Endophthalmitis

The vitreous cavity is a relatively immune-privileged, avascular space, which normally protects the eye from systemic inflammatory triggers but also allows introduced organisms to proliferate with limited immune surveillance once inside. Endophthalmitis is severe intraocular infection/inflammation involving this space and often the anterior chamber, most commonly following cataract surgery or intravitreal injection, and is an ophthalmic emergency.

Most post-cataract endophthalmitis results from introduction of ocular surface/periocular flora into the eye at surgery, with coagulase-negative staphylococci predominating, followed by S. aureus, Streptococcus, and less commonly Gram-negative organisms like Pseudomonas.¹ Once introduced, organisms proliferate in the avascular vitreous, provoking an intense inflammatory response that itself contributes to tissue damage. Antimicrobial resistance complicates this further: coagulase-negative staphylococci frequently show methicillin/fluoroquinolone resistance, and some regions report multidrug-resistant Pseudomonas with near-universal resistance to fluoroquinolones, aminoglycosides, and cephalosporins.¹

Patients present within days of intraocular surgery/injection with acute, worsening pain, redness, and decreased vision, often out of proportion to the expected postoperative course.

Key differentials: toxic anterior segment syndrome (earlier onset within 12-48 hours, sterile, less progressive), retained lens fragments, a coincidental uveitis flare, and vitreous hemorrhage (reduces view but lacks the pain/hypopyon/progressive picture of true endophthalmitis).

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 prognostic determinant; empiric regimens must reflect local resistance trends, particularly for Gram-negative coverage.¹ Tap-and-inject was comparable to early pars plana vitrectomy overall, except in Gram-negative infections where vitrectomy conferred benefit; amikacin resistance correlated with poorer outcomes, while vancomycin/moxifloxacin resistance did not, and systemic antibiotics or intravitreal corticosteroids showed no consistent added benefit.¹ In cases resistant to conventional regimens, alternative agents such as colistin (topical, subconjunctival, and/or intravitreal) have been used successfully for multidrug-resistant Gram-negative organisms when first-line therapy fails.²

• Increasing pain and decreasing vision after intraocular surgery should prompt urgent endophthalmitis evaluation, not reassurance
• Prompt intravitreal antibiotics are the single most important determinant of visual prognosis — do not delay awaiting culture results
• Empiric antibiotic choice should account for local resistance patterns, which vary substantially by region¹
• Tap-and-inject is generally comparable to early vitrectomy except in Gram-negative infections¹
• Colistin is an effective salvage option for multidrug-resistant Gram-negative endophthalmitis²
• Common pitfall: attributing postoperative pain/vision loss to routine inflammation rather than urgent evaluation