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Herpes simplex is a virus which can infect your eye. The infection will probably go away within a couple of weeks. But there's a chance it could cause more serious problems that might damage your eyesight.

Lots of people carry the herpes simplex virus in their body. Usually it doesn't cause problems. But if the virus infects your eye, it can be uncomfortable. And it could damage your eyesight.

There are two types of herpes simplex virus:

• In most people, herpes eye infection is caused by herpes simplex type 1. This is the same virus that causes cold sores on your lips. You catch it from other people through their saliva (for example, if you kiss someone who has the virus).
• In some people, herpes eye infection is caused by herpes simplex type 2. This virus more commonly causes genital herpes. That is, it causes blisters or sores on your genitals.

More than half of all people get infected with the herpes simplex virus at some point in their lives. For most, it happens when they're a child.¹ The herpes simplex virus usually lives inside the nerve cells of the body without causing any problems. But from time to time it may flare up and cause cold sores around your lips and mouth.Or it can travel down the nerves to the eye and cause a flare-up of herpes infection there. To understand how herpes simplex eye infection can affect you, it helps to know about the different parts of the eye.

The front of the eye is called the cornea. The cornea is clear like a window and shaped like a dome. It's very thin: less than 1 millimeter thick. It covers the iris (the colored part of the eye) and the pupil (the black hole in the middle of the iris). The cornea protects the rest of the eye and helps you focus.

The cornea is made of layers of cells. The top layer is called the epithelium. Underneath the epithelium is the stroma, which is the thickest layer. It's made up of thousands of tiny fibers.

Herpes eye infection usually affects the eye's cornea.

• Sometimes it affects the top layer of the cornea (the epithelium). Your doctor may be able to see an ulcer in this layer, where the infection has damaged the tissue.
• Occasionally it affects the middle layer of the cornea (the stroma). This is more serious.
• But in some people the infection affects only the eyelid or the outside of the eye (the conjunctiva).

You're more likely to get a flare-up of the herpes simplex virus:²

• In sunny weather
• If you're feeling stressed or rundown
• During your menstrual period, if you're a woman
• If you've been sick.

These things might also cause a flare-up of herpes infection in the eye.

We don't know why some people get herpes eye infection but others don't.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.