In the next part of our series regarding infectious diseases that may result in the need for a corneal transplant, we’ll be discussing Herpes.
If you are new to the series, be sure to check out our previous articles regarding Fuch’s Endothelial Dystrophy, Keratoconus, Acanthamoeba Keratitis, and Trachoma.
Then, be sure to stay tuned for March’s articles on extreme corneal ulcers, and the final piece of the series over different types of corneal transplants!
What is Herpes?
Herpes is a viral disease often mistaken for only being a sexually transmitted disease. On the contrary, herpes is a viral disease that most individuals carry markers of. In fact, 90% of individuals 50 years or older in the US test positive for herpes simplex!
There are two major categories of Herpes Virus—Herpes Simplex and Herpes Zoster.
Herpes simplex is further broken down into herpes simplex virus type 1 and type 2.
Herpes simplex virus type 1 is the “above the belt” version of herpes. Initial infection is similar to any other virus infection involving flu-like symptoms ranging from mild to severe in intensity.
The virus is then spread from person to person via contact with bodily fluids like saliva or secretions from blisters or sores that may arise with viral infection, and therefore can be spread through the sharing of beverages, makeup brushes/wands, and kissing.
After initial infection, the virus remains dormant in the body for life and may re-activate to cause in itchy rash, and fever blisters or cold sores on the face (especially around the mouth and eye regions), arms, hands, legs, etc. Common triggers for reactivation of the virus include stress, other illness, heat, and UV light exposure.
Herpes simplex virus type 2 is the sexually transmitted disease resulting in genital sores and blisters. It can also impact the rest of the body, including the eyes.
Herpes zoster is the other form of the disease that causes chicken pox. Once an individual has a case of the chicken pox, he/she has contracted herpes zoster, with the virus remaining within the body for life.
For most individuals, the virus will remain dormant, without causing issues. In others, the virus may re-activate in the form of shingles, resulting in a painful rash along the affected dermatome of the body.
The most commonly affected dermatome is the ribcage, followed by cranial nerve 5, branch V1, which extends down the forehead, across the eyes, and down the tip of the nose.
Herpes in The Eye
As briefly mentioned above, both herpes simplex and herpes zoster can cause eye infections.
In fact, herpes simplex is the most common cause of corneal blindness within the United States. Therefore, it is one of the leading causes of corneal transplant in the US.
To best understand how herpes affects the eyes, it will be helpful to have a basic understanding of the anatomy of the cornea.
If you’ll recall from our first part of this series: Fuch’s Endothelial Dystrophy; there are five layers that make up the cornea. From outermost to innermost, we have the epithelium, Bowman’s layer, stroma, Descemet’s layer, and the endothelium.
Herpes can affect any layer of the cornea, or multiple layers at the same time.
Herpes simplex can cause blepharoconjunctivitis, dendritic keratitis, disciform keratitis, endothelitis, necrotizing stromal keratitis and neurotrophic keratitis.
Herpes Zoster can cause epithelial disease, pseudodendrites, stromal disease, neurotrophic keratopathy, and corneal scarring.
We know this is a lot of different versions of herpetic eye infections, so we will keep our focus on those most commonly to cause scarring and therefore require treatment with corneal transplant.
Blepharoconjunctivitis is herpes simplex infection affecting the eyelids, but not the cornea. It involves painful sore or blister like lesions forming on the eyelid margins.
It is important to note that while blepharoconjunctivitis does not initially involve the cornea, lesions of the eyelid margins can pop, and the fluid secreted from the lesions can lead to secondary epithelial corneal infection.
Epithelial involvement of a herpes infection can present as dendritic keratitis in herpes simplex infections or as pseudodendrites in zoster infections.
Dendritic keratitis is the classic presentation of herpes simplex in the cornea.
A dendrite is a terminal branch of the nervous system. The cornea is the one part of the eye that contains nerves (outside of the optic nerve), and thus can be affected by herpes simplex flare-ups.
In dendritic keratitis, a herpes outbreak results in one of the dendrites in the cornea becoming actively infected and inflamed, causing eye pain, irritation, sensitivity, redness, and sometimes blurred vision.
What’s dangerous about dendritic keratitis is that if the infection is not carefully monitored and treated, it can fester, becoming larger and larger until forming a dendritic ulcer.
An ulcer, by definition, is a break in the epithelium with underlying inflammation. Ulcers are very painful, and when caused by herpes, can be rather difficult to treat.
An ulcer is of concern because the eye at this point is scratched open. While the epithelium does have a repair process, any time we have an ulcer we are at risk for secondary scarring to ensue.
Scar tissue in the cornea is not a good thing. While scar tissue is part of the natural healing process, it replaces normal tissue with opaque, collagenous material to close the wound opening. When this occurs in the eye, it can obstruct the passage of light into the eye, and thus cause vision loss.
The Importance of Diagnosis
Therefore, it is important to diagnose and treat an outbreak of herpes epithelial keratitis as quickly as possible, to help reduce the risk of ulceration.
Moving deeper into the cornea, herpes can also affect the stroma. If you’ll recall, the stroma is the center layer of the cornea, making up a majority of the cornea’s structure. Disciform keratitis and necrotizing stromal keratitis are two disease entities that affect the stroma.
Disciform keratitis occurs when the body mounts an inflammatory reaction against the virus, seen as white, fluffy material called precipitates within the corneal stroma. Typically in disciform keratitis, there is no epithelial involvement—just inflammation of the stroma, and sometimes the endothelium.
The inflammation in disciform keratitis is typically significant, making the eye appear white and vision blurred and very fuzzy.
Inflammation needs to be dampened as quickly as possible, as increased inflammation in the stroma greatly increases the risk of scarring and permanent vision obstruction.
Additionally, increased inflammation in the stroma puts excess pressure on the endothelial cells, which are needed to pump excess fluid out of the cornea and keep it in its slightly dehydrated state.
When endothelial cells are knocked out by this inflammation, it causes excess aqueous humor to accumulate within the stroma resulting in further stroma swelling. This swelling further interferes with vision creating a hazy view and causes irritation and pain.
Necrotizing stromal keratitis, is a similar, but potentially more severe and devasting version of disciform keratitis. In necrotizing stromal keratitis, the inflammation within the stroma is so great that it slowly eats away at the stroma.
To combat the vast amount of inflammation, the body upregulates blood vessel growth into the stroma to provide a greater strength immune response. This blood vessel growth further breaks apart the stroma, and is opaque, causing massive interference with vision.
Necrotizing stromal keratitis is considered an ophthalmic emergency. Treatment is required ASAP, and prognosis is not great. Individuals with necrotizing stromal keratitis have a high likelihood of needing a corneal transplant to restore vision, as the blood vessel laden cornea will need to be removed so that blood vessels do not obstruct the pathway of light through the eye.
Last but not least, we will travel deeper into the cornea and talk about endothelitis. Endothelitis is inflammation of the endothelium of the cornea secondary to an active herpes infection.
Endothelitis often goes hand in hand with disciform keratitis as the endothelial cells become inflamed and function poorly. This results in poor pumping of excess aqueous humor out of the cornea, causing swelling and discomfort of the stroma.
Like disciform keratitis, endothelitis carries an increased risk of stromal scarring and permanent vision loss.
Ultimately, regardless of what type of herpes infection is wreaking havoc on the eye, the main concern is scarring resulting in vision loss.
Treating Eye Herpes
What makes treating herpes infections so hard to manage is the fact that steroids are normally the drug of choice for reducing inflammation to prevent scarring from occurring. However, steroids are known to make active herpes infections worse—therefore it is a delicate balance between treating the active infection and inflammatory component without causing further damage.
In many cases, anti-viral eye drops and oral medications are enough to limit the extent of damage with a herpes eye infection. However, in some cases the scarring becomes too great and a corneal transplant is the only option for regaining sight.
The most common type of corneal transplant performed post-herpes infection is a full thickness corneal transplant, or penetrating keratoplasty.
Individuals who have a history of herpes eye infections, however, still need to be careful after receiving a corneal transplant, as the virus remains dormant in other parts of the body and can return to infect the transplant.
For this reason, many individuals who suffer from recurring herpes infections will be put on an oral preventative anti-viral.
If you or someone you know has a history of herpes, simplex or zoster, and begins to have eye pain, redness, light sensitivity, or foreign body sensation, it is of upmost importance to see your eye doctor as quickly as possible for a thorough evaluation and proper treatment. The sooner therapy is started, the better the outcome will likely be!
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