**Core Concept**
The prevention of postoperative infection in cataract surgery involves the use of antimicrobial agents to reduce the risk of bacterial contamination and subsequent endophthalmitis. This is a critical aspect of ophthalmic surgery, as endophthalmitis can lead to severe visual impairment or even blindness.

**Why the Correct Answer is Right**
The use of topical antibiotics is the most effective method to prevent postoperative infection after cataract surgery. This is because topical antibiotics can effectively reduce the bacterial load on the ocular surface, thereby minimizing the risk of endophthalmitis. The most commonly used topical antibiotics for this purpose include fluoroquinolones, such as moxifloxacin, and aminoglycosides, such as gentamicin.

**Why Each Wrong Option is Incorrect**
**Option B:** Eye brow shaving is not a necessary step in preventing postoperative infection after cataract surgery. In fact, shaving the eyebrows can lead to skin irritation and potentially increase the risk of infection. The use of antibiotic drops or ointments is a more effective and safer approach.
**Option C:** Irrigation of the ocular surface is not a substitute for antibiotic prophylaxis. While irrigation can help to remove debris and reduce the risk of infection, it is not a reliable method for preventing postoperative infection.
**Option D:** The use of antibiotics is indeed a crucial step in preventing postoperative infection after cataract surgery, making this option incorrect.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the use of antibiotic prophylaxis should be continued for a minimum of 2-3 days after cataract surgery to ensure optimal protection against postoperative infection.

**✓ Correct Answer: A. Antibiotics**