Pseudomonas aeruginosa is an opportunistic, rod-shaped bacterium found widely in water, soil, and moist environments. When it infects the eye, it typically causes a severe form of bacterial keratitis, an infection of the cornea, the clear front dome of the eye. This infection is considered an urgent medical situation due to the organism’s capacity for rapid tissue destruction. Untreated P. aeruginosa keratitis can progress quickly, potentially leading to corneal perforation and permanent loss of vision within a day or two. Immediate identification and highly concentrated antibiotic treatment are necessary to preserve the integrity of the eye.
The Virulence of Pseudomonas Aeruginosa
P. aeruginosa damages the cornea by secreting destructive enzymes known as exoproteins directly into the corneal layers. These include metalloproteases, such as elastase (LasB), and alkaline protease. These enzymes break down collagen and elastin, the major proteins that give the cornea its strength and shape.
This enzymatic activity causes rapid necrosis of the corneal stroma, leading to the characteristic “melting” appearance of the tissue. Furthermore, P. aeruginosa uses the Type Three Secretion System (TTSS) to inject potent toxins like ExoU and ExoS directly into host cells. ExoU is a cytotoxic phospholipase that destroys the host cell membrane.
The bacteria also form biofilms, which are complex communities encased in a self-produced matrix. This biofilm layer acts as a physical shield, making the bacteria resistant to the body’s immune defenses and rendering standard antibiotic concentrations ineffective. Biofilms can form directly on the contact lens surface or in the storage case, allowing the bacteria to persist and be repeatedly introduced to the eye.
Key Risk Factors and Exposure Routes
The most common factor allowing P. aeruginosa to cause keratitis is the misuse of contact lenses. Wearing soft lenses for extended periods, especially sleeping in them, creates a low-oxygen environment that stresses the corneal surface. The lens itself can harbor the bacteria and deposit it directly onto the eye.
Contamination of the lens case or solution is another primary route of exposure. This often occurs when wearers use tap water or saliva to clean or store their lenses. Tap water contains P. aeruginosa, and introducing it bypasses the natural protective barrier of the corneal epithelium. Reusing or “topping off” old disinfecting solution also promotes bacterial growth in the lens case.
Other exposure routes involve any situation that compromises the physical integrity of the cornea. Ocular trauma, such as a scratch from a foreign body, creates a direct opening for the bacterium to invade the corneal stroma. Prior eye surgery or the use of contaminated eye drops can also introduce the organism directly to the ocular surface.
Identifying Signs and Symptoms
The onset of P. aeruginosa keratitis is rapid, often progressing within 24 to 48 hours. Patients typically experience intense eye pain that feels disproportionate to the infection’s appearance. This pain is accompanied by pronounced redness and heightened sensitivity to light.
A dense, gray or yellowish-green infiltrate becomes visible on the cornea, often with a “soupy” or necrotic appearance. This infiltrate is a collection of inflammatory cells and bacteria. It is frequently accompanied by a copious, thick discharge that is yellow or greenish in color, and vision becomes noticeably blurred.
To confirm the diagnosis and guide treatment, a medical professional must perform a corneal scraping. This involves gently collecting a sample of the infected tissue from the ulcer bed. The sample is sent for Gram stain and culture to identify the organism and determine its antibiotic sensitivities, ensuring the most effective therapy is initiated.
Urgent Medical Treatment and Management
Treatment requires an immediate and aggressive therapeutic strategy. The standard initial approach involves using high-concentration, or fortified, topical antibiotics to achieve bactericidal levels in the cornea. These drops are custom-prepared by a compounding pharmacy, often using aminoglycosides like tobramycin or gentamicin, or a broad-spectrum fluoroquinolone.
The initial dosing regimen is highly intensive, starting with a loading dose every five to fifteen minutes for the first hour. This is followed by one drop every hour, around the clock. Frequent application is necessary because the cornea is avascular, meaning drugs struggle to penetrate the tissue. While less severe cases may use fluoroquinolone monotherapy (e.g., moxifloxacin), severe ulcers often require the fortified combination.
The patient’s response must be monitored closely, often with daily examinations, to confirm the infection is stabilizing. Stabilization is indicated by a blunting of the ulcer borders and decreased density of the infiltrate. As the eye heals, the frequency of antibiotic drops is gradually tapered over one to two weeks, but never stopped abruptly. If the infection is unresponsive or has led to corneal perforation, surgical intervention, such as a corneal transplant, may be necessary to salvage the eye.
Preventing Future Infections
Preventing P. aeruginosa eye infections centers on meticulous hygiene, particularly for contact lens wearers. Always wash hands thoroughly with soap and water and dry them completely before handling lenses or touching the eyes. Lenses should never be exposed to tap water, saliva, or any non-sterile solution, as these are common sources of the bacterium.
Lenses must be removed before sleeping, showering, or swimming, since extended wear and water exposure increase infection risk. The lens case should be cleaned by rubbing it with fresh solution and allowing it to air dry upside down. The case itself should be replaced at least once every three months to prevent the buildup of bacterial biofilms.
Strict adherence to the prescribed lens replacement schedule is a fundamental preventive measure. If any symptoms of irritation, pain, or redness occur, remove the contact lenses immediately and seek prompt medical attention. These behavioral modifications are the most effective way to maintain the cornea’s defenses and avoid this sight-threatening infection.