacterial corneal ulcers are more common in people who wear contact lenses. Viral corneal ulcers are more common in people who frequently get cold sores. More severe ulcers could lead to permanent loss of vision if not treated quickly.

A scratch to the cornea or grit in the eye

A red and painful eye can sometimes be caused by a particle, such as a piece of grit, getting in your eye. If there’s something in your eye, your optician will try to remove it with the assistance of an anaesthetic drop.

These can be serious and could threaten your sight if not managed appropriately. Contact your optician, GP or NHS 111 immediately for appropriate advice if:

  • You have a painful red eye
  • You have other symptoms, including reduced vision, sensitivity to light, a severe headache and feeling sick
  • You recently injured your eye – particularly if something has pierced your eye

Did you know?

Specsavers stores provide a range of additional eye care services to help maintain the health of your eyes. In some areas of the country, this may be provided free of charge on behalf of the NHS. Where NHS services are not available, there is a private service. Rather than booking an appointment online, contact your local store for more information and to arrange an eye health clinic appointment.