Late onset endophthalmitis after cataract surgery is caused by?
**Core Concept**
Late onset endophthalmitis after cataract surgery is a rare but serious complication, typically occurring 1-14 days after the procedure. It is an intraocular infection caused by bacterial, fungal, or occasionally, parasitic organisms.
**Why the Correct Answer is Right**
Late onset endophthalmitis is predominantly caused by bacterial pathogens, primarily Coagulase-negative Staphylococci (CoNS), such as Staphylococcus epidermidis. These organisms contaminate the ocular surface during surgery, and their biofilm formation on the intraocular lens or other surgical devices facilitates the development of endophthalmitis. The pathogenesis involves the interaction of these bacteria with the host's immune system and the release of virulence factors that lead to inflammation and tissue damage.
**Why Each Wrong Option is Incorrect**
**Option A:** While fungal endophthalmitis can occur, it is less common than bacterial endophthalmitis and usually presents earlier than late onset endophthalmitis.
**Option B:** Parasitic endophthalmitis is extremely rare and typically associated with tropical regions or specific exposures.
**Option C:** Viral endophthalmitis is not a recognized cause of late onset endophthalmitis.
**Clinical Pearl / High-Yield Fact**
Coagulase-negative Staphylococci (CoNS) are the most common cause of late onset endophthalmitis, highlighting the importance of sterile technique and proper infection control measures during cataract surgery.
**Correct Answer: D. Coagulase-negative Staphylococci (CoNS).**