Bacterial Keratitis

What is Bacterial Keratitis?

Bacterial keratitis, or a corneal ulcer, is an infection of the clear front layer of the eye known as the cornea, usually caused by various types of bacteria. This condition takes different forms: it can happen suddenly, slowly over time or appear and disappear. It can affect any part of the cornea, and symptoms may include gradual or quick decaying of the corneal tissue.

The cornea can be affected by many different types of microorganisms like viruses, fungi, and single-celled organisms known as protozoa. However, bacteria are the biggest concern because they can cause a rapidly worsening condition that threatens vision and can result in irreversible vision changes.

When the body’s physical and immune defenses against these infections fail, it can lead to severe eye conditions that can damage sight. Over the years, more and more people have started using contact lenses worldwide. Unfortunately, this has also led to a higher number of bacterial keratitis infections.

Doctors make a diagnosis by examining the patient and carrying out lab tests. Thanks to advancements in diagnosis methods, more research in lab investigations, and targeted antibiotic treatment, the negative effect on vision has been reduced. Nevertheless, this condition is still a significant cause of vision-threatening diseases, especially in less developed and rural regions around the world.

What Causes Bacterial Keratitis?

Microbial infections, such as bacterial keratitis, are often prevented by various barriers in our body. These include physical structures like the bony rim around the eye, eyelids, and the clear layer covering the front of the eye, as well as mechanisms like tear films and your body’s defense systems found in tears. If these barriers are compromised, it can result in infections like bacterial keratitis.

One main cause of bacterial keratitis is the use of contact lenses. This can be due to reasons such as wearing contact lenses for too long or overnight, not cleaning them properly, rinsing them in tap water, not maintaining good lens hygiene, sharing lenses, or swimming with lenses on. Bacterial keratitis can also be caused by external factors like injuries, previous surgeries, suppressed immunity, certain drug use, and substance abuse.

Different diseases that affect the eye surface, whether localized or systemic, can also lead to bacterial keratitis. Local factors include dry eyes, issues with eyelid structure or function, inflammation of the eyelid margins, recurring corneal erosions, or damage to the cornea following viral keratitis. Systemic conditions that may make someone more susceptible include diabetes, malnutrition, autoimmune disorders, certain skin conditions, chronic inflammation of the eye, nerve damage, and immunosuppression due to conditions like AIDS or chronic alcoholism.

Different types of bacteria can cause keratitis, including Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Pseudomonas aeruginosa, and other species belonging to the Enterobacteriaceae family. Some of these bacteria, such as Neisseria gonorrhoeae and Listeria monocytogenes, can even penetrate an intact clear layer of the eye.

Risk Factors and Frequency for Bacterial Keratitis

The occurrence and frequency of bacterial keratitis, or bacteria-caused corneal infection, varies depending on environmental and other factors specific to geographic locations. The rates of bacterial keratitis are vastly different in developed nations like the USA and Europe compared to developing countries such as India, Nepal, Pakistan, and Bangladesh. This is largely due to the lower number of contact lens users in less industrialized countries, which reduces instances of contact lens-related bacterial keratitis.

In the United States, bacterial keratitis affects 11 per 100,000 contact lens users compared to 799 per 100,000 in Nepal. The US records around 71,000 new cases of microbial keratitis each year. The human eye rarely contracts bacterial keratitis because the cornea, the eye’s outside layer, naturally resists infection.

• Microbial keratitis in the US is often caused by staphylococcal, Pseudomonas, and Streptococcus bacteria.
• Staphylococcus aureus and Staphylococcus epidermidis are the most common gram-positive bacteria, and Pseudomonas is the most prevalent gram-negative bacteria.

The rate of corneal ulcers has grown from nearly zero in the early 1960s to 52% in the 1990s. It was observed that the use of contact lens played a big role in this increase. About 4 to 21 per 10,000 contact lens wearers experience ulcerative keratitis annually. The most common causes of bacterial keratitis are bacteria in the Staphylococcus and Pseudomonas families.

In research conducted in Italy and the UK, contact lens usage was a more common risk factor for bacterial keratitis. Hospitals in Los Angeles mostly report gram-positive pathogens. However, the most common bacteria vary by location within the US. For example, the southern part of the US has more cases involving gram-negative bacteria than the North.

Polymicrobial keratitis, an infection caused by multiple bacterial organisms, can also occur. Approximately 43% of cultures analyzed in one study contained two or more bacterial microorganisms mostly involving Staph. epidermidis and Fusarium. Trauma is the most common risk factor for this condition. In Southern India, most of the cases of bacterial keratitis were due to Streptococcus pneumoniae, Pseudomonas, and Nocardia.

Signs and Symptoms of Bacterial Keratitis

Patients who come to the doctor’s office may have a history of foreign body fall, insect injury, chemical injury, or stroke. They might have lagophthalmos, a condition where the eye does not fully close, which can lead to bacterial keratitis. It is essential to note the onset and duration of symptoms. Important patient background to know includes their contact lens habits such as how often the lenses are worn, whether they are worn overnight, the type of lens and cleaning solution used, whether they have been cleaned with tap water, whether the patient has swum with them, and whether they use colored cosmetic lenses. Also crucial to understand is the history of viral keratitis, any medications used, possible allergies, any previous eye surgery, whether the patient suffers from dry eyes, prior instances of bacterial keratitis, vitamin A deficiency, malnutrition, HIV, and whether the immune system is compromised.

Based on the clinical features, bacterial keratitis r can be broadly divided into two categories:

• Non-hypopyon Purulent Bacterial Ulcer
• Hypopyon Bacterial Ulcer

Common symptoms of bacterial ulcers include pain, redness, wateriness, discharge from the eye that can be either clear or pus-like, sensitivity to light, vision defects, and a feeling of a foreign body in the eye.

Signs of bacterial keratitis may include swollen eyelids, excessive blinking, tangled eyelashes, pus discharge, inflammation of the eye and surrounding areas, redness, defects in the skin of the eyes, swelling, and red, inflamed, and sore tissues. Scleritis, which is a severe process of infection, can also occur. In rare cases, perforation, or the making of a hole, can lead to endophthalmitis, which is inflammation of the interior of the eye.

Depending on the type of bacteria, bacterial keratitis can present differently. For instance, Staphylococcal aureus usually shows up as a deep abscess in the skin of the eye and is seen in eyes that have been previously compromised. On the other hand, Streptococcus pneumoniae usually appears as a round or oval ulcer in the center of the eye. Similarly, Pseudomonas aeruginosa is associated with quick progression of major symptoms and the forming of plaques, or deposits, in the eye. Other bacteria like Proteus, Klebsiella, Moraxella, Neisseria gonorrhoea, Nocardia, Mycobacteria, and Bacillus Cereus, also have specific characteristics. Knowing these can help in the diagnosis and treatment of bacterial keratitis.

Testing for Bacterial Keratitis

Corneal Scraping is a procedure done under local anesthesia, often with a type of eyedrop like proparacaine or proxymetacaine. It’s most commonly undertaken in confused cases like central corneal infection with significant damage, long-standing eye surface inflammation that doesn’t respond to typical antibiotics, weird clinical symptoms, or cases where multiple points of infection appear in different parts of the cornea. Usually, care is given if a patient had prior corneal surgery.

In prepping for the procedure, it first involves clearing up the ulcer surface of any loose mucus or dead tissue. A sterile blade or needle is then used to lightly scrape the surface of the cornea. The collected material is spread out on glass slides for microscopic examination and staining — which uses certain dyes to visualize bacteria better.

The scraping process is performed again to provide a sample for various culture media. These media provide an environment for any potential bacteria to grow and be identified. The mark of the collected sample is usually in the form of a “C” without cutting into the agar, a gelatinous substance in the culture media. Liquid media are used as well by submerging the collected specimen thoroughly into it.

The samples undergo staining to identify different types of bacteria. Gram stain helps differentiate positive gram (appearing purple) and negative gram (appearing pink) bacteria. Acridine orange makes bacteria appear yellow-green. Meanwhile, Acid Fast makes the bacteria Mycobacterium appear pink.

Moreover, different culture media are used to grow and identify diverse types of bacteria, each living at different temperatures and requiring unique environmental factors.

Another essential factor in diagnosing and treating bacterial keratitis is quantifying its severity. It can be categorized into mild, moderate, or severe, based on the size and depth of the infiltrate and whether the sclera, the white part of the eye, is involved or not.

In some cases, when attempting to treat a severe case but the culture growth turns out negative, the conjunctiva, the thin clear tissue lining inside the eyelid and the white part of the eye, can be swabbed for culture. Even the patient’s contact lenses and their case can be cultured for additional data, under a specific condition – they must not have been cleaned by the patient.

Culture and sensitivity reports are beneficial tools in the treatment plan. These reports indicate the bacteria’s susceptibility to antibiotics, aiding in choosing the effective therapeutic agent. These reports can even reveal if bacteria are resistant to certain antibiotics, helping the clinician to adjust the treatment for better results.

In complicated cases, anterior chamber paracentesis, a procedure of fluid sample extraction from the front chamber of the eye, might be needed. This might also include a corneal biopsy, where a tissue sample is collected from the cornea. All these additional steps can help differentiate bacterial from other types of eye infections.

An ultrasound scan of the eye or “B Scan” can help visualize the back part of the eye if inhibited by corneal edema, bloody or inflammatory accumulation in the anterior chamber of the eye, or any disruptions in eye transparency. It helps rule out other serious eye conditions.

Several other diagnostic methods include immunohistochemistry, enzyme immunoassay, polymerase chain reaction, and radioimmunoassay; these are upcoming techniques but have a limited role in diagnosing bacterial keratitis for now.

Treatment Options for Bacterial Keratitis

As soon as a patient reports to the doctor with a health issue, medical treatment should start immediately. Tests are usually done and the results get ready within an hour. After reviewing the test results, doctors usually prescribe broad-spectrum antibiotics that fight both types of bacteria that cause disease – gram-positive and negative. However, after 2-3 days, when the results of a more detailed test (called culture) come back, the treatment may change to target the specific bacteria causing the disease. Smaller and less severe ulcers, not affecting the center of vision, can be treated with just one type of antibiotic. For larger, more severe ulcers, a combination of two antibiotics is usually prescribed.

Among the antibiotics used, one group is called Cephalosporins, like Cefazolin. This is effective against a certain type of bacteria that does not produce a specific enzyme (penicillinase). However, for resistance against a different type of bacteria, such as pneumococci, aminoglycosides like Tobramycin, Gentamicin and Amikacin are used. Sometimes, fortified Cefazolin is combined with Tobramycin to create a common treatment for a disease called bacterial keratitis. A glycopeptide called Fortified Vancomycin is particularly effective against a resistant kind of bacteria called methicillin-resistant staphylococcus aureus (MRSA). Fluoroquinolones like ciprofloxacin, ofloxacin, moxifloxacin, and gatifloxacin are normally used alone for treatment. However, the last two are often preferred nowadays because of increased resistance to the first two.

Systemic antibiotics, or those that work throughout the body, have limited use in bacterial keratitis. They are only used for certain conditions such as scleritis, endophthalmitis, or non-healing, progressively worsening bacterial ulcers. Some other medicines called Cycloplegics are used to reduce pain and inflammation. Antiglaucoma drugs are useful for controlling eye pressure. Lubricating eye drops aid in healing, reduce irritation and smooth the eye surface. Pain and inflammation are also reduced with certain systemic anti-inflammatory drugs.

Along with targeting the disease, patients are asked to take care of their eyes, such as using dark glasses, protecting the eyes from direct sunlight and water, giving the eyes ample rest and taking timely meals.

If the situation calls for it, surgery may also be performed. Gunderson Flap surgery is used when a donor cornea is not available for treating a corneal ulcer that has perforated. Another surgical procedure, Therapeutic Penetrating Keratoplasty (TPK), is the preferred treatment for non-healing corneal ulcers and helps in eliminating the infection. In some cases, a Penetrating Keratoplasty (PKP) is done once the cornea gets healed and the infection gets eliminated; its aim is to restore the vision of the patients.

Treatment is considered successful if the symptoms get reduced, the size of the ulcer decreases, the pain reduces, and the vision improves. However, if the symptoms worsen, the ulcer size increases, the pain gets worse, and the vision deteriorates, the treatment is considered unsuccessful.

What else can Bacterial Keratitis be?

Infections can cause a variety of conditions that affect the cornea, the clear front surface of the eye. These include:

• Fungal keratitis: caused by fungus
• Pythium keratitis: caused by water-borne organisms
• Viral keratitis: resulting from a virus
• Neurotrophic keratitis: related to decreased corneal sensitivity
• Neuroparalytic keratitis: caused by damage to the nerves of the eye
• Interstitial keratitis: involving inflammation between the layers of the cornea
• Disciform keratitis: a form of the viral keratitis
• Acanthamoeba keratitis: caused by a microorganism found in water
• Exposure keratopathy: caused by the eye not closing properly
• Chemical injury: resulting from a harmful substance getting into the eye
• Thermal keratitis: produced by heat injury to the eye
• Atopic keratoconjunctivitis: an allergic condition affecting the eye
• Shield ulcer: associated with severe cases of eye allergies
• Rosacea keratitis: a condition related to the skin disorder rosacea

There are also cornea conditions not caused by infections, including:

• Peripheral Ulcerative keratitis: an inflammation and thinning of the outer edge of the cornea
• Margin keratitis: an inflammation around the edge of the cornea
• Mooren’s Ulcer: a painful ulceration of the cornea
• Toxic keratitis: a reaction to a toxin or drug
• Sterile inflammatory corneal infiltrate: an inflammation in the cornea not caused by bacteria, viruses, fungi or parasites

What to expect with Bacterial Keratitis

The outcome of bacterial keratitis, an infection of the cornea, depends on many factors. If the ulcer from the infection only affects the superficial layers of the cornea up to the outer third part of the corneal tissue, the chances of healing and a good outcome are high. However, ulcers that involve more than two-thirds of the corneal tissue, affect your line of sight, or lead to thinning and dissolution of the cornea generally have a poor outcome.

Other factors that can influence the outcome include regular use of prescribed medications, patient compliance to treatment, whether the infection has spread to the sclera (the white part of the eye) or caused endophthalmitis (inflammation of the inside of the eye), and regular follow-ups with health care providers alongside proper patient counseling.

Possible Complications When Diagnosed with Bacterial Keratitis

Here are some potential complications that could occur after corneal surgery:

• Corneal scarring
• Corneal melt
• Corneal anesthesia
• Neurotrophic keratopathy
• Descemetocele
• Perforation
• Secondary glaucoma
• New blood vessels in the eye (Neovascular glaucoma, Iris Neovascularization)
• Hyphema
• Hemorrhage
• Toxic iridocyclitis
• Lens shifting in the eye (Subluxation of lens)
• Cloudy front of the lens (Anterior subcapsular cataract)
• Corneal fistula
• Scleritis
• Retinal detachment
• Choroidal detachment
• Eye inflammation (Endophthalmitis, Panophthalmitis)
• Keratectasia
• Atrophic bulbi
• Autoevisceration
• Phthisis bulbi

Possible complications directly related to surgery include:

• Wound leak
• Irregular trephination
• Small size graft
• Secondary glaucoma
• Flat anterior chamber
• Iridodialysis
• Pupillary block
• Expulsive choroidal hemorrhage
• Retinal detachment
• Choroidal detachment
• Vitreous hemorrhage

Complications related to sutures may consist of:

• Vascularization
• Infection
• Loose sutures
• Wound leak
• Exposed knots

Recovery from Bacterial Keratitis

Having regular check-ins and understanding the process are key to a successful recovery after an operation. It is recommended for the patient to use antibiotic eye drops every hour for 48 hours to one week. This treatment can be adjusted depending on how the patient responds. If the patient has a large ulcer that could potentially affect their vision, it is best to use two types of hourly antibacterials. If the patient responds well, they can continue using the same medicine. However, if the response is poor, it might be best to reassess their condition. Additional medicines are also used along with antibacterials to enhance their effect and speed up recovery.

The patient must fully grasp the medication schedule and the importance of each drug. Once they’ve been infection-free for 3 to 4 weeks after a keratoplasty, they can shift to topical steroids which are necessary for graft survival. The steroid regimen lasts for 3 months with usage reducing gradually – first 4 times daily, then 3, then 2 and finally once daily while they’ll be constantly monitored. It’s also recommended to use 0.5% timolol twice daily in order to prevent secondary cataracts or glaucoma. Stitches can be removed when they get loose or at least after 12 months.

Preventing Bacterial Keratitis

Patients with bacterial keratitis, an infection of the cornea, should be educated about the nature of their condition, along with the long-term outlook. It’s also important for patients to understand how to avoid factors that could worsen their condition, such as contact lens use, drinking alcohol, and poor nutrition. Wearing glasses or other forms of eye protection can be very helpful, and should be emphasized.

Moreover, it’s crucial that patients know about the importance of consistently taking their prescribed medications and attending their medical appointments on time. Patients should also be informed about the possible need for a future procedure called Therapeutic Penetrating Keratoplasty (TPK), which can help to get rid of the infection and stabilize the eye structure.

Finally, patients should understand that their vision or the functional outcome will depend on having the keratoplasty procedure later. Therefore, it’s important that they have realistic expectations when it comes to their vision.