Late onset endophthalmitis after cataract surgery is caused by
**Core Concept**
Late-onset endophthalmitis after cataract surgery refers to the inflammatory response of the inner eye, specifically the vitreous and retina, following a delayed infection. This condition can be caused by various microorganisms, including bacteria, fungi, and viruses.
**Why the Correct Answer is Right**
The most common cause of late-onset endophthalmitis is _Propionibacterium acnes_ (P. acnes), a gram-positive, anaerobic bacterium. P. acnes can persist in the eye for months or even years after cataract surgery, leading to a delayed inflammatory response. The bacteria typically enter the eye through the surgical site, where they can adhere to the intraocular lens (IOL) or other foreign bodies.
**Why Each Wrong Option is Incorrect**
* **Option A:** Coagulase-negative staphylococci (CoNS) are a common cause of early-onset endophthalmitis, typically within 6 weeks of surgery, not late-onset.
* **Option B:** Fungal endophthalmitis is usually caused by _Fusarium_, _Aspergillus_, or _Candida_ species, which are more commonly associated with trauma or pre-existing ocular conditions.
* **Option C:** Viral endophthalmitis is rare and typically caused by herpes simplex virus (HSV) or cytomegalovirus (CMV), which are not commonly associated with late-onset endophthalmitis after cataract surgery.
**Clinical Pearl / High-Yield Fact**
P. acnes endophthalmitis often presents with a delayed onset, typically 1-3 months after surgery, and may be asymptomatic until significant inflammation occurs. Regular follow-up and surveillance are crucial to detect and manage this condition.
**Correct Answer: C. _Fusarium_.