A corneal infection is no laughing matter. While some corneal infections cause only a mildly irritated eye, other cases can present as a serious eye health concern with the potential to cause permanent vision loss. A corneal infection may arise due to a number of reasons, including bacterial or viral infections, or even due to fungi or parasites.
The cornea is the transparent dome of tissue at the very front surface of the eye. This anatomical structure is the first surface that light passes through in order to reach the back of the eye and form what we call vision; disruption to the clarity of this tissue can be a real problem for your sight. The cornea is also the most sensitive structure, something that becomes apparent when even the finest eyelash falls into your eye.
You may come across the word “keratitis” when reading about corneal infections – keratitis technically refers to any inflammatory condition of the cornea and may or may not involve an active infection. However, all corneal infections involve some degree of inflammation at some stage of the disease, and so will often include keratitis in its medical naming.
Causes of Corneal Infection
Infectious causes of keratitis include:
The most common viruses involved in viral infections of the cornea are herpes viruses and adenoviruses – viruses that are often responsible for conditions beyond eye health. Type 1 herpes simplex is the same strain that causes cold sores and also has the ability to cause an eye infection known as herpes simplex keratitis.
Another virus of the herpes family is varicella zoster virus, which is also the virus behind conditions like chickenpox and shingles. Unfortunately, both these viruses are never cleared from the body but instead lie dormant; reactivation of the virus from various triggers can cause recurrent infection and inflammation, which can be sight-threatening. Adenoviruses are very common viruses often responsible for symptoms such as sore throat, pneumonia, and the common cold. Viral infections of the eye associated with adenoviruses are highly contagious, so much so that an eye infection caused by adenoviruses is called “epidemic keratoconjunctivitis”.
Viral corneal infections often present as a sore, watery, red eye. There is also often glare sensitivity and blurred vision in the affected eye. The infection may be present only on one side, however, due to the highly contagious nature of the adenovirus, it can be expected to soon spread to the other eye. Patients with herpes-associated keratitis may have a history of cold sores while patients with adenoviral keratoconjunctivitis may report having had a recent cold or been in contact with someone else with a cold. Unlike herpes keratitis, which is treated with antiviral medication, there is no consensus on effective treatment for adenoviral keratitis, which will often self-resolve over a couple of weeks.
Bacteria are the most common culprits of corneal infections, typically staphylococcus aureus and pseudomonas aeruginosa. Bacterial keratitis should never be ignored as it can have serious consequences for eye health, including permanent scarring and loss of vision. People who wear contact lenses, especially those with contact lens habits contrary to the recommendations of their eyecare practitioner, are at a greater risk of bacterial keratitis; additional risk factors include other causes of compromised eye health such as chronic dry eye, recent eye surgery, or eye trauma.
Similar to a viral corneal infection, bacterial keratitis will also present with a painful, red eye but the discharge will often be of a pus or mucous consistency rather than watery. Depending on the site and severity of the infection, your vision may be significantly impaired from a large, central corneal ulcer, or perhaps only slightly blurry from the mucous discharge.
Corneal infections due to fungi can be more difficult to identify as it develops slowly, often presenting symptoms only days after the initial infection. However, the effect on eye health and vision can be devastating if not treated appropriately. Many cases of fungal keratitis are preceded with some sort of vegetation-related trauma to the eye, such as plant matter flicking into the eye during gardening or being scratched in the eye by a tree branch or leaf while outdoors. Contact lens wearers are also at a higher risk of contracting fungal keratitis, as are people who are immunocompromised, such as those using steroid medications. Common fungal pathogens include Candida, Aspergillus, and Fusarium. It’s been noted that the likelihood of specific fungal infections can vary by geography and climate.
A fungal keratitis can present with the typical eye infection symptoms of pain, redness, glare sensitivity, tearing, and decreased vision. However, some cases actually present with very little pain or discomfort in the eye, which can delay diagnosis and prompt treatment.
Luckily, parasitic keratitis is rare. The most common parasite to cause keratitis is acanthamoeba, a common, hardy protozoa found in water, soil, and even air. Similar to other types of infectious keratitis, contact lens wearers are at an increased risk of contracting acanthamoeba keratitis, particularly when proper lens disinfection and hygiene is disregarded.
The distinguishing symptom of acanthamoeba keratitis is severe pain, disproportionate to the other symptoms such as watering, redness, and glare sensitivity; this is thought to be due to the microorganism specifically targeting the corneal nerves. If not treated promptly and appropriately, uncontrolled Acanthamoeba keratitis can cause permanent loss of vision in the affected eye.
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The best thing to do if you think you may have a corneal infection is to see your eyecare practitioner immediately. Depending on the underlying cause of the keratitis, its severity, and your risk of permanent vision loss, corneal infections may be treated with topical eye drop medications, systemic medications, or a combination of both.