Keratitis: symptoms, causes, treatment and when to get urgent help

Keratitis means inflammation of the cornea, the clear window at the front of the eye. Moorfields Eye Hospital NHS Foundation Trust describes several forms with different causes: microbial keratitis, an infection of the cornea; marginal keratitis, inflammation usually due to blepharitis; and herpes simplex virus keratitis, a viral infection of the cornea.

Because the cornea helps you see clearly, a red, painful eye with blurred vision should be taken seriously. Moorfields says microbial keratitis can be a serious condition if it is not treated and can sometimes affect your vision and leave a scar, even with the correct treatment.

Moorfields says microbial keratitis causes a painful red eye and sometimes blurred vision. At first it feels as though there is something in the eye. The eye becomes increasingly painful because of an ulcer that develops on the surface of the cornea. Sometimes you can see the ulcer as a small white spot on the cornea over the coloured part of the eye.

For herpes simplex virus keratitis, Moorfields lists a red eye, eye pain or a foreign body sensation, sensitivity to light, blurred vision and small blisters around the eyelid. The NHS lists similar symptoms for herpes simplex eye infections, including watering, a swollen eyelid and blisters or a rash on the eyelid or skin around the eye.

In marginal keratitis, Moorfields says the eye becomes red and sore and may develop small white ulcers around the edge of the cornea.

Moorfields says to seek advice if your eyesight becomes more blurred, if your eye becomes more red or painful rather than improving, or if you can see a white spot getting bigger on the cornea. It advises contacting an eye service for advice or attending your local A&E department.

The NHS says to ask for an urgent GP appointment or get help from NHS 111 for eye pain, a red eye that is getting worse or any change to your eyesight such as blurred vision. Call 999 or go to A&E if you have a red eye and it hurts to look at light, your eye is very dark red, or one pupil is bigger than the other.

The main types described by Moorfields and the NHS differ in cause and treatment.

Moorfields says microbial keratitis is often related to contact lens wear and, less commonly, to a scratch on the surface of the eye or a pre-existing eye condition. Infection is more likely with incorrect contact lens cleaning or storage, incorrect use of disposable lenses or wearing lenses overnight.

HSV-1, the virus behind herpes simplex keratitis, is very common and passed on by direct skin-to-skin contact, according to Moorfields. After the first infection the virus remains in the nerves of the face and can re-emerge at any time, causing a cold sore or an ulcer in the eye. It can be spread directly to the eye from a cold sore, so avoid touching your eyes if you have one. Symptoms can be worse if you have eczema or a reduced ability to fight infection.

Marginal keratitis is usually due to blepharitis, in which the oil glands of the eyelids become blocked and the eyelids are irritated. Moorfields says it is thought that, in some people, blepharitis is partly caused by sensitivity to the staphylococcus bacteria which normally live on the skin.

For microbial keratitis, Moorfields says antibiotic drops are usually used. You are likely to need to put the drops in very frequently at first, up to every hour and sometimes through the night if the infection is severe, with the frequency reduced once the ulcer is seen to be getting smaller. It is very important to put in the drops regularly, because these infections can get much worse if not treated properly. In some cases a sample is taken from the ulcer, after numbing drops, to find out which bacteria are involved; results can take several days.

For herpes simplex virus keratitis, Moorfields says a course of antiviral eye gel (ganciclovir) is the treatment for most cases, antiviral tablets for 7 days may be needed in severe or recurrent cases, and steroid drops are sometimes used to reduce inflammation and minimise scarring. The NHS says you will usually be seen by an eye specialist the same day so that treatment can start quickly.

For marginal keratitis, Moorfields says treatment aims at the blepharitis. Good lid hygiene once or twice a day, even when you have no symptoms, helps prevent recurrence, using warm compresses, lid massage and lid scrubs, with antibiotic and steroid drops or ointment if your eye doctor feels they are suitable.

The NHS says most herpes simplex eye infections get better with treatment in a couple of weeks and do not permanently affect eyesight. Moorfields adds that herpes keratitis can come back: around half the people who get it will get it again within five years, and your eye doctor may recommend daily antiviral tablets if it keeps recurring. Severe or repeated episodes can leave corneal scarring, which can blur vision.

For microbial keratitis, Moorfields says follow-up may be needed within a few days to check that the infection is improving, with drop frequency reduced as the ulcer shrinks. The infection can sometimes affect vision and leave a scar even with the correct treatment.

Moorfields advises not wearing contact lenses while a microbial infection is present and for a few weeks after it clears, as this can lead to a serious deterioration. After the infection has fully recovered, return to your contact lens practitioner to check your lens fit and use. For herpes simplex virus keratitis, Moorfields says not to wear contact lenses until all symptoms have gone, and the NHS says not until 24 hours after all symptoms have gone.

• Clean and store lenses as instructed, and do not wear them overnight unless advised.

• Use disposable lenses exactly as intended.

• Remove lenses and seek advice if your eye becomes red and painful.

A painful red eye is usually assessed urgently: through an eye casualty or A&E department, an optometrist or your GP, who can refer to an ophthalmologist. The NHS says that you can get treatment on the NHS for some eye conditions at some opticians, so check before making an appointment.

Some people choose a private eye clinic for quicker assessment, but anyone with a painful, red, light-sensitive eye or blurred vision should be seen the same day, whichever route is used.