Shingles, or herpes zoster, is a viral infection known for its characteristic painful, burning, or itchy rash. This rash occurs along a specific affected nerve, such as a ligament on one side of the chest or abdomen that extends to the back. In fact, the name shingles comes from Cingulum, the Latin word for belt, belt or sash.
Shingles is caused by reactivation of the varicella zoster virus, the virus that causes chickenpox. After the initial chickenpox infection subsides, the virus lives on in nerves throughout the body, but is kept in check by the immune system. The risk of shingles increases with any process that can weaken the immune system, including age, illness, and immunosuppressive drugs. About a million cases of shingles occur in the United States each year.
Up to 20% of shingles episodes affect nerves of the head, where the infection can affect different parts of the eye, including the eyelid, the surface of the eye, and the deeper parts of the eye. Viral infection of the eye can cause pain, drainage, redness, and sensitivity to light. In some cases, vision problems, including blindness, can occur.
Shingles in front of the eye
Shingles can affect the cornea, the curved, transparent dome of tissue at the front of the eye. This is known as keratitis and can appear as a complication of ophthalmic herpes zoster (HZO), which refers to shingles with a rash that typically involves one side of the top, forehead, and scalp. More than half of people with HZO can have keratitis.
If you have shingles of the upper face, forehead, or scalp, it is important to see an ophthalmologist for a formal eye exam, whether or not you notice any eye symptoms. Keratitis usually develops within a month of the shingles rash and can lead to corneal numbness, scarring, additional infection, and further corneal damage that can ultimately lead to blindness.
HZO, like episodes of shingles in other areas of the body, is typically treated with oral antiviral drugs to fight the underlying viral infection. The treatment reduces the risk of later eye complications by about 40% to 60%. If antiviral treatment is started within 72 hours of symptoms appearing, it will also reduce the overall severity of the infection and the risk of post-therapeutic neuralgia, a form of long-term pain that can occur after shingles.
Shingles in the back of the eye
Shingles that involve the retina or the optic nerve – structures in the back of the eye – is usually not associated with a rash or other symptoms on the surface of the eye. This type of shingles infection is known as viral retinitis and is much less common than HZO. However, a combination of infection and inflammation can cause significant damage to the retina. Viral retinitis can take the form of acute retinal necrosis (ARN) or progressive external retinal necrosis (PORN).
Unlike patients with HZO or other forms of shingles associated with a rash, patients with ARN are often middle-aged and generally healthy. Diagnosing ARN requires a careful eye exam by an ophthalmologist, and a sample may be taken from inside the eye to test whether the infection is caused by the varicella zoster virus. In mild cases, ARN can be treated with oral antiviral drugs, with or without injections of antiviral drugs into the eye. In more severe cases, or when oral medications and intraocular injections don’t get better, these infections are treated with intravenous (IV) antiviral drugs until the infection starts to improve.
Fortunately, PORN is rare. It typically occurs in people with severely compromised immune function and progresses rapidly. PORN is treated aggressively with intraocular injections and iv antiviral drugs.
In patients with shingles, including those with HZO or ARN, attempts are often made to boost the immune system until the infection is controlled. For people taking immunosuppressive drugs, this may mean lowering the dose or giving the infection time to respond to antiviral treatment before giving another dose of immunosuppressive drugs. Sometimes the inflammation associated with shingles is so severe that steroids are needed to control the inflammation before it harms the eye.
Shingles vaccine is the best prevention
The best way to prevent shingles, including shingles, is with a shingles vaccine. The live vaccine, Zostavax, is no longer used in the United States. Shingrix is a newer, more effective, non-living vaccine for shingles. Shingrix is a two-dose vaccine recommended for adults over 50. It is over 90% effective in preventing shingles. Unfortunately, the shingles vaccine does not treat shingles or post-therapeutic neuralgia. The vaccine is only effective as a prevention strategy.