Herpes simplex eye infections are usually caused by the herpes simplex virus type 1 (HSV-1), which can also cause cold sores on your mouth or face.

Symptoms of a herpes simplex eye infection may include:

• eye redness
• swelling (inflammation) and pain in or around the eye
• blurred vision

However, some people have an active herpes simplex eye infection without any noticeable symptoms.

Herpes simplex eye infections are quite common and usually affect middle-aged people. They affect around 1 to 2 people in every 1,000 in the UK.

When to see your GP

It's important to see your GP as soon as possible if you have symptoms of a herpes simplex eye infection. An untreated infection can permanently damage your eyes (see complications, below).

Your GP will ask about your symptoms and examine your eyes to rule out any other conditions.

They may put a harmless yellow dye into your eye to see any irregular areas or injury (fluorescein staining). They may also test your vision using a chart.

Eye specialist

If your GP thinks you may have a herpes simplex eye infection, they will send you to an eye specialist (ophthalmologist), who should see you as quickly as possible.

This is because herpes simplex infection is difficult to diagnose without specialist knowledge and equipment. It can also permanently affect your eyesight if not treated quickly.

Causes of herpes simplex eye infections

Herpes simplex eye infections are eye infections caused by the herpes simplex virus type 1 (HSV-1), which can also cause cold sores on your mouth or face.

The herpes simplex virus type 2 (HSV-2) usually causes genital herpes and rarely causes eye infections.

Nearly everyone is exposed to the virus during childhood. The first time you're infected is known as the "primary infection", which doesn't cause any symptoms. The virus stays inactive in the root of a facial nerve.

Triggers of a herpes simplex eye infection

The virus can be reactivated spontaneously or by certain trigger factors. These include:

• another illness or feeling run down
• exposure to strong sunlight
• having a fever (high temperature above 38C)
• stress
• (in women) having your period

Having a weakened immune system can also trigger regular cold sores or herpes simplex eye infections – for example, if you have HIV or are receiving chemotherapy.

Treating herpes simplex eye infections

Treating a herpes simplex eye infection depends on how severe the infection is and which part of the eye is affected.

Most people with a mild herpes simplex eye infection get better in a few weeks, even without treatment. You may be asked to attend regular check-ups to make sure the infection clears up.

Eye drops and ointments

Your eye specialist may prescribe eye drops or eye ointment that contain either:

• antiviral medicine
• a corticosteroid (steroid medication, which reduces inflammation)

You may be advised by your eye specialist to take antiviral and steroid eye drops or ointment at the same time.

It's important to follow the advice you are given and take any prescribed treatment carefully and for the complete course.

Tablets

In some cases, antiviral tablets may be prescribed after treatment to stop the infection returning. You may have to keep taking them for up to a year after the infection has gone.

Wearing contact lenses

It's best not to wear contact lenses until you have finished treatment and the symptoms have completely gone away.

Complications of herpes simplex eye infections

Complications of herpes simplex eye infections can include:

• an ulcer on your cornea (the front of your eye)
• scarring of your cornea – which can cause vision problems and may require a cornea transplant (an operation to replace the cornea in your eye)
• further infections caused – for example, by bacteria or fungi
• glaucoma (an eye condition that can affect your vision)
• acute retinal necrosis (ARN) – extremely rare development that can cause loss of vision in patients with severely compromised immune systems, such as those with HIV

If you develop vision problems, this may affect your driving. If this happens, you should contact the DVLA about your vision problem.