Endophthalmitis

Overview

Endophthalmitis is a severe, vision-threatening infection or inflammation involving the vitreous cavity and often the anterior chamber, most commonly occurring as a complication of intraocular surgery (particularly cataract surgery) or intravitreal injection, and less commonly from endogenous (bloodstream) spread or penetrating trauma. It is an ophthalmic emergency requiring rapid diagnosis and treatment to preserve vision.

Epidemiology & Risk Factors

Post-cataract surgery endophthalmitis, while rare, remains an important and increasingly challenging complication due to rising antimicrobial resistance (AMR).¹ Risk factors include posterior capsule rupture or vitreous loss during surgery, prolonged surgical time, use of a clear corneal (versus scleral tunnel) incision, and pre-existing blepharitis or other periocular infection. Endophthalmitis can also follow intravitreal injection (for anti-VEGF or other therapy), penetrating trauma, or, less commonly, arise endogenously from bacteremia or fungemia in a systemically ill or immunocompromised patient.

Pathophysiology

Most post-cataract endophthalmitis results from introduction of ocular surface or periocular flora into the eye at the time of surgery, with coagulase-negative staphylococci the predominant causative organisms, followed by Staphylococcus aureus, Streptococcus species, and, less commonly, Gram-negative organisms such as Pseudomonas.¹ Once introduced, these organisms proliferate within the relatively immune-privileged, avascular vitreous cavity, provoking an intense inflammatory response that itself contributes substantially to tissue damage and vision loss, in addition to direct microbial toxicity. Antimicrobial resistance further complicates this picture: coagulase-negative staphylococci frequently show methicillin and fluoroquinolone resistance, and some regions report multidrug-resistant Pseudomonas isolates with near-universal resistance to fluoroquinolones, aminoglycosides, and cephalosporins.¹

Clinical Presentation

Patients typically present within days of intraocular surgery or injection with acute, progressively worsening pain, redness, and decreased vision, often out of proportion to the expected postoperative course. Any patient reporting increasing pain and decreasing vision in the days following intraocular surgery should be evaluated urgently for endophthalmitis rather than assumed to have routine postoperative inflammation.

Exam Findings

• Marked anterior chamber inflammation, often with hypopyon (a layered collection of white blood cells in the anterior chamber)
• Vitritis, often severe enough to obscure the fundus view ("no view" or significantly hazy view)
• Conjunctival injection and eyelid edema
• Corneal edema or infiltrate, particularly if there is a concurrent corneal source (e.g., a case of combined endophthalmitis and corneal ulcer)²
• Decreased red reflex and significantly reduced visual acuity, often to hand motion or worse in severe cases

Differential Diagnosis

• Sterile postoperative inflammation (toxic anterior segment syndrome, TASS), which typically presents earlier (within 12-48 hours) and lacks the progressive pain and hypopyon severity of true infectious endophthalmitis
• Retained lens fragments causing inflammation without infection
• Uveitis flare from a pre-existing inflammatory condition, coincidentally occurring in the postoperative period
• Vitreous hemorrhage (can reduce the view but should not produce the pain, hypopyon, and progressive inflammatory picture of endophthalmitis)

Management

Diagnosis is clinical, supported by vitreous (and often aqueous) tap for Gram stain, culture, and susceptibility testing, ideally obtained immediately before starting empiric intravitreal therapy so as not to delay treatment. Prompt intravitreal antibiotic therapy is the cornerstone of treatment and the key determinant of prognosis; empiric regimens must reflect local resistance trends, particularly for Gram-negative coverage, given the geographic variability in resistance patterns.¹ In a systematic review, visual outcomes with tap-and-inject (vitreous tap plus intravitreal antibiotics) were comparable to early pars plana vitrectomy overall, except in Gram-negative infections, where vitrectomy conferred additional benefit; amikacin resistance specifically correlated with poorer outcomes, whereas vancomycin or moxifloxacin resistance did not, and systemic antibiotics or intravitreal corticosteroids showed no consistent additional benefit.¹

In cases resistant to conventional intravitreal regimens, alternative agents such as colistin (fortified topical, subconjunctival, and/or intravitreal) have been used successfully for multidrug-resistant Gram-negative organisms (e.g., certain Acinetobacter or Pseudomonas isolates) when standard first-line therapy fails, illustrating the importance of prompt vitreous culture data to guide targeted, rather than purely empiric, therapy in resistant cases.²

Complications

• Permanent, severe vision loss or blindness if treatment is delayed or the organism is highly resistant/virulent
• Retinal detachment, either from the inflammatory process itself or as a consequence of vitrectomy surgery
• Phthisis bulbi (globe shrinkage) in the most severe, treatment-refractory cases
• Need for evisceration or enucleation in rare, fulminant, treatment-resistant cases
• Prolonged, complex antimicrobial courses (including non-standard agents like colistin) in multidrug-resistant infections²

Clinical Pearls

• Increasing pain and decreasing vision in the days after intraocular surgery should prompt urgent endophthalmitis evaluation, not reassurance
• Prompt intravitreal antibiotic therapy is the single most important determinant of visual prognosis — do not delay treatment awaiting culture results
• Empiric antibiotic selection should account for local resistance patterns, since AMR (especially among coagulase-negative staphylococci and some Gram-negative organisms) varies substantially by region¹
• Tap-and-inject is generally comparable to early vitrectomy except in Gram-negative infections, where vitrectomy provides additional benefit¹
• Colistin and other non-standard agents are effective salvage options for multidrug-resistant Gram-negative endophthalmitis when first-line therapy fails²

Common Pitfalls

• Attributing postoperative pain and decreased vision to routine inflammation rather than urgently evaluating for endophthalmitis
• Delaying intravitreal antibiotic administration while awaiting culture confirmation
• Using a fixed empiric antibiotic regimen without considering local resistance patterns, particularly for Gram-negative organisms
• Confusing toxic anterior segment syndrome (earlier onset, sterile) with true infectious endophthalmitis, leading to inappropriate management
• Failing to consider vitrectomy in Gram-negative or treatment-resistant cases where tap-and-inject alone may be insufficient