**Core Concept**
Peribulbar block is a type of regional anesthesia where a local anesthetic is injected around the eyeball to provide anesthesia for eye surgeries. The block involves injecting the anesthetic into the extraocular muscles, which can lead to complications.

**Why the Correct Answer is Right**
The correct answer is **D. Optic nerve injury**. This is because the optic nerve is a critical structure located near the injection site, and it can be inadvertently damaged during the procedure. The optic nerve is responsible for transmitting visual information from the eye to the brain, and damage to this nerve can result in permanent vision loss.

**Why Each Wrong Option is Incorrect**
**Option A:** **Intraocular injection**. While intraocular injections can be a complication of peribulbar block, they are not the most common or significant complication.

**Option B:** **Chemical conjunctivitis**. Chemical conjunctivitis is a potential complication of peribulbar block, but it is typically mild and self-limiting.

**Option C:** **Infection**. Infection is a potential complication of any invasive procedure, including peribulbar block. However, it is not the most direct or significant complication of this specific type of block.

**Clinical Pearl / High-Yield Fact**
To minimize the risk of optic nerve injury during peribulbar block, it is essential to use a high-volume, low-concentration anesthetic solution and to inject the anesthetic slowly and carefully around the extraocular muscles.

**Correct Answer:** D. Optic nerve injury.