Most common cause of acute postoperative endophthalmitis?

• A. Staph aureus
• B. Staph epidermidis
• C. Streptococcus pneumoniae
• D. Streptococcus pyogenes

Answer: (B)

The most common cause of acute postoperative endophthalmitis is Staphylococcus epidermidis, a coagulase-negative Staphylococcus that normally resides on the skin and eyelids. During intraocular surgery, especially cataract procedures with implants like an intraocular lens, this organism can contaminate the operative field. It tends to be less virulent than Staphylococcus aureus or streptococcal species, which helps explain why the presentation may be less dramatic, but its abundance on the skin and its ability to adhere to and form biofilms on implanted devices make it the leading cause in this setting.

Staphylococcus aureus, while capable of causing severe, rapidly progressive endophthalmitis, is less commonly the source after uncomplicated postoperative procedures. Streptococcus pneumoniae and Streptococcus pyogenes can cause endophthalmitis as well, but they’re not the typical culprits in the postoperative context and are often associated with more fulminant infections or different routes of infection.