Unit 2: Common Bacterial Infections of the Eye
Bacterial infections of the eye represent some of the most frequently encountered ocular problems in optometric and ophthalmic practice. These infections may range from mild and self-limiting to vision-threatening emergencies requiring immediate intervention. The eye, though protected by eyelids, tears, and immune defense mechanisms, is still vulnerable to bacterial invasion, particularly when local defense barriers are compromised. Understanding the etiology, clinical features, diagnostic strategies, and management of these conditions is essential for optometry students and practitioners.
1. Conjunctivitis (Bacterial Conjunctivitis)
Conjunctivitis is the inflammation of the conjunctiva, often referred to as "pink eye." Bacterial conjunctivitis is a common cause, especially in children and individuals living in close communities. It is usually caused by pathogens such as Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. In neonates, Neisseria gonorrhoeae and Chlamydia trachomatis are important causes.
Etiology and Risk Factors
- Direct contact with infected secretions (hands, towels, cosmetics).
- Overcrowded environments such as schools and daycare centers.
- Poor eyelid hygiene or chronic blepharitis.
- Contact lens misuse.
Clinical Features
- Redness and diffuse conjunctival hyperemia.
- Purulent or mucopurulent discharge that causes eyelids to stick together, especially in the morning.
- Foreign body sensation and mild irritation (usually no severe pain).
- Usually unilateral at onset but may spread to both eyes.
- Vision typically unaffected except for blur from discharge.
Diagnosis
- Primarily clinical based on signs and symptoms.
- Gram staining and culture in severe, recurrent, or neonatal cases.
Management
- Topical broad-spectrum antibiotics: fluoroquinolones, aminoglycosides, or macrolides.
- Lubricants to reduce discomfort.
- Hygiene advice: frequent handwashing, avoiding sharing towels or cosmetics.
- In neonatal conjunctivitis: urgent referral and systemic antibiotics (e.g., ceftriaxone for gonococcal infections).
2. Keratitis (Bacterial Keratitis)
Bacterial keratitis is a potentially vision-threatening infection of the cornea. It is most often associated with contact lens misuse but can also occur following trauma or ocular surface disease. The most common pathogens are Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pneumoniae, and Enterobacteriaceae.
Etiology and Predisposing Factors
- Contact lens wear, especially overnight or poor hygiene practices.
- Trauma or corneal foreign bodies.
- Ocular surface disorders such as dry eye or exposure keratopathy.
- Previous ocular surgery.
Clinical Features
- Severe pain and photophobia.
- Reduced vision depending on ulcer location.
- Corneal infiltrate with stromal edema.
- Hypopyon (collection of pus in the anterior chamber) in severe cases.
- Conjunctival injection and discharge.
Diagnosis
- Slit-lamp biomicroscopy: identifies ulcer, infiltrate, and epithelial defect.
- Corneal scraping for Gram stain and culture.
- Sensitivity testing to guide antibiotic therapy.
Management
- Intensive topical broad-spectrum antibiotics (e.g., fortified cefazolin and tobramycin, or fluoroquinolones).
- Cycloplegic agents for pain relief.
- Avoidance of topical steroids in the acute stage.
- Hospitalization in severe cases.
3. Endophthalmitis
Endophthalmitis is a severe, sight-threatening bacterial infection involving the intraocular tissues and fluids. It is most commonly seen after ocular surgery (especially cataract extraction), penetrating trauma, or endogenous spread from systemic infections.
Etiology
- Postoperative: Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus species.
- Post-traumatic: Bacillus species (highly virulent).
- Endogenous: spread from systemic infection such as bacteremia or endocarditis.
Clinical Features
- Severe ocular pain.
- Marked vision loss, sometimes reduced to light perception.
- Hypopyon, vitritis, and corneal edema.
- Redness, swollen eyelids, and chemosis.
Diagnosis
- Clinical suspicion is key.
- Vitreous tap or biopsy for microbiological analysis.
Management
- Intravitreal injection of antibiotics (vancomycin, ceftazidime).
- Vitrectomy in severe or non-responsive cases.
- Systemic antibiotics in endogenous cases.
4. Dacryocystitis
Dacryocystitis is an infection of the lacrimal sac due to obstruction of the nasolacrimal duct. It may be acute or chronic and is more common in women due to narrow bony nasolacrimal canals.
Etiology
- Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae are common pathogens.
Clinical Features
- Acute: painful swelling at the medial canthus, redness, tearing, pus discharge on pressure over sac.
- Chronic: recurrent epiphora and mucoid discharge.
Diagnosis
- Clinical examination and regurgitation test.
- Dacryocystography or probing in chronic cases.
Management
- Acute: systemic and topical antibiotics, warm compresses, analgesics.
- Definitive: dacryocystorhinostomy (DCR) surgery to restore drainage.
5. Blepharitis
Blepharitis is a common chronic infection and inflammation of the eyelid margins. It may be anterior (affecting eyelashes and follicles) or posterior (meibomian gland dysfunction). Bacterial colonization, especially Staphylococcus aureus, plays a major role.
Etiology
- Chronic staphylococcal infection.
- Association with seborrheic dermatitis or rosacea.
Clinical Features
- Redness, burning, and irritation.
- Crusting and scales at the eyelid margin.
- Recurrent styes or chalazia.
- Dry eye symptoms due to meibomian dysfunction.
Diagnosis
- Clinical examination of eyelid margins.
- Meibomian gland expression for quality of secretions.
Management
- Eyelid hygiene: warm compresses, lid scrubs.
- Topical antibiotics: erythromycin or bacitracin ointment.
- Systemic tetracyclines for posterior blepharitis with rosacea.
- Lubricating eye drops for symptomatic relief.
Conclusion
Bacterial infections of the eye encompass a wide spectrum of conditions ranging from superficial conjunctivitis to deep sight-threatening endophthalmitis. For an optometrist, early recognition, proper referral, and appropriate management are vital in preventing complications and preserving vision. Knowledge of risk factors, clinical signs, and available therapies ensures effective care and patient safety.
