Late onset endophthalmitis after cataract surgery is most often caused by:
**Core Concept**
Late onset endophthalmitis after cataract surgery refers to an inflammatory response within the eye, specifically within the vitreous and aqueous humor, occurring weeks to months after surgery. This condition is a serious complication of cataract surgery, often resulting from contamination during the procedure or postoperative infection.
**Why the Correct Answer is Right**
The most common cause of late onset endophthalmitis is _Staphylococcus epidermidis_, a type of coagulase-negative staphylococci. This organism is typically found on the skin and can contaminate the ocular surface during surgery. The pathogenesis involves the adhesion of _S. epidermidis_ to the intraocular lens (IOL) or other implanted materials, leading to biofilm formation and subsequent infection. The late onset is thought to be due to the slow growth of _S. epidermidis_ and the body's delayed immune response.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is often incorrect because _Staphylococcus aureus_ is more commonly associated with acute onset endophthalmitis, which typically occurs within the first week after surgery.
**Option B:** Although _Pseudomonas aeruginosa_ can cause endophthalmitis, it is more commonly seen in contact lens-related infections or in patients with compromised ocular surface disease.
**Option C:** _Bacillus cereus_ is a type of endospore-forming bacteria that can cause endophthalmitis, but it is relatively rare and usually associated with contamination from the environment.
**Clinical Pearl / High-Yield Fact**
It is essential to note that the risk of endophthalmitis can be minimized by using proper aseptic techniques during surgery, including the use of sterile gloves, drapes, and instruments, as well as proper wound closure and postoperative care.
**Correct Answer:** C.