Dr Ben Wild
Overview |
The cornea is a clear tissue located infront of the iris. Its main functions are as a barrier to protect the inner eye and to focus light on the retina. It is composed of 5 layers. The 3 main layers include the epithelium (outermost barrier layer), the stroma (the middle layer providing the refractive power), and the endothelium (responsible for pumping fluid out of the stroma so that the cornea does not swell and cloud over).
Frontal view of a healthy eye.
Herpes simplex virus (HSV) is a virus that can affect every part of the eye but usually only presents in the cornea. It accounts for 60% of all corneal ulcers and is the leading cause of corneal blindness in developed countries. There are 2 strains of the HSV. 1 is commonly referred to as the cold sore virus and stays above the waist, 2 is genital in origin but can affect the eyes through direct contact.
Primary infection, meaning the first time a patient is infected by HSV, usually does not produce any symptoms or may present as a mild fever, upper respiratory tract infection, or mild conjunctivitis. It is transmitted via droplets. The virus DNA then incorporates into the patient’s DNA and becomes dormant. Usually within the trigeminal nerve.
Recurrent infection occurs when the dormant virus DNA re-activates. This usually occurs due to various life stressors and is what causes damage to the eye in the form of epithelial keratitis (swollen epithelial cells of the cornea that can lead to ulceration), disciform keratitis (swollen endothelial cells caused by an intense immune reaction to the virus that leads to a swollen cornea), stromal keratitis (advanced form of disciform keratitis that can lead to the cornea melting), neurotrophic keratopathy (where the eye becomes numb, loses touch sensation and cannot heal), and more.
An eye showing a dendritic corneal ulcer (the branching lesion) and disciform keratitis (circular area) from an HSV infection.
Signs and Symptoms |
Signs
Epithelial | Eye redness, watery eyes, decreased corneal sensitivity, swollen epithelial cells, ulceration of epithelial cells in the shape of a dendrite, corneal haze, mild anterior uveitis, eyelid vesicles (small white bumps), large bumps on inner eyelids. |
Disciform | Swollen endothelial cells, swollen cornea, white blood cells stuck to the endothelium, maybe elevated eye pressures, decreased corneal sensitivity. |
Stromal | White blood cells attached to the inner cornea, thinning cornea, if longstanding, scarring and blood vessels growing into the cornea. |
Symptoms
Epithelial | Mild to moderate discomfort, light sensitivity, blurred vision. |
Disciform | Blurred vision, haloes/glare, mild discomfort and redness. |
Stromal | Extreme blurred vision, intense glare, light sensitivity, moderate discomfort. |
Causes and Risk Factors |
Causes
Re-activation of HSV in the trigeminal nerve.
Risk Factors
Fever, hormonal changes, ultra-violet radiation, eye surgeries, atopic allergies, immune-suppression, malnutrition, other viral infections, topical steroid use.
Prevention and Treatment |
Prevention
Avoiding infection would be the best prevention but it is not practical as roughly 90% of the world’s population is estimated to have been infected by HSV1 or HSV2.
Treatments
· Topical acyclovir or trifluridine eye drops.
· Oral acyclovir, valacyclovir or famciclovir pills.
· Cyclogyl dilating drops for discomfort.
· Topical antibiotic to avoid superinfection with bacteria.
· Debride ulcer (remove infected epithelial).
· Steroid eye drops if not epithelial keratitis.
· Rigid gas permeable lenses to improve vision through scarring.
· Keratoplasty (cornea transplant) if there is permanent scarring but this comes with a high rejection rate.
Prognosis |
Herpes simplex keratitis infections are typically recurrent, just like cold sores, and most often only affect the epithelium. These infections are easy to treat and do not usually cause much scarring or vision loss unless they are not treated in a timely manner. Each episode needs to be treated promptly. In order of treatment difficulty; disciform, neurotrophic and stromal keratitis’ are much less common. They can lead to permanent vision loss although that likelihood decreases dramatically with prompt treatment.
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