Keratitis

What is Keratitis?

Keratitis is an inflammation or swelling of the cornea, the clear front surface of the eye. This condition is commonly associated with diseases – both infectious like bacteria and viruses and non-infectious like allergies – which can affect either the whole body or only the eye. A common type of this condition, known as “microbial keratitis,” is a significant concern primarily in developing countries. However, non-infectious keratitis is also significant, particularly in developed countries.

Our body’s first line of defense, the skin or outer layer of cells, usually does a good job at keeping infections out. But some harmful organisms are sneaky and can get through this line to cause an infection. The cornea’s outer layer is one such barrier. Most harmful organisms can’t break through this layer unless it’s damaged. But, there are some organisms, including Neisseria meningitides, N. gonorrhea, Corynebacterium diphtheria, Haemophilus influenzae, and Listeria species, that are so powerful they can penetrate even this intact outer layer and cause keratitis. This article explores the causes and existing, as well as potential future, treatment options for different types of keratitis.

What Causes Keratitis?

Keratitis is an eye condition where the cornea, which is the clear front surface of the eye, becomes inflamed. There are different types of keratitis, and they can be classified based on what causes them:

Infectious Keratitis

This type of keratitis is caused by germs, including:

* Bacterial keratitis – Such bacteria can include Pseudomonas, Staphylococcus, Streptococcus, Moraxella, Nocardia, and a kind called Atypical Mycobacteria.
* Protozoal keratitis – An organism called Acanthamoeba can cause this.
* Pythium keratitis – This is caused by an organism that resembles a fungus. Unlike other fungi, this one has a specific structure in its cell wall.
* Fungal keratitis – This can be caused by various fungi, including types called Aspergillus, Fusarium, Candida, Cladosporium, Alternaria, Curvularia, and Microsporidia.
* Viral keratitis – Different viruses like the Herpes simplex virus, Herpes zoster virus, Adenovirus, and others can cause this type.
* Helminths keratitis – This is caused by a type of worm. One example is the worm that causes a condition called Onchocercal keratitis.

Non-infectious Keratitis

This type is not caused by germs, but other factors:

* Local causes – These include conditions where eyelashes grow inwards (trichiasis), large bumps on the eyelid (giant papillae), and having a foreign object stuck under the eyelid.
* Peripheral ulcerative keratitis – This type is linked to diseases that affect the body’s connective tissues, which include rheumatoid arthritis, conditions called granulomatosis with polyangiitis, polyarteritis nodosa, relapsing polychondritis, systemic lupus erythematosus, and others.
* Neurotrophic corneal ulcer – This is caused by damage to the nerves of the eye. The damage can be caused by conditions like herpes zoster or due to eye surgery or a tumour.
* Xerophthalmia – This is an extreme form of dry eye.

Risk Factors and Frequency for Keratitis

According to a study in California, ulcerative keratitis – a type of eye inflammation – was found in about 27.6 people out of every 100,000 per year. This kind of eye problem was found more frequently in people who wear contact lenses.

In South India, research showed that middle-aged men are more likely to develop corneal ulcers compared to women. People working as farmers were also found to be at high risk. Fungal corneal ulcers are quite common in developing countries, although the Herpes Simplex Virus is a major concern in developed countries. In a study from Rochester, Minnesota, the occurrence rate of epithelial disease, another type of eye condition, was roughly 15.6 people out of every 100,000 per year, while for stromal keratitis, inflammation of the cornea, it was about 2.6 out of every 100,000 per year.

Autoimmune disorders related to keratitis are estimated to happen at a rate of about 3 per million people per year.

A study in rural Ethiopia found that about 21% of people had xerophthalmia, or dry eyes due to vitamin A deficiency. This condition was largely linked with malnutrition, and it mainly affected young, undernourished children.

Signs and Symptoms of Keratitis

Keratitis is a condition where the eye’s cornea becomes inflamed. Patients with this condition often complain about redness, pain, and eye irritation, as well as possible light sensitivity, vision deterioration, or aesthetic concerns for the eye.

Different types of organisms can cause keratitis, each with their unique effects:

• Staphylococcal Keratitis: This is caused by the bacteria Staphylococcus, and it typically affects the peripheral cornea, the outer ring of the cornea.
• Streptococcal Keratitis: Most often, a blocked tear duct causes this.
• Pseudomonas Keratitis: This is a severe form that can lead to corneal perforation if left untreated and is characterized by rapid growth and spread.
• Nocardia Keratitis: Typically linked to physical trauma or eye surgery. Its manifestations include granular infiltrations in the cornea.
• Mycobacterial Keratitis: This typically has a long, fluctuating course and is often linked to trauma or surgery. Its signature manifestation is a ‘cracked windshield’ pattern on the cornea.
• Adenoviral Keratitis: This often goes hand in hand with conjunctivitis, leading to corneal inflammation and swollen lymph nodes.
• Herpes Simplex Keratitis: This can affect the outer, middle, or inner layer of the cornea, causing blisters, inflammation, and deposits on the cornea. It’s more common in those with a weakened immune system and may lead to scarring and poor vision if untreated.
• Herpes Zoster Keratitis: This type causes a very noticeable rash over the forehead and eyelids, reaching the tip of the nose.
• Protozoal Keratitis: One such variant is Acanthamoeba keratitis, which is often linked to exposure to soil or contaminated water, especially in developing countries. Contact lens use is another common cause in developed nations.
• Oomycetes Keratitis: Pythium keratitis is one example of this type of infection, caused by a unique type of fungus-like microorganism.
• Fungal Keratitis: This is often linked to trauma, especially from vegetative matter. The cornea infiltration resembles a dry-looking growth with a feathery edge accompanied by satellite lesions.
• Non-Infectious Keratitis: Conditions like Rheumatoid arthritis, Wegner granulomatosis, systemic lupus erythematosus, relapsing polychondritis, and polyarteritis nodosa can cause this. Symptoms typically include dry eyes and inflammation.
• Xerophthalmia: This leads to ulceration of the cornea that can potentially perforate if left untreated. Usually caused by vitamin A deficiency, this condition is an extreme form of dry eye syndrome.

Though these are some typical types of keratitis, the exact symptoms can vary depending on the specific type and cause.

Testing for Keratitis

If you are a patient with a corneal ulcer, your doctor might perform a specific examination known as the “Regurgitation on pressure over the lacrimal sac area” (ROPLAS). They might also use a procedure known as sac syringing. These tests are important and are normally done to check for the possibility of infections caused by a blockage in the nasolacrimal duct, which is the pipe that drains your tears from your eyes to your nose.

Usually, when you have a corneal ulcer, your doctor will examine the ulcer closely for any special features. This is usually followed by a procedure called corneal scraping which is done to identify the actual germs causing the ulcer. This sample scraped off from your ulcer is sent to a lab where it’s used to prepare two slides. One slide for Gram staining, which is a technique used to detect bacteria and another for a 10% KOH mount, a test used to identify fungal infections.

Depending on what the doctor finds under the microscope, you may be prescribed certain medications. This treatment can later be adjusted based on the results of the culture reports. The culture reports indicate the exact type of bacteria, fungus or other microorganisms that are causing the ulcer. For bacterial growth, blood and chocolate agar are commonly used in the culture media. For fungus growth, potato dextrose agar and Saboraud’s dextrose agar are used. For a type of parasite called Acanthamoeba, non-nutrient agar with E. coli is used.

Now, in some cases, corneal ulcers can be due to autoimmune diseases. Here, serology, which is a blood test that looks for antibodies against your own body, forms the basis for diagnosis. But for the diagnosis of a specific condition called xerophthalmia, which is a severe drying of the eye surface, the diagnosis is mostly based on the symptoms and signs you are experiencing.

Treatment Options for Keratitis

Bacterial keratitis is an infection of the cornea, the clear cover on the front of the eye. To treat this, patients are given antibiotic eye drops and ointments until further test results come in. These antibiotics help kill both types of bacteria that can cause infection.

There are different causes of keratitis. One of them is Pseudomonas, a type of bacteria. For this, doctors start by giving patients eye drops that contain fluoroquinolones, a kind of antibiotic. If the bacteria is hard to treat, other drugs can be added.

Nocardia and atypical mycobacteria are other bacteria that can cause keratitis. They can be identified by tests and treatment involves antibiotic eye drops.

Acanthamoeba, a type of microscopic amoeba, can also cause keratitis. It’s diagnosed based on the patient’s symptoms and history of eye issues. The treatment involves a combination of medications.

Pythium insidiosum, a type of parasitic organism, can cause an infection known as Oomycete. Special stains and tests can help identify it, and treatment involves several different kinds of antibiotics.

Fungal infections can also lead to keratitis. The treatment varies depending on the type of fungus and can include antifungal and topical eye drops.

Viral keratitis is another cause, often caused by the herpes simplex virus (HSV) or the varicella-zoster virus. Antiviral medications are given in these cases. Cases of adenoviral keratitis are typically diagnosed based on symptoms and can be treated with antibiotics.

Non-infectious keratitis can occur due to other medical conditions or injuries. It can be caused by local eye issues or by systemic diseases that affect the whole body, such as rheumatoid arthritis. The treatment can include managing the underlying condition, along with using steroids and various medical procedures.

Sometimes, it’s necessary to apply a special adhesive or conduct surgery to repair perforations in the cornea or to replace the damaged cornea entirely.

What else can Keratitis be?

Diagnosing keratitis, an inflammation of the eye’s cornea, is straightforward. However, determining its cause can be challenging. Sometimes, microscopic examinations and culture reports don’t reveal anything unusual, which means treatment has to rely on clinical symptoms. In the early stages, it’s often difficult to tell the difference between Acanthamoeba keratitis and HSV stromal keratitis. Also, in later stages, Acanthamoeba keratitis can appear similar to fungal keratitis.

Here are some conditions that might be considered when diagnosing keratitis:

• Atopic keratoconjunctivitis (inflammation of the cornea and conjunctiva)
• Bacterial endophthalmitis (infection of the inner parts of the eye)
• Band keratopathy (calcium deposits on the cornea)
• Blepharitis (inflammation of the eyelid)
• Corneal ulcer (open sores on the cornea)
• Entropion (inward turning of the eyelid)
• Epidemic keratoconjunctivitis (viral eye infection)
• Fungal keratitis (fungal infection of the cornea)
• Herpes simplex virus keratitis (herpes infection of the cornea)
• Herpes zoster (shingles)
• Interstitial keratitis (deep inflammation of the cornea)
• Neurotrophic keratitis (damage to corneal nerves)
• Nasolacrimal duct obstruction (blocked tear duct)
• Ocular rosacea (eye condition related to rosacea skin condition)
• Pseudophakic bullous keratopathy (blistering on the cornea after cataract surgery)
• Scleritis (inflammation of the white part of the eye)
• Viral conjunctivitis (eye infection also known as pink eye)

What to expect with Keratitis

In general, corneal ulcers, which are sores on the clear outer layer of your eye, can take a while to heal. Sores caused by bacteria tend to recover quicker than those due to fungi, whereas Acanthamoeba keratitis, an eye condition caused by a specific type of microorganism, might take several months to improve completely.

The most common result following a corneal ulcer is scarring on the cornea. Fortunately, even if this happens, there are several ways to manage it and restore vision, including using prescription glasses, undergoing a procedure known as optical iridectomy which involves making a small hole in the colored part of the eye, or even an optical keratoplasty, which is a cornea transplant.

Corneal ulcers that have perforated, or created a hole, in your cornea tend to have a worse outcome. Using topical steroids, a type of medicine applied directly to the eye area, can actually worsen the prognosis if the ulcer is caused by fungi or Acanthamoeba.

Possible Complications When Diagnosed with Keratitis

Here are some complications that can arise:

• Toxic inflammation of the iris and ciliary body
• Increased pressure in the eye
• Thinning of the inner layer of the cornea that can bulge forward
• Rupture of a corneal ulcer

Also, there are several potential complications that can occur following a corneal rupture:

• Protrusion of the iris through the wound
• Displacement of the lens toward the front of the eye
• Cataract that primarily affects the front of the lens capsule
• Abnormal connection between the cornea and another part of the eye
• Inflammation of the uvea (the middle layer of the eye) that includes pus
• Bleeding within the eye
• Scarring of the cornea which may be nebula (light), macula (moderate), leucoma (severe), or adherent leucoma (severe with iris adhesion)
• Thinning and bulging of the cornea
• Disorderly front chamber of the eye
• Self-ejection of internal contents of the eye
• Shrinkage and degeneration of the eye

Preventing Keratitis

Keratitis is a condition where the eye’s cornea or front surface becomes inflamed. Often, this is due to injuries in farming environments, especially in developing countries. Therefore, it’s a good idea for people to protect their eyes with shields when they’re working in the fields during harvest season. This can reduce the chance of getting eye injuries and developing keratitis.

There’s also a type of keratitis caused by the herpes simplex virus (HSV), which can reoccur multiple times. If you’ve experienced more than three outbreaks of HSV keratitis in the past year, your doctor will likely suggest you to take medicine that can prevent the virus (antiviral prophylaxis) for a whole year to prevent these outbreaks from coming back.