Corneal injury and foreign bodies

What causes corneal injury?

Corneal scratches/abrasions

The cornea is at the front of the eye. It is a clear disc which lies over the front of the coloured part of the eye and the pupil. It's the window you see out of, and it is protected from harm by:

• Lubrication (in the form of tears).

• Rapid blinking of your eyelid if anything approaches it.

The blink reflex normally protects the cornea well from most injuries. However, scratches and minor injuries to the cornea are quite common. For example, a scratch from a hairbrush, by a fingernail when putting in a contact lens, from walking into a tree branch, etc.

The pain can be quite bad, even from a small scratch, as the cornea is extremely sensitive. The eye will water profusely and you may be unable to bear to open it.

Small flying objects

If you use a drill or other types of power tools like grinders without wearing eye protection, you may injure your cornea. This can happen when small flying particles get into the eye. These can fly out extremely fast. They may be so small that the eye does not see them coming and therefore does not blink. They may also be hard and sharp. Several things can then happen:

Sometimes the particle gets stuck in the cornea and can cause pain similar to a corneal scratch. If the particle is metal it can swiftly begin to produce a rust patch on the eye surface, which can cause damage to the cornea.

Sometimes the particle goes straight through the cornea to a deeper part of the eye. If the particle is small this can be painless, or cause only mild pain. It may also pass through the white part of the eye (the sclera) into the deeper parts too. If this happens there may be no noticeable pain.

Penetration of the eye itself is very serious. It may lead to infection inside the eye. It can cause fluid to leak out from inside the eye and it can permanently affect your vision. You should always see a doctor for an eye examination if you suspect a particle has flown into your eye when you have been drilling, sawing, grinding, chiselling, lawn mowing, etc.

Chemical injuries

Sometimes, a chemical may splash on to the front of the eye and cause a burn to the cornea. Household cleaning products like oven cleaner and bleach can do this. The eye can also be irritated by alkaline substances like plaster dust. The chemicals which most commonly cause eye injury are acids such as battery acid, vinegar and bleach, and alkalis such as plaster, cement caustic soda and fertiliser.

Chemicals in the eye can continue to damage the eye, slowly but seriously, for a long time if they are not washed out immediately. Some chemicals, such as hydrofluoric acid (used in glass polishing) and alkalis, can soak into the eye and can cause damage even after the eye has been washed out. Recently chlorine gas has been used as a weapon of war. Chlorine gas has many toxic effects on the human body but this includes extreme eye irritation, which is like a chemical burn. It should be treated in the same way.

CS gas and pepper spray

Deterrent sprays such as CS gas and pepper spray are highly irritating to the eye. CS gas does not usually cause permanent damage; however, irritation lasts for several days. Pepper spray can cause severe corneal scratching if the particles get into the eyes.

Radiation damage

The most common form of radiation damage is called arc eye. It's also sometimes called snow blindness. It occurs when the eye has been exposed to very bright light without proper eye protection. This is common if welding with an arc lamp without eye protection - hence the name. Symptoms typically include severe eye pain with watering eyes that may not develop until several hours after the exposure. Eyes can be too sore to keep open.

Other causes of radiation damage to the cornea include:

• Exposure to a lot of reflected sunlight (for example, snow blindness).

• After ultraviolet light exposure by looking at the lights in tanning machines.

Although the pain can be severe, the condition usually resolves without complications within 1-2 days.

If you suspect you have a corneal injury, it is best to see a doctor. If you suspect an injury from a flying small particle or from a chemical you should see someone quickly, which may mean attending accident and emergency. A doctor may use a magnifying instrument to examine your eye. A drop of a special dye (fluorescein) is commonly put on the front of the eye if a corneal injury is suspected. This shows up scratches that might otherwise not be seen. The eye examination also checks for serious damage.

Treatment for a chemical burn to the eye

All chemical eye injuries should be treated very seriously as they can damage your vision severely. Treat with immediate first aid by irrigating the eye massively with clean water:

• Remove contact lenses if present.

• Immediately wash out the eye with lots and lots of water for at least 10-15 minutes:

  • The best way of doing this is beneath a running tap. After testing the water temperature, position your eye beneath a running cold tap or hose.

  • Hold your eyelids open with your fingers and allow the water to run over your eye.

  • If both eyes are involved and there is only one source of water try to keep alternating the eyes. Lying on your back in the bath may be easier than positioning your head in a sink.

  • Alkalis are particularly damaging and any loose bits of material such as lime or plaster must be completely washed out, or they will continue to damage the eye. You can lift your upper eyelids away from the eyeball by the lashes to do this, allowing the water to wash in, and pull the lower lids gently down and outwards.

  • You need to check that no bits are left behind the eyelids (the eyelids will feel gritty if there are particles trapped there, although this feeling may persist even after the bits are gone).

• Then go to your nearest accident and emergency department as soon as possible. You should be assessed urgently by an eye specialist.

Treatment for CS gas and pepper spray

CS gas is ideally treated by evaporating the substance off the eyes using a hair dryer on a cool setting. Clothes should be removed and ventilated; you should ideally have a lukewarm shower. Pepper spray should be washed out immediately with copious liquid, as if it were a chemical injury.

Treatment for scratches/abrasions/flying objects/radiation injury

A small corneal scratch or abrasion usually heals over a couple of days or so.

Eye infection is a complication that may follow an injury or scratch to the cornea. Therefore, it is routine to prescribe antibiotic eye drops or ointment for up to a week to prevent infection. Chloramphenicol or fusidic acid are most commonly used, although if you have scratched your eye with a contact lens you may be prescribed gentamicin eye drops. Painkillers such as paracetamol or ibuprofen will ease pain.

Sometimes a small particle becomes slightly embedded in the cornea. This needs to be removed, as it may lead to infection or staining. It is often possible for a doctor to remove it using a cotton wool bud. Sometimes a fine needle may be needed to lift it out. Local anaesthetic eye drops are used if this is done, to make the procedure painless. The surface of the eye is actually surprisingly hard so don't worry. The doctor will not harm your eye with the needle. A particle of metal on the eye is removed in the same way. However, if it has started to produce a ring of rust this is removed using a specially burring tool, to make sure that all the rust spots are removed.

Radiation injury to the eye is treated as for corneal abrasions. Some of the pain in arc eye results from spasm of the iris muscle. A drop of cyclopentolate, which relaxes the pupil's muscles, may ease this. It will, however, make your vision slightly blurred.

Local anaesthetic drops are used in the eye immediately to manage the corneal injury. However, although it seems tempting to keep using these drops in order to keep the eye comfortable, in fact using local anaesthetic repeatedly in the eye delays healing. Therefore, this is not a recommended treatment.

If you normally wear contact lenses, do not wear them while the cornea is healing or whilst using antibiotic eye drops. You also should not wear them for 24 hours after the final dose of antibiotic eye drops, as they can become discoloured.

An eye patch to cover the eye is not normally advised following a corneal scratch or abrasion (as was commonly advised in the past). This is because studies have shown that using a patch does not improve healing rates and does not reduce pain. Removal of the patch tends to result in the healing tissue on the cornea stripping off again as you blink, so you are back to the start of healing again. In addition, if you wear an eye patch you lose your depth vision using two eyes (your binocular vision). The exception is if local anaesthetic eye drops have been used for assessment or treatment and the eye is numb. A patch may then be advised for a few hours until the sensation returns to the eye, in order to protect it. This is needed because an eye with anaesthetic drops in it may not blink if something flies into it.

You will be referred to an eye specialist if you have a deep or penetrating injury to the eye or if there are any concerns that the eye is more seriously damaged. Specialised assessment and treatment may be needed.

Note: do not drive unless you have normal vision in both eyes and the effects of eye drops (if used) have worn off.

Always wear eye protection when you drill, saw, etc - activities which cause flying small particles. Wear specialised ultraviolet protection when welding, skiing, mountaineering, using sunbeds and in any other situation where there is a lot of light radiation. Take particular care when using hazardous chemicals such as acid or alkali, washing your hands regularly and protecting the eyes if there is any risk of material splashing or exploding. Wear protective goggles when dealing with cement and plaster dust.

A leaflet on protecting the eyes is available from the Canadian Ophthalmological Society (see Further reading below).

Depending on the severity of the injury, your doctor may advise that you should be reviewed in 24-48 hours after the injury. This is to see if healing is underway. However, see a doctor as soon as you can if your vision becomes worse, if you have worsening pain (beyond that due to the local anaesthetic wearing off) or if your corneal abrasion does not seem to have healed after 72 hours.

Dr Mary Lowth is an author or the original author of this leaflet.