Local anaesthetic usually used for retrobulbar block –
**Core Concept**
The question is testing the knowledge of local anesthetics used in ophthalmic procedures, specifically for retrobulbar block. Retrobulbar block is a technique used to anesthetize the eye and surrounding structures, often performed for surgeries like cataract extraction.
**Why the Correct Answer is Right**
The correct local anesthetic for retrobulbar block is **Lidocaine**. It is a widely used amide-type local anesthetic that provides effective anesthesia and is suitable for ophthalmic procedures. The mechanism of action involves blocking the sodium channels in the nerve fibers, preventing the transmission of nerve impulses. Lidocaine has a rapid onset and short duration of action, making it ideal for retrobulbar block.
**Why Each Wrong Option is Incorrect**
* **Option A:** **Bupivacaine** is another amide-type local anesthetic, but it is not the first choice for retrobulbar block due to its longer duration of action and potential for toxicity.
* **Option B:** **Procaine** is an ester-type local anesthetic, which is less commonly used in ophthalmic procedures due to its shorter duration of action and potential for allergic reactions.
* **Option C:** **Ropivacaine** is an amide-type local anesthetic with a similar profile to bupivacaine, but it is not typically used for retrobulbar block.
**Clinical Pearl / High-Yield Fact**
When using local anesthetics in ophthalmic procedures, it's essential to choose an agent with a rapid onset and short duration of action to minimize the risk of toxicity and ensure effective anesthesia.
**Correct Answer:** B. Procaine