The cornea is the outermost covering of the front of the eye. It is a transparent and dome-shaped structure that is highly sensitive to touch and pain, protecting the iris and the pupil from external injury. It also filters a reasonable quantity of light which enters the eye. The inflammation of the cornea by an injury or infection to it is known as keratitis.
In the category of infections that can cause keratitis, the herpes simplex virus infection is prominent. Herpes simplex keratitis includes all the disease conditions brought about by the herpes simplex virus in the cornea of a human’s eyes. The herpes simplex virus which invades the eye region is responsible for herpes simplex keratitis.
Every year in the United States alone, an estimated 20,000 cases of new infection with herpes simplex keratitis are recorded. It has been established as one of the most common causes of blindness in the United States. Statistically, more men than women are being infected with herpetic keratitis.
The cornea has three layers namely: the epithelium, the stroma, and the endothelium. The epithelium is the outermost layer of the cornea which functions in protecting the eyes from harmful substances that could come from outside. It nourishes itself with the oxygen and nutrients it absorbs from tears.
The middle layer of the cornea is the stroma. It is the thickest also. The proteins that are mainly housed in the stroma keeps it solidly elastic. It is made up of water.
Finally, the endothelium. It lies behind the stroma as a single layer of cells. The endothelium constantly drains excess water from the stroma, preventing it from getting drenched with water.
Types of Herpes Simplex Keratitis
Herpetic keratitis can affect any one or more of these layers. Infectious epithelial keratitis happens when the virus infects the epithelium. When the stroma of the cornea is infected by the herpes simplex virus, stromal keratitis is the result. The infection of the endothelium is known as endotheliitis. Principally, there are four major types of herpetic keratitis. They are:
- Infectious epithelial keratitis
- Stromal keratitis
- Neurotrophic keratopathy
Infectious epithelial keratitis is defined by injuries regarded as:
- Corneal vesicles
- Dendritic ulcers
- Geographic ulcers
- Marginal ulcers
Corneal vesicles are the earliest signs of infection by herpes simplex virus on the epithelium of the cornea. They appear like blisters synonymous with cold sores which are not easily recognized on a newly infected person. Within 7 hours, the blisters in the epithelium come together to form a tree-like projection known as dendritic ulcers. The linear-shaped dendritic ulcers are always noticed as the most common symptom of herpes simplex keratitis.
As the dendritic ulcers enlarge, they change from being linear to a scalloped shape and referred to as geographic ulcers. When a dendrite formed from blisters develops close to the junction or margin between the cornea and the sclera (the limbus), white blood cells seep into the stroma from the blood vessels in the limbus giving rise to marginal ulcers.
Stromal keratitis may result in scarring of the stroma which eventually may cause blindness. Other complications of stromal keratitis are trabeculitis (inflammation of the trabecula of the eyes), uveitis, and glaucoma (secondary). Persons infected with stromal keratitis are likely to have a recurrence of the disease condition.
Endotheliitis is the inflammation of the endothelium of the cornea by the herpes simplex virus. Common symptoms include:
- Photophobia (fear of light)
- Pain in the eyes
- Blurred vision
- Redness of the eyes
Neurotrophic keratopathy occurs when there is an erosion of the epithelium and the stroma. Unlike geographic ulcers, neurotrophic ulcers are oval-shaped with smooth borders. Tissue death and perforation of the eyes are complications of an untreated neurotrophic ulcer.
Diagnosing Herpes Simplex Keratitis
Laboratory tests to determine the presence of the herpes simplex virus in the infected cornea include:
- Pap stain
- Giemsa stain
- Viral culture
- Polymerase chain reaction assay
- Immunochromatographic assay
Slit-lamp photography is used as an imaging study of the progress and response to treatment of the patient.
Treatment for Herpes Simplex Keratitis
Most cases of herpetic keratitis on the epithelium of the cornea clear on their own within 3 weeks of exposure to the infection. However, it is recommended that epithelial keratitis is treated to reduce the risk of invasion of the stroma by the virus.
Treatment for Infectious Epithelial Keratitis
- The removal of damaged epithelial tissues is done and is also known as debridement
- Topical application of antiviral gel such as ganciclovir
- Giving antiviral eye drops
- Taking oral acyclovir
- Use of cycloplegic agents to relax the eye muscles
Treatment for Stromal Keratitis
Treatment commences after an examination of the epithelium is done. If the epithelium is infected alongside the stroma, the treatment for stromal keratitis will be the same as used in infectious epithelial keratitis.
But if it is just the stroma that is infected, treat with corticosteroids and antivirals that are applied to the eyes. In the place of the antivirals applied on the eyes, oral antivirals can also be used.
Treatment for Endotheliitis
It is treated with the duo of corticosteroids and antivirals.
Treatment for Neurotrophic keratopathy
No antiviral drug is taken for neurotrophic keratopathy. It is managed with patching for the eyelids, non-preserved lubricants for the eyes, and bandage contact lenses. Autologous serum eye drops have been proven to be effective and tolerable for the eyes in treating neurotrophic keratopathy.
To minimize the recurrence of stromal keratitis, an infected person should be on acyclovir in a suppressive therapy.
Ensure that you report any unusual swelling or redness of your eyes. Early detection makes for an effective cure.