**Core Concept**
The prevention of postoperative infections after cataract surgery involves minimizing the risk of bacterial contamination and promoting a sterile environment. This includes the use of antimicrobial agents, proper surgical techniques, and postoperative care.

**Why the Correct Answer is Right**
The best way to prevent infection after cataract surgery is the use of **intracameral antibiotics**. This involves injecting antibiotics directly into the anterior chamber of the eye immediately after surgery. The most commonly used antibiotic is **vancomycin**, which is effective against a broad range of bacteria, including Staphylococcus aureus and Streptococcus pneumoniae. The intracameral injection of vancomycin has been shown to significantly reduce the risk of postoperative endophthalmitis, a severe and potentially sight-threatening infection of the eye.

**Why Each Wrong Option is Incorrect**
**Option A:** **Topical antibiotics** may be used as an adjunct to intracameral antibiotics, but they are not sufficient on their own to prevent postoperative infections.
**Option B:** **Preoperative antibiotics** are not effective in preventing postoperative infections, as the bacteria that cause endophthalmitis are typically introduced during surgery.
**Option C:** **Postoperative oral antibiotics** are not effective in preventing postoperative infections, as the bacteria that cause endophthalmitis are typically introduced during surgery.

**Clinical Pearl / High-Yield Fact**
Intracameral antibiotics should be administered immediately after surgery, and the antibiotic should be injected into the anterior chamber of the eye to maximize its effectiveness in preventing postoperative infections.

**Correct Answer: C. Intracameral antibiotics**